Elep

# Crypto

> Stability: 2 - Stable

The `crypto` module provides cryptographic functionality that includes a set of
wrappers for OpenSSL's hash, HMAC, cipher, decipher, sign, and verify functions.

Use `require('crypto')` to access this module.

```js
const crypto = require('crypto');

const secret = 'abcdefg';
const hash = crypto.createHmac('sha256', secret)
                   .update('I love cupcakes')
                   .digest('hex');
console.log(hash);
// Prints:
//   c0fa1bc00531bd78ef38c628449c5102aeabd49b5dc3a2a516ea6ea959d6658e
```

## Determining if crypto support is unavailable

It is possible for Node.js to be built without including support for the
`crypto` module. In such cases, calling `require('crypto')` will result in an
error being thrown.

```js
let crypto;
try {
  crypto = require('crypto');
} catch (err) {
  console.log('crypto support is disabled!');
}
```

## Class: Certificate

SPKAC is a Certificate Signing Request mechanism originally implemented by
Netscape and was specified formally as part of [HTML5's `keygen` element][].

Note that `<keygen>` is deprecated since [HTML 5.2][] and new projects
should not use this element anymore.

The `crypto` module provides the `Certificate` class for working with SPKAC
data. The most common usage is handling output generated by the HTML5
`<keygen>` element. Node.js uses [OpenSSL's SPKAC implementation][] internally.

### Certificate.exportChallenge(spkac)

* `spkac` {string | Buffer | TypedArray | DataView}
* Returns: {Buffer} The challenge component of the `spkac` data structure, which
  includes a public key and a challenge.

```js
const { Certificate } = require('crypto');
const spkac = getSpkacSomehow();
const challenge = Certificate.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints: the challenge as a UTF8 string
```

### Certificate.exportPublicKey(spkac[, encoding])

* `spkac` {string | Buffer | TypedArray | DataView}
* `encoding` {string} The [encoding][] of the `spkac` string.
* Returns: {Buffer} The public key component of the `spkac` data structure,
  which includes a public key and a challenge.

```js
const { Certificate } = require('crypto');
const spkac = getSpkacSomehow();
const publicKey = Certificate.exportPublicKey(spkac);
console.log(publicKey);
// Prints: the public key as <Buffer ...>
```

### Certificate.verifySpkac(spkac)

* `spkac` {Buffer | TypedArray | DataView}
* Returns: {boolean} `true` if the given `spkac` data structure is valid,
  `false` otherwise.

```js
const { Certificate } = require('crypto');
const spkac = getSpkacSomehow();
console.log(Certificate.verifySpkac(Buffer.from(spkac)));
// Prints: true or false
```

### Legacy API

As a still supported legacy interface, it is possible (but not recommended) to
create new instances of the `crypto.Certificate` class as illustrated in the
examples below.

#### new crypto.Certificate()

Instances of the `Certificate` class can be created using the `new` keyword
or by calling `crypto.Certificate()` as a function:

```js
const crypto = require('crypto');

const cert1 = new crypto.Certificate();
const cert2 = crypto.Certificate();
```

#### certificate.exportChallenge(spkac)

* `spkac` {string | Buffer | TypedArray | DataView}
* Returns: {Buffer} The challenge component of the `spkac` data structure, which
  includes a public key and a challenge.

```js
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
const challenge = cert.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints: the challenge as a UTF8 string
```

#### certificate.exportPublicKey(spkac)

* `spkac` {string | Buffer | TypedArray | DataView}
* Returns: {Buffer} The public key component of the `spkac` data structure,
  which includes a public key and a challenge.

```js
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
const publicKey = cert.exportPublicKey(spkac);
console.log(publicKey);
// Prints: the public key as <Buffer ...>
```

#### certificate.verifySpkac(spkac)

* `spkac` {Buffer | TypedArray | DataView}
* Returns: {boolean} `true` if the given `spkac` data structure is valid,
  `false` otherwise.

```js
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
console.log(cert.verifySpkac(Buffer.from(spkac)));
// Prints: true or false
```

## Class: Cipher

Instances of the `Cipher` class are used to encrypt data. The class can be
used in one of two ways:

- As a [stream][] that is both readable and writable, where plain unencrypted
  data is written to produce encrypted data on the readable side, or
- Using the [`cipher.update()`][] and [`cipher.final()`][] methods to produce
  the encrypted data.

The [`crypto.createCipher()`][] or [`crypto.createCipheriv()`][] methods are
used to create `Cipher` instances. `Cipher` objects are not to be created
directly using the `new` keyword.

Example: Using `Cipher` objects as streams:

```js
const crypto = require('crypto');

const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Key length is dependent on the algorithm. In this case for aes192, it is
// 24 bytes (192 bits).
// Use async `crypto.scrypt()` instead.
const key = crypto.scryptSync(password, 'salt', 24);
// Use `crypto.randomBytes()` to generate a random iv instead of the static iv
// shown here.
const iv = Buffer.alloc(16, 0); // Initialization vector.

const cipher = crypto.createCipheriv(algorithm, key, iv);

cipher.write('some clear text data');
cipher.end();
```

Example: Using `Cipher` and piped streams:

```js
const crypto = require('crypto');
const fs = require('fs');

const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Use the async `crypto.scrypt()` instead.
const key = crypto.scryptSync(password, 'salt', 24);
// Use `crypto.randomBytes()` to generate a random iv instead of the static iv
// shown here.
const iv = Buffer.alloc(16, 0); // Initialization vector.

const cipher = crypto.createCipheriv(algorithm, key, iv);

const input = fs.createReadStream('test.js');
const output = fs.createWriteStream('test.enc');

input.pipe(cipher).pipe(output);
```

Example: Using the [`cipher.update()`][] and [`cipher.final()`][] methods:

```js
const crypto = require('crypto');

const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Use the async `crypto.scrypt()` instead.
const key = crypto.scryptSync(password, 'salt', 24);
// Use `crypto.randomBytes` to generate a random iv instead of the static iv
// shown here.
const iv = Buffer.alloc(16, 0); // Initialization vector.

const cipher = crypto.createCipheriv(algorithm, key, iv);

let encrypted = cipher.update('some clear text data', 'utf8', 'hex');
encrypted += cipher.final('hex');
console.log(encrypted);
// Prints: e5f79c5915c02171eec6b212d5520d44480993d7d622a7c4c2da32f6efda0ffa
```

### cipher.final([outputEncoding])

* `outputEncoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string} Any remaining enciphered contents.
  If `outputEncoding` is specified, a string is
  returned. If an `outputEncoding` is not provided, a [`Buffer`][] is returned.

Once the `cipher.final()` method has been called, the `Cipher` object can no
longer be used to encrypt data. Attempts to call `cipher.final()` more than
once will result in an error being thrown.

### cipher.setAAD(buffer[, options])

* `buffer` {Buffer}
* `options` {Object} [`stream.transform` options][]
  - `plaintextLength` {number}
* Returns: {Cipher} for method chaining.

When using an authenticated encryption mode (`GCM`, `CCM` and `OCB` are
currently supported), the `cipher.setAAD()` method sets the value used for the
_additional authenticated data_ (AAD) input parameter.

The `options` argument is optional for `GCM` and `OCB`. When using `CCM`, the
`plaintextLength` option must be specified and its value must match the length
of the plaintext in bytes. See [CCM mode][].

The `cipher.setAAD()` method must be called before [`cipher.update()`][].

### cipher.getAuthTag()

* Returns: {Buffer} When using an authenticated encryption mode (`GCM`, `CCM`
  and `OCB` are currently supported), the `cipher.getAuthTag()` method returns a
  [`Buffer`][] containing the _authentication tag_ that has been computed from
  the given data.

The `cipher.getAuthTag()` method should only be called after encryption has
been completed using the [`cipher.final()`][] method.

### cipher.setAutoPadding([autoPadding])

* `autoPadding` {boolean} **Default:** `true`
* Returns: {Cipher} for method chaining.

When using block encryption algorithms, the `Cipher` class will automatically
add padding to the input data to the appropriate block size. To disable the
default padding call `cipher.setAutoPadding(false)`.

When `autoPadding` is `false`, the length of the entire input data must be a
multiple of the cipher's block size or [`cipher.final()`][] will throw an error.
Disabling automatic padding is useful for non-standard padding, for instance
using `0x0` instead of PKCS padding.

The `cipher.setAutoPadding()` method must be called before
[`cipher.final()`][].

### cipher.update(data[, inputEncoding][, outputEncoding])

* `data` {string | Buffer | TypedArray | DataView}
* `inputEncoding` {string} The [encoding][] of the data.
* `outputEncoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Updates the cipher with `data`. If the `inputEncoding` argument is given,
the `data`
argument is a string using the specified encoding. If the `inputEncoding`
argument is not given, `data` must be a [`Buffer`][], `TypedArray`, or
`DataView`. If `data` is a [`Buffer`][], `TypedArray`, or `DataView`, then
`inputEncoding` is ignored.

The `outputEncoding` specifies the output format of the enciphered
data. If the `outputEncoding`
is specified, a string using the specified encoding is returned. If no
`outputEncoding` is provided, a [`Buffer`][] is returned.

The `cipher.update()` method can be called multiple times with new data until
[`cipher.final()`][] is called. Calling `cipher.update()` after
[`cipher.final()`][] will result in an error being thrown.

## Class: Decipher

Instances of the `Decipher` class are used to decrypt data. The class can be
used in one of two ways:

- As a [stream][] that is both readable and writable, where plain encrypted
  data is written to produce unencrypted data on the readable side, or
- Using the [`decipher.update()`][] and [`decipher.final()`][] methods to
  produce the unencrypted data.

The [`crypto.createDecipher()`][] or [`crypto.createDecipheriv()`][] methods are
used to create `Decipher` instances. `Decipher` objects are not to be created
directly using the `new` keyword.

Example: Using `Decipher` objects as streams:

```js
const crypto = require('crypto');

const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Key length is dependent on the algorithm. In this case for aes192, it is
// 24 bytes (192 bits).
// Use the async `crypto.scrypt()` instead.
const key = crypto.scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.

const decipher = crypto.createDecipheriv(algorithm, key, iv);

// Encrypted with same algorithm, key and iv.
const encrypted =
  'e5f79c5915c02171eec6b212d5520d44480993d7d622a7c4c2da32f6efda0ffa';
decipher.write(encrypted, 'hex');
decipher.end();
```

Example: Using `Decipher` and piped streams:

```js
const crypto = require('crypto');
const fs = require('fs');

const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Use the async `crypto.scrypt()` instead.
const key = crypto.scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.

const decipher = crypto.createDecipheriv(algorithm, key, iv);

const input = fs.createReadStream('test.enc');
const output = fs.createWriteStream('test.js');

input.pipe(decipher).pipe(output);
```

Example: Using the [`decipher.update()`][] and [`decipher.final()`][] methods:

```js
const crypto = require('crypto');

const algorithm = 'aes-192-cbc';
const password = 'Password used to generate key';
// Use the async `crypto.scrypt()` instead.
const key = crypto.scryptSync(password, 'salt', 24);
// The IV is usually passed along with the ciphertext.
const iv = Buffer.alloc(16, 0); // Initialization vector.

const decipher = crypto.createDecipheriv(algorithm, key, iv);

// Encrypted using same algorithm, key and iv.
const encrypted =
  'e5f79c5915c02171eec6b212d5520d44480993d7d622a7c4c2da32f6efda0ffa';
let decrypted = decipher.update(encrypted, 'hex', 'utf8');
decrypted += decipher.final('utf8');
console.log(decrypted);
// Prints: some clear text data
```

### decipher.final([outputEncoding])

* `outputEncoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string} Any remaining deciphered contents.
  If `outputEncoding` is specified, a string is
  returned. If an `outputEncoding` is not provided, a [`Buffer`][] is returned.

Once the `decipher.final()` method has been called, the `Decipher` object can
no longer be used to decrypt data. Attempts to call `decipher.final()` more
than once will result in an error being thrown.

### decipher.setAAD(buffer[, options])

* `buffer` {Buffer | TypedArray | DataView}
* `options` {Object} [`stream.transform` options][]
  - `plaintextLength` {number}
* Returns: {Decipher} for method chaining.

When using an authenticated encryption mode (`GCM`, `CCM` and `OCB` are
currently supported), the `decipher.setAAD()` method sets the value used for the
_additional authenticated data_ (AAD) input parameter.

The `options` argument is optional for `GCM`. When using `CCM`, the
`plaintextLength` option must be specified and its value must match the length
of the plaintext in bytes. See [CCM mode][].

The `decipher.setAAD()` method must be called before [`decipher.update()`][].

### decipher.setAuthTag(buffer)

* `buffer` {Buffer | TypedArray | DataView}
* Returns: {Decipher} for method chaining.

When using an authenticated encryption mode (`GCM`, `CCM` and `OCB` are
currently supported), the `decipher.setAuthTag()` method is used to pass in the
received _authentication tag_. If no tag is provided, or if the cipher text
has been tampered with, [`decipher.final()`][] will throw, indicating that the
cipher text should be discarded due to failed authentication.

Note that this Node.js version does not verify the length of GCM authentication
tags. Such a check *must* be implemented by applications and is crucial to the
authenticity of the encrypted data, otherwise, an attacker can use an
arbitrarily short authentication tag to increase the chances of successfully
passing authentication (up to 0.39%). It is highly recommended to associate one
of the values 16, 15, 14, 13, 12, 8 or 4 bytes with each key, and to only permit
authentication tags of that length, see [NIST SP 800-38D][].

The `decipher.setAuthTag()` method must be called before
[`decipher.final()`][].

### decipher.setAutoPadding([autoPadding])

* `autoPadding` {boolean} **Default:** `true`
* Returns: {Decipher} for method chaining.

When data has been encrypted without standard block padding, calling
`decipher.setAutoPadding(false)` will disable automatic padding to prevent
[`decipher.final()`][] from checking for and removing padding.

Turning auto padding off will only work if the input data's length is a
multiple of the ciphers block size.

The `decipher.setAutoPadding()` method must be called before
[`decipher.final()`][].

### decipher.update(data[, inputEncoding][, outputEncoding])

* `data` {string | Buffer | TypedArray | DataView}
* `inputEncoding` {string} The [encoding][] of the `data` string.
* `outputEncoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Updates the decipher with `data`. If the `inputEncoding` argument is given,
the `data`
argument is a string using the specified encoding. If the `inputEncoding`
argument is not given, `data` must be a [`Buffer`][]. If `data` is a
[`Buffer`][] then `inputEncoding` is ignored.

The `decipher.update()` method can be called multiple times with new data until
[`decipher.final()`][] is called. Calling `decipher.update()` after
[`decipher.final()`][] will result in an error being thrown.

## Class: DiffieHellman

The `DiffieHellman` class is a utility for creating Diffie-Hellman key
exchanges.

Instances of the `DiffieHellman` class can be created using the
[`crypto.createDiffieHellman()`][] function.

```js
const crypto = require('crypto');
const assert = require('assert');

// Generate Alice's keys...
const alice = crypto.createDiffieHellman(2048);
const aliceKey = alice.generateKeys();

// Generate Bob's keys...
const bob = crypto.createDiffieHellman(alice.getPrime(), alice.getGenerator());
const bobKey = bob.generateKeys();

// Exchange and generate the secret...
const aliceSecret = alice.computeSecret(bobKey);
const bobSecret = bob.computeSecret(aliceKey);

// OK
assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex'));
```

### diffieHellman.computeSecret(otherPublicKey[, inputEncoding][, outputEncoding])

* `otherPublicKey` {string | Buffer | TypedArray | DataView}
* `inputEncoding` {string} The [encoding][] of an `otherPublicKey` string.
* `outputEncoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Computes the shared secret using `otherPublicKey` as the other
party's public key and returns the computed shared secret. The supplied
key is interpreted using the specified `inputEncoding`, and secret is
encoded using specified `outputEncoding`.
If the `inputEncoding` is not
provided, `otherPublicKey` is expected to be a [`Buffer`][],
`TypedArray`, or `DataView`.

If `outputEncoding` is given a string is returned; otherwise, a
[`Buffer`][] is returned.

### diffieHellman.generateKeys([encoding])

* `encoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Generates private and public Diffie-Hellman key values, and returns
the public key in the specified `encoding`. This key should be
transferred to the other party.
If `encoding` is provided a string is returned; otherwise a
[`Buffer`][] is returned.

### diffieHellman.getGenerator([encoding])

* `encoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Returns the Diffie-Hellman generator in the specified `encoding`.
If `encoding` is provided a string is
returned; otherwise a [`Buffer`][] is returned.

### diffieHellman.getPrime([encoding])

* `encoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Returns the Diffie-Hellman prime in the specified `encoding`.
If `encoding` is provided a string is
returned; otherwise a [`Buffer`][] is returned.

### diffieHellman.getPrivateKey([encoding])

* `encoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Returns the Diffie-Hellman private key in the specified `encoding`.
If `encoding` is provided a
string is returned; otherwise a [`Buffer`][] is returned.

### diffieHellman.getPublicKey([encoding])

* `encoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Returns the Diffie-Hellman public key in the specified `encoding`.
If `encoding` is provided a
string is returned; otherwise a [`Buffer`][] is returned.

### diffieHellman.setPrivateKey(privateKey[, encoding])

* `privateKey` {string | Buffer | TypedArray | DataView}
* `encoding` {string} The [encoding][] of the `privateKey` string.

Sets the Diffie-Hellman private key. If the `encoding` argument is provided,
`privateKey` is expected
to be a string. If no `encoding` is provided, `privateKey` is expected
to be a [`Buffer`][], `TypedArray`, or `DataView`.

### diffieHellman.setPublicKey(publicKey[, encoding])

* `publicKey` {string | Buffer | TypedArray | DataView}
* `encoding` {string} The [encoding][] of the `publicKey` string.

Sets the Diffie-Hellman public key. If the `encoding` argument is provided,
`publicKey` is expected
to be a string. If no `encoding` is provided, `publicKey` is expected
to be a [`Buffer`][], `TypedArray`, or `DataView`.

### diffieHellman.verifyError

A bit field containing any warnings and/or errors resulting from a check
performed during initialization of the `DiffieHellman` object.

The following values are valid for this property (as defined in `constants`
module):

* `DH_CHECK_P_NOT_SAFE_PRIME`
* `DH_CHECK_P_NOT_PRIME`
* `DH_UNABLE_TO_CHECK_GENERATOR`
* `DH_NOT_SUITABLE_GENERATOR`

## Class: ECDH

The `ECDH` class is a utility for creating Elliptic Curve Diffie-Hellman (ECDH)
key exchanges.

Instances of the `ECDH` class can be created using the
[`crypto.createECDH()`][] function.

```js
const crypto = require('crypto');
const assert = require('assert');

// Generate Alice's keys...
const alice = crypto.createECDH('secp521r1');
const aliceKey = alice.generateKeys();

// Generate Bob's keys...
const bob = crypto.createECDH('secp521r1');
const bobKey = bob.generateKeys();

// Exchange and generate the secret...
const aliceSecret = alice.computeSecret(bobKey);
const bobSecret = bob.computeSecret(aliceKey);

assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex'));
// OK
```

### Class Method: ECDH.convertKey(key, curve[, inputEncoding[, outputEncoding[, format]]])

* `key` {string | Buffer | TypedArray | DataView}
* `curve` {string}
* `inputEncoding` {string} The [encoding][] of the `key` string.
* `outputEncoding` {string} The [encoding][] of the return value.
* `format` {string} **Default:** `'uncompressed'`
* Returns: {Buffer | string}

Converts the EC Diffie-Hellman public key specified by `key` and `curve` to the
format specified by `format`. The `format` argument specifies point encoding
and can be `'compressed'`, `'uncompressed'` or `'hybrid'`. The supplied key is
interpreted using the specified `inputEncoding`, and the returned key is encoded
using the specified `outputEncoding`.

Use [`crypto.getCurves()`][] to obtain a list of available curve names.
On recent OpenSSL releases, `openssl ecparam -list_curves` will also display
the name and description of each available elliptic curve.

If `format` is not specified the point will be returned in `'uncompressed'`
format.

If the `inputEncoding` is not provided, `key` is expected to be a [`Buffer`][],
`TypedArray`, or `DataView`.

Example (uncompressing a key):

```js
const { createECDH, ECDH } = require('crypto');

const ecdh = createECDH('secp256k1');
ecdh.generateKeys();

const compressedKey = ecdh.getPublicKey('hex', 'compressed');

const uncompressedKey = ECDH.convertKey(compressedKey,
                                        'secp256k1',
                                        'hex',
                                        'hex',
                                        'uncompressed');

// the converted key and the uncompressed public key should be the same
console.log(uncompressedKey === ecdh.getPublicKey('hex'));
```

### ecdh.computeSecret(otherPublicKey[, inputEncoding][, outputEncoding])

* `otherPublicKey` {string | Buffer | TypedArray | DataView}
* `inputEncoding` {string} The [encoding][] of the `otherPublicKey` string.
* `outputEncoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Computes the shared secret using `otherPublicKey` as the other
party's public key and returns the computed shared secret. The supplied
key is interpreted using specified `inputEncoding`, and the returned secret
is encoded using the specified `outputEncoding`.
If the `inputEncoding` is not
provided, `otherPublicKey` is expected to be a [`Buffer`][], `TypedArray`, or
`DataView`.

If `outputEncoding` is given a string will be returned; otherwise a
[`Buffer`][] is returned.

`ecdh.computeSecret` will throw an
`ERR_CRYPTO_ECDH_INVALID_PUBLIC_KEY` error when `otherPublicKey`
lies outside of the elliptic curve. Since `otherPublicKey` is
usually supplied from a remote user over an insecure network,
its recommended for developers to handle this exception accordingly.

### ecdh.generateKeys([encoding[, format]])

* `encoding` {string} The [encoding][] of the return value.
* `format` {string} **Default:** `'uncompressed'`
* Returns: {Buffer | string}

Generates private and public EC Diffie-Hellman key values, and returns
the public key in the specified `format` and `encoding`. This key should be
transferred to the other party.

The `format` argument specifies point encoding and can be `'compressed'` or
`'uncompressed'`. If `format` is not specified, the point will be returned in
`'uncompressed'` format.

If `encoding` is provided a string is returned; otherwise a [`Buffer`][]
is returned.

### ecdh.getPrivateKey([encoding])

* `encoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string} The EC Diffie-Hellman in the specified `encoding`.

If `encoding` is specified, a string is returned; otherwise a [`Buffer`][] is
returned.

### ecdh.getPublicKey([encoding][, format])

* `encoding` {string} The [encoding][] of the return value.
* `format` {string} **Default:** `'uncompressed'`
* Returns: {Buffer | string} The EC Diffie-Hellman public key in the specified
  `encoding` and `format`.

The `format` argument specifies point encoding and can be `'compressed'` or
`'uncompressed'`. If `format` is not specified the point will be returned in
`'uncompressed'` format.

If `encoding` is specified, a string is returned; otherwise a [`Buffer`][] is
returned.

### ecdh.setPrivateKey(privateKey[, encoding])

* `privateKey` {string | Buffer | TypedArray | DataView}
* `encoding` {string} The [encoding][] of the `privateKey` string.

Sets the EC Diffie-Hellman private key.
If `encoding` is provided, `privateKey` is expected
to be a string; otherwise `privateKey` is expected to be a [`Buffer`][],
`TypedArray`, or `DataView`.

If `privateKey` is not valid for the curve specified when the `ECDH` object was
created, an error is thrown. Upon setting the private key, the associated
public point (key) is also generated and set in the `ECDH` object.

### ecdh.setPublicKey(publicKey[, encoding])

> Stability: 0 - Deprecated

* `publicKey` {string | Buffer | TypedArray | DataView}
* `encoding` {string} The [encoding][] of the `publicKey` string.

Sets the EC Diffie-Hellman public key.
If `encoding` is provided `publicKey` is expected to
be a string; otherwise a [`Buffer`][], `TypedArray`, or `DataView` is expected.

Note that there is not normally a reason to call this method because `ECDH`
only requires a private key and the other party's public key to compute the
shared secret. Typically either [`ecdh.generateKeys()`][] or
[`ecdh.setPrivateKey()`][] will be called. The [`ecdh.setPrivateKey()`][] method
attempts to generate the public point/key associated with the private key being
set.

Example (obtaining a shared secret):

```js
const crypto = require('crypto');
const alice = crypto.createECDH('secp256k1');
const bob = crypto.createECDH('secp256k1');

// This is a shortcut way of specifying one of Alice's previous private
// keys. It would be unwise to use such a predictable private key in a real
// application.
alice.setPrivateKey(
  crypto.createHash('sha256').update('alice', 'utf8').digest()
);

// Bob uses a newly generated cryptographically strong
// pseudorandom key pair
bob.generateKeys();

const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex');

// aliceSecret and bobSecret should be the same shared secret value
console.log(aliceSecret === bobSecret);
```

## Class: Hash

The `Hash` class is a utility for creating hash digests of data. It can be
used in one of two ways:

- As a [stream][] that is both readable and writable, where data is written
  to produce a computed hash digest on the readable side, or
- Using the [`hash.update()`][] and [`hash.digest()`][] methods to produce the
  computed hash.

The [`crypto.createHash()`][] method is used to create `Hash` instances. `Hash`
objects are not to be created directly using the `new` keyword.

Example: Using `Hash` objects as streams:

```js
const crypto = require('crypto');
const hash = crypto.createHash('sha256');

hash.on('readable', () => {
  // Only one element is going to be produced by the
  // hash stream.
  const data = hash.read();
  if (data) {
    console.log(data.toString('hex'));
    // Prints:
    //   6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
  }
});

hash.write('some data to hash');
hash.end();
```

Example: Using `Hash` and piped streams:

```js
const crypto = require('crypto');
const fs = require('fs');
const hash = crypto.createHash('sha256');

const input = fs.createReadStream('test.js');
input.pipe(hash).pipe(process.stdout);
```

Example: Using the [`hash.update()`][] and [`hash.digest()`][] methods:

```js
const crypto = require('crypto');
const hash = crypto.createHash('sha256');

hash.update('some data to hash');
console.log(hash.digest('hex'));
// Prints:
//   6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
```

### hash.digest([encoding])

* `encoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Calculates the digest of all of the data passed to be hashed (using the
[`hash.update()`][] method).
If `encoding` is provided a string will be returned; otherwise
a [`Buffer`][] is returned.

The `Hash` object can not be used again after `hash.digest()` method has been
called. Multiple calls will cause an error to be thrown.

### hash.update(data[, inputEncoding])

* `data` {string | Buffer | TypedArray | DataView}
* `inputEncoding` {string} The [encoding][] of the `data` string.

Updates the hash content with the given `data`, the encoding of which
is given in `inputEncoding`.
If `encoding` is not provided, and the `data` is a string, an
encoding of `'utf8'` is enforced. If `data` is a [`Buffer`][], `TypedArray`, or
`DataView`, then `inputEncoding` is ignored.

This can be called many times with new data as it is streamed.

## Class: Hmac

The `Hmac` Class is a utility for creating cryptographic HMAC digests. It can
be used in one of two ways:

- As a [stream][] that is both readable and writable, where data is written
  to produce a computed HMAC digest on the readable side, or
- Using the [`hmac.update()`][] and [`hmac.digest()`][] methods to produce the
  computed HMAC digest.

The [`crypto.createHmac()`][] method is used to create `Hmac` instances. `Hmac`
objects are not to be created directly using the `new` keyword.

Example: Using `Hmac` objects as streams:

```js
const crypto = require('crypto');
const hmac = crypto.createHmac('sha256', 'a secret');

hmac.on('readable', () => {
  // Only one element is going to be produced by the
  // hash stream.
  const data = hmac.read();
  if (data) {
    console.log(data.toString('hex'));
    // Prints:
    //   7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
  }
});

hmac.write('some data to hash');
hmac.end();
```

Example: Using `Hmac` and piped streams:

```js
const crypto = require('crypto');
const fs = require('fs');
const hmac = crypto.createHmac('sha256', 'a secret');

const input = fs.createReadStream('test.js');
input.pipe(hmac).pipe(process.stdout);
```

Example: Using the [`hmac.update()`][] and [`hmac.digest()`][] methods:

```js
const crypto = require('crypto');
const hmac = crypto.createHmac('sha256', 'a secret');

hmac.update('some data to hash');
console.log(hmac.digest('hex'));
// Prints:
//   7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
```

### hmac.digest([encoding])

* `encoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Calculates the HMAC digest of all of the data passed using [`hmac.update()`][].
If `encoding` is
provided a string is returned; otherwise a [`Buffer`][] is returned;

The `Hmac` object can not be used again after `hmac.digest()` has been
called. Multiple calls to `hmac.digest()` will result in an error being thrown.

### hmac.update(data[, inputEncoding])

* `data` {string | Buffer | TypedArray | DataView}
* `inputEncoding` {string} The [encoding][] of the `data` string.

Updates the `Hmac` content with the given `data`, the encoding of which
is given in `inputEncoding`.
If `encoding` is not provided, and the `data` is a string, an
encoding of `'utf8'` is enforced. If `data` is a [`Buffer`][], `TypedArray`, or
`DataView`, then `inputEncoding` is ignored.

This can be called many times with new data as it is streamed.

## Class: Sign

The `Sign` Class is a utility for generating signatures. It can be used in one
of two ways:

- As a writable [stream][], where data to be signed is written and the
  [`sign.sign()`][] method is used to generate and return the signature, or
- Using the [`sign.update()`][] and [`sign.sign()`][] methods to produce the
  signature.

The [`crypto.createSign()`][] method is used to create `Sign` instances. The
argument is the string name of the hash function to use. `Sign` objects are not
to be created directly using the `new` keyword.

Example: Using `Sign` objects as streams:

```js
const crypto = require('crypto');
const sign = crypto.createSign('SHA256');

sign.write('some data to sign');
sign.end();

const privateKey = getPrivateKeySomehow();
console.log(sign.sign(privateKey, 'hex'));
// Prints: the calculated signature using the specified private key and
// SHA-256. For RSA keys, the algorithm is RSASSA-PKCS1-v1_5 (see padding
// parameter below for RSASSA-PSS). For EC keys, the algorithm is ECDSA.
```

Example: Using the [`sign.update()`][] and [`sign.sign()`][] methods:

```js
const crypto = require('crypto');
const sign = crypto.createSign('SHA256');

sign.update('some data to sign');

const privateKey = getPrivateKeySomehow();
console.log(sign.sign(privateKey, 'hex'));
// Prints: the calculated signature
```

In some cases, a `Sign` instance can also be created by passing in a signature
algorithm name, such as 'RSA-SHA256'. This will use the corresponding digest
algorithm. This does not work for all signature algorithms, such as
'ecdsa-with-SHA256'. Use digest names instead.

Example: signing using legacy signature algorithm name

```js
const crypto = require('crypto');
const sign = crypto.createSign('RSA-SHA256');

sign.update('some data to sign');

const privateKey = getPrivateKeySomehow();
console.log(sign.sign(privateKey, 'hex'));
// Prints: the calculated signature
```

### sign.sign(privateKey[, outputEncoding])

* `privateKey` {string | Object}
  - `key` {string}
  - `passphrase` {string}
  - `padding` {integer}
  - `saltLength` {integer}
* `outputEncoding` {string} The [encoding][] of the return value.
* Returns: {Buffer | string}

Calculates the signature on all the data passed through using either
[`sign.update()`][] or [`sign.write()`][stream-writable-write].

The `privateKey` argument can be an object or a string. If `privateKey` is a
string, it is treated as a raw key with no passphrase. If `privateKey` is an
object, it must contain one or more of the following properties:

* `key`: {string} - PEM encoded private key (required)
* `passphrase`: {string} - passphrase for the private key
* `padding`: {integer} - Optional padding value for RSA, one of the following:
  * `crypto.constants.RSA_PKCS1_PADDING` (default)
  * `crypto.constants.RSA_PKCS1_PSS_PADDING`

Note that `RSA_PKCS1_PSS_PADDING` will use MGF1 with the same hash function
  used to sign the message as specified in section 3.1 of [RFC 4055][].
* `saltLength`: {integer} - salt length for when padding is
  `RSA_PKCS1_PSS_PADDING`. The special value
  `crypto.constants.RSA_PSS_SALTLEN_DIGEST` sets the salt length to the digest
  size, `crypto.constants.RSA_PSS_SALTLEN_MAX_SIGN` (default) sets it to the
  maximum permissible value.

If `outputEncoding` is provided a string is returned; otherwise a [`Buffer`][]
is returned.

The `Sign` object can not be again used after `sign.sign()` method has been
called. Multiple calls to `sign.sign()` will result in an error being thrown.

### sign.update(data[, inputEncoding])

* `data` {string | Buffer | TypedArray | DataView}
* `inputEncoding` {string} The [encoding][] of the `data` string.

Updates the `Sign` content with the given `data`, the encoding of which
is given in `inputEncoding`.
If `encoding` is not provided, and the `data` is a string, an
encoding of `'utf8'` is enforced. If `data` is a [`Buffer`][], `TypedArray`, or
`DataView`, then `inputEncoding` is ignored.

This can be called many times with new data as it is streamed.

## Class: Verify

The `Verify` class is a utility for verifying signatures. It can be used in one
of two ways:

- As a writable [stream][] where written data is used to validate against the
  supplied signature, or
- Using the [`verify.update()`][] and [`verify.verify()`][] methods to verify
  the signature.

The [`crypto.createVerify()`][] method is used to create `Verify` instances.
`Verify` objects are not to be created directly using the `new` keyword.

Example: Using `Verify` objects as streams:

```js
const crypto = require('crypto');
const verify = crypto.createVerify('SHA256');

verify.write('some data to sign');
verify.end();

const publicKey = getPublicKeySomehow();
const signature = getSignatureToVerify();
console.log(verify.verify(publicKey, signature));
// Prints: true or false
```

Example: Using the [`verify.update()`][] and [`verify.verify()`][] methods:

```js
const crypto = require('crypto');
const verify = crypto.createVerify('SHA256');

verify.update('some data to sign');

const publicKey = getPublicKeySomehow();
const signature = getSignatureToVerify();
console.log(verify.verify(publicKey, signature));
// Prints: true or false
```

### verify.update(data[, inputEncoding])

* `data` {string | Buffer | TypedArray | DataView}
* `inputEncoding` {string} The [encoding][] of the `data` string.

Updates the `Verify` content with the given `data`, the encoding of which
is given in `inputEncoding`.
If `inputEncoding` is not provided, and the `data` is a string, an
encoding of `'utf8'` is enforced. If `data` is a [`Buffer`][], `TypedArray`, or
`DataView`, then `inputEncoding` is ignored.

This can be called many times with new data as it is streamed.

### verify.verify(object, signature[, signatureEncoding])

* `object` {string | Object}
* `signature` {string | Buffer | TypedArray | DataView}
* `signatureEncoding` {string} The [encoding][] of the `signature` string.
* Returns: {boolean} `true` or `false` depending on the validity of the
  signature for the data and public key.

Verifies the provided data using the given `object` and `signature`.
The `object` argument can be either a string containing a PEM encoded object,
which can be an RSA public key, a DSA public key, or an X.509 certificate,
or an object with one or more of the following properties:

* `key`: {string} - PEM encoded public key (required)
* `padding`: {integer} - Optional padding value for RSA, one of the following:
  * `crypto.constants.RSA_PKCS1_PADDING` (default)
  * `crypto.constants.RSA_PKCS1_PSS_PADDING`

Note that `RSA_PKCS1_PSS_PADDING` will use MGF1 with the same hash function
  used to verify the message as specified in section 3.1 of [RFC 4055][].
* `saltLength`: {integer} - salt length for when padding is
  `RSA_PKCS1_PSS_PADDING`. The special value
  `crypto.constants.RSA_PSS_SALTLEN_DIGEST` sets the salt length to the digest
  size, `crypto.constants.RSA_PSS_SALTLEN_AUTO` (default) causes it to be
  determined automatically.

The `signature` argument is the previously calculated signature for the data, in
the `signatureEncoding`.
If a `signatureEncoding` is specified, the `signature` is expected to be a
string; otherwise `signature` is expected to be a [`Buffer`][],
`TypedArray`, or `DataView`.

The `verify` object can not be used again after `verify.verify()` has been
called. Multiple calls to `verify.verify()` will result in an error being
thrown.

## `crypto` module methods and properties

### crypto.constants

* Returns: {Object} An object containing commonly used constants for crypto and
  security related operations. The specific constants currently defined are
  described in [Crypto Constants][].

### crypto.DEFAULT_ENCODING

> Stability: 0 - Deprecated

The default encoding to use for functions that can take either strings
or [buffers][`Buffer`]. The default value is `'buffer'`, which makes methods
default to [`Buffer`][] objects.

The `crypto.DEFAULT_ENCODING` mechanism is provided for backwards compatibility
with legacy programs that expect `'latin1'` to be the default encoding.

New applications should expect the default to be `'buffer'`.

This property is deprecated.

### crypto.fips

> Stability: 0 - Deprecated

Property for checking and controlling whether a FIPS compliant crypto provider
is currently in use. Setting to true requires a FIPS build of Node.js.

This property is deprecated. Please use `crypto.setFips()` and
`crypto.getFips()` instead.

### crypto.createCipher(algorithm, password[, options])

> Stability: 0 - Deprecated: Use [`crypto.createCipheriv()`][] instead.

* `algorithm` {string}
* `password` {string | Buffer | TypedArray | DataView}
* `options` {Object} [`stream.transform` options][]
* Returns: {Cipher}

Creates and returns a `Cipher` object that uses the given `algorithm` and
`password`.

The `options` argument controls stream behavior and is optional except when a
cipher in CCM or OCB mode is used (e.g. `'aes-128-ccm'`). In that case, the
`authTagLength` option is required and specifies the length of the
authentication tag in bytes, see [CCM mode][]. In GCM mode, the `authTagLength`
option is not required but can be used to set the length of the authentication
tag that will be returned by `getAuthTag()` and defaults to 16 bytes.

The `algorithm` is dependent on OpenSSL, examples are `'aes192'`, etc. On
recent OpenSSL releases, `openssl list -cipher-algorithms`
(`openssl list-cipher-algorithms` for older versions of OpenSSL) will
display the available cipher algorithms.

The `password` is used to derive the cipher key and initialization vector (IV).
The value must be either a `'latin1'` encoded string, a [`Buffer`][], a
`TypedArray`, or a `DataView`.

The implementation of `crypto.createCipher()` derives keys using the OpenSSL
function [`EVP_BytesToKey`][] with the digest algorithm set to MD5, one
iteration, and no salt. The lack of salt allows dictionary attacks as the same
password always creates the same key. The low iteration count and
non-cryptographically secure hash algorithm allow passwords to be tested very
rapidly.

In line with OpenSSL's recommendation to use a more modern algorithm instead of
[`EVP_BytesToKey`][] it is recommended that developers derive a key and IV on
their own using [`crypto.scrypt()`][] and to use [`crypto.createCipheriv()`][]
to create the `Cipher` object. Users should not use ciphers with counter mode
(e.g. CTR, GCM, or CCM) in `crypto.createCipher()`. A warning is emitted when
they are used in order to avoid the risk of IV reuse that causes
vulnerabilities. For the case when IV is reused in GCM, see [Nonce-Disrespecting
Adversaries][] for details.

### crypto.createCipheriv(algorithm, key, iv[, options])

* `algorithm` {string}
* `key` {string | Buffer | TypedArray | DataView}
* `iv` {string | Buffer | TypedArray | DataView}
* `options` {Object} [`stream.transform` options][]
* Returns: {Cipher}

Creates and returns a `Cipher` object, with the given `algorithm`, `key` and
initialization vector (`iv`).

The `key` is the raw key used by the `algorithm` and `iv` is an
[initialization vector][]. Both arguments must be `'utf8'` encoded strings,
[Buffers][`Buffer`], `TypedArray`, or `DataView`s. If the cipher does not need
an initialization vector, `iv` may be `null`.

Initialization vectors should be unpredictable and unique; ideally, they will be
cryptographically random. They do not have to be secret: IVs are typically just
added to ciphertext messages unencrypted. It may sound contradictory that
something has to be unpredictable and unique, but does not have to be secret;
it is important to remember that an attacker must not be able to predict ahead
of time what a given IV will be.

### crypto.createCredentials(details)

> Stability: 0 - Deprecated: Use [`tls.createSecureContext()`][] instead.

- `details` {Object} Identical to [`tls.createSecureContext()`][].
- Returns: {tls.SecureContext}

The `crypto.createCredentials()` method is a deprecated function for creating
and returning a `tls.SecureContext`. It should not be used. Replace it with
[`tls.createSecureContext()`][] which has the exact same arguments and return
value.

Returns a `tls.SecureContext`, as-if [`tls.createSecureContext()`][] had been
called.

### crypto.createDecipher(algorithm, password[, options])

> Stability: 0 - Deprecated: Use [`crypto.createDecipheriv()`][] instead.

* `algorithm` {string}
* `password` {string | Buffer | TypedArray | DataView}
* `options` {Object} [`stream.transform` options][]
* Returns: {Decipher}

Creates and returns a `Decipher` object that uses the given `algorithm` and
`password` (key).

The implementation of `crypto.createDecipher()` derives keys using the OpenSSL
function [`EVP_BytesToKey`][] with the digest algorithm set to MD5, one
iteration, and no salt. The lack of salt allows dictionary attacks as the same
password always creates the same key. The low iteration count and
non-cryptographically secure hash algorithm allow passwords to be tested very
rapidly.

### crypto.createDecipheriv(algorithm, key, iv[, options])

* `algorithm` {string}
* `key` {string | Buffer | TypedArray | DataView}
* `iv` {string | Buffer | TypedArray | DataView}
* `options` {Object} [`stream.transform` options][]
* Returns: {Decipher}

Creates and returns a `Decipher` object that uses the given `algorithm`, `key`
and initialization vector (`iv`).

The `options` argument controls stream behavior and is optional except when a
cipher in CCM or OCB mode is used (e.g. `'aes-128-ccm'`). In that case, the
`authTagLength` option is required and specifies the length of the
authentication tag in bytes, see [CCM mode][]. In GCM mode, the `authTagLength`
option is not required but can be used to restrict accepted authentication tags
to those with the specified length.

### crypto.createDiffieHellman(prime[, primeEncoding][, generator][, generatorEncoding])

* `prime` {string | Buffer | TypedArray | DataView}
* `primeEncoding` {string} The [encoding][] of the `prime` string.
* `generator` {number | string | Buffer | TypedArray | DataView} **Default:**
  `2`
* `generatorEncoding` {string} The [encoding][] of the `generator` string.
* Returns: {DiffieHellman}

Creates a `DiffieHellman` key exchange object using the supplied `prime` and an
optional specific `generator`.

The `generator` argument can be a number, string, or [`Buffer`][]. If
`generator` is not specified, the value `2` is used.

If `primeEncoding` is specified, `prime` is expected to be a string; otherwise
a [`Buffer`][], `TypedArray`, or `DataView` is expected.

If `generatorEncoding` is specified, `generator` is expected to be a string;
otherwise a number, [`Buffer`][], `TypedArray`, or `DataView` is expected.

### crypto.createDiffieHellman(primeLength[, generator])

* `primeLength` {number}
* `generator` {number | string | Buffer | TypedArray | DataView} **Default:**
  `2`
* Returns: {DiffieHellman}

Creates a `DiffieHellman` key exchange object and generates a prime of
`primeLength` bits using an optional specific numeric `generator`.
If `generator` is not specified, the value `2` is used.

### crypto.createECDH(curveName)

* `curveName` {string}
* Returns: {ECDH}

Creates an Elliptic Curve Diffie-Hellman (`ECDH`) key exchange object using a
predefined curve specified by the `curveName` string. Use
[`crypto.getCurves()`][] to obtain a list of available curve names. On recent
OpenSSL releases, `openssl ecparam -list_curves` will also display the name
and description of each available elliptic curve.

### crypto.createHash(algorithm[, options])

* `algorithm` {string}
* `options` {Object} [`stream.transform` options][]
* Returns: {Hash}

Creates and returns a `Hash` object that can be used to generate hash digests
using the given `algorithm`. Optional `options` argument controls stream
behavior.

The `algorithm` is dependent on the available algorithms supported by the
version of OpenSSL on the platform. Examples are `'sha256'`, `'sha512'`, etc.
On recent releases of OpenSSL, `openssl list -digest-algorithms`
(`openssl list-message-digest-algorithms` for older versions of OpenSSL) will
display the available digest algorithms.

Example: generating the sha256 sum of a file

```js
const filename = process.argv[2];
const crypto = require('crypto');
const fs = require('fs');

const hash = crypto.createHash('sha256');

### crypto.createHmac(algorithm, key[, options])

* `algorithm` {string}
* `key` {string | Buffer | TypedArray | DataView}
* `options` {Object} [`stream.transform` options][]
* Returns: {Hmac}

Creates and returns an `Hmac` object that uses the given `algorithm` and `key`.
Optional `options` argument controls stream behavior.

The `key` is the HMAC key used to generate the cryptographic HMAC hash.

Example: generating the sha256 HMAC of a file

```js
const filename = process.argv[2];
const crypto = require('crypto');
const fs = require('fs');

const hmac = crypto.createHmac('sha256', 'a secret');

### crypto.createSign(algorithm[, options])

* `algorithm` {string}
* `options` {Object} [`stream.Writable` options][]
* Returns: {Sign}

Creates and returns a `Sign` object that uses the given `algorithm`.
Use [`crypto.getHashes()`][] to obtain an array of names of the available
signing algorithms. Optional `options` argument controls the
`stream.Writable` behavior.

### crypto.createVerify(algorithm[, options])

* `algorithm` {string}
* `options` {Object} [`stream.Writable` options][]
* Returns: {Verify}

Creates and returns a `Verify` object that uses the given algorithm.
Use [`crypto.getHashes()`][] to obtain an array of names of the available
signing algorithms. Optional `options` argument controls the
`stream.Writable` behavior.

### crypto.generateKeyPair(type, options, callback)

* `type`: {string} Must be `'rsa'`, `'dsa'` or `'ec'`.
* `options`: {Object}
  - `modulusLength`: {number} Key size in bits (RSA, DSA).
  - `publicExponent`: {number} Public exponent (RSA). **Default:** `0x10001`.
  - `divisorLength`: {number} Size of `q` in bits (DSA).
  - `namedCurve`: {string} Name of the curve to use (EC).
  - `publicKeyEncoding`: {Object}
    - `type`: {string} Must be one of `'pkcs1'` (RSA only) or `'spki'`.
    - `format`: {string} Must be `'pem'` or `'der'`.
  - `privateKeyEncoding`: {Object}
    - `type`: {string} Must be one of `'pkcs1'` (RSA only), `'pkcs8'` or
      `'sec1'` (EC only).
    - `format`: {string} Must be `'pem'` or `'der'`.
    - `cipher`: {string} If specified, the private key will be encrypted with
      the given `cipher` and `passphrase` using PKCS#5 v2.0 password based
      encryption.
    - `passphrase`: {string} The passphrase to use for encryption, see `cipher`.
* `callback`: {Function}
  - `err`: {Error}
  - `publicKey`: {string|Buffer}
  - `privateKey`: {string|Buffer}

Generates a new asymmetric key pair of the given `type`. Only RSA, DSA and EC
are currently supported.

It is recommended to encode public keys as `'spki'` and private keys as
`'pkcs8'` with encryption:

```js
const { generateKeyPair } = require('crypto');
generateKeyPair('rsa', {
  modulusLength: 4096,
  publicKeyEncoding: {
    type: 'spki',
    format: 'pem'
  },
  privateKeyEncoding: {
    type: 'pkcs8',
    format: 'pem',
    cipher: 'aes-256-cbc',
    passphrase: 'top secret'
  }
}, (err, publicKey, privateKey) => {
  // Handle errors and use the generated key pair.
});
```

On completion, `callback` will be called with `err` set to `undefined` and
`publicKey` / `privateKey` representing the generated key pair. When PEM
encoding was selected, the result will be a string, otherwise it will be a
buffer containing the data encoded as DER. Note that Node.js itself does not
accept DER, it is supported for interoperability with other libraries such as
WebCrypto only.

If this method is invoked as its [`util.promisify()`][]ed version, it returns
a `Promise` for an `Object` with `publicKey` and `privateKey` properties.

### crypto.generateKeyPairSync(type, options)

* `type`: {string} Must be `'rsa'`, `'dsa'` or `'ec'`.
* `options`: {Object}
  - `modulusLength`: {number} Key size in bits (RSA, DSA).
  - `publicExponent`: {number} Public exponent (RSA). **Default:** `0x10001`.
  - `divisorLength`: {number} Size of `q` in bits (DSA).
  - `namedCurve`: {string} Name of the curve to use (EC).
  - `publicKeyEncoding`: {Object}
    - `type`: {string} Must be one of `'pkcs1'` (RSA only) or `'spki'`.
    - `format`: {string} Must be `'pem'` or `'der'`.
  - `privateKeyEncoding`: {Object}
    - `type`: {string} Must be one of `'pkcs1'` (RSA only), `'pkcs8'` or
      `'sec1'` (EC only).
    - `format`: {string} Must be `'pem'` or `'der'`.
    - `cipher`: {string} If specified, the private key will be encrypted with
      the given `cipher` and `passphrase` using PKCS#5 v2.0 password based
      encryption.
    - `passphrase`: {string} The passphrase to use for encryption, see `cipher`.
* Returns: {Object}
  - `publicKey`: {string|Buffer}
  - `privateKey`: {string|Buffer}

Generates a new asymmetric key pair of the given `type`. Only RSA, DSA and EC
are currently supported.

It is recommended to encode public keys as `'spki'` and private keys as
`'pkcs8'` with encryption:

```js
const { generateKeyPairSync } = require('crypto');
const { publicKey, privateKey } = generateKeyPairSync('rsa', {
  modulusLength: 4096,
  publicKeyEncoding: {
    type: 'spki',
    format: 'pem'
  },
  privateKeyEncoding: {
    type: 'pkcs8',
    format: 'pem',
    cipher: 'aes-256-cbc',
    passphrase: 'top secret'
  }
});
```

The return value `{ publicKey, privateKey }` represents the generated key pair.
When PEM encoding was selected, the respective key will be a string, otherwise
it will be a buffer containing the data encoded as DER.

### crypto.getCiphers()

* Returns: {string[]} An array with the names of the supported cipher
  algorithms.

```js
const ciphers = crypto.getCiphers();
console.log(ciphers); // ['aes-128-cbc', 'aes-128-ccm', ...]
```

### crypto.getCurves()

* Returns: {string[]} An array with the names of the supported elliptic curves.

```js
const curves = crypto.getCurves();
console.log(curves); // ['Oakley-EC2N-3', 'Oakley-EC2N-4', ...]
```

### crypto.getDiffieHellman(groupName)

* `groupName` {string}
* Returns: {DiffieHellman}

Creates a predefined `DiffieHellman` key exchange object. The
supported groups are: `'modp1'`, `'modp2'`, `'modp5'` (defined in
[RFC 2412][], but see [Caveats][]) and `'modp14'`, `'modp15'`,
`'modp16'`, `'modp17'`, `'modp18'` (defined in [RFC 3526][]). The
returned object mimics the interface of objects created by
[`crypto.createDiffieHellman()`][], but will not allow changing
the keys (with [`diffieHellman.setPublicKey()`][], for example). The
advantage of using this method is that the parties do not have to
generate nor exchange a group modulus beforehand, saving both processor
and communication time.

Example (obtaining a shared secret):

```js
const crypto = require('crypto');
const alice = crypto.getDiffieHellman('modp14');
const bob = crypto.getDiffieHellman('modp14');

alice.generateKeys();
bob.generateKeys();

const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex');

/* aliceSecret and bobSecret should be the same */
console.log(aliceSecret === bobSecret);
```

### crypto.getFips()

* Returns: {boolean} `true` if and only if a FIPS compliant crypto provider is
  currently in use.

### crypto.getHashes()

* Returns: {string[]} An array of the names of the supported hash algorithms,
  such as `'RSA-SHA256'`.

```js
const hashes = crypto.getHashes();
console.log(hashes); // ['DSA', 'DSA-SHA', 'DSA-SHA1', ...]
```

### crypto.pbkdf2(password, salt, iterations, keylen, digest, callback)

* `password` {string|Buffer|TypedArray|DataView}
* `salt` {string|Buffer|TypedArray|DataView}
* `iterations` {number}
* `keylen` {number}
* `digest` {string}
* `callback` {Function}
  - `err` {Error}
  - `derivedKey` {Buffer}

Provides an asynchronous Password-Based Key Derivation Function 2 (PBKDF2)
implementation. A selected HMAC digest algorithm specified by `digest` is
applied to derive a key of the requested byte length (`keylen`) from the
`password`, `salt` and `iterations`.

The supplied `callback` function is called with two arguments: `err` and
`derivedKey`. If an error occurs while deriving the key, `err` will be set;
otherwise `err` will be `null`. By default, the successfully generated
`derivedKey` will be passed to the callback as a [`Buffer`][]. An error will be
thrown if any of the input arguments specify invalid values or types.

If `digest` is `null`, `'sha1'` will be used. This behavior will be deprecated
in a future version of Node.js.

The `iterations` argument must be a number set as high as possible. The
higher the number of iterations, the more secure the derived key will be,
but will take a longer amount of time to complete.

The `salt` should be as unique as possible. It is recommended that a salt is
random and at least 16 bytes long. See [NIST SP 800-132][] for details.

```js
const crypto = require('crypto');
crypto.pbkdf2('secret', 'salt', 100000, 64, 'sha512', (err, derivedKey) => {
  if (err) throw err;
  console.log(derivedKey.toString('hex'));  // '3745e48...08d59ae'
});
```

The `crypto.DEFAULT_ENCODING` property can be used to change the way the
`derivedKey` is passed to the callback. This property, however, has been
deprecated and use should be avoided.

```js
const crypto = require('crypto');
crypto.DEFAULT_ENCODING = 'hex';
crypto.pbkdf2('secret', 'salt', 100000, 512, 'sha512', (err, derivedKey) => {
  if (err) throw err;
  console.log(derivedKey);  // '3745e48...aa39b34'
});
```

An array of supported digest functions can be retrieved using
[`crypto.getHashes()`][].

Note that this API uses libuv's threadpool, which can have surprising and
negative performance implications for some applications, see the
[`UV_THREADPOOL_SIZE`][] documentation for more information.

### crypto.pbkdf2Sync(password, salt, iterations, keylen, digest)

* `password` {string|Buffer|TypedArray|DataView}
* `salt` {string|Buffer|TypedArray|DataView}
* `iterations` {number}
* `keylen` {number}
* `digest` {string}
* Returns: {Buffer}

Provides a synchronous Password-Based Key Derivation Function 2 (PBKDF2)
implementation. A selected HMAC digest algorithm specified by `digest` is
applied to derive a key of the requested byte length (`keylen`) from the
`password`, `salt` and `iterations`.

If an error occurs an `Error` will be thrown, otherwise the derived key will be
returned as a [`Buffer`][].

If `digest` is `null`, `'sha1'` will be used. This behavior will be deprecated
in a future version of Node.js.

The `iterations` argument must be a number set as high as possible. The
higher the number of iterations, the more secure the derived key will be,
but will take a longer amount of time to complete.

The `salt` should be as unique as possible. It is recommended that a salt is
random and at least 16 bytes long. See [NIST SP 800-132][] for details.

```js
const crypto = require('crypto');
const key = crypto.pbkdf2Sync('secret', 'salt', 100000, 64, 'sha512');
console.log(key.toString('hex'));  // '3745e48...08d59ae'
```

The `crypto.DEFAULT_ENCODING` property may be used to change the way the
`derivedKey` is returned. This property, however, is deprecated and use
should be avoided.

```js
const crypto = require('crypto');
crypto.DEFAULT_ENCODING = 'hex';
const key = crypto.pbkdf2Sync('secret', 'salt', 100000, 512, 'sha512');
console.log(key);  // '3745e48...aa39b34'
```

An array of supported digest functions can be retrieved using
[`crypto.getHashes()`][].

### crypto.privateDecrypt(privateKey, buffer)

* `privateKey` {Object | string}
  - `key` {string} A PEM encoded private key.
  - `passphrase` {string} An optional passphrase for the private key.
  - `padding` {crypto.constants} An optional padding value defined in
    `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING`,
    `crypto.constants.RSA_PKCS1_PADDING`, or
    `crypto.constants.RSA_PKCS1_OAEP_PADDING`.
* `buffer` {Buffer | TypedArray | DataView}
* Returns: {Buffer} A new `Buffer` with the decrypted content.

Decrypts `buffer` with `privateKey`. `buffer` was previously encrypted using
the corresponding public key, for example using [`crypto.publicEncrypt()`][].

`privateKey` can be an object or a string. If `privateKey` is a string, it is
treated as the key with no passphrase and will use `RSA_PKCS1_OAEP_PADDING`.

### crypto.privateEncrypt(privateKey, buffer)

* `privateKey` {Object | string}
  - `key` {string} A PEM encoded private key.
  - `passphrase` {string} An optional passphrase for the private key.
  - `padding` {crypto.constants} An optional padding value defined in
    `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING` or
    `crypto.constants.RSA_PKCS1_PADDING`.
* `buffer` {Buffer | TypedArray | DataView}
* Returns: {Buffer} A new `Buffer` with the encrypted content.

Encrypts `buffer` with `privateKey`. The returned data can be decrypted using
the corresponding public key, for example using [`crypto.publicDecrypt()`][].

`privateKey` can be an object or a string. If `privateKey` is a string, it is
treated as the key with no passphrase and will use `RSA_PKCS1_PADDING`.

### crypto.publicDecrypt(key, buffer)

* `key` {Object | string}
  - `key` {string} A PEM encoded public or private key.
  - `passphrase` {string} An optional passphrase for the private key.
  - `padding` {crypto.constants} An optional padding value defined in
    `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING` or
    `crypto.constants.RSA_PKCS1_PADDING`.
* `buffer` {Buffer | TypedArray | DataView}
* Returns: {Buffer} A new `Buffer` with the decrypted content.

Decrypts `buffer` with `key`.`buffer` was previously encrypted using
the corresponding private key, for example using [`crypto.privateEncrypt()`][].

`key` can be an object or a string. If `key` is a string, it is treated as
the key with no passphrase and will use `RSA_PKCS1_PADDING`.

Because RSA public keys can be derived from private keys, a private key may
be passed instead of a public key.

### crypto.publicEncrypt(key, buffer)

* `key` {Object | string}
  - `key` {string} A PEM encoded public or private key.
  - `passphrase` {string} An optional passphrase for the private key.
  - `padding` {crypto.constants} An optional padding value defined in
    `crypto.constants`, which may be: `crypto.constants.RSA_NO_PADDING`,
    `crypto.constants.RSA_PKCS1_PADDING`, or
    `crypto.constants.RSA_PKCS1_OAEP_PADDING`.
* `buffer` {Buffer | TypedArray | DataView}
* Returns: {Buffer} A new `Buffer` with the encrypted content.

Encrypts the content of `buffer` with `key` and returns a new
[`Buffer`][] with encrypted content. The returned data can be decrypted using
the corresponding private key, for example using [`crypto.privateDecrypt()`][].

`key` can be an object or a string. If `key` is a string, it is treated as
the key with no passphrase and will use `RSA_PKCS1_OAEP_PADDING`.

Because RSA public keys can be derived from private keys, a private key may
be passed instead of a public key.

### crypto.randomBytes(size[, callback])

* `size` {number}
* `callback` {Function}
  - `err` {Error}
  - `buf` {Buffer}
* Returns: {Buffer} if the `callback` function is not provided.

Generates cryptographically strong pseudo-random data. The `size` argument
is a number indicating the number of bytes to generate.

If a `callback` function is provided, the bytes are generated asynchronously
and the `callback` function is invoked with two arguments: `err` and `buf`.
If an error occurs, `err` will be an `Error` object; otherwise it is `null`. The
`buf` argument is a [`Buffer`][] containing the generated bytes.

```js
// Asynchronous
const crypto = require('crypto');
crypto.randomBytes(256, (err, buf) => {
  if (err) throw err;
  console.log(`${buf.length} bytes of random data: ${buf.toString('hex')}`);
});
```

If the `callback` function is not provided, the random bytes are generated
synchronously and returned as a [`Buffer`][]. An error will be thrown if
there is a problem generating the bytes.

```js
// Synchronous
const buf = crypto.randomBytes(256);
console.log(
  `${buf.length} bytes of random data: ${buf.toString('hex')}`);
```

The `crypto.randomBytes()` method will not complete until there is
sufficient entropy available.
This should normally never take longer than a few milliseconds. The only time
when generating the random bytes may conceivably block for a longer period of
time is right after boot, when the whole system is still low on entropy.

Note that this API uses libuv's threadpool, which can have surprising and
negative performance implications for some applications, see the
[`UV_THREADPOOL_SIZE`][] documentation for more information.

The asynchronous version of `crypto.randomBytes()` is carried out in a single
threadpool request. To minimize threadpool task length variation, partition
large `randomBytes` requests when doing so as part of fulfilling a client
request.

### crypto.randomFillSync(buffer[, offset][, size])

* `buffer` {Buffer|TypedArray|DataView} Must be supplied.
* `offset` {number} **Default:** `0`
* `size` {number} **Default:** `buffer.length - offset`
* Returns: {Buffer|TypedArray|DataView} The object passed as `buffer` argument.

Synchronous version of [`crypto.randomFill()`][].

```js
const buf = Buffer.alloc(10);
console.log(crypto.randomFillSync(buf).toString('hex'));

crypto.randomFillSync(buf, 5);
console.log(buf.toString('hex'));

// The above is equivalent to the following:
crypto.randomFillSync(buf, 5, 5);
console.log(buf.toString('hex'));
```

Any `TypedArray` or `DataView` instance may be passed as `buffer`.

```js
const a = new Uint32Array(10);
console.log(Buffer.from(crypto.randomFillSync(a).buffer,
                        a.byteOffset, a.byteLength).toString('hex'));

const b = new Float64Array(10);
console.log(Buffer.from(crypto.randomFillSync(b).buffer,
                        b.byteOffset, b.byteLength).toString('hex'));

const c = new DataView(new ArrayBuffer(10));
console.log(Buffer.from(crypto.randomFillSync(c).buffer,
                        c.byteOffset, c.byteLength).toString('hex'));
```

### crypto.randomFill(buffer[, offset][, size], callback)

* `buffer` {Buffer|TypedArray|DataView} Must be supplied.
* `offset` {number} **Default:** `0`
* `size` {number} **Default:** `buffer.length - offset`
* `callback` {Function} `function(err, buf) {}`.

This function is similar to [`crypto.randomBytes()`][] but requires the first
argument to be a [`Buffer`][] that will be filled. It also
requires that a callback is passed in.

If the `callback` function is not provided, an error will be thrown.

```js
const buf = Buffer.alloc(10);
crypto.randomFill(buf, (err, buf) => {
  if (err) throw err;
  console.log(buf.toString('hex'));
});

crypto.randomFill(buf, 5, (err, buf) => {
  if (err) throw err;
  console.log(buf.toString('hex'));
});

// The above is equivalent to the following:
crypto.randomFill(buf, 5, 5, (err, buf) => {
  if (err) throw err;
  console.log(buf.toString('hex'));
});
```

Any `TypedArray` or `DataView` instance may be passed as `buffer`.

```js
const a = new Uint32Array(10);
crypto.randomFill(a, (err, buf) => {
  if (err) throw err;
  console.log(Buffer.from(buf.buffer, buf.byteOffset, buf.byteLength)
    .toString('hex'));
});

const b = new Float64Array(10);
crypto.randomFill(b, (err, buf) => {
  if (err) throw err;
  console.log(Buffer.from(buf.buffer, buf.byteOffset, buf.byteLength)
    .toString('hex'));
});

const c = new DataView(new ArrayBuffer(10));
crypto.randomFill(c, (err, buf) => {
  if (err) throw err;
  console.log(Buffer.from(buf.buffer, buf.byteOffset, buf.byteLength)
    .toString('hex'));
});
```

Note that this API uses libuv's threadpool, which can have surprising and
negative performance implications for some applications, see the
[`UV_THREADPOOL_SIZE`][] documentation for more information.

The asynchronous version of `crypto.randomFill()` is carried out in a single
threadpool request. To minimize threadpool task length variation, partition
large `randomFill` requests when doing so as part of fulfilling a client
request.

### crypto.scrypt(password, salt, keylen[, options], callback)

* `password` {string|Buffer|TypedArray|DataView}
* `salt` {string|Buffer|TypedArray|DataView}
* `keylen` {number}
* `options` {Object}
  - `cost` {number} CPU/memory cost parameter. Must be a power of two greater
  - `N` {number} CPU/memory cost parameter. Must be a power of two greater
    than one. **Default:** `16384`.
  - `blockSize` {number} Block size parameter. **Default:** `8`.
  - `parallelization` {number} Parallelization parameter. **Default:** `1`.
  - `N` {number} Alias for `cost`. Only one of both may be specified.
  - `r` {number} Alias for `blockSize`. Only one of both may be specified.
  - `p` {number} Alias for `parallelization`. Only one of both may be specified.
  - `maxmem` {number} Memory upper bound. It is an error when (approximately)
    `128 * N * r > maxmem`. **Default:** `32 * 1024 * 1024`.
* `callback` {Function}
  - `err` {Error}
  - `derivedKey` {Buffer}

Provides an asynchronous [scrypt][] implementation. Scrypt is a password-based
key derivation function that is designed to be expensive computationally and
memory-wise in order to make brute-force attacks unrewarding.

The `salt` should be as unique as possible. It is recommended that a salt is
random and at least 16 bytes long. See [NIST SP 800-132][] for details.

The `callback` function is called with two arguments: `err` and `derivedKey`.
`err` is an exception object when key derivation fails, otherwise `err` is
`null`. `derivedKey` is passed to the callback as a [`Buffer`][].

An exception is thrown when any of the input arguments specify invalid values
or types.

```js
const crypto = require('crypto');
// Using the factory defaults.
crypto.scrypt('secret', 'salt', 64, (err, derivedKey) => {
  if (err) throw err;
  console.log(derivedKey.toString('hex'));  // '3745e48...08d59ae'
});
// Using a custom N parameter. Must be a power of two.
crypto.scrypt('secret', 'salt', 64, { N: 1024 }, (err, derivedKey) => {
  if (err) throw err;
  console.log(derivedKey.toString('hex'));  // '3745e48...aa39b34'
});
```

### crypto.scryptSync(password, salt, keylen[, options])

* `password` {string|Buffer|TypedArray|DataView}
* `salt` {string|Buffer|TypedArray|DataView}
* `keylen` {number}
* `options` {Object}
  - `cost` {number} CPU/memory cost parameter. Must be a power of two greater
  - `N` {number} CPU/memory cost parameter. Must be a power of two greater
    than one. **Default:** `16384`.
  - `blockSize` {number} Block size parameter. **Default:** `8`.
  - `parallelization` {number} Parallelization parameter. **Default:** `1`.
  - `N` {number} Alias for `cost`. Only one of both may be specified.
  - `r` {number} Alias for `blockSize`. Only one of both may be specified.
  - `p` {number} Alias for `parallelization`. Only one of both may be specified.
  - `maxmem` {number} Memory upper bound. It is an error when (approximately)
    `128 * N * r > maxmem`. **Default:** `32 * 1024 * 1024`.
* Returns: {Buffer}

Provides a synchronous [scrypt][] implementation. Scrypt is a password-based
key derivation function that is designed to be expensive computationally and
memory-wise in order to make brute-force attacks unrewarding.

The `salt` should be as unique as possible. It is recommended that a salt is
random and at least 16 bytes long. See [NIST SP 800-132][] for details.

An exception is thrown when key derivation fails, otherwise the derived key is
returned as a [`Buffer`][].

An exception is thrown when any of the input arguments specify invalid values
or types.

```js
const crypto = require('crypto');
// Using the factory defaults.
const key1 = crypto.scryptSync('secret', 'salt', 64);
console.log(key1.toString('hex'));  // '3745e48...08d59ae'
// Using a custom N parameter. Must be a power of two.
const key2 = crypto.scryptSync('secret', 'salt', 64, { N: 1024 });
console.log(key2.toString('hex'));  // '3745e48...aa39b34'
```

### crypto.setEngine(engine[, flags])

* `engine` {string}
* `flags` {crypto.constants} **Default:** `crypto.constants.ENGINE_METHOD_ALL`

Load and set the `engine` for some or all OpenSSL functions (selected by flags).

`engine` could be either an id or a path to the engine's shared library.

The optional `flags` argument uses `ENGINE_METHOD_ALL` by default. The `flags`
is a bit field taking one of or a mix of the following flags (defined in
`crypto.constants`):

* `crypto.constants.ENGINE_METHOD_RSA`
* `crypto.constants.ENGINE_METHOD_DSA`
* `crypto.constants.ENGINE_METHOD_DH`
* `crypto.constants.ENGINE_METHOD_RAND`
* `crypto.constants.ENGINE_METHOD_EC`
* `crypto.constants.ENGINE_METHOD_CIPHERS`
* `crypto.constants.ENGINE_METHOD_DIGESTS`
* `crypto.constants.ENGINE_METHOD_PKEY_METHS`
* `crypto.constants.ENGINE_METHOD_PKEY_ASN1_METHS`
* `crypto.constants.ENGINE_METHOD_ALL`
* `crypto.constants.ENGINE_METHOD_NONE`

The flags below are deprecated in OpenSSL-1.1.0.

* `crypto.constants.ENGINE_METHOD_ECDH`
* `crypto.constants.ENGINE_METHOD_ECDSA`
* `crypto.constants.ENGINE_METHOD_STORE`

### crypto.setFips(bool)

* `bool` {boolean} `true` to enable FIPS mode.

Enables the FIPS compliant crypto provider in a FIPS-enabled Node.js build.
Throws an error if FIPS mode is not available.

### crypto.timingSafeEqual(a, b)

* `a` {Buffer | TypedArray | DataView}
* `b` {Buffer | TypedArray | DataView}
* Returns: {boolean}

This function is based on a constant-time algorithm.
Returns true if `a` is equal to `b`, without leaking timing information that
would allow an attacker to guess one of the values. This is suitable for
comparing HMAC digests or secret values like authentication cookies or
[capability urls](https://www.w3.org/TR/capability-urls/).

`a` and `b` must both be `Buffer`s, `TypedArray`s, or `DataView`s, and they
must have the same length.

Use of `crypto.timingSafeEqual` does not guarantee that the *surrounding* code
is timing-safe. Care should be taken to ensure that the surrounding code does
not introduce timing vulnerabilities.

## Notes

### Legacy Streams API (pre Node.js v0.10)

The Crypto module was added to Node.js before there was the concept of a
unified Stream API, and before there were [`Buffer`][] objects for handling
binary data. As such, the many of the `crypto` defined classes have methods not
typically found on other Node.js classes that implement the [streams][stream]
API (e.g. `update()`, `final()`, or `digest()`). Also, many methods accepted
and returned `'latin1'` encoded strings by default rather than `Buffer`s. This
default was changed after Node.js v0.8 to use [`Buffer`][] objects by default
instead.

### Recent ECDH Changes

Usage of `ECDH` with non-dynamically generated key pairs has been simplified.
Now, [`ecdh.setPrivateKey()`][] can be called with a preselected private key
and the associated public point (key) will be computed and stored in the object.
This allows code to only store and provide the private part of the EC key pair.
[`ecdh.setPrivateKey()`][] now also validates that the private key is valid for
the selected curve.

The [`ecdh.setPublicKey()`][] method is now deprecated as its inclusion in the
API is not useful. Either a previously stored private key should be set, which
automatically generates the associated public key, or [`ecdh.generateKeys()`][]
should be called. The main drawback of using [`ecdh.setPublicKey()`][] is that
it can be used to put the ECDH key pair into an inconsistent state.

### Support for weak or compromised algorithms

The `crypto` module still supports some algorithms which are already
compromised and are not currently recommended for use. The API also allows
the use of ciphers and hashes with a small key size that are considered to be
too weak for safe use.

Users should take full responsibility for selecting the crypto
algorithm and key size according to their security requirements.

Based on the recommendations of [NIST SP 800-131A][]:

- MD5 and SHA-1 are no longer acceptable where collision resistance is
  required such as digital signatures.
- The key used with RSA, DSA, and DH algorithms is recommended to have
  at least 2048 bits and that of the curve of ECDSA and ECDH at least
  224 bits, to be safe to use for several years.
- The DH groups of `modp1`, `modp2` and `modp5` have a key size
  smaller than 2048 bits and are not recommended.

See the reference for other recommendations and details.

### CCM mode

CCM is one of the supported [AEAD algorithms][]. Applications which use this
mode must adhere to certain restrictions when using the cipher API:

- The authentication tag length must be specified during cipher creation by
  setting the `authTagLength` option and must be one of 4, 6, 8, 10, 12, 14 or
  16 bytes.
- The length of the initialization vector (nonce) `N` must be between 7 and 13
  bytes (`7 ≤ N ≤ 13`).
- The length of the plaintext is limited to `2 ** (8 * (15 - N))` bytes.
- When decrypting, the authentication tag must be set via `setAuthTag()` before
  specifying additional authenticated data or calling `update()`.
  Otherwise, decryption will fail and `final()` will throw an error in
  compliance with section 2.6 of [RFC 3610][].
- Using stream methods such as `write(data)`, `end(data)` or `pipe()` in CCM
  mode might fail as CCM cannot handle more than one chunk of data per instance.
- When passing additional authenticated data (AAD), the length of the actual
  message in bytes must be passed to `setAAD()` via the `plaintextLength`
  option. This is not necessary if no AAD is used.
- As CCM processes the whole message at once, `update()` can only be called
  once.
- Even though calling `update()` is sufficient to encrypt/decrypt the message,
  applications *must* call `final()` to compute or verify the
  authentication tag.

```js
const crypto = require('crypto');

const key = 'keykeykeykeykeykeykeykey';
const nonce = crypto.randomBytes(12);

const aad = Buffer.from('0123456789', 'hex');

const cipher = crypto.createCipheriv('aes-192-ccm', key, nonce, {
  authTagLength: 16
});
const plaintext = 'Hello world';
cipher.setAAD(aad, {
  plaintextLength: Buffer.byteLength(plaintext)
});
const ciphertext = cipher.update(plaintext, 'utf8');
cipher.final();
const tag = cipher.getAuthTag();

// Now transmit { ciphertext, nonce, tag }.

const decipher = crypto.createDecipheriv('aes-192-ccm', key, nonce, {
  authTagLength: 16
});
decipher.setAuthTag(tag);
decipher.setAAD(aad, {
  plaintextLength: ciphertext.length
});
const receivedPlaintext = decipher.update(ciphertext, null, 'utf8');

try {
  decipher.final();
} catch (err) {
  console.error('Authentication failed!');
}

console.log(receivedPlaintext);
```

## Crypto Constants

The following constants exported by `crypto.constants` apply to various uses of
the `crypto`, `tls`, and `https` modules and are generally specific to OpenSSL.

### OpenSSL Options

<table>
  <tr>
    <th>Constant</th>
    <th>Description</th>
  </tr>
  <tr>
    <td><code>SSL_OP_ALL</code></td>
    <td>Applies multiple bug workarounds within OpenSSL. See
    <a href="https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html">https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html</a>
    for detail.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION</code></td>
    <td>Allows legacy insecure renegotiation between OpenSSL and unpatched
    clients or servers. See
    <a href="https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html">https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html</a>.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_CIPHER_SERVER_PREFERENCE</code></td>
    <td>Attempts to use the server's preferences instead of the client's when
    selecting a cipher. Behavior depends on protocol version. See
    <a href="https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html">https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html</a>.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_CISCO_ANYCONNECT</code></td>
    <td>Instructs OpenSSL to use Cisco's "speshul" version of DTLS_BAD_VER.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_COOKIE_EXCHANGE</code></td>
    <td>Instructs OpenSSL to turn on cookie exchange.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_CRYPTOPRO_TLSEXT_BUG</code></td>
    <td>Instructs OpenSSL to add server-hello extension from an early version
    of the cryptopro draft.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS</code></td>
    <td>Instructs OpenSSL to disable a SSL 3.0/TLS 1.0 vulnerability
    workaround added in OpenSSL 0.9.6d.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_EPHEMERAL_RSA</code></td>
    <td>Instructs OpenSSL to always use the tmp_rsa key when performing RSA
    operations.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_LEGACY_SERVER_CONNECT</code></td>
    <td>Allows initial connection to servers that do not support RI.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_MICROSOFT_SESS_ID_BUG</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_MSIE_SSLV2_RSA_PADDING</code></td>
    <td>Instructs OpenSSL to disable the workaround for a man-in-the-middle
    protocol-version vulnerability in the SSL 2.0 server implementation.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_NETSCAPE_CA_DN_BUG</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_NETSCAPE_CHALLENGE_BUG</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_NO_COMPRESSION</code></td>
    <td>Instructs OpenSSL to disable support for SSL/TLS compression.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_NO_QUERY_MTU</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION</code></td>
    <td>Instructs OpenSSL to always start a new session when performing
    renegotiation.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_NO_SSLv2</code></td>
    <td>Instructs OpenSSL to turn off SSL v2</td>
  </tr>
  <tr>
    <td><code>SSL_OP_NO_SSLv3</code></td>
    <td>Instructs OpenSSL to turn off SSL v3</td>
  </tr>
  <tr>
    <td><code>SSL_OP_NO_TICKET</code></td>
    <td>Instructs OpenSSL to disable use of RFC4507bis tickets.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_NO_TLSv1</code></td>
    <td>Instructs OpenSSL to turn off TLS v1</td>
  </tr>
  <tr>
    <td><code>SSL_OP_NO_TLSv1_1</code></td>
    <td>Instructs OpenSSL to turn off TLS v1.1</td>
  </tr>
  <tr>
    <td><code>SSL_OP_NO_TLSv1_2</code></td>
    <td>Instructs OpenSSL to turn off TLS v1.2</td>
  </tr>
    <td><code>SSL_OP_PKCS1_CHECK_1</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_PKCS1_CHECK_2</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_SINGLE_DH_USE</code></td>
    <td>Instructs OpenSSL to always create a new key when using
    temporary/ephemeral DH parameters.</td>
  </tr>
  <tr>
    <td><code>SSL_OP_SINGLE_ECDH_USE</code></td>
    <td>Instructs OpenSSL to always create a new key when using
    temporary/ephemeral ECDH parameters.</td>
  </tr>
    <td><code>SSL_OP_SSLEAY_080_CLIENT_DH_BUG</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_TLS_BLOCK_PADDING_BUG</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_TLS_D5_BUG</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>SSL_OP_TLS_ROLLBACK_BUG</code></td>
    <td>Instructs OpenSSL to disable version rollback attack detection.</td>
  </tr>
</table>

### OpenSSL Engine Constants

<table>
  <tr>
    <th>Constant</th>
    <th>Description</th>
  </tr>
  <tr>
    <td><code>ENGINE_METHOD_RSA</code></td>
    <td>Limit engine usage to RSA</td>
  </tr>
  <tr>
    <td><code>ENGINE_METHOD_DSA</code></td>
    <td>Limit engine usage to DSA</td>
  </tr>
  <tr>
    <td><code>ENGINE_METHOD_DH</code></td>
    <td>Limit engine usage to DH</td>
  </tr>
  <tr>
    <td><code>ENGINE_METHOD_RAND</code></td>
    <td>Limit engine usage to RAND</td>
  </tr>
  <tr>
    <td><code>ENGINE_METHOD_EC</code></td>
    <td>Limit engine usage to EC</td>
  </tr>
  <tr>
    <td><code>ENGINE_METHOD_CIPHERS</code></td>
    <td>Limit engine usage to CIPHERS</td>
  </tr>
  <tr>
    <td><code>ENGINE_METHOD_DIGESTS</code></td>
    <td>Limit engine usage to DIGESTS</td>
  </tr>
  <tr>
    <td><code>ENGINE_METHOD_PKEY_METHS</code></td>
    <td>Limit engine usage to PKEY_METHDS</td>
  </tr>
  <tr>
    <td><code>ENGINE_METHOD_PKEY_ASN1_METHS</code></td>
    <td>Limit engine usage to PKEY_ASN1_METHS</td>
  </tr>
  <tr>
    <td><code>ENGINE_METHOD_ALL</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>ENGINE_METHOD_NONE</code></td>
    <td></td>
  </tr>
</table>

### Other OpenSSL Constants

<table>
  <tr>
    <th>Constant</th>
    <th>Description</th>
  </tr>
  <tr>
    <td><code>DH_CHECK_P_NOT_SAFE_PRIME</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>DH_CHECK_P_NOT_PRIME</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>DH_UNABLE_TO_CHECK_GENERATOR</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>DH_NOT_SUITABLE_GENERATOR</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>ALPN_ENABLED</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>RSA_PKCS1_PADDING</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>RSA_SSLV23_PADDING</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>RSA_NO_PADDING</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>RSA_PKCS1_OAEP_PADDING</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>RSA_X931_PADDING</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>RSA_PKCS1_PSS_PADDING</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>RSA_PSS_SALTLEN_DIGEST</code></td>
    <td>Sets the salt length for <code>RSA_PKCS1_PSS_PADDING</code> to the
        digest size when signing or verifying.</td>
  </tr>
  <tr>
    <td><code>RSA_PSS_SALTLEN_MAX_SIGN</code></td>
    <td>Sets the salt length for <code>RSA_PKCS1_PSS_PADDING</code> to the
        maximum permissible value when signing data.</td>
  </tr>
  <tr>
    <td><code>RSA_PSS_SALTLEN_AUTO</code></td>
    <td>Causes the salt length for <code>RSA_PKCS1_PSS_PADDING</code> to be
        determined automatically when verifying a signature.</td>
  </tr>
  <tr>
    <td><code>POINT_CONVERSION_COMPRESSED</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>POINT_CONVERSION_UNCOMPRESSED</code></td>
    <td></td>
  </tr>
  <tr>
    <td><code>POINT_CONVERSION_HYBRID</code></td>
    <td></td>
  </tr>
</table>

### Node.js Crypto Constants

<table>
  <tr>
    <th>Constant</th>
    <th>Description</th>
  </tr>
  <tr>
    <td><code>defaultCoreCipherList</code></td>
    <td>Specifies the built-in default cipher list used by Node.js.</td>
  </tr>
  <tr>
    <td><code>defaultCipherList</code></td>
    <td>Specifies the active default cipher list used by the current Node.js
    process.</td>
  </tr>
</table>

[`Buffer`]: buffer.html
[`EVP_BytesToKey`]: https://www.openssl.org/docs/man1.1.0/crypto/EVP_BytesToKey.html
[`UV_THREADPOOL_SIZE`]: cli.html#cli_uv_threadpool_size_size
[`cipher.final()`]: #crypto_cipher_final_outputencoding
[`cipher.update()`]: #crypto_cipher_update_data_inputencoding_outputencoding
[`crypto.createCipher()`]: #crypto_crypto_createcipher_algorithm_password_options
[`crypto.createCipheriv()`]: #crypto_crypto_createcipheriv_algorithm_key_iv_options
[`crypto.createDecipher()`]: #crypto_crypto_createdecipher_algorithm_password_options
[`crypto.createDecipheriv()`]: #crypto_crypto_createdecipheriv_algorithm_key_iv_options
[`crypto.createDiffieHellman()`]: #crypto_crypto_creatediffiehellman_prime_primeencoding_generator_generatorencoding
[`crypto.createECDH()`]: #crypto_crypto_createecdh_curvename
[`crypto.createHash()`]: #crypto_crypto_createhash_algorithm_options
[`crypto.createHmac()`]: #crypto_crypto_createhmac_algorithm_key_options
[`crypto.createSign()`]: #crypto_crypto_createsign_algorithm_options
[`crypto.createVerify()`]: #crypto_crypto_createverify_algorithm_options
[`crypto.getCurves()`]: #crypto_crypto_getcurves
[`crypto.getHashes()`]: #crypto_crypto_gethashes
[`crypto.privateDecrypt()`]: #crypto_crypto_privatedecrypt_privatekey_buffer
[`crypto.privateEncrypt()`]: #crypto_crypto_privateencrypt_privatekey_buffer
[`crypto.publicDecrypt()`]: #crypto_crypto_publicdecrypt_key_buffer
[`crypto.publicEncrypt()`]: #crypto_crypto_publicencrypt_key_buffer
[`crypto.randomBytes()`]: #crypto_crypto_randombytes_size_callback
[`crypto.randomFill()`]: #crypto_crypto_randomfill_buffer_offset_size_callback
[`crypto.scrypt()`]: #crypto_crypto_scrypt_password_salt_keylen_options_callback
[`decipher.final()`]: #crypto_decipher_final_outputencoding
[`decipher.update()`]: #crypto_decipher_update_data_inputencoding_outputencoding
[`diffieHellman.setPublicKey()`]: #crypto_diffiehellman_setpublickey_publickey_encoding
[`ecdh.generateKeys()`]: #crypto_ecdh_generatekeys_encoding_format
[`ecdh.setPrivateKey()`]: #crypto_ecdh_setprivatekey_privatekey_encoding
[`ecdh.setPublicKey()`]: #crypto_ecdh_setpublickey_publickey_encoding
[`hash.digest()`]: #crypto_hash_digest_encoding
[`hash.update()`]: #crypto_hash_update_data_inputencoding
[`hmac.digest()`]: #crypto_hmac_digest_encoding
[`hmac.update()`]: #crypto_hmac_update_data_inputencoding
[`sign.sign()`]: #crypto_sign_sign_privatekey_outputencoding
[`sign.update()`]: #crypto_sign_update_data_inputencoding
[`stream.Writable` options]: stream.html#stream_constructor_new_stream_writable_options
[`stream.transform` options]: stream.html#stream_new_stream_transform_options
[`tls.createSecureContext()`]: tls.html#tls_tls_createsecurecontext_options
[`util.promisify()`]: util.html#util_util_promisify_original
[`verify.update()`]: #crypto_verify_update_data_inputencoding
[`verify.verify()`]: #crypto_verify_verify_object_signature_signatureencoding
[AEAD algorithms]: https://en.wikipedia.org/wiki/Authenticated_encryption
[CCM mode]: #crypto_ccm_mode
[Caveats]: #crypto_support_for_weak_or_compromised_algorithms
[Crypto Constants]: #crypto_crypto_constants_1
[HTML 5.2]: https://www.w3.org/TR/html52/changes.html#features-removed
[HTML5's `keygen` element]: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/keygen
[NIST SP 800-131A]: https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-131Ar1.pdf
[NIST SP 800-132]: https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-132.pdf
[NIST SP 800-38D]: https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf
[Nonce-Disrespecting Adversaries]: https://github.com/nonce-disrespect/nonce-disrespect
[OpenSSL's SPKAC implementation]: https://www.openssl.org/docs/man1.1.0/apps/openssl-spkac.html
[RFC 2412]: https://www.rfc-editor.org/rfc/rfc2412.txt
[RFC 3526]: https://www.rfc-editor.org/rfc/rfc3526.txt
[RFC 3610]: https://www.rfc-editor.org/rfc/rfc3610.txt
[RFC 4055]: https://www.rfc-editor.org/rfc/rfc4055.txt
[encoding]: buffer.html#buffer_buffers_and_character_encodings
[initialization vector]: https://en.wikipedia.org/wiki/Initialization_vector
[scrypt]: https://en.wikipedia.org/wiki/Scrypt
[stream-writable-write]: stream.html#stream_writable_write_chunk_encoding_callback
[stream]: stream.html