Crypto Node.js v4.4.6 Manual & Documentation

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# 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.

    const crypto = require('crypto');

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

## Class: Certificate#

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

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.

### new crypto.Certificate()#

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

    const crypto = require('crypto');

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

### certificate.exportChallenge(spkac)#

The `spkac` data structure includes a public key and a challenge. The `certificate.exportChallenge()` returns the challenge component in the form of a Node.js `Buffer`. The `spkac` argument can be either a string or a `Buffer`.

    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)#

The `spkac` data structure includes a public key and a challenge. The `certificate.exportPublicKey()` returns the public key component in the form of a Node.js `Buffer`. The `spkac` argument can be either a string or a `Buffer`.

    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)#

Returns `true` if the given `spkac` data structure is valid, `false` otherwise. The `spkac` argument must be a Node.js `Buffer`.

    const cert = require('crypto').Certificate();
    const spkac = getSpkacSomehow();
    console.log(cert.verifySpkac(new Buffer(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:

    const crypto = require('crypto');
    const cipher = crypto.createCipher('aes192', 'a password');

    var encrypted = '';
    cipher.on('readable', () => {
      var data = cipher.read();
      if (data)
        encrypted += data.toString('hex');
    });
    cipher.on('end', () => {
      console.log(encrypted);
      // Prints: ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504
    });

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

Example: Using `Cipher` and piped streams:

    const crypto = require('crypto');
    const fs = require('fs');
    const cipher = crypto.createCipher('aes192', 'a password');

    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:

    const crypto = require('crypto');
    const cipher = crypto.createCipher('aes192', 'a password');

    var encrypted = cipher.update('some clear text data', 'utf8', 'hex');
    encrypted += cipher.final('hex');
    console.log(encrypted);
      // Prints: ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504

### cipher.final([output_encoding])#

Returns any remaining enciphered contents. If `output_encoding` parameter is one of `'binary'`, `'base64'` or `'hex'`, a string is returned. If an `output_encoding` 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)#

When using an authenticated encryption mode (only `GCM` is currently supported), the `cipher.setAAD()` method sets the value used for the additional authenticated data (AAD) input parameter.

### cipher.getAuthTag()#

When using an authenticated encryption mode (only `GCM` is 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(auto_padding=true)#

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 `auto_padding` 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[, input_encoding][, output_encoding])#

Updates the cipher with `data`. If the `input_encoding` argument is given, it's value must be one of `'utf8'`, `'ascii'`, or `'binary'` and the `data` argument is a string using the specified encoding. If the `input_encoding` argument is not given, `data` must be a `Buffer`. If `data` is a `Buffer` then `input_encoding` is ignored.

The `output_encoding` specifies the output format of the enciphered data, and can be `'binary'`, `'base64'` or `'hex'`. If the `output_encoding` is specified, a string using the specified encoding is returned. If no `output_encoding` 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:

    const crypto = require('crypto');
    const decipher = crypto.createDecipher('aes192', 'a password');

    var decrypted = '';
    decipher.on('readable', () => {
      var data = decipher.read();
      if (data)
      decrypted += data.toString('utf8');
    });
    decipher.on('end', () => {
      console.log(decrypted);
      // Prints: some clear text data
    });

    var encrypted = 'ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504';
    decipher.write(encrypted, 'hex');
    decipher.end();

Example: Using `Decipher` and piped streams:

    const crypto = require('crypto');
    const fs = require('fs');
    const decipher = crypto.createDecipher('aes192', 'a password');

    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:

    const crypto = require('crypto');
    const decipher = crypto.createDecipher('aes192', 'a password');

    var encrypted = 'ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504';
    var decrypted = decipher.update(encrypted, 'hex', 'utf8');
    decrypted += decipher.final('utf8');
    console.log(decrypted);
      // Prints: some clear text data

### decipher.final([output_encoding])#

Returns any remaining deciphered contents. If `output_encoding` parameter is one of `'binary'`, `'base64'` or `'hex'`, a string is returned. If an `output_encoding` 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)#

When using an authenticated encryption mode (only `GCM` is currently supported), the `cipher.setAAD()` method sets the value used for the additional authenticated data (AAD) input parameter.

### decipher.setAuthTag(buffer)#

When using an authenticated encryption mode (only `GCM` is 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()` with throw, indicating that the cipher text should be discarded due to failed authentication.

### decipher.setAutoPadding(auto_padding=true)#

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.update()`.

### decipher.update(data[, input_encoding][, output_encoding])#

Updates the decipher with `data`. If the `input_encoding` argument is given, it's value must be one of `'binary'`, `'base64'`, or `'hex'` and the `data` argument is a string using the specified encoding. If the `input_encoding` argument is not given, `data` must be a `Buffer`. If `data` is a `Buffer` then `input_encoding` is ignored.

The `output_encoding` specifies the output format of the enciphered data, and can be `'binary'`, `'ascii'` or `'utf8'`. If the `output_encoding` is specified, a string using the specified encoding is returned. If no `output_encoding` is provided, a `Buffer` is returned.

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.

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

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

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

    // Exchange and generate the secret...
    const alice_secret = alice.computeSecret(bob_key);
    const bob_secret = bob.computeSecret(alice_key);

    // OK
    assert.equal(alice_secret.toString('hex'), bob_secret.toString('hex'));

### diffieHellman.computeSecret(other_public_key[, input_encoding][, output_encoding])#

Computes the shared secret using `other_public_key` as the other party's public key and returns the computed shared secret. The supplied key is interpreted using the specified `input_encoding`, and secret is encoded using specified `output_encoding`. Encodings can be `'binary'`, `'hex'`, or `'base64'`. If the `input_encoding` is not provided, `other_public_key` is expected to be a `Buffer`.

If `output_encoding` is given a string is returned; otherwise, a `Buffer` is returned.

### diffieHellman.generateKeys([encoding])#

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. Encoding can be `'binary'`, `'hex'`, or `'base64'`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned.

### diffieHellman.getGenerator([encoding])#

Returns the Diffie-Hellman generator in the specified `encoding`, which can be `'binary'`, `'hex'`, or `'base64'`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned.

### diffieHellman.getPrime([encoding])#

Returns the Diffie-Hellman prime in the specified `encoding`, which can be `'binary'`, `'hex'`, or `'base64'`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned.

### diffieHellman.getPrivateKey([encoding])#

Returns the Diffie-Hellman private key in the specified `encoding`, which can be `'binary'`, `'hex'`, or `'base64'`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned.

### diffieHellman.getPublicKey([encoding])#

Returns the Diffie-Hellman public key in the specified `encoding`, which can be `'binary'`, `'hex'`, or `'base64'`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned.

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

Sets the Diffie-Hellman private key. If the `encoding` argument is provided and is either `'binary'`, `'hex'`, or `'base64'`, `private_key` is expected to be a string. If no `encoding` is provided, `private_key` is expected to be a `Buffer`.

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

Sets the Diffie-Hellman public key. If the `encoding` argument is provided and is either `'binary'`, `'hex'` or `'base64'`, `public_key` is expected to be a string. If no `encoding` is provided, `public_key` is expected to be a `Buffer`.

### 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.

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

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

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

    // Exchange and generate the secret...
    const alice_secret = alice.computeSecret(bob_key);
    const bob_secret = bob.computeSecret(alice_key);

    assert(alice_secret, bob_secret);
      // OK

### ecdh.computeSecret(other_public_key[, input_encoding][, output_encoding])#

Computes the shared secret using `other_public_key` as the other party's public key and returns the computed shared secret. The supplied key is interpreted using specified `input_encoding`, and the returned secret is encoded using the specified `output_encoding`. Encodings can be `'binary'`, `'hex'`, or `'base64'`. If the `input_encoding` is not provided, `other_public_key` is expected to be a `Buffer`.

If `output_encoding` is given a string will be returned; otherwise a `Buffer` is returned.

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

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

The `encoding` argument can be `'binary'`, `'hex'`, or `'base64'`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned.

### ecdh.getPrivateKey([encoding])#

Returns the EC Diffie-Hellman private key in the specified `encoding`, which can be `'binary'`, `'hex'`, or `'base64'`. If `encoding` is provided a string is returned; otherwise a `Buffer` is returned.

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

Returns the EC Diffie-Hellman public key in the specified `encoding` and `format`.

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

The `encoding` argument can be `'binary'`, `'hex'`, or `'base64'`. If `encoding` is specified, a string is returned; otherwise a `Buffer` is returned.

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

Sets the EC Diffie-Hellman private key. The `encoding` can be `'binary'`, `'hex'` or `'base64'`. If `encoding` is provided, `private_key` is expected to be a string; otherwise `private_key` is expected to be a `Buffer`. If `private_key` 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(public_key[, encoding])#

    Stability: 0 - Deprecated

Sets the EC Diffie-Hellman public key. Key encoding can be `'binary'`, `'hex'` or `'base64'`. If `encoding` is provided `public_key` is expected to be a string; otherwise a `Buffer` 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):

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

    // Note: This is a shortcut way to specify 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 alice_secret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
    const bob_secret = bob.computeSecret(alice.getPublicKey(), null, 'hex');

    // alice_secret and bob_secret should be the same shared secret value
    console.log(alice_secret === bob_secret);

## 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:

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

    hash.on('readable', () => {
      var 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:

    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:

    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])#

Calculates the digest of all of the data passed to be hashed (using the `hash.update()` method). The `encoding` can be `'hex'`, `'binary'` or `'base64'`. 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[, input_encoding])#

Updates the hash content with the given `data`, the encoding of which is given in `input_encoding` and can be `'utf8'`, `'ascii'` or `'binary'`. If `encoding` is not provided, and the `data` is a string, an encoding of `'binary'` is enforced. If `data` is a `Buffer` then `input_encoding` 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:

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

    hmac.on('readable', () => {
      var 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:

    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:

    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])#

Calculates the HMAC digest of all of the data passed using `hmac.update()`. The `encoding` can be `'hex'`, `'binary'` or `'base64'`. 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[, input_encoding])#

Updates the `Hmac` content with the given `data`, the encoding of which is given in `input_encoding` and can be `'utf8'`, `'ascii'` or `'binary'`. If `encoding` is not provided, and the `data` is a string, an encoding of `'utf8'` is enforced. If `data` is a `Buffer` then `input_encoding` 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. `Sign` objects are not to be created directly using the `new` keyword.

Example: Using `Sign` objects as streams:

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

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

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

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

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

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

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

A [`sign`][] instance can also be created by just passing in the digest algorithm name, in which case OpenSSL will infer the full signature algorithm from the type of the PEM-formatted private key, including algorithms that do not have directly exposed name constants, e.g. 'ecdsa-with-SHA256'.

Example: signing using ECDSA with SHA256

    const crypto = require('crypto');
    const sign = crypto.createSign('sha256');

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

    const private_key = '-----BEGIN EC PRIVATE KEY-----\n' +
            'MHcCAQEEIF+jnWY1D5kbVYDNvxxo/Y+ku2uJPDwS0r/VuPZQrjjVoAoGCCqGSM49\n' +
            'AwEHoUQDQgAEurOxfSxmqIRYzJVagdZfMMSjRNNhB8i3mXyIMq704m2m52FdfKZ2\n' +
            'pQhByd5eyj3lgZ7m7jbchtdgyOF8Io/1ng==\n' +
            '-----END EC PRIVATE KEY-----\n';

    console.log(sign.sign(private_key).toString('hex'));

### sign.sign(private_key[, output_format])#

Calculates the signature on all the data passed through using either `sign.update()` or `sign.write()`.

The `private_key` argument can be an object or a string. If `private_key` is a string, it is treated as a raw key with no passphrase. If `private_key` is an object, it is interpreted as a hash containing two properties:

- `key` : <String> - PEM encoded private key
- `passphrase` : <String> - passphrase for the private key

The `output_format` can specify one of `'binary'`, `'hex'` or `'base64'`. If `output_format` 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[, input_encoding])#

Updates the `Sign` content with the given `data`, the encoding of which is given in `input_encoding` and can be `'utf8'`, `'ascii'` or `'binary'`. If `encoding` is not provided, and the `data` is a string, an encoding of `'utf8'` is enforced. If `data` is a `Buffer` then `input_encoding` 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.createSign()` method is used to create `Sign` instances. `Sign` objects are not to be created directly using the `new` keyword.

Example: Using `Verify` objects as streams:

    const crypto = require('crypto');
    const verify = crypto.createVerify('RSA-SHA256');

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

    const public_key = getPublicKeySomehow();
    const signature = getSignatureToVerify();
    console.log(sign.verify(public_key, signature));
      // Prints true or false

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

    const crypto = require('crypto');
    const verify = crypto.createVerify('RSA-SHA256');

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

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

### verifier.update(data[, input_encoding])#

Updates the `Verify` content with the given `data`, the encoding of which is given in `input_encoding` and can be `'utf8'`, `'ascii'` or `'binary'`. If `encoding` is not provided, and the `data` is a string, an encoding of `'utf8'` is enforced. If `data` is a `Buffer` then `input_encoding` is ignored.

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

### verifier.verify(object, signature[, signature_format])#

Verifies the provided data using the given `object` and `signature`. The `object` argument is a string containing a PEM encoded object, which can be one an RSA public key, a DSA public key, or an X.509 certificate. The `signature` argument is the previously calculated signature for the data, in the `signature_format` which can be `'binary'`, `'hex'` or `'base64'`. If a `signature_format` is specified, the `signature` is expected to be a string; otherwise `signature` is expected to be a `Buffer`.

Returns `true` or `false` depending on the validity of the signature for the data and public key.

The `verifier` 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.DEFAULT_ENCODING#

The default encoding to use for functions that can take either strings or buffers. 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 `'binary'` to be the default encoding.

New applications should expect the default to be `'buffer'`. This property may become deprecated in a future Node.js release.

### crypto.createCipher(algorithm, password)#

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

The `algorithm` is dependent on OpenSSL, examples are `'aes192'`, etc. On recent OpenSSL releases, `openssl list-cipher-algorithms` 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 `'binary'` encoded string or a `Buffer`.

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 pbkdf2 instead of `EVP_BytesToKey` it is recommended that developers derive a key and IV on their own using `crypto.pbkdf2()` and to use `crypto.createCipheriv()` to create the `Cipher` object.

### crypto.createCipheriv(algorithm, key, iv)#

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

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

The `key` is the raw key used by the `algorithm` and `iv` is an initialization vector. Both arguments must be `'binary'` encoded strings or buffers.

### crypto.createCredentials(details)#

    Stability: 0 - Deprecated: Use tls.createSecureContext() instead.

The `crypto.createCredentials()` method is a deprecated alias for creating and returning a `tls.SecureContext` object. The `crypto.createCredentials()` method should not be used.

The optional `details` argument is a hash object with keys:

- `pfx` : <String> | <Buffer> - PFX or PKCS12 encoded private key, certificate and CA certificates
- `key` : <String> - PEM encoded private key
- `passphrase` : <String> - passphrase for the private key or PFX
- `cert` : <String> - PEM encoded certificate
- `ca` : <String> | <Array> - Either a string or array of strings of PEM encoded CA certificates to trust.
- `crl` : <String> | <Array> - Either a string or array of strings of PEM encoded CRLs (Certificate Revocation List)
- `ciphers`: <String> using the OpenSSL cipher list format describing the cipher algorithms to use or exclude.

If no 'ca' details are given, Node.js will use Mozilla's default publicly trusted list of CAs.

### crypto.createDecipher(algorithm, password)#

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.

In line with OpenSSL's recommendation to use pbkdf2 instead of `EVP_BytesToKey` it is recommended that developers derive a key and IV on their own using `crypto.pbkdf2()` and to use `crypto.createDecipheriv()` to create the `Decipher` object.

### crypto.createDecipheriv(algorithm, key, iv)#

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

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

The `key` is the raw key used by the `algorithm` and `iv` is an initialization vector. Both arguments must be `'binary'` encoded strings or buffers.

### crypto.createDiffieHellman(prime[, prime_encoding][, generator][, generator_encoding])#

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.

The `prime_encoding` and `generator_encoding` arguments can be `'binary'`, `'hex'`, or `'base64'`.

If `prime_encoding` is specified, `prime` is expected to be a string; otherwise a `Buffer` is expected.

If `generator_encoding` is specified, `generator` is expected to be a string; otherwise either a number or `Buffer` is expected.

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

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

### crypto.createECDH(curve_name)#

Creates an Elliptic Curve Diffie-Hellman (`ECDH`) key exchange object using a predefined curve specified by the `curve_name` 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)#

Creates and returns a `Hash` object that can be used to generate hash digests using the given `algorithm`.

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-message-digest-algorithms` will display the available digest algorithms.

Example: generating the sha256 sum of a file

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

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

    const input = fs.createReadStream(filename);
    input.on('readable', () => {
      var data = input.read();
      if (data)
        hash.update(data);
      else {
        console.log(`${hash.digest('hex')} ${filename}`);
      }
    });

### crypto.createHmac(algorithm, key)#

Creates and returns an `Hmac` object that uses the given `algorithm` and `key`.

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-message-digest-algorithms` will display the available digest algorithms.

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

Example: generating the sha256 HMAC of a file

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

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

    const input = fs.createReadStream(filename);
    input.on('readable', () => {
      var data = input.read();
      if (data)
        hmac.update(data);
      else {
        console.log(`${hmac.digest('hex')} ${filename}`);
      }
    });

### crypto.createSign(algorithm)#

Creates and returns a `Sign` object that uses the given `algorithm`. On recent OpenSSL releases, `openssl list-public-key-algorithms` will display the available signing algorithms. One example is `'RSA-SHA256'`.

### crypto.createVerify(algorithm)#

Creates and returns a `Verify` object that uses the given algorithm. On recent OpenSSL releases, `openssl list-public-key-algorithms` will display the available signing algorithms. One example is `'RSA-SHA256'`.

### crypto.getCiphers()#

Returns an array with the names of the supported cipher algorithms.

Example:

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

### crypto.getCurves()#

Returns an array with the names of the supported elliptic curves.

Example:

    const curves = crypto.getCurves();
    console.log(curves); // ['secp256k1', 'secp384r1', ...]

### crypto.getDiffieHellman(group_name)#

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):

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

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

    const alice_secret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
    const bob_secret = bob.computeSecret(alice.getPublicKey(), null, 'hex');

    /* alice_secret and bob_secret should be the same */
    console.log(alice_secret == bob_secret);

### crypto.getHashes()#

Returns an array with the names of the supported hash algorithms.

Example:

    const hashes = crypto.getHashes();
    console.log(hashes); // ['sha', 'sha1', 'sha1WithRSAEncryption', ...]

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

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`. If the `digest` algorithm is not specified, a default of `'sha1'` is used.

The supplied `callback` function is called with two arguments: `err` and `derivedKey`. If an error occurs, `err` will be set; otherwise `err` will be null. The successfully generated `derivedKey` will be passed as a `Buffer`.

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 also be as unique as possible. It is recommended that the salts are random and their lengths are greater than 16 bytes. See NIST SP 800-132 for details.

Example:

    const crypto = require('crypto');
    crypto.pbkdf2('secret', 'salt', 100000, 512, 'sha512', (err, key) => {
      if (err) throw err;
      console.log(key.toString('hex'));  // 'c5e478d...1469e50'
    });

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

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

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 the `digest` algorithm is not specified, a default of `'sha1'` is used.

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

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 also be as unique as possible. It is recommended that the salts are random and their lengths are greater than 16 bytes. See NIST SP 800-132 for details.

Example:

    const crypto = require('crypto');
    const key = crypto.pbkdf2Sync('secret', 'salt', 100000, 512, 'sha512');
    console.log(key.toString('hex'));  // 'c5e478d...1469e50'

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

### crypto.privateDecrypt(private_key, buffer)#

Decrypts `buffer` with `private_key`.

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

- `key` : <String> - PEM encoded private key
- `passphrase` : <String> - Optional passphrase for the private key
- `padding` : An optional padding value, one of the following:
  - `constants.RSA_NO_PADDING`
  - `constants.RSA_PKCS1_PADDING`
  - `constants.RSA_PKCS1_OAEP_PADDING`

All paddings are defined in the `constants` module.

### crypto.privateEncrypt(private_key, buffer)#

Encrypts `buffer` with `private_key`.

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

- `key` : <String> - PEM encoded private key
- `passphrase` : <String> - Optional passphrase for the private key
- `padding` : An optional padding value, one of the following:
  - `constants.RSA_NO_PADDING`
  - `constants.RSA_PKCS1_PADDING`
  - `constants.RSA_PKCS1_OAEP_PADDING`

All paddings are defined in the `constants` module.

### crypto.publicDecrypt(public_key, buffer)#

Decrypts `buffer` with `public_key`.

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

- `key` : <String> - PEM encoded public key
- `passphrase` : <String> - Optional passphrase for the private key
- `padding` : An optional padding value, one of the following:
  - `constants.RSA_NO_PADDING`
  - `constants.RSA_PKCS1_PADDING`
  - `constants.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.

All paddings are defined in the `constants` module.

### crypto.publicEncrypt(public_key, buffer)#

Encrypts `buffer` with `public_key`.

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

- `key` : <String> - PEM encoded public key
- `passphrase` : <String> - Optional passphrase for the private key
- `padding` : An optional padding value, one of the following:
  - `constants.RSA_NO_PADDING`
  - `constants.RSA_PKCS1_PADDING`
  - `constants.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.

All paddings are defined in the `constants` module.

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

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.

    // 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.

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

The `crypto.randomBytes()` method will block until there is sufficient entropy. 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.

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

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 the `constants` module):

- `ENGINE_METHOD_RSA`
- `ENGINE_METHOD_DSA`
- `ENGINE_METHOD_DH`
- `ENGINE_METHOD_RAND`
- `ENGINE_METHOD_ECDH`
- `ENGINE_METHOD_ECDSA`
- `ENGINE_METHOD_CIPHERS`
- `ENGINE_METHOD_DIGESTS`
- `ENGINE_METHOD_STORE`
- `ENGINE_METHOD_PKEY_METH`
- `ENGINE_METHOD_PKEY_ASN1_METH`
- `ENGINE_METHOD_ALL`
- `ENGINE_METHOD_NONE`

## 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 API (e.g. `update()`, `final()`, or `digest()`). Also, many methods accepted and returned `'binary'` encoded strings by default rather than Buffers. 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.