# Crypto

    Stability: 2 - Unstable; API changes are being discussed for
    future versions.  Breaking changes will be minimized.  See below.

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

The crypto module requires OpenSSL to be available on the underlying platform.
It offers a way of encapsulating secure credentials to be used as part
of a secure HTTPS net or http connection.

It also offers a set of wrappers for OpenSSL's hash, hmac, cipher, decipher, sign and verify methods.

## crypto.createCredentials(details)

Creates a credentials object, with the optional details being a dictionary with keys:

* `pfx` : A string or buffer holding the PFX or PKCS12 encoded private key, certificate and CA certificates
* `key` : A string holding the PEM encoded private key
* `passphrase` : A string of passphrase for the private key or pfx
* `cert` : A string holding the PEM encoded certificate
* `ca` : Either a string or list of strings of PEM encoded CA certificates to trust.
* `crl` : Either a string or list of strings of PEM encoded CRLs (Certificate Revocation List)
* `ciphers`: A string describing the ciphers to use or exclude. Consult
  <http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT> for details
  on the format.

If no 'ca' details are given, then node.js will use the default publicly trusted list of CAs as given in
<http://mxr.mozilla.org/mozilla/source/security/nss/lib/ckfw/builtins/certdata.txt>.


## crypto.createHash(algorithm)

Creates and returns a hash object, a cryptographic hash with the given algorithm
which can be used to generate hash digests.

`algorithm` is dependent on the available algorithms supported by the version
of OpenSSL on the platform. Examples are `'sha1'`, `'md5'`, `'sha256'`, `'sha512'`, etc.
On recent releases, `openssl list-message-digest-algorithms` will display the available digest algorithms.

Example: this program that takes the sha1 sum of a file

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

    var shasum = crypto.createHash('sha1');

    var s = fs.ReadStream(filename);
    s.on('data', function(d) {
      shasum.update(d);
    });

    s.on('end', function() {
      var d = shasum.digest('hex');
      console.log(d + '  ' + filename);
    });

## Class: Hash

The class for creating hash digests of data.

Returned by `crypto.createHash`.

### 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'`.
Defaults to `'binary'`.
This can be called many times with new data as it is streamed.

### hash.digest([encoding])

Calculates the digest of all of the passed data to be hashed.
The `encoding` can be `'hex'`, `'binary'` or `'base64'`.
Defaults to `'binary'`.

Note: `hash` object can not be used after `digest()` method has been called.


## crypto.createHmac(algorithm, key)

Creates and returns a hmac object, a cryptographic hmac with the given algorithm and key.

`algorithm` is dependent on the available algorithms supported by OpenSSL - see createHash above.
`key` is the hmac key to be used.

## Class: Hmac

Class for creating cryptographic hmac content.

Returned by `crypto.createHmac`.

### hmac.update(data)

Update the hmac content with the given `data`.
This can be called many times with new data as it is streamed.

### hmac.digest([encoding])

Calculates the digest of all of the passed data to the hmac.
The `encoding` can be `'hex'`, `'binary'` or `'base64'`.
Defaults to `'binary'`.

Note: `hmac` object can not be used after `digest()` method been called.


## crypto.createCipher(algorithm, password)

Creates and returns a cipher object, with the given algorithm and password.

`algorithm` is dependent on OpenSSL, examples are `'aes192'`, etc.
On recent releases, `openssl list-cipher-algorithms` will display the
available cipher algorithms.
`password` is used to derive key and IV, which must be a `'binary'` encoded
string or a [buffer](buffer.html).

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

Creates and returns a cipher object, with the given algorithm, key and iv.

`algorithm` is the same as the argument to `createCipher()`.
`key` is the raw key used by the algorithm.
`iv` is an [initialization
vector](http://en.wikipedia.org/wiki/Initialization_vector).

`key` and `iv` must be `'binary'` encoded strings or [buffers](buffer.html).

## Class: Cipher

Class for encrypting data.

Returned by `crypto.createCipher` and `crypto.createCipheriv`.

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

Updates the cipher with `data`, the encoding of which is given in
`input_encoding` and can be `'utf8'`, `'ascii'` or `'binary'`.
Defaults to `'binary'`.

The `output_encoding` specifies the output format of the enciphered data,
and can be `'binary'`, `'base64'` or `'hex'`. Defaults to `'binary'`.

Returns the enciphered contents, and can be called many times with new data as it is streamed.

### cipher.final([output_encoding])

Returns any remaining enciphered contents, with `output_encoding` being one of:
`'binary'`, `'base64'` or `'hex'`. Defaults to `'binary'`.

Note: `cipher` object can not be used after `final()` method been called.

### cipher.setAutoPadding(auto_padding=true)

You can disable automatic padding of the input data to block size. If `auto_padding` is false,
the length of the entire input data must be a multiple of the cipher's block size or `final` will fail.
Useful for non-standard padding, e.g. using `0x0` instead of PKCS padding. You must call this before `cipher.final`.


## crypto.createDecipher(algorithm, password)

Creates and returns a decipher object, with the given algorithm and key.
This is the mirror of the [createCipher()][] above.

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

Creates and returns a decipher object, with the given algorithm, key and iv.
This is the mirror of the [createCipheriv()][] above.

## Class: Decipher

Class for decrypting data.

Returned by `crypto.createDecipher` and `crypto.createDecipheriv`.

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

Updates the decipher with `data`, which is encoded in `'binary'`, `'base64'`
or `'hex'`. Defaults to `'binary'`.

The `output_decoding` specifies in what format to return the deciphered
plaintext: `'binary'`, `'ascii'` or `'utf8'`. Defaults to `'binary'`.

### decipher.final([output_encoding])

Returns any remaining plaintext which is deciphered,
with `output_encoding` being one of: `'binary'`, `'ascii'` or `'utf8'`.
Defaults to `'binary'`.

Note: `decipher` object can not be used after `final()` method been called.

### decipher.setAutoPadding(auto_padding=true)

You can disable auto padding if the data has been encrypted without standard block padding to prevent
`decipher.final` from checking and removing it. Can only work if the input data's length is a multiple of the
ciphers block size. You must call this before streaming data to `decipher.update`.

## crypto.createSign(algorithm)

Creates and returns a signing object, with the given algorithm.
On recent OpenSSL releases, `openssl list-public-key-algorithms` will display
the available signing algorithms. Examples are `'RSA-SHA256'`.

## Class: Signer

Class for generating signatures.

Returned by `crypto.createSign`.

### signer.update(data)

Updates the signer object with data.
This can be called many times with new data as it is streamed.

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

Calculates the signature on all the updated data passed through the signer.
`private_key` is a string containing the PEM encoded private key for signing.

Returns the signature in `output_format` which can be `'binary'`, `'hex'` or
`'base64'`. Defaults to `'binary'`.

Note: `signer` object can not be used after `sign()` method been called.

## crypto.createVerify(algorithm)

Creates and returns a verification object, with the given algorithm.
This is the mirror of the signing object above.

## Class: Verify

Class for verifying signatures.

Returned by `crypto.createVerify`.

### verifier.update(data)

Updates the verifier object with data.
This can be called many times with new data as it is streamed.

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

Verifies the signed data by using the `object` and `signature`. `object` is  a
string containing a PEM encoded object, which can be one of RSA public key,
DSA public key, or X.509 certificate. `signature` is the previously calculated
signature for the data, in the `signature_format` which can be `'binary'`,
`'hex'` or `'base64'`. Defaults to `'binary'`.

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

Note: `verifier` object can not be used after `verify()` method been called.

## crypto.createDiffieHellman(prime_length)

Creates a Diffie-Hellman key exchange object and generates a prime of the
given bit length. The generator used is `2`.

## crypto.createDiffieHellman(prime, [encoding])

Creates a Diffie-Hellman key exchange object using the supplied prime. The
generator used is `2`. Encoding can be `'binary'`, `'hex'`, or `'base64'`.
Defaults to `'binary'`.

## Class: DiffieHellman

The class for creating Diffie-Hellman key exchanges.

Returned by `crypto.createDiffieHellman`.

### 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'`.
Defaults to `'binary'`.

### 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. Supplied key is
interpreted using specified `input_encoding`, and secret is encoded using
specified `output_encoding`. Encodings can be `'binary'`, `'hex'`, or
`'base64'`. The input encoding defaults to `'binary'`.
If no output encoding is given, the input encoding is used as output encoding.

### diffieHellman.getPrime([encoding])

Returns the Diffie-Hellman prime in the specified encoding, which can be
`'binary'`, `'hex'`, or `'base64'`. Defaults to `'binary'`.

### diffieHellman.getGenerator([encoding])

Returns the Diffie-Hellman prime in the specified encoding, which can be
`'binary'`, `'hex'`, or `'base64'`. Defaults to `'binary'`.

### diffieHellman.getPublicKey([encoding])

Returns the Diffie-Hellman public key in the specified encoding, which can
be `'binary'`, `'hex'`, or `'base64'`. Defaults to `'binary'`.

### diffieHellman.getPrivateKey([encoding])

Returns the Diffie-Hellman private key in the specified encoding, which can
be `'binary'`, `'hex'`, or `'base64'`. Defaults to `'binary'`.

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

Sets the Diffie-Hellman public key. Key encoding can be `'binary'`, `'hex'`,
or `'base64'`. Defaults to `'binary'`.

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

Sets the Diffie-Hellman private key. Key encoding can be `'binary'`, `'hex'`,
or `'base64'`. Defaults to `'binary'`.

## crypto.getDiffieHellman(group_name)

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

Example (obtaining a shared secret):

    var crypto = require('crypto');
    var alice = crypto.getDiffieHellman('modp5');
    var bob = crypto.getDiffieHellman('modp5');

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

    var alice_secret = alice.computeSecret(bob.getPublicKey(), 'binary', 'hex');
    var bob_secret = bob.computeSecret(alice.getPublicKey(), 'binary', 'hex');

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

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

Asynchronous PBKDF2 applies pseudorandom function HMAC-SHA1 to derive
a key of given length from the given password, salt and iterations.
The callback gets two arguments `(err, derivedKey)`.

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

Generates cryptographically strong pseudo-random data. Usage:

    // async
    crypto.randomBytes(256, function(ex, buf) {
      if (ex) throw ex;
      console.log('Have %d bytes of random data: %s', buf.length, buf);
    });

    // sync
    try {
      var buf = crypto.randomBytes(256);
      console.log('Have %d bytes of random data: %s', buf.length, buf);
    } catch (ex) {
      // handle error
    }

## Proposed API Changes in Future Versions of Node

The Crypto module was added to Node before there was the concept of a
unified Stream API, and before there were Buffer objects for handling
binary data.

As such, the streaming classes don't have the typical methods found on
other Node classes, and many methods accept and return Binary-encoded
strings by default rather than Buffers.

A future version of node will make Buffers the default data type.
This will be a breaking change for some use cases, but not all.

For example, if you currently use the default arguments to the Sign
class, and then pass the results to the Verify class, without ever
inspecting the data, then it will continue to work as before.  Where
you now get a binary string and then present the binary string to the
Verify object, you'll get a Buffer, and present the Buffer to the
Verify object.

However, if you are doing things with the string data that will not
work properly on Buffers (such as, concatenating them, storing in
databases, etc.), or you are passing binary strings to the crypto
functions without an encoding argument, then you will need to start
providing encoding arguments to specify which encoding you'd like to
use.

Also, a Streaming API will be provided, but this will be done in such
a way as to preserve the legacy API surface.


[createCipher()]: #crypto_crypto_createcipher_algorithm_password
[createCipheriv()]: #crypto_crypto_createcipheriv_algorithm_key_iv
[crypto.createDiffieHellman()]: #crypto_crypto_creatediffiehellman_prime_encoding
[diffieHellman.setPublicKey()]: #crypto_diffiehellman_setpublickey_public_key_encoding
[RFC 2412]: http://www.rfc-editor.org/rfc/rfc2412.txt
[RFC 3526]: http://www.rfc-editor.org/rfc/rfc3526.txt
