Node.js v5.4.0 Documentation

Table of Contents

Crypto#

Stability: 2 - Stable

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

The crypto module 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.

Class: Certificate#

The class used for working with signed public key & challenges. The most common usage for this series of functions is when dealing with the <keygen> element. https://www.openssl.org/docs/apps/spkac.html

Returned by crypto.Certificate.

Certificate.exportChallenge(spkac)#

Exports the encoded challenge associated with the SPKAC.

Certificate.exportPublicKey(spkac)#

Exports the encoded public key from the supplied SPKAC.

Certificate.verifySpkac(spkac)#

Returns true of false based on the validity of the SPKAC.

Class: Cipher#

Class for encrypting data.

Returned by crypto.createCipher and crypto.createCipheriv.

Cipher objects are streams that are both readable and writable. The written plain text data is used to produce the encrypted data on the readable side. The legacy update and final methods are also supported.

cipher.final([output_encoding])#

Returns any remaining enciphered contents, with output_encoding being one of: 'binary', 'base64' or 'hex'. If no encoding is provided, then a buffer is returned.

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

cipher.getAuthTag()#

For authenticated encryption modes (currently supported: GCM), this method returns a Buffer that represents the authentication tag that has been computed from the given data. Should be called after encryption has been completed using the final method!

cipher.setAAD(buffer)#

For authenticated encryption modes (currently supported: GCM), this method sets the value used for the additional authenticated data (AAD) input parameter.

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.

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'. If no encoding is provided, then a buffer is expected. 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 no encoding is provided, then a buffer is returned.

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

Class: Decipher#

Class for decrypting data.

Returned by crypto.createDecipher and crypto.createDecipheriv.

Decipher objects are streams that are both readable and writable. The written enciphered data is used to produce the plain-text data on the the readable side. The legacy update and final methods are also supported.

decipher.final([output_encoding])#

Returns any remaining plaintext which is deciphered, with output_encoding being one of: 'binary', 'ascii' or 'utf8'. If no encoding is provided, then a buffer is returned.

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

decipher.setAAD(buffer)#

For authenticated encryption modes (currently supported: GCM), this method sets the value used for the additional authenticated data (AAD) input parameter.

decipher.setAuthTag(buffer)#

For authenticated encryption modes (currently supported: GCM), this method must be used to pass in the received authentication tag. If no tag is provided or if the ciphertext has been tampered with, final will throw, thus indicating that the ciphertext should be discarded due to failed authentication.

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. This will 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.

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

Updates the decipher with data, which is encoded in 'binary', 'base64' or 'hex'. If no encoding is provided, then a buffer is expected. If data is a Buffer then input_encoding is ignored.

The output_decoding specifies in what format to return the deciphered plaintext: 'binary', 'ascii' or 'utf8'. If no encoding is provided, then a buffer is returned.

Class: DiffieHellman#

The class for creating Diffie-Hellman key exchanges.

Returned by crypto.createDiffieHellman.

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'. If the input encoding is not provided, then a buffer is expected.

If no output encoding is given, then 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 no encoding is provided, then a buffer is returned.

diffieHellman.getGenerator([encoding])#

Returns the Diffie-Hellman generator in the specified encoding, which can be 'binary', 'hex', or 'base64'. If no encoding is provided, then a buffer is returned.

diffieHellman.getPrime([encoding])#

Returns the Diffie-Hellman prime in the specified encoding, which can be 'binary', 'hex', or 'base64'. If no encoding is provided, then 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 no encoding is provided, then 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 no encoding is provided, then a buffer is returned.

diffieHellman.setPrivateKey(private_key[, encoding])#

Sets the Diffie-Hellman private key. Key encoding can be 'binary', 'hex' or 'base64'. If no encoding is provided, then a buffer is expected.

diffieHellman.setPublicKey(public_key[, encoding])#

Sets the Diffie-Hellman public key. Key encoding can be 'binary', 'hex' or 'base64'. If no encoding is provided, then a buffer is expected.

diffieHellman.verifyError#

A bit field containing any warnings and/or errors as a result of a check performed during initialization. The following values are valid for this property (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 class for creating EC Diffie-Hellman key exchanges.

Returned by crypto.createECDH.

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. Supplied key is interpreted using 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, then a buffer is expected.

If no output encoding is given, then 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.

Format specifies point encoding and can be 'compressed', 'uncompressed', or 'hybrid'. If no format is provided - the point will be returned in 'uncompressed' format.

Encoding can be 'binary', 'hex', or 'base64'. If no encoding is provided, then 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 no encoding is provided, then a buffer is returned.

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

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

Format specifies point encoding and can be 'compressed', 'uncompressed', or 'hybrid'. If no format is provided - the point will be returned in 'uncompressed' format.

Encoding can be 'binary', 'hex', or 'base64'. If no encoding is provided, then a buffer is returned.

ECDH.setPrivateKey(private_key[, encoding])#

Sets the EC Diffie-Hellman private key. Key encoding can be 'binary', 'hex' or 'base64'. If no encoding is provided, then a buffer is expected. If private_key is not valid for the curve specified when the ECDH object was created, then 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 no encoding is provided, then a buffer is expected. Note that there is not normally a reason to call this method. This is because ECDH only needs your private key and the other party's public key to compute the shared secret. Thus, usually either generateKeys or setPrivateKey will be called. Note that setPrivateKey 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 class for creating hash digests of data.

It is a stream that is both readable and writable. The written data is used to compute the hash. Once the writable side of the stream is ended, use the read() method to get the computed hash digest. The legacy update and digest methods are also supported.

Returned by crypto.createHash.

hash.digest([encoding])#

Calculates the digest of all of the passed data to be hashed. The encoding can be 'hex', 'binary' or 'base64'. If no encoding is provided, then a buffer is returned.

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

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 no encoding is provided, and the input 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#

Class for creating cryptographic hmac content.

Returned by crypto.createHmac.

hmac.digest([encoding])#

Calculates the digest of all of the passed data to the hmac. The encoding can be 'hex', 'binary' or 'base64'. If no encoding is provided, then a buffer is returned.

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

hmac.update(data)#

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

Class: Sign#

Class for generating signatures.

Returned by crypto.createSign.

Sign objects are writable streams. The written data is used to generate the signature. Once all of the data has been written, the sign method will return the signature. The legacy update method is also supported.

sign.sign(private_key[, output_format])#

Calculates the signature on all the updated data passed through the sign.

private_key can be an object or a string. If private_key is a string, it is treated as the key with no passphrase.

private_key:

  • key : A string holding the PEM encoded private key
  • passphrase : A string of passphrase for the private key

Returns the signature in output_format which can be 'binary', 'hex' or 'base64'. If no encoding is provided, then a buffer is returned.

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

sign.update(data)#

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

Class: Verify#

Class for verifying signatures.

Returned by crypto.createVerify.

Verify objects are writable streams. The written data is used to validate against the supplied signature. Once all of the data has been written, the verify method will return true if the supplied signature is valid. The legacy update method is also supported.

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'. If no encoding is specified, then a buffer is expected.

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 has been called.

crypto.DEFAULT_ENCODING#

The default encoding to use for functions that can take either strings or buffers. The default value is 'buffer', which makes it default to using Buffer objects. This is here to make the crypto module more easily compatible with legacy programs that expected 'binary' to be the default encoding.

Note that new programs will probably expect buffers, so only use this as a temporary measure.

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.

It is a stream that is both readable and writable. The written data is used to compute the hash. Once the writable side of the stream is ended, use the read() method to get the enciphered contents. The legacy update and final methods are also supported.

Note: createCipher derives keys with 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 you derive a key and iv yourself with crypto.pbkdf2 and to then use createCipheriv() to create the cipher stream.

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.

key and iv must be 'binary' encoded strings or buffers.

crypto.createCredentials(details)#

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

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 https://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.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.

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

Creates a Diffie-Hellman key exchange object using the supplied prime and an optional specific generator. generator can be a number, string, or Buffer. If no generator is specified, then 2 is used. prime_encoding and generator_encoding can be 'binary', 'hex', or 'base64'. If no prime_encoding is specified, then a Buffer is expected for prime. If no generator_encoding is specified, then a Buffer is expected for generator.

crypto.createDiffieHellman(prime_length[, generator])#

Creates a Diffie-Hellman key exchange object and generates a prime of prime_length bits and using an optional specific numeric generator. If no generator is specified, then 2 is used.

crypto.createECDH(curve_name)#

Creates an Elliptic Curve (EC) Diffie-Hellman key exchange object using a predefined curve specified by the curve_name string. Use getCurves() to obtain a list of available curve names. On recent 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, 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 'sha256', 'sha512', etc. On recent releases, openssl list-message-digest-algorithms will display the available digest algorithms.

Example: this program that takes the sha256 sum of a file 

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

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

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

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

crypto.createHmac(algorithm, key)#

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

It is a stream that is both readable and writable. The written data is used to compute the hmac. Once the writable side of the stream is ended, use the read() method to get the computed digest. The legacy update and digest methods are also supported.

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

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'.

crypto.createVerify(algorithm)#

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

crypto.getCiphers()#

Returns an array with the names of the supported ciphers.

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 Diffie-Hellman 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() above, but will not allow changing the keys (with diffieHellman.setPublicKey() for example). The advantage of using this routine is that the parties do not have to generate nor exchange 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)#

Asynchronous PBKDF2 function. Applies the selected HMAC digest function (default: SHA1) to derive a key of the requested byte length from the password, salt and number of iterations. The callback gets two arguments: (err, derivedKey).

The number of iterations passed to pbkdf2 should be as high as possible, the higher the number, the more secure it will be, but will take a longer amount of time to complete.

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

Example: 

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

You can get a list of supported digest functions with crypto.getHashes().

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

Synchronous PBKDF2 function. Returns derivedKey or throws error.

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.

private_key:

  • key : A string holding the PEM encoded private key
  • passphrase : An optional string of 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

NOTE: All paddings are defined in constants module.

crypto.privateEncrypt(private_key, buffer)#

See above for details. Has the same API as crypto.privateDecrypt. Default padding is RSA_PKCS1_PADDING.

crypto.publicDecrypt(public_key, buffer)#

See above for details. Has the same API as crypto.publicEncrypt. Default padding is RSA_PKCS1_PADDING.

crypto.publicEncrypt(public_key, buffer)#

Encrypts buffer with public_key. Only RSA is currently supported.

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. Since RSA public keys may be derived from private keys you may pass a private key to this method.

public_key:

  • key : A string holding the PEM encoded private key
  • passphrase : An optional string of 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

NOTE: All paddings are defined in constants module.

crypto.randomBytes(size[, callback])#

Generates cryptographically strong pseudo-random data. Usage: 

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

// sync
const buf = crypto.randomBytes(256);
console.log('Have %d bytes of random data: %s', buf.length, buf);

NOTE: This will block if there is insufficient entropy, although it should normally never take longer than a few milliseconds. The only time when this may conceivably block is right after boot, when the whole system is still low on entropy.

crypto.setEngine(engine[, flags])#

Load and set engine for some/all OpenSSL functions (selected by flags).

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

flags is optional and has ENGINE_METHOD_ALL value by default. It could take one of or mix of following flags (defined in 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

Recent API Changes#

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 streaming classes don't have the typical methods found on other Node.js classes, and many methods accepted and returned Binary-encoded strings by default rather than Buffers. This was changed to use Buffers by default instead.

This is 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 once got a binary string and then presented the binary string to the Verify object, you'll now get a Buffer, and present the Buffer to the Verify object.

However, if you were 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. To switch to the previous style of using binary strings by default, set the crypto.DEFAULT_ENCODING field to 'binary'. Note that new programs will probably expect buffers, so only use this as a temporary measure.

Usage of ECDH with non-dynamically generated key pairs has been simplified. Now, 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 you to only store and provide the private part of the EC key pair. setPrivateKey now also validates that the private key is valid for the curve. ECDH.setPublicKey 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 generateKeys should be called. The main drawback of ECDH.setPublicKey is that it can be used to put the ECDH key pair into an inconsistent state.

Caveats#

The crypto module still supports some algorithms which are already compromised. And 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.