node-forge/lib/ssh.js

/**
 * Functions to output keys in SSH-friendly formats.
 *
 * This is part of the Forge project which may be used under the terms of
 * either the BSD License or the GNU General Public License (GPL) Version 2.
 *
 * See: https://github.com/digitalbazaar/forge/blob/cbebca3780658703d925b61b2caffb1d263a6c1d/LICENSE
 *
 * @author https://github.com/shellac
 */
var forge = require('./forge');
require('./aes');
require('./hmac');
require('./md5');
require('./sha1');
require('./util');

var ssh = module.exports = forge.ssh = forge.ssh || {};

/**
 * Encodes (and optionally encrypts) a private RSA key as a Putty PPK file.
 *
 * @param privateKey the key.
 * @param passphrase a passphrase to protect the key (falsy for no encryption).
 * @param comment a comment to include in the key file.
 *
 * @return the PPK file as a string.
 */
ssh.privateKeyToPutty = function(privateKey, passphrase, comment) {
  comment = comment || '';
  passphrase = passphrase || '';
  var algorithm = 'ssh-rsa';
  var encryptionAlgorithm = (passphrase === '') ? 'none' : 'aes256-cbc';

  var ppk = 'PuTTY-User-Key-File-2: ' + algorithm + '\r\n';
  ppk += 'Encryption: ' + encryptionAlgorithm + '\r\n';
  ppk += 'Comment: ' + comment + '\r\n';

  // public key into buffer for ppk
  var pubbuffer = forge.util.createBuffer();
  _addStringToBuffer(pubbuffer, algorithm);
  _addBigIntegerToBuffer(pubbuffer, privateKey.e);
  _addBigIntegerToBuffer(pubbuffer, privateKey.n);

  // write public key
  var pub = forge.util.encode64(pubbuffer.bytes(), 64);
  var length = Math.floor(pub.length / 66) + 1; // 66 = 64 + \r\n
  ppk += 'Public-Lines: ' + length + '\r\n';
  ppk += pub;

  // private key into a buffer
  var privbuffer = forge.util.createBuffer();
  _addBigIntegerToBuffer(privbuffer, privateKey.d);
  _addBigIntegerToBuffer(privbuffer, privateKey.p);
  _addBigIntegerToBuffer(privbuffer, privateKey.q);
  _addBigIntegerToBuffer(privbuffer, privateKey.qInv);

  // optionally encrypt the private key
  var priv;
  if(!passphrase) {
    // use the unencrypted buffer
    priv = forge.util.encode64(privbuffer.bytes(), 64);
  } else {
    // encrypt RSA key using passphrase
    var encLen = privbuffer.length() + 16 - 1;
    encLen -= encLen % 16;

    // pad private key with sha1-d data -- needs to be a multiple of 16
    var padding = _sha1(privbuffer.bytes());

    padding.truncate(padding.length() - encLen + privbuffer.length());
    privbuffer.putBuffer(padding);

    var aeskey = forge.util.createBuffer();
    aeskey.putBuffer(_sha1('\x00\x00\x00\x00', passphrase));
    aeskey.putBuffer(_sha1('\x00\x00\x00\x01', passphrase));

    // encrypt some bytes using CBC mode
    // key is 40 bytes, so truncate *by* 8 bytes
    var cipher = forge.aes.createEncryptionCipher(aeskey.truncate(8), 'CBC');
    cipher.start(forge.util.createBuffer().fillWithByte(0, 16));
    cipher.update(privbuffer.copy());
    cipher.finish();
    var encrypted = cipher.output;

    // Note: this appears to differ from Putty -- is forge wrong, or putty?
    // due to padding we finish as an exact multiple of 16
    encrypted.truncate(16); // all padding

    priv = forge.util.encode64(encrypted.bytes(), 64);
  }

  // output private key
  length = Math.floor(priv.length / 66) + 1; // 64 + \r\n
  ppk += '\r\nPrivate-Lines: ' + length + '\r\n';
  ppk += priv;

  // MAC
  var mackey = _sha1('putty-private-key-file-mac-key', passphrase);

  var macbuffer = forge.util.createBuffer();
  _addStringToBuffer(macbuffer, algorithm);
  _addStringToBuffer(macbuffer, encryptionAlgorithm);
  _addStringToBuffer(macbuffer, comment);
  macbuffer.putInt32(pubbuffer.length());
  macbuffer.putBuffer(pubbuffer);
  macbuffer.putInt32(privbuffer.length());
  macbuffer.putBuffer(privbuffer);

  var hmac = forge.hmac.create();
  hmac.start('sha1', mackey);
  hmac.update(macbuffer.bytes());

  ppk += '\r\nPrivate-MAC: ' + hmac.digest().toHex() + '\r\n';

  return ppk;
};

/**
 * Encodes a public RSA key as an OpenSSH file.
 *
 * @param key the key.
 * @param comment a comment.
 *
 * @return the public key in OpenSSH format.
 */
ssh.publicKeyToOpenSSH = function(key, comment) {
  var type = 'ssh-rsa';
  comment = comment || '';

  var buffer = forge.util.createBuffer();
  _addStringToBuffer(buffer, type);
  _addBigIntegerToBuffer(buffer, key.e);
  _addBigIntegerToBuffer(buffer, key.n);

  return type + ' ' + forge.util.encode64(buffer.bytes()) + ' ' + comment;
};

/**
 * Encodes a private RSA key as an OpenSSH file.
 *
 * @param key the key.
 * @param passphrase a passphrase to protect the key (falsy for no encryption).
 *
 * @return the public key in OpenSSH format.
 */
ssh.privateKeyToOpenSSH = function(privateKey, passphrase) {
  if(!passphrase) {
    return forge.pki.privateKeyToPem(privateKey);
  }
  // OpenSSH private key is just a legacy format, it seems
  return forge.pki.encryptRsaPrivateKey(privateKey, passphrase,
    {legacy: true, algorithm: 'aes128'});
};

/**
 * Gets the SSH fingerprint for the given public key.
 *
 * @param options the options to use.
 *          [md] the message digest object to use (defaults to forge.md.md5).
 *          [encoding] an alternative output encoding, such as 'hex'
 *            (defaults to none, outputs a byte buffer).
 *          [delimiter] the delimiter to use between bytes for 'hex' encoded
 *            output, eg: ':' (defaults to none).
 *
 * @return the fingerprint as a byte buffer or other encoding based on options.
 */
ssh.getPublicKeyFingerprint = function(key, options) {
  options = options || {};
  var md = options.md || forge.md.md5.create();

  var type = 'ssh-rsa';
  var buffer = forge.util.createBuffer();
  _addStringToBuffer(buffer, type);
  _addBigIntegerToBuffer(buffer, key.e);
  _addBigIntegerToBuffer(buffer, key.n);

  // hash public key bytes
  md.start();
  md.update(buffer.getBytes());
  var digest = md.digest();
  if(options.encoding === 'hex') {
    var hex = digest.toHex();
    if(options.delimiter) {
      return hex.match(/.{2}/g).join(options.delimiter);
    }
    return hex;
  } else if(options.encoding === 'binary') {
    return digest.getBytes();
  } else if(options.encoding) {
    throw new Error('Unknown encoding "' + options.encoding + '".');
  }
  return digest;
};

/**
 * Adds len(val) then val to a buffer.
 *
 * @param buffer the buffer to add to.
 * @param val a big integer.
 */
function _addBigIntegerToBuffer(buffer, val) {
  var hexVal = val.toString(16);
  // ensure 2s complement +ve
  if(hexVal[0] >= '8') {
    hexVal = '00' + hexVal;
  }
  var bytes = forge.util.hexToBytes(hexVal);
  buffer.putInt32(bytes.length);
  buffer.putBytes(bytes);
}

/**
 * Adds len(val) then val to a buffer.
 *
 * @param buffer the buffer to add to.
 * @param val a string.
 */
function _addStringToBuffer(buffer, val) {
  buffer.putInt32(val.length);
  buffer.putString(val);
}

/**
 * Hashes the arguments into one value using SHA-1.
 *
 * @return the sha1 hash of the provided arguments.
 */
function _sha1() {
  var sha = forge.md.sha1.create();
  var num = arguments.length;
  for (var i = 0; i < num; ++i) {
    sha.update(arguments[i]);
  }
  return sha.digest();
}