paramiko/ssh/pkey.py

# Copyright (C) 2011  Jeff Forcier <jeff@bitprophet.org>
#
# This file is part of ssh.
#
# 'ssh' is free software; you can redistribute it and/or modify it under the
# terms of the GNU Lesser General Public License as published by the Free
# Software Foundation; either version 2.1 of the License, or (at your option)
# any later version.
#
# 'ssh' is distrubuted in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
# details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with 'ssh'; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Suite 500, Boston, MA  02110-1335  USA.

"""
Common API for all public keys.
"""

import base64
from binascii import hexlify, unhexlify
import os

from Crypto.Hash import MD5
from Crypto.Cipher import DES3, AES

from ssh.common import *
from ssh import util
from ssh.message import Message
from ssh.ssh_exception import SSHException, PasswordRequiredException


class PKey (object):
    """
    Base class for public keys.
    """

    # known encryption types for private key files:
    _CIPHER_TABLE = {
        'AES-128-CBC': { 'cipher': AES, 'keysize': 16, 'blocksize': 16, 'mode': AES.MODE_CBC },
        'DES-EDE3-CBC': { 'cipher': DES3, 'keysize': 24, 'blocksize': 8, 'mode': DES3.MODE_CBC },
    }


    def __init__(self, msg=None, data=None):
        """
        Create a new instance of this public key type.  If C{msg} is given,
        the key's public part(s) will be filled in from the message.  If
        C{data} is given, the key's public part(s) will be filled in from
        the string.

        @param msg: an optional SSH L{Message} containing a public key of this
        type.
        @type msg: L{Message}
        @param data: an optional string containing a public key of this type
        @type data: str

        @raise SSHException: if a key cannot be created from the C{data} or
        C{msg} given, or no key was passed in.
        """
        pass

    def __str__(self):
        """
        Return a string of an SSH L{Message} made up of the public part(s) of
        this key.  This string is suitable for passing to L{__init__} to
        re-create the key object later.

        @return: string representation of an SSH key message.
        @rtype: str
        """
        return ''

    def __cmp__(self, other):
        """
        Compare this key to another.  Returns 0 if this key is equivalent to
        the given key, or non-0 if they are different.  Only the public parts
        of the key are compared, so a public key will compare equal to its
        corresponding private key.

        @param other: key to compare to.
        @type other: L{PKey}
        @return: 0 if the two keys are equivalent, non-0 otherwise.
        @rtype: int
        """
        hs = hash(self)
        ho = hash(other)
        if hs != ho:
            return cmp(hs, ho)
        return cmp(str(self), str(other))

    def get_name(self):
        """
        Return the name of this private key implementation.

        @return: name of this private key type, in SSH terminology (for
        example, C{"ssh-rsa"}).
        @rtype: str
        """
        return ''

    def get_bits(self):
        """
        Return the number of significant bits in this key.  This is useful
        for judging the relative security of a key.

        @return: bits in the key.
        @rtype: int
        """
        return 0

    def can_sign(self):
        """
        Return C{True} if this key has the private part necessary for signing
        data.

        @return: C{True} if this is a private key.
        @rtype: bool
        """
        return False

    def get_fingerprint(self):
        """
        Return an MD5 fingerprint of the public part of this key.  Nothing
        secret is revealed.

        @return: a 16-byte string (binary) of the MD5 fingerprint, in SSH
            format.
        @rtype: str
        """
        return MD5.new(str(self)).digest()

    def get_base64(self):
        """
        Return a base64 string containing the public part of this key.  Nothing
        secret is revealed.  This format is compatible with that used to store
        public key files or recognized host keys.

        @return: a base64 string containing the public part of the key.
        @rtype: str
        """
        return base64.encodestring(str(self)).replace('\n', '')

    def sign_ssh_data(self, rng, data):
        """
        Sign a blob of data with this private key, and return a L{Message}
        representing an SSH signature message.

        @param rng: a secure random number generator.
        @type rng: L{Crypto.Util.rng.RandomPool}
        @param data: the data to sign.
        @type data: str
        @return: an SSH signature message.
        @rtype: L{Message}
        """
        return ''

    def verify_ssh_sig(self, data, msg):
        """
        Given a blob of data, and an SSH message representing a signature of
        that data, verify that it was signed with this key.

        @param data: the data that was signed.
        @type data: str
        @param msg: an SSH signature message
        @type msg: L{Message}
        @return: C{True} if the signature verifies correctly; C{False}
            otherwise.
        @rtype: boolean
        """
        return False

    def from_private_key_file(cls, filename, password=None):
        """
        Create a key object by reading a private key file.  If the private
        key is encrypted and C{password} is not C{None}, the given password
        will be used to decrypt the key (otherwise L{PasswordRequiredException}
        is thrown).  Through the magic of python, this factory method will
        exist in all subclasses of PKey (such as L{RSAKey} or L{DSSKey}), but
        is useless on the abstract PKey class.

        @param filename: name of the file to read
        @type filename: str
        @param password: an optional password to use to decrypt the key file,
            if it's encrypted
        @type password: str
        @return: a new key object based on the given private key
        @rtype: L{PKey}

        @raise IOError: if there was an error reading the file
        @raise PasswordRequiredException: if the private key file is
            encrypted, and C{password} is C{None}
        @raise SSHException: if the key file is invalid
        """
        key = cls(filename=filename, password=password)
        return key
    from_private_key_file = classmethod(from_private_key_file)

    def from_private_key(cls, file_obj, password=None):
        """
        Create a key object by reading a private key from a file (or file-like)
        object.  If the private key is encrypted and C{password} is not C{None},
        the given password will be used to decrypt the key (otherwise
        L{PasswordRequiredException} is thrown).

        @param file_obj: the file to read from
        @type file_obj: file
        @param password: an optional password to use to decrypt the key, if it's
            encrypted
        @type password: str
        @return: a new key object based on the given private key
        @rtype: L{PKey}

        @raise IOError: if there was an error reading the key
        @raise PasswordRequiredException: if the private key file is encrypted,
            and C{password} is C{None}
        @raise SSHException: if the key file is invalid
        """
        key = cls(file_obj=file_obj, password=password)
        return key
    from_private_key = classmethod(from_private_key)

    def write_private_key_file(self, filename, password=None):
        """
        Write private key contents into a file.  If the password is not
        C{None}, the key is encrypted before writing.

        @param filename: name of the file to write
        @type filename: str
        @param password: an optional password to use to encrypt the key file
        @type password: str

        @raise IOError: if there was an error writing the file
        @raise SSHException: if the key is invalid
        """
        raise Exception('Not implemented in PKey')

    def write_private_key(self, file_obj, password=None):
        """
        Write private key contents into a file (or file-like) object.  If the
        password is not C{None}, the key is encrypted before writing.

        @param file_obj: the file object to write into
        @type file_obj: file
        @param password: an optional password to use to encrypt the key
        @type password: str

        @raise IOError: if there was an error writing to the file
        @raise SSHException: if the key is invalid
        """
        raise Exception('Not implemented in PKey')

    def _read_private_key_file(self, tag, filename, password=None):
        """
        Read an SSH2-format private key file, looking for a string of the type
        C{"BEGIN xxx PRIVATE KEY"} for some C{xxx}, base64-decode the text we
        find, and return it as a string.  If the private key is encrypted and
        C{password} is not C{None}, the given password will be used to decrypt
        the key (otherwise L{PasswordRequiredException} is thrown).

        @param tag: C{"RSA"} or C{"DSA"}, the tag used to mark the data block.
        @type tag: str
        @param filename: name of the file to read.
        @type filename: str
        @param password: an optional password to use to decrypt the key file,
            if it's encrypted.
        @type password: str
        @return: data blob that makes up the private key.
        @rtype: str

        @raise IOError: if there was an error reading the file.
        @raise PasswordRequiredException: if the private key file is
            encrypted, and C{password} is C{None}.
        @raise SSHException: if the key file is invalid.
        """
        f = open(filename, 'r')
        data = self._read_private_key(tag, f, password)
        f.close()
        return data

    def _read_private_key(self, tag, f, password=None):
        lines = f.readlines()
        start = 0
        while (start < len(lines)) and (lines[start].strip() != '-----BEGIN ' + tag + ' PRIVATE KEY-----'):
            start += 1
        if start >= len(lines):
            raise SSHException('not a valid ' + tag + ' private key file')
        # parse any headers first
        headers = {}
        start += 1
        while start < len(lines):
            l = lines[start].split(': ')
            if len(l) == 1:
                break
            headers[l[0].lower()] = l[1].strip()
            start += 1
        # find end
        end = start
        while (lines[end].strip() != '-----END ' + tag + ' PRIVATE KEY-----') and (end < len(lines)):
            end += 1
        # if we trudged to the end of the file, just try to cope.
        try:
            data = base64.decodestring(''.join(lines[start:end]))
        except base64.binascii.Error, e:
            raise SSHException('base64 decoding error: ' + str(e))
        if 'proc-type' not in headers:
            # unencryped: done
            return data
        # encrypted keyfile: will need a password
        if headers['proc-type'] != '4,ENCRYPTED':
            raise SSHException('Unknown private key structure "%s"' % headers['proc-type'])
        try:
            encryption_type, saltstr = headers['dek-info'].split(',')
        except:
            raise SSHException('Can\'t parse DEK-info in private key file')
        if encryption_type not in self._CIPHER_TABLE:
            raise SSHException('Unknown private key cipher "%s"' % encryption_type)
        # if no password was passed in, raise an exception pointing out that we need one
        if password is None:
            raise PasswordRequiredException('Private key file is encrypted')
        cipher = self._CIPHER_TABLE[encryption_type]['cipher']
        keysize = self._CIPHER_TABLE[encryption_type]['keysize']
        mode = self._CIPHER_TABLE[encryption_type]['mode']
        salt = unhexlify(saltstr)
        key = util.generate_key_bytes(MD5, salt, password, keysize)
        return cipher.new(key, mode, salt).decrypt(data)

    def _write_private_key_file(self, tag, filename, data, password=None):
        """
        Write an SSH2-format private key file in a form that can be read by
        ssh or openssh.  If no password is given, the key is written in
        a trivially-encoded format (base64) which is completely insecure.  If
        a password is given, DES-EDE3-CBC is used.

        @param tag: C{"RSA"} or C{"DSA"}, the tag used to mark the data block.
        @type tag: str
        @param filename: name of the file to write.
        @type filename: str
        @param data: data blob that makes up the private key.
        @type data: str
        @param password: an optional password to use to encrypt the file.
        @type password: str

        @raise IOError: if there was an error writing the file.
        """
        f = open(filename, 'w', 0600)
        # grrr... the mode doesn't always take hold
        os.chmod(filename, 0600)
        self._write_private_key(tag, f, data, password)
        f.close()

    def _write_private_key(self, tag, f, data, password=None):
        f.write('-----BEGIN %s PRIVATE KEY-----\n' % tag)
        if password is not None:
            # since we only support one cipher here, use it
            cipher_name = self._CIPHER_TABLE.keys()[0]
            cipher = self._CIPHER_TABLE[cipher_name]['cipher']
            keysize = self._CIPHER_TABLE[cipher_name]['keysize']
            blocksize = self._CIPHER_TABLE[cipher_name]['blocksize']
            mode = self._CIPHER_TABLE[cipher_name]['mode']
            salt = rng.read(8)
            key = util.generate_key_bytes(MD5, salt, password, keysize)
            if len(data) % blocksize != 0:
                n = blocksize - len(data) % blocksize
                #data += rng.read(n)
                # that would make more sense ^, but it confuses openssh.
                data += '\0' * n
            data = cipher.new(key, mode, salt).encrypt(data)
            f.write('Proc-Type: 4,ENCRYPTED\n')
            f.write('DEK-Info: %s,%s\n' % (cipher_name, hexlify(salt).upper()))
            f.write('\n')
        s = base64.encodestring(data)
        # re-wrap to 64-char lines
        s = ''.join(s.split('\n'))
        s = '\n'.join([s[i : i+64] for i in range(0, len(s), 64)])
        f.write(s)
        f.write('\n')
        f.write('-----END %s PRIVATE KEY-----\n' % tag)