util.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.

"""
Useful functions used by the rest of ssh.
"""

from __future__ import generators

import array
from binascii import hexlify, unhexlify
import errno
import sys
import struct
import traceback
import threading

from ssh.common import *
from ssh.config import SSHConfig


# Change by RogerB - python < 2.3 doesn't have enumerate so we implement it
if sys.version_info < (2,3):
    class enumerate:
        def __init__ (self, sequence):
            self.sequence = sequence
        def __iter__ (self):
            count = 0
            for item in self.sequence:
                yield (count, item)
                count += 1


def inflate_long(s, always_positive=False):
    "turns a normalized byte string into a long-int (adapted from Crypto.Util.number)"
    out = 0L
    negative = 0
    if not always_positive and (len(s) > 0) and (ord(s[0]) >= 0x80):
        negative = 1
    if len(s) % 4:
        filler = '\x00'
        if negative:
            filler = '\xff'
        s = filler * (4 - len(s) % 4) + s
    for i in range(0, len(s), 4):
        out = (out << 32) + struct.unpack('>I', s[i:i+4])[0]
    if negative:
        out -= (1L << (8 * len(s)))
    return out

def deflate_long(n, add_sign_padding=True):
    "turns a long-int into a normalized byte string (adapted from Crypto.Util.number)"
    # after much testing, this algorithm was deemed to be the fastest
    s = ''
    n = long(n)
    while (n != 0) and (n != -1):
        s = struct.pack('>I', n & 0xffffffffL) + s
        n = n >> 32
    # strip off leading zeros, FFs
    for i in enumerate(s):
        if (n == 0) and (i[1] != '\000'):
            break
        if (n == -1) and (i[1] != '\xff'):
            break
    else:
        # degenerate case, n was either 0 or -1
        i = (0,)
        if n == 0:
            s = '\000'
        else:
            s = '\xff'
    s = s[i[0]:]
    if add_sign_padding:
        if (n == 0) and (ord(s[0]) >= 0x80):
            s = '\x00' + s
        if (n == -1) and (ord(s[0]) < 0x80):
            s = '\xff' + s
    return s

def format_binary_weird(data):
    out = ''
    for i in enumerate(data):
        out += '%02X' % ord(i[1])
        if i[0] % 2:
            out += ' '
        if i[0] % 16 == 15:
            out += '\n'
    return out

def format_binary(data, prefix=''):
    x = 0
    out = []
    while len(data) > x + 16:
        out.append(format_binary_line(data[x:x+16]))
        x += 16
    if x < len(data):
        out.append(format_binary_line(data[x:]))
    return [prefix + x for x in out]

def format_binary_line(data):
    left = ' '.join(['%02X' % ord(c) for c in data])
    right = ''.join([('.%c..' % c)[(ord(c)+63)//95] for c in data])
    return '%-50s %s' % (left, right)

def hexify(s):
    return hexlify(s).upper()

def unhexify(s):
    return unhexlify(s)

def safe_string(s):
    out = ''
    for c in s:
        if (ord(c) >= 32) and (ord(c) <= 127):
            out += c
        else:
            out += '%%%02X' % ord(c)
    return out

# ''.join([['%%%02X' % ord(c), c][(ord(c) >= 32) and (ord(c) <= 127)] for c in s])

def bit_length(n):
    norm = deflate_long(n, 0)
    hbyte = ord(norm[0])
    if hbyte == 0:
        return 1
    bitlen = len(norm) * 8
    while not (hbyte & 0x80):
        hbyte <<= 1
        bitlen -= 1
    return bitlen

def tb_strings():
    return ''.join(traceback.format_exception(*sys.exc_info())).split('\n')

def generate_key_bytes(hashclass, salt, key, nbytes):
    """
    Given a password, passphrase, or other human-source key, scramble it
    through a secure hash into some keyworthy bytes.  This specific algorithm
    is used for encrypting/decrypting private key files.

    @param hashclass: class from L{Crypto.Hash} that can be used as a secure
        hashing function (like C{MD5} or C{SHA}).
    @type hashclass: L{Crypto.Hash}
    @param salt: data to salt the hash with.
    @type salt: string
    @param key: human-entered password or passphrase.
    @type key: string
    @param nbytes: number of bytes to generate.
    @type nbytes: int
    @return: key data
    @rtype: string
    """
    keydata = ''
    digest = ''
    if len(salt) > 8:
        salt = salt[:8]
    while nbytes > 0:
        hash_obj = hashclass.new()
        if len(digest) > 0:
            hash_obj.update(digest)
        hash_obj.update(key)
        hash_obj.update(salt)
        digest = hash_obj.digest()
        size = min(nbytes, len(digest))
        keydata += digest[:size]
        nbytes -= size
    return keydata

def load_host_keys(filename):
    """
    Read a file of known SSH host keys, in the format used by openssh, and
    return a compound dict of C{hostname -> keytype ->} L{PKey <ssh.pkey.PKey>}.
    The hostname may be an IP address or DNS name.  The keytype will be either
    C{"ssh-rsa"} or C{"ssh-dss"}.

    This type of file unfortunately doesn't exist on Windows, but on posix,
    it will usually be stored in C{os.path.expanduser("~/.ssh/known_hosts")}.

    Since 1.5.3, this is just a wrapper around L{HostKeys}.

    @param filename: name of the file to read host keys from
    @type filename: str
    @return: dict of host keys, indexed by hostname and then keytype
    @rtype: dict(hostname, dict(keytype, L{PKey <ssh.pkey.PKey>}))
    """
    from ssh.hostkeys import HostKeys
    return HostKeys(filename)

def parse_ssh_config(file_obj):
    """
    Provided only as a backward-compatible wrapper around L{SSHConfig}.
    """
    config = SSHConfig()
    config.parse(file_obj)
    return config

def lookup_ssh_host_config(hostname, config):
    """
    Provided only as a backward-compatible wrapper around L{SSHConfig}.
    """
    return config.lookup(hostname)

def mod_inverse(x, m):
    # it's crazy how small python can make this function.
    u1, u2, u3 = 1, 0, m
    v1, v2, v3 = 0, 1, x

    while v3 > 0:
        q = u3 // v3
        u1, v1 = v1, u1 - v1 * q
        u2, v2 = v2, u2 - v2 * q
        u3, v3 = v3, u3 - v3 * q
    if u2 < 0:
        u2 += m
    return u2

_g_thread_ids = {}
_g_thread_counter = 0
_g_thread_lock = threading.Lock()
def get_thread_id():
    global _g_thread_ids, _g_thread_counter, _g_thread_lock
    tid = id(threading.currentThread())
    try:
        return _g_thread_ids[tid]
    except KeyError:
        _g_thread_lock.acquire()
        try:
            _g_thread_counter += 1
            ret = _g_thread_ids[tid] = _g_thread_counter
        finally:
            _g_thread_lock.release()
        return ret

def log_to_file(filename, level=DEBUG):
    "send ssh logs to a logfile, if they're not already going somewhere"
    l = logging.getLogger("ssh")
    if len(l.handlers) > 0:
        return
    l.setLevel(level)
    f = open(filename, 'w')
    lh = logging.StreamHandler(f)
    lh.setFormatter(logging.Formatter('%(levelname)-.3s [%(asctime)s.%(msecs)03d] thr=%(_threadid)-3d %(name)s: %(message)s',
                                      '%Y%m%d-%H:%M:%S'))
    l.addHandler(lh)

# make only one filter object, so it doesn't get applied more than once
class PFilter (object):
    def filter(self, record):
        record._threadid = get_thread_id()
        return True
_pfilter = PFilter()

def get_logger(name):
    l = logging.getLogger(name)
    l.addFilter(_pfilter)
    return l

def retry_on_signal(function):
    """Retries function until it doesn't raise an EINTR error"""
    while True:
        try:
            return function()
        except EnvironmentError, e:
            if e.errno != errno.EINTR:
                raise

class Counter (object):
    """Stateful counter for CTR mode crypto"""
    def __init__(self, nbits, initial_value=1L, overflow=0L):
        self.blocksize = nbits / 8
        self.overflow = overflow
        # start with value - 1 so we don't have to store intermediate values when counting
        # could the iv be 0?
        if initial_value == 0:
            self.value = array.array('c', '\xFF' * self.blocksize)
        else:
            x = deflate_long(initial_value - 1, add_sign_padding=False)
            self.value = array.array('c', '\x00' * (self.blocksize - len(x)) + x)

    def __call__(self):
        """Increament the counter and return the new value"""
        i = self.blocksize - 1
        while i > -1:
            c = self.value[i] = chr((ord(self.value[i]) + 1) % 256)
            if c != '\x00':
                return self.value.tostring()
            i -= 1
        # counter reset
        x = deflate_long(self.overflow, add_sign_padding=False)
        self.value = array.array('c', '\x00' * (self.blocksize - len(x)) + x)
        return self.value.tostring()

    def new(cls, nbits, initial_value=1L, overflow=0L):
        return cls(nbits, initial_value=initial_value, overflow=overflow)
    new = classmethod(new)