patch for ARC4 cipher support, and CTR block chaining, from denis bernard.

paramiko/transport.py

@@ -50,8 +50,12 @@ from paramiko.ssh_exception import SSHException, BadAuthenticationType, ChannelE
 # i believe this on the standards track.
 # PyCrypt compiled for Win32 can be downloaded from the HashTar homepage:
 #     http://nitace.bsd.uchicago.edu:8080/hashtar
-from Crypto.Cipher import Blowfish, AES, DES3
+from Crypto.Cipher import Blowfish, AES, DES3, ARC4
 from Crypto.Hash import SHA, MD5
+try:
+    from Crypto.Util import Counter
+except ImportError:
+    from paramiko.util import Counter
 
 
 # for thread cleanup
@@ -196,17 +200,22 @@ class Transport (threading.Thread):
     _PROTO_ID = '2.0'
     _CLIENT_ID = 'paramiko_1.7.4'
 
-    _preferred_ciphers = ( 'aes128-cbc', 'blowfish-cbc', 'aes256-cbc', '3des-cbc' )
+    _preferred_ciphers = ( 'aes128-ctr', 'aes256-ctr', 'aes128-cbc', 'blowfish-cbc', 'aes256-cbc', '3des-cbc',
+        'arcfour128', 'arcfour256' )
     _preferred_macs = ( 'hmac-sha1', 'hmac-md5', 'hmac-sha1-96', 'hmac-md5-96' )
     _preferred_keys = ( 'ssh-rsa', 'ssh-dss' )
     _preferred_kex = ( 'diffie-hellman-group1-sha1', 'diffie-hellman-group-exchange-sha1' )
     _preferred_compression = ( 'none', )
     
     _cipher_info = {
+        'aes128-ctr': { 'class': AES, 'mode': AES.MODE_CTR, 'block-size': 16, 'key-size': 16 },
+        'aes256-ctr': { 'class': AES, 'mode': AES.MODE_CTR, 'block-size': 16, 'key-size': 32 },
         'blowfish-cbc': { 'class': Blowfish, 'mode': Blowfish.MODE_CBC, 'block-size': 8, 'key-size': 16 },
         'aes128-cbc': { 'class': AES, 'mode': AES.MODE_CBC, 'block-size': 16, 'key-size': 16 },
         'aes256-cbc': { 'class': AES, 'mode': AES.MODE_CBC, 'block-size': 16, 'key-size': 32 },
         '3des-cbc': { 'class': DES3, 'mode': DES3.MODE_CBC, 'block-size': 8, 'key-size': 24 },
+        'arcfour128': { 'class': ARC4, 'mode': None, 'block-size': 8, 'key-size': 16 },
+        'arcfour256': { 'class': ARC4, 'mode': None, 'block-size': 8, 'key-size': 32 },
         }
 
     _mac_info = {
@@ -1447,7 +1456,19 @@ class Transport (threading.Thread):
     def _get_cipher(self, name, key, iv):
         if name not in self._cipher_info:
             raise SSHException('Unknown client cipher ' + name)
-        return self._cipher_info[name]['class'].new(key, self._cipher_info[name]['mode'], iv)
+        if name in ('arcfour128', 'arcfour256'):
+            # arcfour cipher
+            cipher = self._cipher_info[name]['class'].new(key)
+            # as per RFC 4345, the first 1536 bytes of keystream
+            # generated by the cipher MUST be discarded
+            cipher.encrypt(" " * 1536)
+            return cipher
+        elif name.endswith("-ctr"):
+            # CTR modes, we need a counter
+            counter = Counter.new(nbits=self._cipher_info[name]['block-size'] * 8, initial_value=util.inflate_long(iv, True))
+            return self._cipher_info[name]['class'].new(key, self._cipher_info[name]['mode'], iv, counter)
+        else:
+            return self._cipher_info[name]['class'].new(key, self._cipher_info[name]['mode'], iv)
 
     def _set_x11_handler(self, handler):
         # only called if a channel has turned on x11 forwarding

paramiko/util.py

@@ -22,6 +22,7 @@ Useful functions used by the rest of paramiko.
 
 from __future__ import generators
 
+import array
 from binascii import hexlify, unhexlify
 import sys
 import struct
@@ -270,3 +271,32 @@ def get_logger(name):
     return l
 
 
+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)