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transport.py
2062 lines (1664 loc) · 71.8 KB
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transport.py
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# -*- test-case-name: twisted.conch.test.test_transport -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
The lowest level SSH protocol. This handles the key negotiation, the
encryption and the compression. The transport layer is described in
RFC 4253.
Maintainer: Paul Swartz
"""
from __future__ import absolute_import, division
import binascii
import hmac
import struct
import zlib
from hashlib import md5, sha1, sha256, sha384, sha512
from cryptography.exceptions import UnsupportedAlgorithm
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.ciphers import algorithms, modes, Cipher
from cryptography.hazmat.primitives.asymmetric import dh, ec
from twisted import __version__ as twisted_version
from twisted.internet import protocol, defer
from twisted.python import log, randbytes
from twisted.python.compat import iterbytes, _bytesChr as chr, networkString
# This import is needed if SHA256 hashing is used.
# from twisted.python.compat import nativeString
from twisted.conch.ssh import address, keys, _kex
from twisted.conch.ssh.common import (
NS, getNS, MP, getMP, ffs
)
class _MACParams(tuple):
"""
L{_MACParams} represents the parameters necessary to compute SSH MAC
(Message Authenticate Codes).
L{_MACParams} is a L{tuple} subclass to maintain compatibility with older
versions of the code. The elements of a L{_MACParams} are::
0. The digest object used for the MAC
1. The inner pad ("ipad") string
2. The outer pad ("opad") string
3. The size of the digest produced by the digest object
L{_MACParams} is also an object lesson in why tuples are a bad type for
public APIs.
@ivar key: The HMAC key which will be used.
"""
class SSHCiphers:
"""
SSHCiphers represents all the encryption operations that need to occur
to encrypt and authenticate the SSH connection.
@cvar cipherMap: A dictionary mapping SSH encryption names to 3-tuples of
(<cryptography.hazmat.primitives.interfaces.CipherAlgorithm>,
<block size>, <cryptography.hazmat.primitives.interfaces.Mode>)
@cvar macMap: A dictionary mapping SSH MAC names to hash modules.
@ivar outCipType: the string type of the outgoing cipher.
@ivar inCipType: the string type of the incoming cipher.
@ivar outMACType: the string type of the incoming MAC.
@ivar inMACType: the string type of the incoming MAC.
@ivar encBlockSize: the block size of the outgoing cipher.
@ivar decBlockSize: the block size of the incoming cipher.
@ivar verifyDigestSize: the size of the incoming MAC.
@ivar outMAC: a tuple of (<hash module>, <inner key>, <outer key>,
<digest size>) representing the outgoing MAC.
@ivar inMAc: see outMAC, but for the incoming MAC.
"""
cipherMap = {
b'3des-cbc': (algorithms.TripleDES, 24, modes.CBC),
b'blowfish-cbc': (algorithms.Blowfish, 16, modes.CBC),
b'aes256-cbc': (algorithms.AES, 32, modes.CBC),
b'aes192-cbc': (algorithms.AES, 24, modes.CBC),
b'aes128-cbc': (algorithms.AES, 16, modes.CBC),
b'cast128-cbc': (algorithms.CAST5, 16, modes.CBC),
b'aes128-ctr': (algorithms.AES, 16, modes.CTR),
b'aes192-ctr': (algorithms.AES, 24, modes.CTR),
b'aes256-ctr': (algorithms.AES, 32, modes.CTR),
b'3des-ctr': (algorithms.TripleDES, 24, modes.CTR),
b'blowfish-ctr': (algorithms.Blowfish, 16, modes.CTR),
b'cast128-ctr': (algorithms.CAST5, 16, modes.CTR),
b'none': (None, 0, modes.CBC),
}
macMap = {
b'hmac-sha2-512': sha512,
b'hmac-sha2-384': sha384,
b'hmac-sha2-256': sha256,
b'hmac-sha1': sha1,
b'hmac-md5': md5,
b'none': None
}
def __init__(self, outCip, inCip, outMac, inMac):
self.outCipType = outCip
self.inCipType = inCip
self.outMACType = outMac
self.inMACType = inMac
self.encBlockSize = 0
self.decBlockSize = 0
self.verifyDigestSize = 0
self.outMAC = (None, b'', b'', 0)
self.inMAC = (None, b'', b'', 0)
def setKeys(self, outIV, outKey, inIV, inKey, outInteg, inInteg):
"""
Set up the ciphers and hashes using the given keys,
@param outIV: the outgoing initialization vector
@param outKey: the outgoing encryption key
@param inIV: the incoming initialization vector
@param inKey: the incoming encryption key
@param outInteg: the outgoing integrity key
@param inInteg: the incoming integrity key.
"""
o = self._getCipher(self.outCipType, outIV, outKey)
self.encryptor = o.encryptor()
self.encBlockSize = o.algorithm.block_size // 8
o = self._getCipher(self.inCipType, inIV, inKey)
self.decryptor = o.decryptor()
self.decBlockSize = o.algorithm.block_size // 8
self.outMAC = self._getMAC(self.outMACType, outInteg)
self.inMAC = self._getMAC(self.inMACType, inInteg)
if self.inMAC:
self.verifyDigestSize = self.inMAC[3]
def _getCipher(self, cip, iv, key):
"""
Creates an initialized cipher object.
@param cip: the name of the cipher, maps into cipherMap
@param iv: the initialzation vector
@param key: the encryption key
@return: the cipher object.
"""
algorithmClass, keySize, modeClass = self.cipherMap[cip]
if algorithmClass is None:
return _DummyCipher()
return Cipher(
algorithmClass(key[:keySize]),
modeClass(iv[:algorithmClass.block_size // 8]),
backend=default_backend(),
)
def _getMAC(self, mac, key):
"""
Gets a 4-tuple representing the message authentication code.
(<hash module>, <inner hash value>, <outer hash value>,
<digest size>)
@type mac: L{bytes}
@param mac: a key mapping into macMap
@type key: L{bytes}
@param key: the MAC key.
@rtype: L{bytes}
@return: The MAC components.
"""
mod = self.macMap[mac]
if not mod:
return (None, b'', b'', 0)
# With stdlib we can only get attributes fron an instantiated object.
hashObject = mod()
digestSize = hashObject.digest_size
blockSize = hashObject.block_size
# Truncation here appears to contravene RFC 2104, section 2. However,
# implementing the hashing behavior prescribed by the RFC breaks
# interoperability with OpenSSH (at least version 5.5p1).
key = key[:digestSize] + (b'\x00' * (blockSize - digestSize))
i = key.translate(hmac.trans_36)
o = key.translate(hmac.trans_5C)
result = _MACParams((mod, i, o, digestSize))
result.key = key
return result
def encrypt(self, blocks):
"""
Encrypt some data.
@type blocks: L{bytes}
@param blocks: The data to encrypt.
@rtype: L{bytes}
@return: The encrypted data.
"""
return self.encryptor.update(blocks)
def decrypt(self, blocks):
"""
Decrypt some data.
@type blocks: L{bytes}
@param blocks: The data to decrypt.
@rtype: L{bytes}
@return: The decrypted data.
"""
return self.decryptor.update(blocks)
def makeMAC(self, seqid, data):
"""
Create a message authentication code (MAC) for the given packet using
the outgoing MAC values.
@type seqid: L{int}
@param seqid: The sequence ID of the outgoing packet.
@type data: L{bytes}
@param data: The data to create a MAC for.
@rtype: L{str}
@return: The serialized MAC.
"""
if not self.outMAC[0]:
return b''
data = struct.pack('>L', seqid) + data
return hmac.HMAC(self.outMAC.key, data, self.outMAC[0]).digest()
def verify(self, seqid, data, mac):
"""
Verify an incoming MAC using the incoming MAC values.
@type seqid: L{int}
@param seqid: The sequence ID of the incoming packet.
@type data: L{bytes}
@param data: The packet data to verify.
@type mac: L{bytes}
@param mac: The MAC sent with the packet.
@rtype: L{bool}
@return: C{True} if the MAC is valid.
"""
if not self.inMAC[0]:
return mac == b''
data = struct.pack('>L', seqid) + data
outer = hmac.HMAC(self.inMAC.key, data, self.inMAC[0]).digest()
return mac == outer
def _getSupportedCiphers():
"""
Build a list of ciphers that are supported by the backend in use.
@return: a list of supported ciphers.
@rtype: L{list} of L{str}
"""
supportedCiphers = []
cs = [b'aes256-ctr', b'aes256-cbc', b'aes192-ctr', b'aes192-cbc',
b'aes128-ctr', b'aes128-cbc', b'cast128-ctr', b'cast128-cbc',
b'blowfish-ctr', b'blowfish-cbc', b'3des-ctr', b'3des-cbc']
for cipher in cs:
algorithmClass, keySize, modeClass = SSHCiphers.cipherMap[cipher]
try:
Cipher(
algorithmClass(b' ' * keySize),
modeClass(b' ' * (algorithmClass.block_size // 8)),
backend=default_backend(),
).encryptor()
except UnsupportedAlgorithm:
pass
else:
supportedCiphers.append(cipher)
return supportedCiphers
class SSHTransportBase(protocol.Protocol):
"""
Protocol supporting basic SSH functionality: sending/receiving packets
and message dispatch. To connect to or run a server, you must use
SSHClientTransport or SSHServerTransport.
@ivar protocolVersion: A string representing the version of the SSH
protocol we support. Currently defaults to '2.0'.
@ivar version: A string representing the version of the server or client.
Currently defaults to 'Twisted'.
@ivar comment: An optional string giving more information about the
server or client.
@ivar supportedCiphers: A list of strings representing the encryption
algorithms supported, in order from most-preferred to least.
@ivar supportedMACs: A list of strings representing the message
authentication codes (hashes) supported, in order from most-preferred
to least. Both this and supportedCiphers can include 'none' to use
no encryption or authentication, but that must be done manually,
@ivar supportedKeyExchanges: A list of strings representing the
key exchanges supported, in order from most-preferred to least.
@ivar supportedPublicKeys: A list of strings representing the
public key types supported, in order from most-preferred to least.
@ivar supportedCompressions: A list of strings representing compression
types supported, from most-preferred to least.
@ivar supportedLanguages: A list of strings representing languages
supported, from most-preferred to least.
@ivar supportedVersions: A container of strings representing supported ssh
protocol version numbers.
@ivar isClient: A boolean indicating whether this is a client or server.
@ivar gotVersion: A boolean indicating whether we have received the
version string from the other side.
@ivar buf: Data we've received but hasn't been parsed into a packet.
@ivar outgoingPacketSequence: the sequence number of the next packet we
will send.
@ivar incomingPacketSequence: the sequence number of the next packet we
are expecting from the other side.
@ivar outgoingCompression: an object supporting the .compress(str) and
.flush() methods, or None if there is no outgoing compression. Used to
compress outgoing data.
@ivar outgoingCompressionType: A string representing the outgoing
compression type.
@ivar incomingCompression: an object supporting the .decompress(str)
method, or None if there is no incoming compression. Used to
decompress incoming data.
@ivar incomingCompressionType: A string representing the incoming
compression type.
@ivar ourVersionString: the version string that we sent to the other side.
Used in the key exchange.
@ivar otherVersionString: the version string sent by the other side. Used
in the key exchange.
@ivar ourKexInitPayload: the MSG_KEXINIT payload we sent. Used in the key
exchange.
@ivar otherKexInitPayload: the MSG_KEXINIT payload we received. Used in
the key exchange
@ivar sessionID: a string that is unique to this SSH session. Created as
part of the key exchange, sessionID is used to generate the various
encryption and authentication keys.
@ivar service: an SSHService instance, or None. If it's set to an object,
it's the currently running service.
@ivar kexAlg: the agreed-upon key exchange algorithm.
@ivar keyAlg: the agreed-upon public key type for the key exchange.
@ivar currentEncryptions: an SSHCiphers instance. It represents the
current encryption and authentication options for the transport.
@ivar nextEncryptions: an SSHCiphers instance. Held here until the
MSG_NEWKEYS messages are exchanged, when nextEncryptions is
transitioned to currentEncryptions.
@ivar first: the first bytes of the next packet. In order to avoid
decrypting data twice, the first bytes are decrypted and stored until
the whole packet is available.
@ivar _keyExchangeState: The current protocol state with respect to key
exchange. This is either C{_KEY_EXCHANGE_NONE} if no key exchange is
in progress (and returns to this value after any key exchange
completqes), C{_KEY_EXCHANGE_REQUESTED} if this side of the connection
initiated a key exchange, and C{_KEY_EXCHANGE_PROGRESSING} if the other
side of the connection initiated a key exchange. C{_KEY_EXCHANGE_NONE}
is the initial value (however SSH connections begin with key exchange,
so it will quickly change to another state).
@ivar _blockedByKeyExchange: Whenever C{_keyExchangeState} is not
C{_KEY_EXCHANGE_NONE}, this is a C{list} of pending messages which were
passed to L{sendPacket} but could not be sent because it is not legal
to send them while a key exchange is in progress. When the key
exchange completes, another attempt is made to send these messages.
"""
protocolVersion = b'2.0'
version = b'Twisted_' + twisted_version.encode('ascii')
comment = b''
ourVersionString = (b'SSH-' + protocolVersion + b'-' + version + b' '
+ comment).strip()
# L{None} is supported as cipher and hmac. For security they are disabled
# by default. To enable them, subclass this class and add it, or do:
# SSHTransportBase.supportedCiphers.append('none')
# List ordered by preference.
supportedCiphers = _getSupportedCiphers()
supportedMACs = [
b'hmac-sha2-512',
b'hmac-sha2-384',
b'hmac-sha2-256',
b'hmac-sha1',
b'hmac-md5',
# `none`,
]
supportedKeyExchanges = _kex.getSupportedKeyExchanges()
supportedPublicKeys = []
# Add the supported EC keys, and change the name from ecdh* to ecdsa*
for eckey in supportedKeyExchanges:
if eckey.find(b'ecdh') != -1:
supportedPublicKeys += [eckey.replace(b'ecdh', b'ecdsa')]
supportedPublicKeys += [b'ssh-rsa', b'ssh-dss']
supportedCompressions = [b'none', b'zlib']
supportedLanguages = ()
supportedVersions = (b'1.99', b'2.0')
isClient = False
gotVersion = False
buf = b''
outgoingPacketSequence = 0
incomingPacketSequence = 0
outgoingCompression = None
incomingCompression = None
sessionID = None
service = None
# There is no key exchange activity in progress.
_KEY_EXCHANGE_NONE = '_KEY_EXCHANGE_NONE'
# Key exchange is in progress and we started it.
_KEY_EXCHANGE_REQUESTED = '_KEY_EXCHANGE_REQUESTED'
# Key exchange is in progress and both sides have sent KEXINIT messages.
_KEY_EXCHANGE_PROGRESSING = '_KEY_EXCHANGE_PROGRESSING'
# There is a fourth conceptual state not represented here: KEXINIT received
# but not sent. Since we always send a KEXINIT as soon as we get it, we
# can't ever be in that state.
# The current key exchange state.
_keyExchangeState = _KEY_EXCHANGE_NONE
_blockedByKeyExchange = None
def connectionLost(self, reason):
"""
When the underlying connection is closed, stop the running service (if
any), and log out the avatar (if any).
@type reason: L{twisted.python.failure.Failure}
@param reason: The cause of the connection being closed.
"""
if self.service:
self.service.serviceStopped()
if hasattr(self, 'avatar'):
self.logoutFunction()
log.msg('connection lost')
def connectionMade(self):
"""
Called when the connection is made to the other side. We sent our
version and the MSG_KEXINIT packet.
"""
self.transport.write(self.ourVersionString + b'\r\n')
self.currentEncryptions = SSHCiphers(b'none', b'none', b'none',
b'none')
self.currentEncryptions.setKeys(b'', b'', b'', b'', b'', b'')
self.sendKexInit()
def sendKexInit(self):
"""
Send a I{KEXINIT} message to initiate key exchange or to respond to a
key exchange initiated by the peer.
@raise RuntimeError: If a key exchange has already been started and it
is not appropriate to send a I{KEXINIT} message at this time.
@return: L{None}
"""
if self._keyExchangeState != self._KEY_EXCHANGE_NONE:
raise RuntimeError(
"Cannot send KEXINIT while key exchange state is %r" % (
self._keyExchangeState,))
self.ourKexInitPayload = b''.join([
chr(MSG_KEXINIT),
randbytes.secureRandom(16),
NS(b','.join(self.supportedKeyExchanges)),
NS(b','.join(self.supportedPublicKeys)),
NS(b','.join(self.supportedCiphers)),
NS(b','.join(self.supportedCiphers)),
NS(b','.join(self.supportedMACs)),
NS(b','.join(self.supportedMACs)),
NS(b','.join(self.supportedCompressions)),
NS(b','.join(self.supportedCompressions)),
NS(b','.join(self.supportedLanguages)),
NS(b','.join(self.supportedLanguages)),
b'\000\000\000\000\000'])
self.sendPacket(MSG_KEXINIT, self.ourKexInitPayload[1:])
self._keyExchangeState = self._KEY_EXCHANGE_REQUESTED
self._blockedByKeyExchange = []
def _allowedKeyExchangeMessageType(self, messageType):
"""
Determine if the given message type may be sent while key exchange is
in progress.
@param messageType: The type of message
@type messageType: L{int}
@return: C{True} if the given type of message may be sent while key
exchange is in progress, C{False} if it may not.
@rtype: L{bool}
@see: U{http://tools.ietf.org/html/rfc4253#section-7.1}
"""
# Written somewhat peculularly to reflect the way the specification
# defines the allowed message types.
if 1 <= messageType <= 19:
return messageType not in (MSG_SERVICE_REQUEST, MSG_SERVICE_ACCEPT)
if 20 <= messageType <= 29:
return messageType not in (MSG_KEXINIT,)
return 30 <= messageType <= 49
def sendPacket(self, messageType, payload):
"""
Sends a packet. If it's been set up, compress the data, encrypt it,
and authenticate it before sending. If key exchange is in progress and
the message is not part of key exchange, queue it to be sent later.
@param messageType: The type of the packet; generally one of the
MSG_* values.
@type messageType: L{int}
@param payload: The payload for the message.
@type payload: L{str}
"""
if self._keyExchangeState != self._KEY_EXCHANGE_NONE:
if not self._allowedKeyExchangeMessageType(messageType):
self._blockedByKeyExchange.append((messageType, payload))
return
payload = chr(messageType) + payload
if self.outgoingCompression:
payload = (self.outgoingCompression.compress(payload)
+ self.outgoingCompression.flush(2))
bs = self.currentEncryptions.encBlockSize
# 4 for the packet length and 1 for the padding length
totalSize = 5 + len(payload)
lenPad = bs - (totalSize % bs)
if lenPad < 4:
lenPad = lenPad + bs
packet = (struct.pack('!LB',
totalSize + lenPad - 4, lenPad) +
payload + randbytes.secureRandom(lenPad))
encPacket = (
self.currentEncryptions.encrypt(packet) +
self.currentEncryptions.makeMAC(
self.outgoingPacketSequence, packet))
self.transport.write(encPacket)
self.outgoingPacketSequence += 1
def getPacket(self):
"""
Try to return a decrypted, authenticated, and decompressed packet
out of the buffer. If there is not enough data, return None.
@rtype: L{str} or L{None}
@return: The decoded packet, if any.
"""
bs = self.currentEncryptions.decBlockSize
ms = self.currentEncryptions.verifyDigestSize
if len(self.buf) < bs:
# Not enough data for a block
return
if not hasattr(self, 'first'):
first = self.currentEncryptions.decrypt(self.buf[:bs])
else:
first = self.first
del self.first
packetLen, paddingLen = struct.unpack('!LB', first[:5])
if packetLen > 1048576: # 1024 ** 2
self.sendDisconnect(
DISCONNECT_PROTOCOL_ERROR,
networkString('bad packet length {}'.format(packetLen)))
return
if len(self.buf) < packetLen + 4 + ms:
# Not enough data for a packet
self.first = first
return
if (packetLen + 4) % bs != 0:
self.sendDisconnect(
DISCONNECT_PROTOCOL_ERROR,
networkString(
'bad packet mod (%i%%%i == %i)' % (
packetLen + 4, bs, (packetLen + 4) % bs)))
return
encData, self.buf = self.buf[:4 + packetLen], self.buf[4 + packetLen:]
packet = first + self.currentEncryptions.decrypt(encData[bs:])
if len(packet) != 4 + packetLen:
self.sendDisconnect(DISCONNECT_PROTOCOL_ERROR,
b'bad decryption')
return
if ms:
macData, self.buf = self.buf[:ms], self.buf[ms:]
if not self.currentEncryptions.verify(self.incomingPacketSequence,
packet, macData):
self.sendDisconnect(DISCONNECT_MAC_ERROR, b'bad MAC')
return
payload = packet[5:-paddingLen]
if self.incomingCompression:
try:
payload = self.incomingCompression.decompress(payload)
except:
# Tolerate any errors in decompression
log.err()
self.sendDisconnect(DISCONNECT_COMPRESSION_ERROR,
b'compression error')
return
self.incomingPacketSequence += 1
return payload
def _unsupportedVersionReceived(self, remoteVersion):
"""
Called when an unsupported version of the ssh protocol is received from
the remote endpoint.
@param remoteVersion: remote ssh protocol version which is unsupported
by us.
@type remoteVersion: L{str}
"""
self.sendDisconnect(DISCONNECT_PROTOCOL_VERSION_NOT_SUPPORTED,
b'bad version ' + remoteVersion)
def dataReceived(self, data):
"""
First, check for the version string (SSH-2.0-*). After that has been
received, this method adds data to the buffer, and pulls out any
packets.
@type data: L{bytes}
@param data: The data that was received.
"""
self.buf = self.buf + data
if not self.gotVersion:
if self.buf.find(b'\n', self.buf.find(b'SSH-')) == -1:
return
# RFC 4253 section 4.2 ask for strict `\r\n` line ending.
# Here we are a bit more relaxed and accept implementations ending
# only in '\n'.
# https://tools.ietf.org/html/rfc4253#section-4.2
lines = self.buf.split(b'\n')
for p in lines:
if p.startswith(b'SSH-'):
self.gotVersion = True
# Since the line was split on '\n' and most of the time
# it uses '\r\n' we may get an extra '\r'.
self.otherVersionString = p.rstrip(b'\r')
remoteVersion = p.split(b'-')[1]
if remoteVersion not in self.supportedVersions:
self._unsupportedVersionReceived(remoteVersion)
return
i = lines.index(p)
self.buf = b'\n'.join(lines[i + 1:])
packet = self.getPacket()
while packet:
messageNum = ord(packet[0:1])
self.dispatchMessage(messageNum, packet[1:])
packet = self.getPacket()
def dispatchMessage(self, messageNum, payload):
"""
Send a received message to the appropriate method.
@type messageNum: L{int}
@param messageNum: The message number.
@type payload: L{bytes}
@param payload: The message payload.
"""
if messageNum < 50 and messageNum in messages:
messageType = messages[messageNum][4:]
f = getattr(self, 'ssh_%s' % (messageType,), None)
if f is not None:
f(payload)
else:
log.msg("couldn't handle %s" % messageType)
log.msg(repr(payload))
self.sendUnimplemented()
elif self.service:
log.callWithLogger(self.service, self.service.packetReceived,
messageNum, payload)
else:
log.msg("couldn't handle %s" % messageNum)
log.msg(repr(payload))
self.sendUnimplemented()
def getPeer(self):
"""
Returns an L{SSHTransportAddress} corresponding to the other (peer)
side of this transport.
@return: L{SSHTransportAddress} for the peer
@rtype: L{SSHTransportAddress}
@since: 12.1
"""
return address.SSHTransportAddress(self.transport.getPeer())
def getHost(self):
"""
Returns an L{SSHTransportAddress} corresponding to the this side of
transport.
@return: L{SSHTransportAddress} for the peer
@rtype: L{SSHTransportAddress}
@since: 12.1
"""
return address.SSHTransportAddress(self.transport.getHost())
@property
def kexAlg(self):
"""
The key exchange algorithm name agreed between client and server.
"""
return self._kexAlg
@kexAlg.setter
def kexAlg(self, value):
"""
Set the key exchange algorithm name.
"""
self._kexAlg = value
# Client-initiated rekeying looks like this:
#
# C> MSG_KEXINIT
# S> MSG_KEXINIT
# C> MSG_KEX_DH_GEX_REQUEST or MSG_KEXDH_INIT
# S> MSG_KEX_DH_GEX_GROUP or MSG_KEXDH_REPLY
# C> MSG_KEX_DH_GEX_INIT or --
# S> MSG_KEX_DH_GEX_REPLY or --
# C> MSG_NEWKEYS
# S> MSG_NEWKEYS
#
# Server-initiated rekeying is the same, only the first two messages are
# switched.
def ssh_KEXINIT(self, packet):
"""
Called when we receive a MSG_KEXINIT message. Payload::
bytes[16] cookie
string keyExchangeAlgorithms
string keyAlgorithms
string incomingEncryptions
string outgoingEncryptions
string incomingAuthentications
string outgoingAuthentications
string incomingCompressions
string outgoingCompressions
string incomingLanguages
string outgoingLanguages
bool firstPacketFollows
unit32 0 (reserved)
Starts setting up the key exchange, keys, encryptions, and
authentications. Extended by ssh_KEXINIT in SSHServerTransport and
SSHClientTransport.
@type packet: L{bytes}
@param packet: The message data.
@return: A L{tuple} of negotiated key exchange algorithms, key
algorithms, and unhandled data, or L{None} if something went wrong.
"""
self.otherKexInitPayload = chr(MSG_KEXINIT) + packet
# This is useless to us:
# cookie = packet[: 16]
k = getNS(packet[16:], 10)
strings, rest = k[:-1], k[-1]
(kexAlgs, keyAlgs, encCS, encSC, macCS, macSC, compCS, compSC, langCS,
langSC) = [s.split(b',') for s in strings]
# These are the server directions
outs = [encSC, macSC, compSC]
ins = [encCS, macSC, compCS]
if self.isClient:
outs, ins = ins, outs # Switch directions
server = (self.supportedKeyExchanges, self.supportedPublicKeys,
self.supportedCiphers, self.supportedCiphers,
self.supportedMACs, self.supportedMACs,
self.supportedCompressions, self.supportedCompressions)
client = (kexAlgs, keyAlgs, outs[0], ins[0], outs[1], ins[1],
outs[2], ins[2])
if self.isClient:
server, client = client, server
self.kexAlg = ffs(client[0], server[0])
self.keyAlg = ffs(client[1], server[1])
self.nextEncryptions = SSHCiphers(
ffs(client[2], server[2]),
ffs(client[3], server[3]),
ffs(client[4], server[4]),
ffs(client[5], server[5]))
self.outgoingCompressionType = ffs(client[6], server[6])
self.incomingCompressionType = ffs(client[7], server[7])
if None in (self.kexAlg, self.keyAlg, self.outgoingCompressionType,
self.incomingCompressionType):
self.sendDisconnect(DISCONNECT_KEY_EXCHANGE_FAILED,
b"couldn't match all kex parts")
return
if None in self.nextEncryptions.__dict__.values():
self.sendDisconnect(DISCONNECT_KEY_EXCHANGE_FAILED,
b"couldn't match all kex parts")
return
log.msg('kex alg, key alg: %r %r' % (self.kexAlg, self.keyAlg))
log.msg('outgoing: %r %r %r' % (self.nextEncryptions.outCipType,
self.nextEncryptions.outMACType,
self.outgoingCompressionType))
log.msg('incoming: %r %r %r' % (self.nextEncryptions.inCipType,
self.nextEncryptions.inMACType,
self.incomingCompressionType))
if self._keyExchangeState == self._KEY_EXCHANGE_REQUESTED:
self._keyExchangeState = self._KEY_EXCHANGE_PROGRESSING
else:
self.sendKexInit()
return kexAlgs, keyAlgs, rest # For SSHServerTransport to use
def ssh_DISCONNECT(self, packet):
"""
Called when we receive a MSG_DISCONNECT message. Payload::
long code
string description
This means that the other side has disconnected. Pass the message up
and disconnect ourselves.
@type packet: L{bytes}
@param packet: The message data.
"""
reasonCode = struct.unpack('>L', packet[: 4])[0]
description, foo = getNS(packet[4:])
self.receiveError(reasonCode, description)
self.transport.loseConnection()
def ssh_IGNORE(self, packet):
"""
Called when we receive a MSG_IGNORE message. No payload.
This means nothing; we simply return.
@type packet: L{bytes}
@param packet: The message data.
"""
def ssh_UNIMPLEMENTED(self, packet):
"""
Called when we receive a MSG_UNIMPLEMENTED message. Payload::
long packet
This means that the other side did not implement one of our packets.
@type packet: L{bytes}
@param packet: The message data.
"""
seqnum, = struct.unpack('>L', packet)
self.receiveUnimplemented(seqnum)
def ssh_DEBUG(self, packet):
"""
Called when we receive a MSG_DEBUG message. Payload::
bool alwaysDisplay
string message
string language
This means the other side has passed along some debugging info.
@type packet: L{bytes}
@param packet: The message data.
"""
alwaysDisplay = bool(ord(packet[0:1]))
message, lang, foo = getNS(packet[1:], 2)
self.receiveDebug(alwaysDisplay, message, lang)
def setService(self, service):
"""
Set our service to service and start it running. If we were
running a service previously, stop it first.
@type service: C{SSHService}
@param service: The service to attach.
"""
log.msg('starting service %r' % (service.name,))
if self.service:
self.service.serviceStopped()
self.service = service
service.transport = self
self.service.serviceStarted()
def sendDebug(self, message, alwaysDisplay=False, language=b''):
"""
Send a debug message to the other side.
@param message: the message to send.
@type message: L{str}
@param alwaysDisplay: if True, tell the other side to always
display this message.
@type alwaysDisplay: L{bool}
@param language: optionally, the language the message is in.
@type language: L{str}
"""
self.sendPacket(MSG_DEBUG, chr(alwaysDisplay) + NS(message) +
NS(language))
def sendIgnore(self, message):
"""
Send a message that will be ignored by the other side. This is
useful to fool attacks based on guessing packet sizes in the
encrypted stream.
@param message: data to send with the message
@type message: L{str}
"""
self.sendPacket(MSG_IGNORE, NS(message))
def sendUnimplemented(self):
"""
Send a message to the other side that the last packet was not
understood.
"""
seqnum = self.incomingPacketSequence
self.sendPacket(MSG_UNIMPLEMENTED, struct.pack('!L', seqnum))
def sendDisconnect(self, reason, desc):
"""
Send a disconnect message to the other side and then disconnect.
@param reason: the reason for the disconnect. Should be one of the
DISCONNECT_* values.
@type reason: L{int}
@param desc: a descrption of the reason for the disconnection.
@type desc: L{str}
"""
self.sendPacket(
MSG_DISCONNECT, struct.pack('>L', reason) + NS(desc) + NS(b''))
log.msg('Disconnecting with error, code %s\nreason: %s' % (reason,
desc))
self.transport.loseConnection()
def _startEphemeralDH(self):
"""