Viewing file: transport.py (50.37 KB) -rw-r--r-- Select action/file-type: (+) | (+) | (+) | Code (+) | Session (+) | (+) | SDB (+) | (+) | (+) | (+) | (+) | (+) |
# -*- test-case-name: twisted.conch.test.test_transport -*- # # Copyright (c) 2001-2008 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 """
# base library imports import struct import zlib import array
# external library imports from Crypto import Util from Crypto.Cipher import XOR
# twisted imports from twisted.internet import protocol, defer from twisted.conch import error from twisted.python import log, randbytes from twisted.python.hashlib import md5, sha1
# sibling imports from twisted.conch.ssh import keys from twisted.conch.ssh.common import NS, getNS, MP, getMP, _MPpow, ffs
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 receieved 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.
"""
protocolVersion = '2.0' version = 'Twisted' comment = '' ourVersionString = ('SSH-' + protocolVersion + '-' + version + ' ' + comment).strip() supportedCiphers = ['aes256-ctr', 'aes256-cbc', 'aes192-ctr', 'aes192-cbc', 'aes128-ctr', 'aes128-cbc', 'cast128-ctr', 'cast128-cbc', 'blowfish-ctr', 'blowfish-cbc', '3des-ctr', '3des-cbc'] # ,'none'] supportedMACs = ['hmac-sha1', 'hmac-md5'] # , 'none'] # both of the above support 'none', but for security are disabled by # default. to enable them, subclass this class and add it, or do: # SSHTransportBase.supportedCiphers.append('none') supportedKeyExchanges = ['diffie-hellman-group-exchange-sha1', 'diffie-hellman-group1-sha1'] supportedPublicKeys = ['ssh-rsa', 'ssh-dss'] supportedCompressions = ['none', 'zlib'] supportedLanguages = () supportedVersions = ('1.99', '2.0') isClient = False gotVersion = False buf = '' outgoingPacketSequence = 0 incomingPacketSequence = 0 outgoingCompression = None incomingCompression = None sessionID = None service = None
def connectionLost(self, reason): 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('%s\r\n' % (self.ourVersionString,)) self.currentEncryptions = SSHCiphers('none', 'none', 'none', 'none') self.currentEncryptions.setKeys('', '', '', '', '', '') self.sendKexInit()
def sendKexInit(self): self.ourKexInitPayload = (chr(MSG_KEXINIT) + randbytes.secureRandom(16) + NS(','.join(self.supportedKeyExchanges)) + NS(','.join(self.supportedPublicKeys)) + NS(','.join(self.supportedCiphers)) + NS(','.join(self.supportedCiphers)) + NS(','.join(self.supportedMACs)) + NS(','.join(self.supportedMACs)) + NS(','.join(self.supportedCompressions)) + NS(','.join(self.supportedCompressions)) + NS(','.join(self.supportedLanguages)) + NS(','.join(self.supportedLanguages)) + '\000' + '\000\000\000\000') self.sendPacket(MSG_KEXINIT, self.ourKexInitPayload[1:])
def sendPacket(self, messageType, payload): """ Sends a packet. If it's been set up, compress the data, encrypt it, and authenticate it before sending.
@param messageType: The type of the packet; generally one of the MSG_* values. @type messageType: C{int} @param payload: The payload for the message. @type payload: C{str} """ 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: C{str}/C{None} """ bs = self.currentEncryptions.decBlockSize ms = self.currentEncryptions.verifyDigestSize if len(self.buf) < bs: return # not enough data 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, 'bad packet length %s' % packetLen) return if len(self.buf) < packetLen + 4 + ms: self.first = first return # not enough packet if(packetLen + 4) % bs != 0: self.sendDisconnect( DISCONNECT_PROTOCOL_ERROR, '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, '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, 'bad MAC') return payload = packet[5:-paddingLen] if self.incomingCompression: try: payload = self.incomingCompression.decompress(payload) except: # bare except, because who knows what kind of errors # decompression can raise log.err() self.sendDisconnect(DISCONNECT_COMPRESSION_ERROR, '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: C{str} """ self.sendDisconnect(DISCONNECT_PROTOCOL_VERSION_NOT_SUPPORTED, '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: C{str} """ self.buf = self.buf + data if not self.gotVersion: if self.buf.find('\n', self.buf.find('SSH-')) == -1: return lines = self.buf.split('\n') for p in lines: if p.startswith('SSH-'): self.gotVersion = True self.otherVersionString = p.strip() remoteVersion = p.split('-')[1] if remoteVersion not in self.supportedVersions: self._unsupportedVersionReceived(remoteVersion) return i = lines.index(p) self.buf = '\n'.join(lines[i + 1:]) packet = self.getPacket() while packet: messageNum = ord(packet[0]) self.dispatchMessage(messageNum, packet[1:]) packet = self.getPacket()
def dispatchMessage(self, messageNum, payload): """ Send a received message to the appropriate method.
@type messageNum: C{int} @type payload: c{str} """ 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 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. """ self.otherKexInitPayload = chr(MSG_KEXINIT) + packet #cookie = packet[: 16] # taking this is useless k = getNS(packet[16:], 10) strings, rest = k[:-1], k[-1] (kexAlgs, keyAlgs, encCS, encSC, macCS, macSC, compCS, compSC, langCS, langSC) = [s.split(',') 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, "couldn't match all kex parts") return if None in self.nextEncryptions.__dict__.values(): self.sendDisconnect(DISCONNECT_KEY_EXCHANGE_FAILED, "couldn't match all kex parts") return log.msg('kex alg, key alg: %s %s' % (self.kexAlg, self.keyAlg)) log.msg('outgoing: %s %s %s' % (self.nextEncryptions.outCipType, self.nextEncryptions.outMACType, self.outgoingCompressionType)) log.msg('incoming: %s %s %s' % (self.nextEncryptions.inCipType, self.nextEncryptions.inMACType, self.incomingCompressionType)) 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. """ 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 receieve a MSG_IGNORE message. No payload. This means nothing; we simply return. """
def ssh_UNIMPLEMENTED(self, packet): """ Called when we receieve a MSG_UNIMPLEMENTED message. Payload:: long packet
This means that the other side did not implement one of our packets. """ seqnum, = struct.unpack('>L', packet) self.receiveUnimplemented(seqnum)
def ssh_DEBUG(self, packet): """ Called when we receieve a MSG_DEBUG message. Payload:: bool alwaysDisplay string message string language
This means the other side has passed along some debugging info. """ alwaysDisplay = bool(packet[0]) 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} """ log.msg('starting service %s' % service.name) if self.service: self.service.serviceStopped() self.service = service service.transport = self self.service.serviceStarted()
def sendDebug(self, message, alwaysDisplay=False, language=''): """ Send a debug message to the other side.
@param message: the message to send. @type message: C{str} @param alwaysDisplay: if True, tell the other side to always display this message. @type alwaysDisplay: C{bool} @param language: optionally, the language the message is in. @type language: C{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: C{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: C{int} @param desc: a descrption of the reason for the disconnection. @type desc: C{str} """ self.sendPacket( MSG_DISCONNECT, struct.pack('>L', reason) + NS(desc) + NS('')) log.msg('Disconnecting with error, code %s\nreason: %s' % (reason, desc)) self.transport.loseConnection()
def _getKey(self, c, sharedSecret, exchangeHash): """ Get one of the keys for authentication/encryption.
@type c: C{str} @type sharedSecret: C{str} @type exchangeHash: C{str} """ k1 = sha1(sharedSecret + exchangeHash + c + self.sessionID) k1 = k1.digest() k2 = sha1(sharedSecret + exchangeHash + k1).digest() return k1 + k2
def _keySetup(self, sharedSecret, exchangeHash): """ Set up the keys for the connection and sends MSG_NEWKEYS when finished,
@param sharedSecret: a secret string agreed upon using a Diffie- Hellman exchange, so it is only shared between the server and the client. @type sharedSecret: C{str} @param exchangeHash: A hash of various data known by both sides. @type exchangeHash: C{str} """ if not self.sessionID: self.sessionID = exchangeHash initIVCS = self._getKey('A', sharedSecret, exchangeHash) initIVSC = self._getKey('B', sharedSecret, exchangeHash) encKeyCS = self._getKey('C', sharedSecret, exchangeHash) encKeySC = self._getKey('D', sharedSecret, exchangeHash) integKeyCS = self._getKey('E', sharedSecret, exchangeHash) integKeySC = self._getKey('F', sharedSecret, exchangeHash) outs = [initIVSC, encKeySC, integKeySC] ins = [initIVCS, encKeyCS, integKeyCS] if self.isClient: # reverse for the client log.msg('REVERSE') outs, ins = ins, outs self.nextEncryptions.setKeys(outs[0], outs[1], ins[0], ins[1], outs[2], ins[2]) self.sendPacket(MSG_NEWKEYS, '')
def isEncrypted(self, direction="out"): """ Return True if the connection is encrypted in the given direction. Direction must be one of ["out", "in", "both"]. """ if direction == "out": return self.currentEncryptions.outCipType != 'none' elif direction == "in": return self.currentEncryptions.inCipType != 'none' elif direction == "both": return self.isEncrypted("in") and self.isEncrypted("out") else: raise TypeError('direction must be "out", "in", or "both"')
def isVerified(self, direction="out"): """ Return True if the connecction is verified/authenticated in the given direction. Direction must be one of ["out", "in", "both"]. """ if direction == "out": return self.currentEncryptions.outMACType != 'none' elif direction == "in": return self.currentEncryptions.inMACType != 'none' elif direction == "both": return self.isVerified("in")and self.isVerified("out") else: raise TypeError('direction must be "out", "in", or "both"')
def loseConnection(self): """ Lose the connection to the other side, sending a DISCONNECT_CONNECTION_LOST message. """ self.sendDisconnect(DISCONNECT_CONNECTION_LOST, "user closed connection")
# client methods def receiveError(self, reasonCode, description): """ Called when we receive a disconnect error message from the other side.
@param reasonCode: the reason for the disconnect, one of the DISCONNECT_ values. @type reasonCode: C{int} @param description: a human-readable description of the disconnection. @type description: C{str} """ log.msg('Got remote error, code %s\nreason: %s' % (reasonCode, description))
def receiveUnimplemented(self, seqnum): """ Called when we receive an unimplemented packet message from the other side.
@param seqnum: the sequence number that was not understood. @type seqnum: C{int} """ log.msg('other side unimplemented packet #%s' % seqnum)
def receiveDebug(self, alwaysDisplay, message, lang): """ Called when we receive a debug message from the other side.
@param alwaysDisplay: if True, this message should always be displayed. @type alwaysDisplay: C{bool} @param message: the debug message @type message: C{str} @param lang: optionally the language the message is in. @type lang: C{str} """ if alwaysDisplay: log.msg('Remote Debug Message: %s' % message)
class SSHServerTransport(SSHTransportBase): """ SSHServerTransport implements the server side of the SSH protocol.
@ivar isClient: since we are never the client, this is always False.
@ivar ignoreNextPacket: if True, ignore the next key exchange packet. This is set when the client sends a guessed key exchange packet but with an incorrect guess.
@ivar dhGexRequest: the KEX_DH_GEX_REQUEST(_OLD) that the client sent. The key generation needs this to be stored.
@ivar g: the Diffie-Hellman group generator.
@ivar p: the Diffie-Hellman group prime. """ isClient = False ignoreNextPacket = 0
def ssh_KEXINIT(self, packet): """ Called when we receive a MSG_KEXINIT message. For a description of the packet, see SSHTransportBase.ssh_KEXINIT(). Additionally, this method checks if a guessed key exchange packet was sent. If it was sent, and it guessed incorrectly, the next key exchange packet MUST be ignored. """ retval = SSHTransportBase.ssh_KEXINIT(self, packet) if not retval: # disconnected return else: kexAlgs, keyAlgs, rest = retval if ord(rest[0]): # first_kex_packet_follows if (kexAlgs[0] != self.supportedKeyExchanges[0] or keyAlgs[0] != self.supportedPublicKeys[0]): self.ignoreNextPacket = True # guess was wrong
def ssh_KEX_DH_GEX_REQUEST_OLD(self, packet): """ This represents two different key exchange methods that share the same integer value.
KEXDH_INIT (for diffie-hellman-group1-sha1 exchanges) payload::
integer e (the client's Diffie-Hellman public key)
We send the KEXDH_REPLY with our host key and signature.
KEX_DH_GEX_REQUEST_OLD (for diffie-hellman-group-exchange-sha1) payload::
integer ideal (ideal size for the Diffie-Hellman prime)
We send the KEX_DH_GEX_GROUP message with the group that is closest in size to ideal.
If we were told to ignore the next key exchange packet by ssh_KEXINIT, drop it on the floor and return. """ if self.ignoreNextPacket: self.ignoreNextPacket = 0 return if self.kexAlg == 'diffie-hellman-group1-sha1': # this is really KEXDH_INIT clientDHpublicKey, foo = getMP(packet) y = Util.number.getRandomNumber(512, randbytes.secureRandom) serverDHpublicKey = _MPpow(DH_GENERATOR, y, DH_PRIME) sharedSecret = _MPpow(clientDHpublicKey, y, DH_PRIME) h = sha1() h.update(NS(self.otherVersionString)) h.update(NS(self.ourVersionString)) h.update(NS(self.otherKexInitPayload)) h.update(NS(self.ourKexInitPayload)) h.update(NS(self.factory.publicKeys[self.keyAlg].blob())) h.update(MP(clientDHpublicKey)) h.update(serverDHpublicKey) h.update(sharedSecret) exchangeHash = h.digest() self.sendPacket( MSG_KEXDH_REPLY, NS(self.factory.publicKeys[self.keyAlg].blob()) + serverDHpublicKey + NS(self.factory.privateKeys[self.keyAlg].sign(exchangeHash))) self._keySetup(sharedSecret, exchangeHash) elif self.kexAlg == 'diffie-hellman-group-exchange-sha1': self.dhGexRequest = packet ideal = struct.unpack('>L', packet)[0] self.g, self.p = self.factory.getDHPrime(ideal) self.sendPacket(MSG_KEX_DH_GEX_GROUP, MP(self.p) + MP(self.g)) else: raise error.ConchError('bad kexalg: %s' % self.kexAlg)
def ssh_KEX_DH_GEX_REQUEST(self, packet): """ Called when we receive a MSG_KEX_DH_GEX_REQUEST message. Payload:: integer minimum integer ideal integer maximum
The client is asking for a Diffie-Hellman group between minimum and maximum size, and close to ideal if possible. We reply with a MSG_KEX_DH_GEX_GROUP message.
If we were told to ignore the next key exchange packekt by ssh_KEXINIT, drop it on the floor and return. """ if self.ignoreNextPacket: self.ignoreNextPacket = 0 return self.dhGexRequest = packet min, ideal, max = struct.unpack('>3L', packet) self.g, self.p = self.factory.getDHPrime(ideal) self.sendPacket(MSG_KEX_DH_GEX_GROUP, MP(self.p) + MP(self.g))
def ssh_KEX_DH_GEX_INIT(self, packet): """ Called when we get a MSG_KEX_DH_GEX_INIT message. Payload:: integer e (client DH public key)
We send the MSG_KEX_DH_GEX_REPLY message with our host key and signature. """ clientDHpublicKey, foo = getMP(packet) # TODO: we should also look at the value they send to us and reject # insecure values of f (if g==2 and f has a single '1' bit while the # rest are '0's, then they must have used a small y also).
# TODO: This could be computed when self.p is set up # or do as openssh does and scan f for a single '1' bit instead
pSize = Util.number.size(self.p) y = Util.number.getRandomNumber(pSize, randbytes.secureRandom)
serverDHpublicKey = _MPpow(self.g, y, self.p) sharedSecret = _MPpow(clientDHpublicKey, y, self.p) h = sha1() h.update(NS(self.otherVersionString)) h.update(NS(self.ourVersionString)) h.update(NS(self.otherKexInitPayload)) h.update(NS(self.ourKexInitPayload)) h.update(NS(self.factory.publicKeys[self.keyAlg].blob())) h.update(self.dhGexRequest) h.update(MP(self.p)) h.update(MP(self.g)) h.update(MP(clientDHpublicKey)) h.update(serverDHpublicKey) h.update(sharedSecret) exchangeHash = h.digest() self.sendPacket( MSG_KEX_DH_GEX_REPLY, NS(self.factory.publicKeys[self.keyAlg].blob()) + serverDHpublicKey + NS(self.factory.privateKeys[self.keyAlg].sign(exchangeHash))) self._keySetup(sharedSecret, exchangeHash)
def ssh_NEWKEYS(self, packet): """ Called when we get a MSG_NEWKEYS message. No payload. When we get this, the keys have been set on both sides, and we start using them to encrypt and authenticate the connection. """ log.msg('NEW KEYS') if packet != '': self.sendDisconnect(DISCONNECT_PROTOCOL_ERROR, "NEWKEYS takes no data") return self.currentEncryptions = self.nextEncryptions if self.outgoingCompressionType == 'zlib': self.outgoingCompression = zlib.compressobj(6) if self.incomingCompressionType == 'zlib': self.incomingCompression = zlib.decompressobj()
def ssh_SERVICE_REQUEST(self, packet): """ Called when we get a MSG_SERVICE_REQUEST message. Payload:: string serviceName
The client has requested a service. If we can start the service, start it; otherwise, disconnect with DISCONNECT_SERVICE_NOT_AVAILABLE. """ service, rest = getNS(packet) cls = self.factory.getService(self, service) if not cls: self.sendDisconnect(DISCONNECT_SERVICE_NOT_AVAILABLE, "don't have service %s" % service) return else: self.sendPacket(MSG_SERVICE_ACCEPT, NS(service)) self.setService(cls())
class SSHClientTransport(SSHTransportBase): """ SSHClientTransport implements the client side of the SSH protocol.
@ivar isClient: since we are always the client, this is always True.
@ivar _gotNewKeys: if we receive a MSG_NEWKEYS message before we are ready to transition to the new keys, this is set to True so we can transition when the keys are ready locally.
@ivar x: our Diffie-Hellman private key.
@ivar e: our Diffie-Hellman public key.
@ivar g: the Diffie-Hellman group generator.
@ivar p: the Diffie-Hellman group prime
@ivar instance: the SSHService object we are requesting. """ isClient = True
def connectionMade(self): """ Called when the connection is started with the server. Just sets up a private instance variable. """ SSHTransportBase.connectionMade(self) self._gotNewKeys = 0
def ssh_KEXINIT(self, packet): """ Called when we receive a MSG_KEXINIT message. For a description of the packet, see SSHTransportBase.ssh_KEXINIT(). Additionally, this method sends the first key exchange packet. If the agreed-upon exchange is diffie-hellman-group1-sha1, generate a public key and send it in a MSG_KEXDH_INIT message. If the exchange is diffie-hellman-group-exchange-sha1, ask for a 2048 bit group with a MSG_KEX_DH_GEX_REQUEST_OLD message. """ if SSHTransportBase.ssh_KEXINIT(self, packet) is None: return # we disconnected if self.kexAlg == 'diffie-hellman-group1-sha1': self.x = Util.number.getRandomNumber(512, randbytes.secureRandom) self.e = _MPpow(DH_GENERATOR, self.x, DH_PRIME) self.sendPacket(MSG_KEXDH_INIT, self.e) elif self.kexAlg == 'diffie-hellman-group-exchange-sha1': self.sendPacket(MSG_KEX_DH_GEX_REQUEST_OLD, '\x00\x00\x08\x00') else: raise error.ConchError("somehow, the kexAlg has been set " "to something we don't support")
def ssh_KEX_DH_GEX_GROUP(self, packet): """ This handles two different message which share an integer value. If the key exchange is diffie-hellman-group1-sha1, this is MSG_KEXDH_REPLY. Payload:: string serverHostKey integer f (server Diffie-Hellman public key) string signature
We verify the host key by calling verifyHostKey, then continue in _continueKEXDH_REPLY.
If the key exchange is diffie-hellman-group-exchange-sha1, this is MSG_KEX_DH_GEX_GROUP. Payload:: string g (group generator) string p (group prime)
We generate a Diffie-Hellman public key and send it in a MSG_KEX_DH_GEX_INIT message. """ if self.kexAlg == 'diffie-hellman-group1-sha1': # actually MSG_KEXDH_REPLY pubKey, packet = getNS(packet) f, packet = getMP(packet) signature, packet = getNS(packet) fingerprint = ':'.join([ch.encode('hex') for ch in md5(pubKey).digest()]) d = self.verifyHostKey(pubKey, fingerprint) d.addCallback(self._continueKEXDH_REPLY, pubKey, f, signature) d.addErrback( lambda unused: self.sendDisconnect( DISCONNECT_HOST_KEY_NOT_VERIFIABLE, 'bad host key')) return d else: self.p, rest = getMP(packet) self.g, rest = getMP(rest) self.x = Util.number.getRandomNumber(320, randbytes.secureRandom) self.e = _MPpow(self.g, self.x, self.p) self.sendPacket(MSG_KEX_DH_GEX_INIT, self.e)
def _continueKEXDH_REPLY(self, ignored, pubKey, f, signature): """ The host key has been verified, so we generate the keys.
@param pubKey: the public key blob for the server's public key. @type pubKey: C{str} @param f: the server's Diffie-Hellman public key. @type f: C{long} @param signature: the server's signature, verifying that it has the correct private key. @type signature: C{str} """ serverKey = keys.Key.fromString(pubKey) sharedSecret = _MPpow(f, self.x, DH_PRIME) h = sha1() h.update(NS(self.ourVersionString)) h.update(NS(self.otherVersionString)) h.update(NS(self.ourKexInitPayload)) h.update(NS(self.otherKexInitPayload)) h.update(NS(pubKey)) h.update(self.e) h.update(MP(f)) h.update(sharedSecret) exchangeHash = h.digest() if not serverKey.verify(signature, exchangeHash): self.sendDisconnect(DISCONNECT_KEY_EXCHANGE_FAILED, 'bad signature') return self._keySetup(sharedSecret, exchangeHash)
def ssh_KEX_DH_GEX_REPLY(self, packet): """ Called when we receieve a MSG_KEX_DH_GEX_REPLY message. Payload:: string server host key integer f (server DH public key)
We verify the host key by calling verifyHostKey, then continue in _continueGEX_REPLY. """ pubKey, packet = getNS(packet) f, packet = getMP(packet) signature, packet = getNS(packet) fingerprint = ':'.join(map(lambda c: '%02x'%ord(c), md5(pubKey).digest())) d = self.verifyHostKey(pubKey, fingerprint) d.addCallback(self._continueGEX_REPLY, pubKey, f, signature) d.addErrback( lambda unused: self.sendDisconnect( DISCONNECT_HOST_KEY_NOT_VERIFIABLE, 'bad host key')) return d
def _continueGEX_REPLY(self, ignored, pubKey, f, signature): """ The host key has been verified, so we generate the keys.
@param pubKey: the public key blob for the server's public key. @type pubKey: C{str} @param f: the server's Diffie-Hellman public key. @type f: C{long} @param signature: the server's signature, verifying that it has the correct private key. @type signature: C{str} """ serverKey = keys.Key.fromString(pubKey) sharedSecret = _MPpow(f, self.x, self.p) h = sha1() h.update(NS(self.ourVersionString)) h.update(NS(self.otherVersionString)) h.update(NS(self.ourKexInitPayload)) h.update(NS(self.otherKexInitPayload)) h.update(NS(pubKey)) h.update('\x00\x00\x08\x00') h.update(MP(self.p)) h.update(MP(self.g)) h.update(self.e) h.update(MP(f)) h.update(sharedSecret) exchangeHash = h.digest() if not serverKey.verify(signature, exchangeHash): self.sendDisconnect(DISCONNECT_KEY_EXCHANGE_FAILED, 'bad signature') return self._keySetup(sharedSecret, exchangeHash)
def _keySetup(self, sharedSecret, exchangeHash): """ See SSHTransportBase._keySetup(). """ SSHTransportBase._keySetup(self, sharedSecret, exchangeHash) if self._gotNewKeys: self.ssh_NEWKEYS('')
def ssh_NEWKEYS(self, packet): """ Called when we receieve a MSG_NEWKEYS message. No payload. If we've finished setting up our own keys, start using them. Otherwise, remeber that we've receieved this message. """ if packet != '': self.sendDisconnect(DISCONNECT_PROTOCOL_ERROR, "NEWKEYS takes no data") return if not self.nextEncryptions.encBlockSize: self._gotNewKeys = 1 return log.msg('NEW KEYS') self.currentEncryptions = self.nextEncryptions if self.outgoingCompressionType == 'zlib': self.outgoingCompression = zlib.compressobj(6) if self.incomingCompressionType == 'zlib': self.incomingCompression = zlib.decompressobj() self.connectionSecure()
def ssh_SERVICE_ACCEPT(self, packet): """ Called when we receieve a MSG_SERVICE_ACCEPT message. Payload:: string service name
Start the service we requested. """ name = getNS(packet)[0] if name != self.instance.name: self.sendDisconnect( DISCONNECT_PROTOCOL_ERROR, "received accept for service we did not request") self.setService(self.instance)
def requestService(self, instance): """ Request that a service be run over this transport.
@type instance: subclass of L{twisted.conch.ssh.service.SSHService} """ self.sendPacket(MSG_SERVICE_REQUEST, NS(instance.name)) self.instance = instance
# client methods def verifyHostKey(self, hostKey, fingerprint): """ Returns a Deferred that gets a callback if it is a valid key, or an errback if not.
@type hostKey: C{str} @type fingerprint: C{str} @rtype: L{twisted.internet.defer.Deferred} """ # return if it's good return defer.fail(NotImplementedError())
def connectionSecure(self): """ Called when the encryption has been set up. Generally, requestService() is called to run another service over the transport. """ raise NotImplementedError()
class _DummyCipher: """ A cipher for the none encryption method.
@ivar block_size: the block size of the encryption. In the case of the none cipher, this is 8 bytes. """ block_size = 8
def encrypt(self, x): return x
decrypt = encrypt
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 (<Crypto.Cipher.* name>, <block size>, <counter 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 = { '3des-cbc':('DES3', 24, 0), 'blowfish-cbc':('Blowfish', 16,0 ), 'aes256-cbc':('AES', 32, 0), 'aes192-cbc':('AES', 24, 0), 'aes128-cbc':('AES', 16, 0), 'cast128-cbc':('CAST', 16, 0), 'aes128-ctr':('AES', 16, 1), 'aes192-ctr':('AES', 24, 1), 'aes256-ctr':('AES', 32, 1), '3des-ctr':('DES3', 24, 1), 'blowfish-ctr':('Blowfish', 16, 1), 'cast128-ctr':('CAST', 16, 1), 'none':(None, 0, 0), } macMap = { 'hmac-sha1': sha1, 'hmac-md5': md5, '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, '', '', 0) self.inMAC = (None, '', '', 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.encrypt = o.encrypt self.encBlockSize = o.block_size o = self._getCipher(self.inCipType, inIV, inKey) self.decrypt = o.decrypt self.decBlockSize = o.block_size 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 Crypto.Cipher.* @param iv: the initialzation vector @param key: the encryption key """ modName, keySize, counterMode = self.cipherMap[cip] if not modName: # no cipher return _DummyCipher() mod = __import__('Crypto.Cipher.%s'%modName, {}, {}, 'x') if counterMode: return mod.new(key[:keySize], mod.MODE_CTR, iv[:mod.block_size], counter=_Counter(iv, mod.block_size)) else: return mod.new(key[:keySize], mod.MODE_CBC, iv[:mod.block_size])
def _getMAC(self, mac, key): """ Gets a 4-tuple representing the message authentication code. (<hash module>, <inner hash value>, <outer hash value>, <digest size>)
@param mac: a key mapping into macMap @type mac: C{str} @param key: the MAC key. @type key: C{str} """ mod = self.macMap[mac] if not mod: return (None, '', '', 0) ds = mod().digest_size key = key[:ds] + '\x00' * (64 - ds) i = XOR.new('\x36').encrypt(key) o = XOR.new('\x5c').encrypt(key) return mod, i, o, ds
def encrypt(self, blocks): """ Encrypt blocks. Overridden by the encrypt method of a Crypto.Cipher.* object in setKeys().
@type blocks: C{str} """ raise NotImplementedError()
def decrypt(self, blocks): """ Decrypt blocks. See encrypt().
@type blocks: C{str} """ raise NotImplementedError()
def makeMAC(self, seqid, data): """ Create a message authentication code (MAC) for the given packet using the outgoing MAC values.
@param seqid: the sequence ID of the outgoing packet @type seqid: C{int} @param data: the data to create a MAC for @type data: C{str} @rtype: C{str} """ if not self.outMAC[0]: return '' data = struct.pack('>L', seqid) + data mod, i, o, ds = self.outMAC inner = mod(i + data) outer = mod(o + inner.digest()) return outer.digest()
def verify(self, seqid, data, mac): """ Verify an incoming MAC using the incoming MAC values. Return True if the MAC is valid.
@param seqid: the sequence ID of the incoming packet @type seqid: C{int} @param data: the packet data to verify @type data: C{str} @param mac: the MAC sent with the packet @type mac: C{str} @rtype: C{bool} """ if not self.inMAC[0]: return mac == '' data = struct.pack('>L', seqid) + data mod, i, o, ds = self.inMAC inner = mod(i + data) outer = mod(o + inner.digest()) return mac == outer.digest()
class _Counter: """ Stateful counter which returns results packed in a byte string """
def __init__(self, initialVector, blockSize): """ @type initialVector: C{str} @param initialVector: A byte string representing the initial counter value. @type blockSize: C{int} @param blockSize: The length of the output buffer, as well as the number of bytes at the beginning of C{initialVector} to consider. """ initialVector = initialVector[:blockSize] self.count = getMP('\xff\xff\xff\xff' + initialVector)[0] self.blockSize = blockSize self.count = Util.number.long_to_bytes(self.count - 1) self.count = '\x00' * (self.blockSize - len(self.count)) + self.count self.count = array.array('c', self.count) self.len = len(self.count) - 1
def __call__(self): """ Increment the counter and return the new value. """ i = self.len while i > -1: self.count[i] = n = chr((ord(self.count[i]) + 1) % 256) if n == '\x00': i -= 1 else: return self.count.tostring()
self.count = array.array('c', '\x00' * self.blockSize) return self.count.tostring()
# Diffie-Hellman primes from Oakley Group 2 [RFC 2409] DH_PRIME = long('17976931348623159077083915679378745319786029604875601170644' '442368419718021615851936894783379586492554150218056548598050364644054819923' '910005079287700335581663922955313623907650873575991482257486257500742530207' '744771258955095793777842444242661733472762929938766870920560605027081084290' '7692932019128194467627007L') DH_GENERATOR = 2L
MSG_DISCONNECT = 1 MSG_IGNORE = 2 MSG_UNIMPLEMENTED = 3 MSG_DEBUG = 4 MSG_SERVICE_REQUEST = 5 MSG_SERVICE_ACCEPT = 6 MSG_KEXINIT = 20 MSG_NEWKEYS = 21 MSG_KEXDH_INIT = 30 MSG_KEXDH_REPLY = 31 MSG_KEX_DH_GEX_REQUEST_OLD = 30 MSG_KEX_DH_GEX_REQUEST = 34 MSG_KEX_DH_GEX_GROUP = 31 MSG_KEX_DH_GEX_INIT = 32 MSG_KEX_DH_GEX_REPLY = 33
DISCONNECT_HOST_NOT_ALLOWED_TO_CONNECT = 1 DISCONNECT_PROTOCOL_ERROR = 2 DISCONNECT_KEY_EXCHANGE_FAILED = 3 DISCONNECT_RESERVED = 4 DISCONNECT_MAC_ERROR = 5 DISCONNECT_COMPRESSION_ERROR = 6 DISCONNECT_SERVICE_NOT_AVAILABLE = 7 DISCONNECT_PROTOCOL_VERSION_NOT_SUPPORTED = 8 DISCONNECT_HOST_KEY_NOT_VERIFIABLE = 9 DISCONNECT_CONNECTION_LOST = 10 DISCONNECT_BY_APPLICATION = 11 DISCONNECT_TOO_MANY_CONNECTIONS = 12 DISCONNECT_AUTH_CANCELLED_BY_USER = 13 DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE = 14 DISCONNECT_ILLEGAL_USER_NAME = 15
messages = {} for name, value in globals().items(): if name.startswith('MSG_'): messages[value] = name
|