twisted.conch.ssh.transport.SSHServerTransport(SSHTransportBase) class documentation

Part of twisted.conch.ssh.transport (View In Hierarchy)

Known subclasses: twisted.conch.test.test_ssh.ConchTestServer

SSHServerTransport implements the server side of the SSH protocol.

Instance Variable isClient since we are never the client, this is always False.
Instance Variable 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.
Instance Variable dhGexRequest the KEX_DH_GEX_REQUEST(_OLD) that the client sent. The key generation needs this to be stored.
Instance Variable g the Diffie-Hellman group generator.
Instance Variable p the Diffie-Hellman group prime.
Method ssh_KEXINIT No summary
Method ssh_KEX_DH_GEX_REQUEST_OLD No summary
Method ssh_KEX_DH_GEX_REQUEST No summary
Method ssh_KEX_DH_GEX_INIT Called when we get a MSG_KEX_DH_GEX_INIT message. Payload:: integer e (client DH public key)
Method ssh_NEWKEYS 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.
Method ssh_SERVICE_REQUEST Called when we get a MSG_SERVICE_REQUEST message. Payload:: string serviceName
Method _ssh_KEX_ECDH_INIT Called from ssh_KEX_DH_GEX_REQUEST_OLD to handle elliptic curve key exchanges.
Method _ssh_KEXDH_INIT Called to handle the beginning of a non-group key exchange.

Inherited from SSHTransportBase:

Instance Variable protocolVersion A string representing the version of the SSH protocol we support. Currently defaults to '2.0'.
Instance Variable version A string representing the version of the server or client. Currently defaults to 'Twisted'.
Instance Variable comment An optional string giving more information about the server or client.
Instance Variable supportedCiphers A list of strings representing the encryption algorithms supported, in order from most-preferred to least.
Instance Variable 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,
Instance Variable supportedKeyExchanges A list of strings representing the key exchanges supported, in order from most-preferred to least.
Instance Variable supportedPublicKeys A list of strings representing the public key types supported, in order from most-preferred to least.
Instance Variable supportedCompressions A list of strings representing compression types supported, from most-preferred to least.
Instance Variable supportedLanguages A list of strings representing languages supported, from most-preferred to least.
Instance Variable supportedVersions A container of strings representing supported ssh protocol version numbers.
Instance Variable gotVersion A boolean indicating whether we have received the version string from the other side.
Instance Variable buf Data we've received but hasn't been parsed into a packet.
Instance Variable outgoingPacketSequence the sequence number of the next packet we will send.
Instance Variable incomingPacketSequence the sequence number of the next packet we are expecting from the other side.
Instance Variable outgoingCompression an object supporting the .compress(str) and .flush() methods, or None if there is no outgoing compression. Used to compress outgoing data.
Instance Variable outgoingCompressionType A string representing the outgoing compression type.
Instance Variable incomingCompression an object supporting the .decompress(str) method, or None if there is no incoming compression. Used to decompress incoming data.
Instance Variable incomingCompressionType A string representing the incoming compression type.
Instance Variable ourVersionString the version string that we sent to the other side. Used in the key exchange.
Instance Variable otherVersionString the version string sent by the other side. Used in the key exchange.
Instance Variable ourKexInitPayload the MSG_KEXINIT payload we sent. Used in the key exchange.
Instance Variable otherKexInitPayload the MSG_KEXINIT payload we received. Used in the key exchange
Instance Variable 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.
Instance Variable service an SSHService instance, or None. If it's set to an object, it's the currently running service.
Instance Variable kexAlg 0 the agreed-upon key exchange algorithm.
Instance Variable keyAlg the agreed-upon public key type for the key exchange.
Instance Variable currentEncryptions an SSHCiphers instance. It represents the current encryption and authentication options for the transport.
Instance Variable nextEncryptions an SSHCiphers instance. Held here until the MSG_NEWKEYS messages are exchanged, when nextEncryptions is transitioned to currentEncryptions.
Instance Variable 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.
Method connectionLost When the underlying connection is closed, stop the running service (if any), and log out the avatar (if any).
Method connectionMade Called when the connection is made to the other side. We sent our version and the MSG_KEXINIT packet.
Method sendKexInit Send a KEXINIT message to initiate key exchange or to respond to a key exchange initiated by the peer.
Method sendPacket 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.
Method getPacket Try to return a decrypted, authenticated, and decompressed packet out of the buffer. If there is not enough data, return None.
Method dataReceived 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.
Method dispatchMessage Send a received message to the appropriate method.
Method getPeer Returns an SSHTransportAddress corresponding to the other (peer) side of this transport.
Method getHost Returns an SSHTransportAddress corresponding to the this side of transport.
Method kexAlg 1 The key exchange algorithm name agreed between client and server.
Method kexAlg Set the key exchange algorithm name.
Method ssh_DISCONNECT Called when we receive a MSG_DISCONNECT message. Payload:: long code string description
Method ssh_IGNORE Called when we receive a MSG_IGNORE message. No payload. This means nothing; we simply return.
Method ssh_UNIMPLEMENTED Called when we receive a MSG_UNIMPLEMENTED message. Payload:: long packet
Method ssh_DEBUG No summary
Method setService Set our service to service and start it running. If we were running a service previously, stop it first.
Method sendDebug Send a debug message to the other side.
Method sendIgnore 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.
Method sendUnimplemented Send a message to the other side that the last packet was not understood.
Method sendDisconnect Send a disconnect message to the other side and then disconnect.
Method isEncrypted Check if the connection is encrypted in the given direction.
Method isVerified Check if the connection is verified/authentication in the given direction.
Method loseConnection Lose the connection to the other side, sending a DISCONNECT_CONNECTION_LOST message.
Method receiveError Called when we receive a disconnect error message from the other side.
Method receiveUnimplemented Called when we receive an unimplemented packet message from the other side.
Method receiveDebug Called when we receive a debug message from the other side.
Instance Variable _keyExchangeState The current protocol state with respect to key exchange. This is either _KEY_EXCHANGE_NONE if no key exchange is in progress (and returns to this value after any key exchange completqes), _KEY_EXCHANGE_REQUESTED if this side of the connection initiated a key exchange, and _KEY_EXCHANGE_PROGRESSING if the other side of the connection initiated a key exchange. _KEY_EXCHANGE_NONE is the initial value (however SSH connections begin with key exchange, so it will quickly change to another state).
Instance Variable _blockedByKeyExchange Whenever _keyExchangeState is not _KEY_EXCHANGE_NONE, this is a list of pending messages which were passed to 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.
Method _allowedKeyExchangeMessageType Determine if the given message type may be sent while key exchange is in progress.
Method _unsupportedVersionReceived Called when an unsupported version of the ssh protocol is received from the remote endpoint.
Method _startEphemeralDH Prepares for a Diffie-Hellman key agreement exchange.
Method _finishEphemeralDH Completes the Diffie-Hellman key agreement started by _startEphemeralDH, and forgets the ephemeral secret key.
Method _getKey Get one of the keys for authentication/encryption.
Method _keySetup Set up the keys for the connection and sends MSG_NEWKEYS when finished,
Method _newKeys No summary
Method _generateECPrivateKey Generate an private key for ECDH key exchange.
Method _encodeECPublicKey Encode an elliptic curve public key to bytes.
Method _generateECSharedSecret Generate a shared secret for ECDH key exchange.

Inherited from Protocol (via SSHTransportBase):

Method logPrefix Return a prefix matching the class name, to identify log messages related to this protocol instance.

Inherited from BaseProtocol (via SSHTransportBase, Protocol):

Method makeConnection Make a connection to a transport and a server.
isClient =
since we are never the client, this is always False.
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.
dhGexRequest =
the KEX_DH_GEX_REQUEST(_OLD) that the client sent. The key generation needs this to be stored.
g =
the Diffie-Hellman group generator.
p =
the Diffie-Hellman group prime.
def ssh_KEXINIT(self, packet):
overrides twisted.conch.ssh.transport.SSHTransportBase.ssh_KEXINIT

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.

def _ssh_KEX_ECDH_INIT(self, packet):

Called from ssh_KEX_DH_GEX_REQUEST_OLD to handle elliptic curve key exchanges.

Payload:

   string client Elliptic Curve Diffie-Hellman public key

Just like _ssh_KEXDH_INIT this message type is also not dispatched directly. Extra check to determine if this is really KEX_ECDH_INIT is required.

First we load the host's public/private keys. Then we generate the ECDH public/private keypair for the given curve. With that we generate the shared secret key. Then we compute the hash to sign and send back to the client Along with the server's public key and the ECDH public key.

ParameterspacketThe message data. (type: bytes)
ReturnsNone.
def _ssh_KEXDH_INIT(self, packet):

Called to handle the beginning of a non-group key exchange.

Unlike other message types, this is not dispatched automatically. It is called from ssh_KEX_DH_GEX_REQUEST_OLD because an extra check is required to determine if this is really a KEXDH_INIT message or if it is a KEX_DH_GEX_REQUEST_OLD message.

The KEXDH_INIT payload:

       integer e (the client's Diffie-Hellman public key)

We send the KEXDH_REPLY with our host key and signature.

ParameterspacketThe message data. (type: bytes)
def ssh_KEX_DH_GEX_REQUEST_OLD(self, packet):

This represents different key exchange methods that share the same integer value. If the message is determined to be a KEXDH_INIT, _ssh_KEXDH_INIT is called to handle it. If it is a KEX_ECDH_INIT, _ssh_KEX_ECDH_INIT is called. Otherwise, for KEX_DH_GEX_REQUEST_OLD 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.

ParameterspacketThe message data. (type: bytes)
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 packet by ssh_KEXINIT, drop it on the floor and return.

ParameterspacketThe message data. (type: bytes)
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.

ParameterspacketThe message data. (type: bytes)
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.

ParameterspacketThe message data. (type: bytes)
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.

ParameterspacketThe message data. (type: bytes)
API Documentation for twisted, generated by pydoctor at 2020-03-25 17:34:30.