class documentation

Protocol supporting basic SSH functionality: sending/receiving packets and message dispatch. To connect to or run a server, you must use SSHClientTransport or SSHServerTransport.

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 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 getHost Returns an SSHTransportAddress corresponding to the this side of transport.
Method getPacket Try to return a decrypted, authenticated, and decompressed packet out of the buffer. If there is not enough data, return None.
Method getPeer Returns an SSHTransportAddress corresponding to the other (peer) side of this transport.
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 kexAlg.setter Set the key exchange algorithm name.
Method loseConnection Lose the connection to the other side, sending a DISCONNECT_CONNECTION_LOST message.
Method receiveDebug Called when we receive a debug message from the other side.
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 sendDebug Send a debug message to the other side.
Method sendDisconnect Send a disconnect message to the other side and then disconnect.
Method sendExtInfo Send an RFC 8308 extension advertisement to the remote peer.
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 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 sendUnimplemented Send a message to the other side that the last packet was not understood.
Method setService Set our service to service and start it running. If we were running a service previously, stop it first.
Method ssh_DEBUG Called when we receive a MSG_DEBUG message. Payload:
Method ssh_DISCONNECT Called when we receive a MSG_DISCONNECT message. Payload:
Method ssh_EXT_INFO Called when we get a MSG_EXT_INFO message. Payload:
Method ssh_IGNORE Called when we receive a MSG_IGNORE message. No payload. This means nothing; we simply return.
Method ssh_KEXINIT Called when we receive a MSG_KEXINIT message. Payload:
Method ssh_UNIMPLEMENTED Called when we receive a MSG_UNIMPLEMENTED message. Payload:
Instance Variable buf Data we've received but hasn't been parsed into a packet.
Instance Variable comment An optional string giving more information about the server or client.
Instance Variable currentEncryptions an SSHCiphers instance. It represents the current encryption and authentication options for the transport.
Instance Variable dhSecretKey Undocumented
Instance Variable dhSecretKeyPublicMP Undocumented
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.
Instance Variable gotVersion A boolean indicating whether we have received the version string from the other side.
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 incomingPacketSequence the sequence number of the next packet we are expecting from the other side.
Instance Variable isClient A boolean indicating whether this is a client or server.
Instance Variable kexAlg The key exchange algorithm name agreed between client and server.
Instance Variable keyAlg the agreed-upon public key type for the key exchange.
Instance Variable nextEncryptions an SSHCiphers instance. Held here until the MSG_NEWKEYS messages are exchanged, when nextEncryptions is transitioned to currentEncryptions.
Instance Variable otherKexInitPayload the MSG_KEXINIT payload we received. 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 ourVersionString the version string that we sent to the other side. Used in the key exchange.
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 outgoingPacketSequence the sequence number of the next packet we will send.
Instance Variable peerExtensions a dict of extensions supported by the other side of the connection.
Instance Variable protocolVersion A string representing the version of the SSH protocol we support. Currently defaults to '2.0'.
Instance Variable service an SSHService instance, or None. If it's set to an object, it's the currently running service.
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 supportedCiphers A list of strings representing the encryption algorithms 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 supportedKeyExchanges A list of strings representing the key exchanges supported, in order from most-preferred to least.
Instance Variable supportedLanguages A list of strings representing languages supported, 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 supportedPublicKeys A list of strings representing the public key algorithms supported, in order from most-preferred to least.
Instance Variable supportedVersions A container of strings representing supported ssh protocol version numbers.
Instance Variable version A string representing the version of the server or client. Currently defaults to 'Twisted'.
Method _allowedKeyExchangeMessageType Determine if the given message type may be sent while key exchange is in progress.
Method _encodeECPublicKey Encode an elliptic curve public key to bytes.
Method _finishEphemeralDH Completes the Diffie-Hellman key agreement started by _startEphemeralDH, and forgets the ephemeral secret key.
Method _generateECPrivateKey Generate an private key for ECDH key exchange.
Method _generateECSharedSecret Generate a shared secret for ECDH key exchange.
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 Called back by a subclass once a MSG_NEWKEYS message has been received. This indicates key exchange has completed and new encryption and compression parameters should be adopted. Any messages which were queued during key exchange will also be flushed.
Method _startEphemeralDH Prepares for a Diffie-Hellman key agreement exchange.
Method _unsupportedVersionReceived Called when an unsupported version of the ssh protocol is received from the remote endpoint.
Constant _EXT_INFO_C Undocumented
Constant _EXT_INFO_S Undocumented
Constant _KEY_EXCHANGE_NONE Undocumented
Constant _KEY_EXCHANGE_PROGRESSING Undocumented
Constant _KEY_EXCHANGE_REQUESTED Undocumented
Class Variable _log Undocumented
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...
Instance Variable _kexAlg Undocumented
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...
Instance Variable _peerSupportsExtensions a boolean indicating whether the other side of the connection supports RFC 8308 extension negotiation.

Inherited from Protocol:

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

Inherited from BaseProtocol (via Protocol):

Method makeConnection Make a connection to a transport and a server.
Instance Variable connected Undocumented
Instance Variable transport Undocumented
def connectionLost(self, reason): (source)

When the underlying connection is closed, stop the running service (if any), and log out the avatar (if any).

Parameters
reason:twisted.python.failure.FailureThe cause of the connection being closed.
def connectionMade(self): (source)

Called when the connection is made to the other side. We sent our version and the MSG_KEXINIT packet.

def dataReceived(self, data): (source)

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.

Parameters
data:bytesThe data that was received.
def dispatchMessage(self, messageNum, payload): (source)

Send a received message to the appropriate method.

Parameters
messageNum:intThe message number.
payload:bytesThe message payload.
def getHost(self): (source)

Returns an SSHTransportAddress corresponding to the this side of transport.

Returns
SSHTransportAddressSSHTransportAddress for the peer
Present Since
12.1
def getPacket(self): (source)

Try to return a decrypted, authenticated, and decompressed packet out of the buffer. If there is not enough data, return None.

Returns
str or NoneThe decoded packet, if any.
def getPeer(self): (source)

Returns an SSHTransportAddress corresponding to the other (peer) side of this transport.

Returns
SSHTransportAddressSSHTransportAddress for the peer
Present Since
12.1
def isEncrypted(self, direction='out'): (source)

Check if the connection is encrypted in the given direction.

Parameters
direction:strThe direction: one of 'out', 'in', or 'both'.
Returns
boolTrue if it is encrypted.
def isVerified(self, direction='out'): (source)

Check if the connection is verified/authentication in the given direction.

Parameters
direction:strThe direction: one of 'out', 'in', or 'both'.
Returns
boolTrue if it is verified.
@kexAlg.setter
def kexAlg(self, value): (source)

Set the key exchange algorithm name.

def loseConnection(self): (source)

Lose the connection to the other side, sending a DISCONNECT_CONNECTION_LOST message.

def receiveDebug(self, alwaysDisplay, message, lang): (source)

Called when we receive a debug message from the other side.

Parameters
alwaysDisplay:boolif True, this message should always be displayed.
message:strthe debug message
lang:stroptionally the language the message is in.
def receiveError(self, reasonCode, description): (source)

Called when we receive a disconnect error message from the other side.

Parameters
reasonCode:intthe reason for the disconnect, one of the DISCONNECT_ values.
description:stra human-readable description of the disconnection.
def receiveUnimplemented(self, seqnum): (source)

Called when we receive an unimplemented packet message from the other side.

Parameters
seqnum:intthe sequence number that was not understood.
def sendDebug(self, message, alwaysDisplay=False, language=b''): (source)

Send a debug message to the other side.

Parameters
message:strthe message to send.
alwaysDisplay:boolif True, tell the other side to always display this message.
language:stroptionally, the language the message is in.
def sendDisconnect(self, reason, desc): (source)

Send a disconnect message to the other side and then disconnect.

Parameters
reason:intthe reason for the disconnect. Should be one of the DISCONNECT_* values.
desc:stra descrption of the reason for the disconnection.
def sendExtInfo(self, extensions): (source)

Send an RFC 8308 extension advertisement to the remote peer.

Nothing is sent if the peer doesn't support negotiations.

Parameters
extensions:list of (bytes, bytes)a list of (extension-name, extension-value) pairs.
def sendIgnore(self, message): (source)

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.

Parameters
message:strdata to send with the message
def sendKexInit(self): (source)

Send a KEXINIT message to initiate key exchange or to respond to a key exchange initiated by the peer.

Returns
None
Raises
RuntimeErrorIf a key exchange has already been started and it is not appropriate to send a KEXINIT message at this time.
def sendPacket(self, messageType, payload): (source)

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.

Parameters
messageType:intThe type of the packet; generally one of the MSG_* values.
payload:strThe payload for the message.
def sendUnimplemented(self): (source)

Send a message to the other side that the last packet was not understood.

def setService(self, service): (source)

Set our service to service and start it running. If we were running a service previously, stop it first.

Parameters
service:SSHServiceThe service to attach.
def ssh_DEBUG(self, packet): (source)

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.

Parameters
packet:bytesThe message data.
def ssh_DISCONNECT(self, packet): (source)

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.

Parameters
packet:bytesThe message data.
def ssh_EXT_INFO(self, packet): (source)

Called when we get a MSG_EXT_INFO message. Payload:

    uint32 nr-extensions
    repeat the following 2 fields "nr-extensions" times:
      string extension-name
      string extension-value (binary)
Parameters
packet:bytesThe message data.
def ssh_IGNORE(self, packet): (source)

Called when we receive a MSG_IGNORE message. No payload. This means nothing; we simply return.

Parameters
packet:bytesThe message data.
def ssh_KEXINIT(self, packet): (source)

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.

Parameters
packet:bytesThe message data.
Returns
A tuple of negotiated key exchange algorithms, key algorithms, and unhandled data, or None if something went wrong.
def ssh_UNIMPLEMENTED(self, packet): (source)

Called when we receive a MSG_UNIMPLEMENTED message. Payload:

    long packet

This means that the other side did not implement one of our packets.

Parameters
packet:bytesThe message data.

Data we've received but hasn't been parsed into a packet.

An optional string giving more information about the server or client.

currentEncryptions = (source)

an SSHCiphers instance. It represents the current encryption and authentication options for the transport.

dhSecretKey = (source)

Undocumented

dhSecretKeyPublicMP = (source)

Undocumented

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.

gotVersion: bool = (source)

A boolean indicating whether we have received the version string from the other side.

incomingCompression = (source)

an object supporting the .decompress(str) method, or None if there is no incoming compression. Used to decompress incoming data.

incomingCompressionType = (source)

A string representing the incoming compression type.

incomingPacketSequence: int = (source)

the sequence number of the next packet we are expecting from the other side.

isClient: bool = (source)

A boolean indicating whether this is a client or server.

The key exchange algorithm name agreed between client and server.

the agreed-upon public key type for the key exchange.

nextEncryptions = (source)

an SSHCiphers instance. Held here until the MSG_NEWKEYS messages are exchanged, when nextEncryptions is transitioned to currentEncryptions.

otherKexInitPayload = (source)

the MSG_KEXINIT payload we received. Used in the key exchange

otherVersionString = (source)

the version string sent by the other side. Used in the key exchange.

ourKexInitPayload = (source)

the MSG_KEXINIT payload we sent. Used in the key exchange.

ourVersionString = (source)

the version string that we sent to the other side. Used in the key exchange.

outgoingCompression = (source)

an object supporting the .compress(str) and .flush() methods, or None if there is no outgoing compression. Used to compress outgoing data.

outgoingCompressionType = (source)

A string representing the outgoing compression type.

outgoingPacketSequence: int = (source)

the sequence number of the next packet we will send.

peerExtensions: Dict[bytes, bytes] = (source)

a dict of extensions supported by the other side of the connection.

protocolVersion: bytes = (source)

A string representing the version of the SSH protocol we support. Currently defaults to '2.0'.

an SSHService instance, or None. If it's set to an object, it's the currently running service.

sessionID = (source)

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.

supportedCiphers = (source)

A list of strings representing the encryption algorithms supported, in order from most-preferred to least.

supportedCompressions: list[bytes] = (source)

A list of strings representing compression types supported, from most-preferred to least.

supportedKeyExchanges = (source)

A list of strings representing the key exchanges supported, in order from most-preferred to least.

supportedLanguages: tuple = (source)

A list of strings representing languages supported, from most-preferred to least.

supportedMACs: list[bytes] = (source)

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,

supportedPublicKeys = (source)

A list of strings representing the public key algorithms supported, in order from most-preferred to least.

supportedVersions: tuple[bytes, ...] = (source)

A container of strings representing supported ssh protocol version numbers.

A string representing the version of the server or client. Currently defaults to 'Twisted'.

def _allowedKeyExchangeMessageType(self, messageType): (source)

Determine if the given message type may be sent while key exchange is in progress.

Parameters
messageType:intThe type of message
Returns
boolTrue if the given type of message may be sent while key exchange is in progress, False if it may not.
See Also
http://tools.ietf.org/html/rfc4253#section-7.1
def _encodeECPublicKey(self, ecPub): (source)

Encode an elliptic curve public key to bytes.

Parameters
ecPub:The appropriate public key type matching self.kexAlg: ec.EllipticCurvePublicKey for ecdh-sha2-nistp*, or x25519.X25519PublicKey for curve25519-sha256.The public key to encode.
Returns
bytesThe encoded public key.
def _finishEphemeralDH(self, remoteDHpublicKey): (source)

Completes the Diffie-Hellman key agreement started by _startEphemeralDH, and forgets the ephemeral secret key.

Parameters
remoteDHpublicKey:intUndocumented
Returns
bytesThe new shared secret, in SSH mpint format.
def _generateECPrivateKey(self): (source)

Generate an private key for ECDH key exchange.

Returns
The appropriate private key type matching self.kexAlg: ec.EllipticCurvePrivateKey for ecdh-sha2-nistp*, or x25519.X25519PrivateKey for curve25519-sha256.The generated private key.
def _generateECSharedSecret(self, ecPriv, theirECPubBytes): (source)

Generate a shared secret for ECDH key exchange.

Parameters
ecPriv:The appropriate private key type matching self.kexAlg: ec.EllipticCurvePrivateKey for ecdh-sha2-nistp*, or x25519.X25519PrivateKey for curve25519-sha256.Our private key.
theirECPubBytesUndocumented
Returns
bytesThe generated shared secret, as an SSH multiple-precision integer.
def _getKey(self, c, sharedSecret, exchangeHash): (source)

Get one of the keys for authentication/encryption.

Parameters
c:bytesThe letter identifying which key this is.
sharedSecret:bytesThe shared secret K.
exchangeHash:bytesThe hash H from key exchange.
Returns
bytesThe derived key.
def _keySetup(self, sharedSecret, exchangeHash): (source)

Set up the keys for the connection and sends MSG_NEWKEYS when finished,

Parameters
sharedSecret:stra secret string agreed upon using a Diffie- Hellman exchange, so it is only shared between the server and the client.
exchangeHash:strA hash of various data known by both sides.
def _newKeys(self): (source)

Called back by a subclass once a MSG_NEWKEYS message has been received. This indicates key exchange has completed and new encryption and compression parameters should be adopted. Any messages which were queued during key exchange will also be flushed.

def _startEphemeralDH(self): (source)

Prepares for a Diffie-Hellman key agreement exchange.

Creates an ephemeral keypair in the group defined by (self.g, self.p) and stores it.

def _unsupportedVersionReceived(self, remoteVersion): (source)

Called when an unsupported version of the ssh protocol is received from the remote endpoint.

Parameters
remoteVersion:strremote ssh protocol version which is unsupported by us.
_EXT_INFO_C: bytes = (source)

Undocumented

Value
b'ext-info-c'
_EXT_INFO_S: bytes = (source)

Undocumented

Value
b'ext-info-s'
_KEY_EXCHANGE_NONE: str = (source)

Undocumented

Value
'_KEY_EXCHANGE_NONE'
_KEY_EXCHANGE_PROGRESSING: str = (source)

Undocumented

Value
'_KEY_EXCHANGE_PROGRESSING'
_KEY_EXCHANGE_REQUESTED: str = (source)

Undocumented

Value
'_KEY_EXCHANGE_REQUESTED'

Undocumented

_blockedByKeyExchange = (source)

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.

Undocumented

_keyExchangeState = (source)

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).

_peerSupportsExtensions = (source)

a boolean indicating whether the other side of the connection supports RFC 8308 extension negotiation.