Go to the latest version of this document.

# ``twisted`.`conch`.`ssh`.`transport`.`SSHServerTransport``

class documentation

`class SSHServerTransport(SSHTransportBase): (source)`

View In Hierarchy

SSHServerTransport implements the server side of the SSH protocol.

Method | `ssh_KEX_DH_GEX_INIT` | Called when we get a MSG_KEX_DH_GEX_INIT message. Payload:
Method | `ssh_KEX_DH_GEX_REQUEST` | Called when we receive a MSG_KEX_DH_GEX_REQUEST message. Payload:
Method | `ssh_KEX_DH_GEX_REQUEST_OLD` | 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`...
Method | `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.
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:
Instance Variable | `dhGexRequest` | the KEX_DH_GEX_REQUEST(_OLD) that the client sent. The key generation needs this to be stored.
Instance Variable | `ecPub` | Undocumented
Instance Variable | `g` | the Diffie-Hellman group generator.
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 | `isClient` | since we are never the client, this is always False.
Instance Variable | `p` | the Diffie-Hellman group prime.
Method | `_getHostKeys` | Get the public and private host keys corresponding to the given public key signature algorithm.
Method | `_keySetup` | See SSHTransportBase._keySetup().
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`:

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_UNIMPLEMENTED` | Called when we receive a MSG_UNIMPLEMENTED message. Payload:
Class Variable | `avatar` | Undocumented
Class Variable | `factory` | Undocumented
Class Variable | `logoutFunction` | Undocumented
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 | `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 | `_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` (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.
Instance Variable | `connected` | Undocumented
Instance Variable | `transport` | Undocumented

def ssh_KEX_DH_GEX_INIT(self, packet: `bytes`): (source)

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.

Parameters
packet:`bytes` | The message data.

def ssh_KEX_DH_GEX_REQUEST(self, packet: `bytes`): (source)

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.

Parameters
packet:`bytes` | The message data.

def ssh_KEX_DH_GEX_REQUEST_OLD(self, packet: `bytes`): (source)

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.

Parameters
packet:`bytes` | The message data.

def ssh_KEXINIT(self, packet: `bytes`): (source)
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_NEWKEYS(self, packet: `bytes`): (source)

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.

Parameters
packet:`bytes` | The message data.

def ssh_SERVICE_REQUEST(self, packet: `bytes`): (source)

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.

Parameters
packet:`bytes` | The message data.

dhGexRequest = (source)

the KEX_DH_GEX_REQUEST(_OLD) that the client sent. The key generation needs this to be stored.

ecPub = (source)

Undocumented

g = (source)

the Diffie-Hellman group generator.

ignoreNextPacket: `int` = (source)

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.

isClient: `bool` = (source)
overrides `twisted.conch.ssh.transport.SSHTransportBase.isClient`

since we are never the client, this is always False.

p = (source)

the Diffie-Hellman group prime.

def _getHostKeys(self, keyAlg: `bytes`) -> `tuple[keys.Key, keys.Key]`: (source)

Get the public and private host keys corresponding to the given public key signature algorithm.

The factory stores public and private host keys by their key format, which is not quite the same as the key signature algorithm: for example, an ssh-rsa key can sign using any of the ssh-rsa, rsa-sha2-256, or rsa-sha2-512 algorithms.

Parameters
keyAlg:`bytes` | A public key signature algorithm name.

Returns
2-`tuple` of `keys.Key` | The public and private host keys.

Raises
`KeyError` | if the factory does not have both a public and a private host key for this signature algorithm.

def _keySetup(self, sharedSecret: `bytes`, exchangeHash: `bytes`): (source)
overrides `twisted.conch.ssh.transport.SSHTransportBase._keySetup`

See SSHTransportBase._keySetup().

def _ssh_KEX_ECDH_INIT(self, packet: `bytes`): (source)

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.

Parameters
packet:`bytes` | The message data.

def _ssh_KEXDH_INIT(self, packet: `bytes`): (source)

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.

Parameters
packet:`bytes` | The message data.