OpenSSH Specifications

OpenSSH implements the following specifications.

SSH protocol version 1

ssh-rfc-v1.3.txt SSH protocol version 1.3
ssh-rfc-v1.5.txt SSH protocol version 1.5

SSH protocol version 2 Core RFCs

Source: secsh working group

rfc4250.txt SSH Protocol Assigned Numbers
rfc4251.txt SSH Protocol Architecture
rfc4252.txt (e) SSH Authentication Protocol
rfc4253.txt (e) SSH Transport Layer Protocol
rfc4254.txt (e) SSH Connection Protocol

SSH protocol version 2 Extension RFCs

rfc4255.txt (e) Using DNS to Securely Publish SSH Key Fingerprints (SSHFP)
rfc4256.txt (e) Generic Message Exchange Authentication (aka "keyboard-interactive")
rfc4335.txt (e) SSH Session Channel Break Extension
rfc4344.txt SSH Transport Layer Encryption Modes
rfc4345.txt Improved Arcfour Modes for the SSH Transport Layer Protocol
rfc4419.txt Diffie-Hellman Group Exchange
rfc4462.txt (e) GSS-API Authentication and Key Exchange (only authentication implemented)
rfc4462.txt SSH Public Key File Format
rfc5656.txt (e) Elliptic Curve Algorithm Integration in SSH
rfc6594.txt (e) SHA-256 SSHFP Resource Records (new in OpenSSH 6.1).
rfc7479.txt ED25519 SSHFP Resource Records (new in OpenSSH 6.5).
rfc6668.txt SHA-2 Data Integrity Algorithms (new in OpenSSH 5.9)

SSH protocol version 2 draft specifications

draft-ietf-secsh-filexfer-02.txt SSH File Transfer Protocol version 3

SSH protocol version 2 vendor extensions.

usr/bin/ssh/PROTOCOL An overview of all vendor extensions detailed below, and the specifications of the SSH2 extensions,, and the sftp extensions,
draft-miller-secsh-umac-01.txt a new transport-layer MAC.
draft-miller-secsh-compression-delayed-00.txt Delayed compression until after authentication.
usr/bin/ssh/PROTOCOL.certkeys,,,, : new public key algorithms supporting certificates. key exchange method.

Other specifications

socks4.protocol SOCKS protocol version 4. Used for ssh -D.
socks4a.protocol SOCKS protocol version 4a. Used for ssh -D.
rfc1928.txt SOCKS protocol version 5. Used for ssh -D.
IP Type of Service (ToS) and Differentiated Services. ssh and sshd will automatically set the ToS as per rfc1349 unless specified otherwise via the IPQoS keyword in ssh_config and sshd_config.