Specifications implemented by OpenSSH

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 SSH Authentication Protocol
rfc4253.txt (e) SSH Transport Layer Protocol
rfc4254.txt 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 eow@openssh.com, no-more-sessions@openssh.com, tun@openssh.com and the sftp extensions posix-rename@openssh.com statvfs@openssh.com, fstatvfs@openssh.com
draft-miller-secsh-umac-01.txt umac-64@openssh.com: a new transport-layer MAC.
draft-miller-secsh-compression-delayed-00.txt zlib@openssh.com: Delayed compression until after authentication.
usr/bin/ssh/PROTOCOL.certkeys ssh-rsa-cert-v00@openssh.com, ssh-dsa-cert-v00@openssh.com, ecdsa-sha2-nistp256-cert-v01@openssh.com, ecdsa-sha2-nistp384-cert-v01@openssh.com, ecdsa-sha2-nistp521-cert-v01@openssh.com : new public key algorithms supporting certificates.
curve25519-sha256@libssh.org.txt curve25519-sha256@libssh.org 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.