SSH Frequently Asked Questions
What's the difference between versions 1 and 2 of the SSH protocol?
|SSH protocol, version 2
|SSH protocol, version 1
|Separate transport, authentication, and connection protocols
|One monolithic protocol
|Strong cryptographic integrity check
|Weak CRC-32 integrity check; admits an insertion attack in conjunction with some bulk ciphers.
|Supports password changing
|Any number of session channels per connection (including none)
|Exactly one session channel per connection (requires issuing a remote command even when you don't want one)
|Full negotiation of modular cryptographic and compression algorithms, including bulk encryption, MAC, and public-key
|Negotiates only the bulk cipher; all others are fixed
|Encryption, MAC, and compression are negotiated separately for each direction, with independent keys
|The same algorithms and keys are used in both directions (although RC4 uses separate keys, since the algorithm's design demands that keys not be reused)
|Extensible algorithm/protocol naming scheme allows local extensions while preserving interoperability
|Fixed encoding precludes interoperable additions
|User authentication methods:
|Supports a wider variety:
|Use of Diffie-Hellman key agreement removes the need for a server key
|Server key used for forward secrecy on the session key
|Supports public-key certificates
|User authentication exchange is more flexible, and allows requiring multiple forms of authentication for access.
|Allows for exactly one form of authentication per session.
|hostbased authentication is in principle independent of client network address, and so can work with proxying, mobile clients, etc. (though this is not currently implemented).
|RhostsRSA authentication is effectively tied to the client host address, limiting its usefulness.
|periodic replacement of session keys
* Not all SSH-2 implementations support RSA yet for user authentication or host keys, since it's a relatively recent addition. The RSA algorithm was originally omitted from the protocol due to its patent status, but that patent has since expired.