On Wed, Jun 12, 2024 at 12:45:49PM -0400, Antoine Beaupre wrote: > In Debian stable, the manual page says: > > KexAlgorithms > Specifies the available KEX (Key Exchange) algorithms. > Multiple algorithms must be comma-separated. If the spec‐ > ified list begins with a ‘+’ character, then the specified > algorithms will be appended to the default set instead of > replacing them. If the specified list begins with a ‘-’ > character, then the specified algorithms (including wild‐ > cards) will be removed from the default set instead of re‐ > placing them. If the specified list begins with a ‘^’ > character, then the specified algorithms will be placed at > the head of the default set. The default is: > > sntrup761x25519-sha...@openssh.com, > curve25519-sha256,curve25519-sha...@libssh.org, > ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521, > diffie-hellman-group-exchange-sha256, > diffie-hellman-group16-sha512, > diffie-hellman-group18-sha512, > diffie-hellman-group14-sha256 > > The list of available key exchange algorithms may also be > obtained using "ssh -Q kex". > > Yet that command, `ssh -Q kex`, has a *different* list:
I think this is mainly an error of emphasis. The list that's explicitly spelled out in the manual page is the list of algorithms used by *default*, but the list shown by "ssh -Q kex" is the list that's *available*. Some old algorithms are still implemented for legacy compatibility reasons but aren't sent to servers by default. It would probably be less confusing if the word "also" were removed from the last sentence, but also "available" is used in two slightly different senses in this documentation, which doesn't help. While the similar passage in sshd_config(5) still isn't ideal, it has a slightly clearer distinction between "supported" and "default" which is an improvement. -- Colin Watson (he/him) [cjwat...@debian.org]
