simon-git: putty-wishlist (main): Jacob Nevins

[Commits to Tartarus hosted VCS]

TL;DR:
  4b9571b rfc4419: more on OpenSSH server behaviour.

Repository:     https://git.tartarus.org/simon/putty-wishlist.git
On the web:     https://git.tartarus.org/?p=simon/putty-wishlist.git
Branch updated: main
Committer:      Jacob Nevins <jacobn at chiark.greenend.org.uk>
Date:           2022-09-02 19:03:56

commit 4b9571bfb0f55ae78f79c51002d2245f0c81f63d
web diff https://git.tartarus.org/?p=simon/putty-wishlist.git;a=commitdiff;h=4b9571bfb0f55ae78f79c51002d2245f0c81f63d;hp=53d89a98289c9ef987deb50ef3bd1640aa5d0067
Author: Jacob Nevins <jacobn at chiark.greenend.org.uk>
Date:   Fri Sep 2 18:45:46 2022 +0100

    rfc4419: more on OpenSSH server behaviour.
    
    When I did a web search to find out who uses our algorithm preference
    lists and why, I found a whole load of people complaining at various
    times about getting a SSH2_MSG_UNIMPLEMENTED response OpenSSH versions
    like 7.4p1, and reordering the kex preferences to demote DH gex as a
    workaround. But it doesn't look like anyone ever emailed us about this
    problem.
    
    I've found where OpenSSH started replying to the old gex messages with
    UNIMPLEMENTED, and verified experimentally that using old PuTTY code
    with an unusual SSH banner produces the symptom described. It seems
    plausible that this only affected forks and unofficial builds which
    OpenSSH doesn't have a bug-compatibility mode for, explaining why we
    didn't see the complaints.
    
    It seems worth having a write-up here, for people searching for the
    error message.

 data/rfc4419 | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)