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docs: Stop recommending DH gex over fixed groups.

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With the new larger fixed-group methods, it's less clearly always the
right answer. (Really it seems more sensible to use ECDH over any of
the integer DH, these days.)

Also, reword other kex descriptions a bit.
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Jacob Nevins 2022-09-11 22:37:47 +01:00
parent 25ef6a233a
commit 3f3f1987aa
1 changed files with 9 additions and 10 deletions
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doc/config.but
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@ -2357,8 +2357,8 @@ hopefully also resistant to a new class of attacks.
\b \q{ECDH}: \i{elliptic curve} \i{Diffie-Hellman key exchange},
with a variety of standard curves and hash algorithms.
\b \q{Diffie-Hellman} key exchange with a variety of well-known groups
and hashes:
\b The original form of \q{Diffie-Hellman} key exchange, with a
variety of well-known groups and hashes:
\lcont{
\b \q{Group 18}, a well-known 8192-bit group, used with the SHA-512
@ -2383,14 +2383,13 @@ installations; however, it may be the only method supported by very
old server software.
}
\b \q{\ii{Group exchange}}: with this method, instead of using a fixed
group, PuTTY requests that the server suggest a group to use for key
exchange; the server can avoid groups known to be weak, and possibly
invent new ones over time, without any changes required to PuTTY's
configuration. This key exchange method uses the SHA-256 hash or,
if the server doesn't support that, SHA-1. \#{FIXME: still true?:}
We recommend use of this method instead of the well-known groups,
if possible.
\b \q{Diffie-Hellman \i{group exchange}}: with this method, instead
of using a fixed group, PuTTY requests that the server suggest a group
to use for a subsequent Diffie-Hellman key exchange; the server can
avoid groups known to be weak, and possibly invent new ones over time,
without any changes required to PuTTY's configuration. This key
exchange method uses the SHA-256 hash or, if the server doesn't
support that, SHA-1.
\b \q{\i{RSA-based key exchange}}: this requires much less computational
effort on the part of the client, and somewhat less on the part of