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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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@ -2357,8 +2357,8 @@ hopefully also resistant to a new class of attacks.
\b \q{ECDH}: \i{elliptic curve} \i{Diffie-Hellman key exchange}, \b \q{ECDH}: \i{elliptic curve} \i{Diffie-Hellman key exchange},
with a variety of standard curves and hash algorithms. with a variety of standard curves and hash algorithms.
\b \q{Diffie-Hellman} key exchange with a variety of well-known groups \b The original form of \q{Diffie-Hellman} key exchange, with a
and hashes: variety of well-known groups and hashes:
\lcont{ \lcont{
\b \q{Group 18}, a well-known 8192-bit group, used with the SHA-512 \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. old server software.
} }
\b \q{\ii{Group exchange}}: with this method, instead of using a fixed \b \q{Diffie-Hellman \i{group exchange}}: with this method, instead
group, PuTTY requests that the server suggest a group to use for key of using a fixed group, PuTTY requests that the server suggest a group
exchange; the server can avoid groups known to be weak, and possibly to use for a subsequent Diffie-Hellman key exchange; the server can
invent new ones over time, without any changes required to PuTTY's avoid groups known to be weak, and possibly invent new ones over time,
configuration. This key exchange method uses the SHA-256 hash or, without any changes required to PuTTY's configuration. This key
if the server doesn't support that, SHA-1. \#{FIXME: still true?:} exchange method uses the SHA-256 hash or, if the server doesn't
We recommend use of this method instead of the well-known groups, support that, SHA-1.
if possible.
\b \q{\i{RSA-based key exchange}}: this requires much less computational \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 effort on the part of the client, and somewhat less on the part of