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Re: Suggested way to ssh into obsolete devices (with old ssh crypto)?

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On 7/6/21, Ralph Aichinger <ra@pi.h5.or.at> wrote:
> Hi, everybody, as a bullseye user I am seeing messages like
>
> | Unable to negotiate with 10.0.17.52 port 22: no matching
> | key exchange method found. Their offer: diffie-hellman-group1-sha1
>
> with increasing frequency, especially when trying to ssh into
> proprietary, obsolete stuff. Above comes from a Cisco 7941 IP
> phone I toy around with at home, with no expectation of security
> whatsoever, I might as well use telnet.
>
> Some algorithms can be activated by using e.g.
>  -oKexAlgorithms=+diffie-hellman-group1-sha1
> but I suppose it is only a question of time before some of this
> really old and insecure stuff is compiled out or removed from
> sources. It is also a bit difficult to find working combinations
> of keyexchange algorithms and ciphers for unknown older servers
> (a lot of trial and error?).

"ssh -v" might tell you enough about what's missing.  And then
ssh -Q kex
  to show available key exchange algorithms, and
ssh -Q cipher
  to show available ciphers

> What is the suggested way to work around that problem?

I like adding that stuff in the ~/.ssh/config file - ref. man ssh_config
for example:
$ head ~/.ssh/config

Host cerberus 10.10.2.1

User dante

KexAlgorithms +diffie-hellman-group1-sha1
# ssh -Q kex
#   show available key exchange algorithms

> What I do not want to do is change my "normal" configuration, e.g.
> add these algorithms to my normal .ssh/config.

Put all the special cases at the top of the config file and all of the
"normal" config stuff at the end, under
Host *

Regards,
Lee

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Thread

Suggested way to ssh into obsolete devices (with old ssh crypto)? Ralph Aichinger <ra@pi.h5.or.at> - 2021-07-06 11:10 +0200
  Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? "Andrew M.A. Cater" <amacater@einval.com> - 2021-07-06 11:30 +0200
  Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Roberto C. Sánchez <roberto@debian.org> - 2021-07-06 15:00 +0200
    Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Stefan Monnier <monnier@iro.umontreal.ca> - 2021-07-06 18:10 +0200
      Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? "Andrew M.A. Cater" <amacater@einval.com> - 2021-07-06 18:40 +0200
        Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Stefan Monnier <monnier@iro.umontreal.ca> - 2021-07-06 19:10 +0200
          Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Michael Stone <mstone@debian.org> - 2021-07-06 19:50 +0200
            Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? <tomas@tuxteam.de> - 2021-07-06 20:10 +0200
              Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Michael Stone <mstone@debian.org> - 2021-07-06 20:20 +0200
                Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Roberto C. Sánchez <roberto@debian.org> - 2021-07-06 20:20 +0200
                Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Michael Stone <mstone@debian.org> - 2021-07-06 20:40 +0200
                Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? <tomas@tuxteam.de> - 2021-07-06 22:20 +0200
                Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Michael Stone <mstone@debian.org> - 2021-07-06 22:50 +0200
                Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? <tomas@tuxteam.de> - 2021-07-06 23:50 +0200
                Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Stefan Monnier <monnier@iro.umontreal.ca> - 2021-07-06 23:40 +0200
                Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? <tomas@tuxteam.de> - 2021-07-07 00:00 +0200
                Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Stefan Monnier <monnier@iro.umontreal.ca> - 2021-07-07 05:10 +0200
                Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? <tomas@tuxteam.de> - 2021-07-07 10:00 +0200
                Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Karen Lewellen <klewellen@shellworld.net> - 2021-07-07 00:00 +0200
            Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Stefan Monnier <monnier@iro.umontreal.ca> - 2021-07-06 21:30 +0200
              Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Michael Stone <mstone@debian.org> - 2021-07-06 21:30 +0200
  Re: Suggested way to ssh into obsolete devices (with old ssh crypto)? Lee <ler762@gmail.com> - 2021-07-07 01:20 +0200

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