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OpenSSH: Why ssh-rsa but not rsa-sha2-256/512 for HostKeyAlgorithms? #119

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kevinoid opened this issue Mar 6, 2020 · 1 comment · May be fixed by Jakuje/infosec.mozilla.org#1 or #162
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OpenSSH: Why ssh-rsa but not rsa-sha2-256/512 for HostKeyAlgorithms? #119

kevinoid opened this issue Mar 6, 2020 · 1 comment · May be fixed by Jakuje/infosec.mozilla.org#1 or #162

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@kevinoid
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kevinoid commented Mar 6, 2020

The OpenSSH client guidelines include ssh-rsa, but not rsa-sha2-256 or rsa-sha2-512 in HostKeyAlgorithms. I couldn't find the rationale and wondered if that's worth reconsidering.

I'm raising the issue because the OpenSSH 8.2 release notes mention disabling ssh-rsa in "a near-future release" and list rsa-sha2-256/512 as alternatives. Testing on my own systems revealed that github.com currently offers ssh-dss,rsa-sha2-512,rsa-sha2-256,ssh-rsa which is not acceptable with ssh-rsa removed from the current recommendation.

Thanks for considering,
Kevin
Jakuje added a commit to Jakuje/infosec.mozilla.org that referenced this issue May 25, 2022
@Jakuje
Add algorithms using RSA with SHA2
f539a26 
The recommendation for clients is very outdated not mentioning any RSA-SHA2 algorithms that are standardized for 4 years and the old RSA-SHA1 disabled in OpenSSH upstream causing interoperability problems for people following these guides

https://datatracker.ietf.org/doc/html/rfc8332
https://www.openssh.com/txt/release-8.8

Resolves: mozilla#119
This was referenced May 25, 2022
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@ofifoto
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ofifoto commented Oct 9, 2023

If this isn't going to be maintained (even has a PR pending), it should be unpublished and archived, lest Mozilla recommend bad security practices for the world to stumble upon. The default configuration is more secure than your "modern" configuration and both of your configurations can not connect to some modern servers (offering only an RSA hostkey and thus only rsa-sha2-512,rsa-sha2-256).

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@kevinoid @ofifoto