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ssh: Disable DSA keys
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Authored by emaste on Mon, Feb 10, 1:28 PM.
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Details

Summary

This is the upstream default -- from the 9.8p1 release notes:

Future deprecation notice

OpenSSH plans to remove support for the DSA signature algorithm in
early 2025. This release disables DSA by default at compile time.

DSA, as specified in the SSHv2 protocol, is inherently weak - being
limited to a 160 bit private key and use of the SHA1 digest. Its
estimated security level is only 80 bits symmetric equivalent.

OpenSSH has disabled DSA keys by default since 2015 but has retained
run-time optional support for them. DSA was the only mandatory-to-
implement algorithm in the SSHv2 RFCs, mostly because alternative
algorithms were encumbered by patents when the SSHv2 protocol was
specified.

This has not been the case for decades at this point and better
algorithms are well supported by all actively-maintained SSH
implementations. We do not consider the costs of maintaining DSA
in OpenSSH to be justified and hope that removing it from OpenSSH
can accelerate its wider deprecation in supporting cryptography
libraries.

This release, and its deactivation of DSA by default at compile-time,
marks the second step in our timeline to finally deprecate DSA. The
final step of removing DSA support entirely is planned for the first
OpenSSH release of 2025.

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Event Timeline

emaste created this revision.
emaste added a subscriber: secteam.
crypto/openssh/config.h
1980–1981

This comment is somewhat confusing, but is what upstream's ./configure generates

We'll want to make note of this (upcoming) change in the 13.5 release notes too.

jlduran added inline comments.
crypto/openssh/config.h
1980–1981

Yes, comparing it with the artifacts (config.h) generated by the test matrix (from the "save config" step on GitHub).

This revision is now accepted and ready to land.Mon, Feb 10, 4:37 PM
This revision was automatically updated to reflect the committed changes.