drop DSA (ssh-dss) support by vszakats · Pull Request #2598 · libssh2/libssh2

vszakats · 2026-09-11T15:26:51Z

DSA was deprecated in the last stable libssh2 release in 2024, with
its deletion scheduled for April 2025.
It has been considered insecure for well over a decade.
It was fully dropped by OpenSSH 10.0 (2025-04-09).
Ref: https://www.openssh.org/txt/release-10.0

Maintenance, fixing bugs and vulnerabilities and further development is
a pointless effort for the reasons above.

Supported alternatives:

RSA, with all crypto backends
ECDSA, with mbedTLS, OpenSSL/forks/wolfSSL, WinCNG (build-time option)
ED25519, with OpenSSL/forks

Ref: GHSA-9mh3-9gqq-mxgv

shall we do this now?

Copilot

🟡 Changes recommended

A remaining negative authentication test becomes a false positive, and several public documentation statements no longer match behavior.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Removes deprecated ssh-dss support across cryptographic backends, host-key handling, tests, and build metadata.

Changes:

Removes DSA implementations and capability flags.
Removes DSA test fixtures and CI configuration.
Updates release and backend documentation.

File summaries

File	Description
`.github/workflows/ci.yml`	Removes DSA build flags.
`RELEASE-NOTES`	Announces DSA removal.
`os400/README400`	Updates crypto support wording.
`src/HACKING-CRYPTO.md`	Removes DSA backend documentation.
`src/crypto.h`	Removes DSA interfaces and PEM constants.
`src/crypto_config.h`	Removes DSA feature configuration.
`src/hostkey.c`	Removes `ssh-dss` host-key support.
`src/knownhost.c`	Removes dedicated DSA known-host handling.
`src/libgcrypt.c`	Removes libgcrypt DSA operations.
`src/libgcrypt.h`	Removes libgcrypt DSA declarations.
`src/mbedtls.h`	Removes obsolete DSA capability flag.
`src/openssl.c`	Removes OpenSSL DSA operations.
`src/openssl.h`	Removes OpenSSL DSA configuration and types.
`src/os400qc3.c`	Removes dormant QC3 DSA registration.
`src/os400qc3.h`	Removes obsolete DSA capability flag.
`src/version.c`	Removes DSA from build options.
`src/wincng.c`	Removes WinCNG DSA implementation.
`src/wincng.h`	Removes WinCNG DSA declarations.
`tests/.gitignore`	Removes deleted DSA test binary.
`tests/Makefile.inc`	Removes DSA test and fixtures.
`tests/keys-generate.sh`	Stops generating DSA keys.
`tests/keys/id_dsa`	Deletes DSA private key fixture.
`tests/keys/id_dsa.pub`	Deletes DSA public key fixture.
`tests/keys/id_dsa_wrong`	Deletes negative DSA private key fixture.
`tests/keys/id_dsa_wrong.pub`	Deletes negative DSA public key fixture.
`tests/openssh_server/authorized_keys`	Removes authorized DSA key.
`tests/test_auth_pubkey_ok_dsa.c`	Deletes DSA authentication test.

Review details

Suppressed comments (1)

tests/keys/id_dsa_wrong:1

Deleting this key pair leaves test_auth_pubkey_fail.c pointing at nonexistent files. Because test_auth_pubkey() treats any nonzero result as the expected authentication failure, the test now passes on a local file-open error without exercising server-side rejection. Repoint it to a retained, unauthorized key pair (for example, the host CA key) or add a replacement negative fixture.

Files reviewed: 27/27 changed files
Comments generated: 4
Review effort level: Balanced

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Copilot

🟡 Changes recommended

The negative authentication test now passes on missing fixture errors, and several edited API descriptions remain incomplete.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

Suppressed comments (1)

tests/keys/id_dsa_wrong:1

Deleting this key pair leaves test_auth_pubkey_fail.c pointing at files that no longer exist. That test treats every nonzero authentication result as success (session_fixture.c:538-549), so it will now pass on a local file-open error without exercising rejection of a valid but unauthorized key. Replace these fixtures and references with a supported, unauthorized key pair (and keep it out of authorized_keys).

Files reviewed: 31/31 changed files
Comments generated: 4
Review effort level: Balanced

Copilot

🟡 Changes recommended

The retained negative public-key authentication test silently passes using deleted DSA fixtures instead of testing server rejection.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

Files reviewed: 31/31 changed files
Comments generated: 1
Review effort level: Balanced

Copilot

🔵 Needs a closer look

The broad cryptographic and public compatibility impact warrants final human validation across supported backends.

Review details

Files reviewed: 34/34 changed files
Comments generated: 0 new
Review effort level: Balanced

MichaelBuckley · 2026-09-11T23:19:07Z

From a purely code perspective, the changes look good and accomplish what this PR sets out to do.

On a personal note, we recently polled users about the upcoming removal of DSA support and heard from users who still rely on it to access old hardware. They had setups with servers on discontinued architectures running on local networks not connected to the internet.

So we'll probably have to retain DSA support in our personal fork of libssh2. It's a bummer for us since we were very close to being able to use libssh2 unmodified. But the removal was announced long ago and the deadline has passed. DSA is totally busted and no one should use it, so it makes sense to remove it. It's just unfortunate users are still using it.

To use a key type that is: - supported by all backends. - can be generated with the most recent `ssh-keygen` version. - here to stay for the foreseeable future. (DSA is scheduled for removal from the libssh2 codebase.) Cherry-picked from #2598 Closes #2604

vszakats marked this pull request as draft September 11, 2026 15:26

vszakats requested review from MichaelBuckley and willco007 and a balanced review from Copilot September 11, 2026 15:37

Copilot started reviewing on behalf of vszakats September 11, 2026 15:38 View session

Copilot AI reviewed Sep 11, 2026

View reviewed changes

Comment thread RELEASE-NOTES Outdated

Comment thread os400/README400 Outdated

Comment thread src/hostkey.c

Comment thread src/knownhost.c

vszakats force-pushed the drop-dsa branch from 9c693ee to da568c8 Compare September 11, 2026 16:03

vszakats requested a balanced review from Copilot September 11, 2026 16:03

Copilot started reviewing on behalf of vszakats September 11, 2026 16:05 View session

Copilot AI reviewed Sep 11, 2026

View reviewed changes

Comment thread docs/libssh2_knownhost_add.md Outdated

Comment thread docs/libssh2_knownhost_addc.md Outdated

Comment thread docs/libssh2_session_hostkey.md Outdated

Comment thread src/knownhost.c Outdated

vszakats force-pushed the drop-dsa branch from da568c8 to 3488acb Compare September 11, 2026 16:49

vszakats requested a balanced review from Copilot September 11, 2026 16:49

Copilot started reviewing on behalf of vszakats September 11, 2026 16:53 View session

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Comment thread tests/Makefile.inc

vszakats force-pushed the drop-dsa branch from 3488acb to f33e5dd Compare September 11, 2026 18:54

vszakats requested a balanced review from Copilot September 11, 2026 19:02

Copilot started reviewing on behalf of vszakats September 11, 2026 19:03 View session

Copilot AI reviewed Sep 11, 2026

View reviewed changes

vszakats marked this pull request as ready for review September 11, 2026 19:16

vszakats mentioned this pull request Sep 11, 2026

tests: replace DSA with RSA key for fail test #2604

Closed

vszakats force-pushed the drop-dsa branch 3 times, most recently from b53668e to 1ae2aaa Compare September 13, 2026 14:25

vszakats added 5 commits September 14, 2026 00:59

relnotes

ff40a4b

tests

dd81e65

ci

21322cd

os400

56ceb9c

manual

7be318b

vszakats added 12 commits September 14, 2026 00:59

HACKING-CRYPTO.md

614defc

crypto.h

1109345

crypto_config.h

fbdfabe

hostkey.c

1d1cd64

knownhost.c

a5aadf0

version.c

e1256b6

openssl

2b8874e

wincng

53395ca

os400qc3

e09604a

mbedtls.h

c9fa217

libgcrypt

61cef36

libssh2.h

e361c9b

vszakats force-pushed the drop-dsa branch from 1ae2aaa to e361c9b Compare September 13, 2026 23:05

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drop DSA (ssh-dss) support - #2598

drop DSA (ssh-dss) support#2598
vszakats wants to merge 17 commits into
libssh2:masterfrom
vszakats:drop-dsa

vszakats commented Sep 11, 2026 •

edited

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MichaelBuckley commented Sep 11, 2026

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🟡 Changes recommended

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🟡 Changes recommended

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🔵 Needs a closer look

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MichaelBuckley commented Sep 11, 2026

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vszakats commented Sep 11, 2026 •

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