libopendkim: fix sig_signalg left as rsa-sha1 when unsupported algorithm skipped - #334
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thegushi merged 3 commits intoMay 25, 2026
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…tup() When opendkim is compiled without Ed25519 support and receives a message signed with ed25519-sha256, sig_signalg was left at its memset default (0 = DKIM_SIGN_RSASHA1) because the continue statement in the feature check jumped past the assignment. The AR header would then incorrectly report header.a=rsa-sha1 instead of header.a=ed25519-sha256. Assign sig_signalg immediately when signalg is decoded from the a= tag, before any continue that might skip the signature. Fixes trusteddomainproject#27
…kipping unsupported algorithm Distinguish between a genuinely invalid a= tag value (DKIM_SIGERROR_INVALID_A) and a valid algorithm that was not compiled into this build (DKIM_SIGERROR_UNSUPPORTED_A, e.g. ed25519-sha256 without Ed25519 support). Ed25519 is in wide deployment now; silently skipping these signatures without any log output makes it hard to diagnose why valid signatures are being ignored. opendkim now logs LOG_WARNING when a signature is skipped for this reason, naming the algorithm so operators know exactly what support to add.
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Note: Ed25519 is now in wide deployment (many major senders use it as their primary or secondary signing algorithm). This means the 'compiled without Ed25519 support' code path is no longer a rare edge case - operators running older builds or non-OpenSSL crypto are silently ignoring a meaningful portion of legitimate signatures. The warning added here makes that visible in syslog rather than leaving it as a mystery. |
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When opendkim is compiled without Ed25519 support and receives a message signed with
ed25519-sha256,sig_signalgwas left at itsmemsetdefault of 0 (DKIM_SIGN_RSASHA1). Thecontinuein theDKIM_FEATURE_ED25519check jumped past thesig_signalg = signalgassignment, so the Authentication-Results header would incorrectly reportheader.a=rsa-sha1instead ofheader.a=ed25519-sha256.Fix: assign
sig_signalgimmediately whensignalgis decoded from thea=tag, before anycontinuethat might skip the signature.Closes #27