* fix: verify-blob should not force SHA256 for non-default key hash algorithms
Motivation:
cosign verify-blob fails to verify legacy-bundle blob signatures made
with keys whose conventional digest algorithm is not SHA256 (e.g. an
ECDSA P-521 key, which pairs with SHA-512), unless the user explicitly
passes the deprecated --signature-digest-algorithm flag. Without it,
verification fails with "invalid signature when validating ASN.1
encoded signature".
Approach:
The --signature-digest-algorithm flag had a hardcoded default value of
"sha256", so its value was indistinguishable from an explicit
--signature-digest-algorithm sha256. SignatureDigestOptions.HashAlgorithm()
compounded this by also returning SHA256 for an empty/unset value.
VerifyBlobCmd.Exec then forced any zero HashAlgorithm to SHA256 before
loading the verifier, discarding the zero-value sentinel that
LoadPublicKeyRaw (pkg/signature/keys.go) relies on to fall back to
signature.LoadDefaultVerifier, which selects the correct digest
algorithm for the given key type (SHA256 for P-256/RSA, SHA384 for
P-384, SHA512 for P-521).
This change makes the flag default to an empty string, has
HashAlgorithm() return 0 (unset) when the flag isn't provided, and
removes the forced-SHA256 default in VerifyBlobCmd.Exec, letting the
key-loading path pick the digest algorithm that matches the key. The
same forced-default pattern still exists, unchanged, in the image
verify, verify-attestation, and verify-blob-attestation commands,
which are out of scope for this fix.
Validation:
Added TestVerifyBlobWithUnsetHashAlgorithmMatchesKeyDefault
(cmd/cosign/cli/verify/verify_blob_test.go), which signs a blob with a
generated P-521 key using SHA-512 and verifies it via VerifyBlobCmd.Exec
with HashAlgorithm left unset. Confirmed this test fails with the
exact reported error before this change (verified by reverting only
the implementation files) and passes after. Also added
TestSignatureDigestOptionsHashAlgorithm
(cmd/cosign/cli/options/signature_digest_test.go) covering the
unset/explicit/invalid cases for HashAlgorithm().
Ran:
go build ./...
go vet ./cmd/... ./pkg/...
go test ./cmd/... ./pkg/...
golangci-lint run ./cmd/cosign/cli/options/... ./cmd/cosign/cli/verify/...
All passed with no regressions.
Report: https://github.com/sigstore/cosign/issues/5063
Signed-off-by: Pujitha Paladugu <10557236+pujitha24@users.noreply.github.com>
* fix: verify, verify-attestation, verify-blob-attestation should not force SHA256 for non-default key hash algorithms
Applies the same fix as verify-blob to the sibling verify commands, per
review feedback on #5064: stop forcing HashAlgorithm to SHA256 when
unset, and let LoadVerifierFromKeyOrCert pick the digest algorithm
that matches the provided key (e.g. SHA-512 for P-521 ECDSA keys).
Signed-off-by: Pujitha Paladugu <10557236+pujitha24@users.noreply.github.com>
---------
Signed-off-by: Pujitha Paladugu <10557236+pujitha24@users.noreply.github.com>
Co-authored-by: Pujitha Paladugu <10557236+pujitha24@users.noreply.github.com>
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