Backport of #5040
Remove the fallback that loaded a raw public key from a legacy bundle's cert field when X.509 certificate parsing failed. Previously, an attacker could supply a bare public key in b.Cert to populate co.SigVerifier, skipping X.509 certificate chain validation and CheckCertificatePolicy enforcement during keyless verification. This would use the key without any additional checks. The key-as-certificate in the bundle would take priority over a key being provided via --key as well.
This updates the attest-blob code paths to never set a key in the certificate field in the legacy bundle. sign-blob does not already.
For verification, verify-blob and verify-blob-attestation have been updated to not fallback to parsing a certificate as a key. If a bundle is supplied that contains a key, it fails with a parsing error.
Note that no change is needed for sign/attest and
verify/verify-attestation, as the container signing path never stored a public key in the certificate field and the container verification path would only load a certificate as a certificate.
Signed-off-by: Hayden <8418760+Hayden-IO@users.noreply.github.com>
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