x509.nx

x509.nx -- minimal X.509 v3 certificate parser (RFC 5280). Reader-only subset that extracts the fields needed for TLS 1.3 certificate chain verification: - tbsCertificate bytes + length (to hash for signature verify) - serialNumber (for revocation / pinning) - subjectPublicKeyInfo (the public key we trust) - signatureAlgorithm OID (tells us which verify to use) - signatureValue BIT STRING (the actual signature bytes) ASN.1 structure (abbreviated from RFC 5280 §4.1): Certificate ::= SEQUENCE { tbsCertificate TBSCertificate, signatureAlgorithm AlgorithmIdentifier, signatureValue BIT STRING } TBSCertificate ::= SEQUENCE { version [0] EXPLICIT Version DEFAULT v1, serialNumber CertificateSerialNumber, signature AlgorithmIdentifier, issuer Name, validity Validity, subject Name, subjectPublicKeyInfo SubjectPublicKeyInfo, ... optional extensions } Invariants: X1 Returns pointers into the caller's DER buffer; nothing copied. Caller owns the buffer's lifetime. X2 All bounds-checks delegated to asn1.nx (A1 invariant). Malformed certs fail with a negative return code, never silent truncation. X3 Version field is optional (DEFAULT v1); we detect the [0] EXPLICIT wrapper and skip over it if present. X4 Extensions (v3 only) are parsed enough to find Subject Alternative Name -- the rest is skipped. Extension OID matching is caller-driven via x509_next_extension.