verifyTimeStampToken function

TimeStampVerification verifyTimeStampToken(TimeStampToken token, List<int> stampedData)

Verifies token against stampedData - the exact bytes whose digest the token should attest to (the signature value for a signature timestamp, the signed byte ranges for a document timestamp). Confirms the embedded MessageImprint matches and the TSA's CMS signature is cryptographically valid against its embedded certificate. Trust in the TSA certificate is the caller's to establish (via a trust store) and is out of scope here.

Implementation

TimeStampVerification verifyTimeStampToken(
    TimeStampToken token, List<int> stampedData) {
  final hash = hashForDigestOid(token.messageImprint.hashAlgorithmOid);
  if (hash == null) {
    return TimeStampVerification(
      imprintMatches: false,
      signatureValid: false,
      genTime: token.genTime,
      problem: 'unsupported imprint digest '
          '${token.messageImprint.hashAlgorithmOid}',
    );
  }
  final digest = hash.convert(stampedData).bytes;
  final imprintMatches = _bytesEqual(digest, token.messageImprint.hashedMessage);

  // The token's CMS signs the TSTInfo (the eContent), via signed attributes.
  final verification = cmsVerify(token.cms, token.signer, token.cms.eContent!);
  return TimeStampVerification(
    imprintMatches: imprintMatches,
    signatureValid: verification.signatureValid && verification.digestMatches,
    genTime: token.genTime,
    problem: verification.problem,
  );
}