fotisl/ctutils

Javascript Certificate Transparency Utilities

ctutils's Issues

Incorrect SignedCertificateTimestamp encoding/decoding

Good job, Fotis!

But your decoding/encoding of SignedCertificateTimestamp is not precisely correct. Your problem that you missed just one detail in documentation.

So, definition of the SignedCertificateTimestamp class looks like:

struct {
	Version sct_version;
	LogID id;
	uint64 timestamp;
	CtExtensions extensions;
	digitally-signed struct {
		Version sct_version;
		SignatureType signature_type = certificate_timestamp;
		uint64 timestamp;
		LogEntryType entry_type;
		select(entry_type) {
			case x509_entry: ASN.1Cert;
			case precert_entry: PreCert;
		} signed_entry;
		CtExtensions extensions;
	};
} SignedCertificateTimestamp;

And in fact you decoded almost all from the data. Except that you missed that digitally-signed is itself a pre-defined type:

struct {
   SignatureAndHashAlgorithm algorithm;
   opaque signature<0..2^16-1>;
} DigitallySigned;

And the SignatureAndHashAlgorithm has this definition:

enum {
    none(0), md5(1), sha1(2), sha224(3), sha256(4), sha384(5),
    sha512(6), (255)
} HashAlgorithm;

enum { anonymous(0), rsa(1), dsa(2), ecdsa(3), (255) }
  SignatureAlgorithm;

struct {
      HashAlgorithm hash;
      SignatureAlgorithm signature;
} SignatureAndHashAlgorithm;

And when you decode signature like this:

const signature = sctBinView.slice(43 + extLen).buffer;

then you loose information about hashAlgorithm, signatureAlgorithm and correct signatureLength - all these would be in your incorrect block for signature.

For the further reading I do recommend you this link.

Also I want to say that recently I append to PKIjs support for decoding/encoding the SignedCertificateTimestamp class - check it here. There is no verify function there, but probably I would implement it soon.