This implements encoding of the structure defined in
<https://tools.ietf.org/html/rfc6962#section-3.2>.
IMPORTANT: Because SCT records timestamps in milliseconds
rather than seconds, this module requires a 64-bit Perl interpreter.
<https://letsencrypt.org/2018/04/04/sct-encoding.html> has an excellent
walkthrough of the format that this module deals with.
For now this always encodes a version 1 structure.
%opts is:
- "key_id" - 32-byte string
- "timestamp" - integer (NB:
milliseconds)
- "hash_algorithm" - See
<https://tools.ietf.org/html/rfc5246#section-7.4.1.4.1> for allowed
values (e.g., "sha256").
- "signature_algorithm" - Currently
accepted values are "rsa" and
"ecdsa". (cf. the URL for
"hash_algorithm" values)
- "signature" - The signature (binary
string).