The salt is stored base64-encoded. With the old 10 bytes raw length, it was
always padded to 16 bytes after encoding. We might as well use 12 raw bytes
for the salt, and it's still encoded into 16 bytes.
Similarly for the random nonces, use a raw length that's divisible by 3, so
that there's no padding after base64 encoding. Make the nonces longer while
we're at it. 10 bytes was probably enough to prevent replay attacks, but
there's no reason to be skimpy here.
Per suggestion from Álvaro Hernández Tortosa.
Discussion: https://www.postgresql.org/message-id/df8c6e27-4d8e-5281-96e5-131a4e638fc8@8kdata.com
It doesn't make any immediate difference to PostgreSQL, but might as well
follow the standard, since one exists. (I looked at RFC 5803 earlier, but
didn't fully understand it back then.)
The new format uses Base64 instead of hex to encode StoredKey and
ServerKey, which makes the verifiers slightly smaller. Using the same
encoding for the salt and the keys also means that you only need one
encoder/decoder instead of two. Although we have code in the backend to
do both, we are talking about teaching libpq how to create SCRAM verifiers
for PQencodePassword(), and libpq doesn't currently have any code for hex
encoding.
Bump catversion, because this renders any existing SCRAM verifiers in
pg_authid invalid.
Discussion: https://www.postgresql.org/message-id/351ba574-85ea-d9b8-9689-8c928dd0955d@iki.fi
Per discussion, plain "scram" is confusing because we actually implement
SCRAM-SHA-256 rather than the original SCRAM that uses SHA-1 as the hash
algorithm. If we add support for SCRAM-SHA-512 or some other mechanism in
the SCRAM family in the future, that would become even more confusing.
Most of the internal files and functions still use just "scram" as a
shorthand for SCRMA-SHA-256, but I did change PASSWORD_TYPE_SCRAM to
PASSWORD_TYPE_SCRAM_SHA_256, as that could potentially be used by 3rd
party extensions that hook into the password-check hook.
Michael Paquier did this in an earlier version of the SCRAM patch set
already, but I didn't include that in the version that was committed.
Discussion: https://www.postgresql.org/message-id/fde71ff1-5858-90c8-99a9-1c2427e7bafb@iki.fi
