KDFs: allow for a fixed sized fixed info

[smuellerDD]

According to the SP800-56 series, uPartyInfo and vPartyInfo is required, but there is no requirement about the size other than it must be non-NULL.

However, SP800-56A rev 3 section 5.8.2.1.1 it is required that the components forming the fixed info are either a fixed length bit string or has a form of datalen||data.

When requesting a HKDF test vector with the demo server uPartyInfo||vPartyInfo||literal, we find that the party info strings are not always 32 bytes, but sometimes more.

For the implementation we currently work with we need a fixed size of the party info.

Thus, would it be possible to either allow the vector request to specify the size of the party info or to change the ACVP server to produce always fixed sized party info?