pub const MIN_FIPS_DIGEST_LEN: usize = 4;Expand description
Per FIPS 140-2 IG A.8 Use of a truncated HMAC (matching NIST SP 800-107-r1 Section 5.3.3. Truncation of HMAC), says that the minimum truncation of a HMAC for tagging should be 32 bits; this exceeds the lower bound set by IETF RFC 2104 Section 5 Truncated output, which sets the lower bound to be half of the hash’s length and no fewer than 80 bits.
However, as we feel there should be a minimum limit (and have an author work around this via explicit truncation manually afterwards), but not be too strict about it, = 32 bits / 8 = 4 bytes;