Module hmac 

HMAC_DRBG — SP 800-90A Rev.1 §10.1.2.

Generic over any [tessera::Digest], driving tessera::hmac; used in practice over HMAC-SHA-256 / -384 / -512. Both the state size and the output block equal the digest’s output length outlen.

Parameters (SP 800-90A §10.1, Table 2)

Hash	security_strength	outlen (octets)
SHA-1	128	20
SHA-224	192	28
SHA-256	256	32
SHA-384	256	48
SHA-512	256	64

reseed_interval = 2^48, max_number_of_bits_per_request = 2^19.

Side-channel posture

(K, V) are secret. The construction is branch-free by shape: the only value-dependent control flow is the provided_data.is_empty() test of the Update (§10.1.2.2), which is on the (public) presence of additional input, not on secret content. HMAC-SHA-2 inherits the carry-based DPA of T2-D (see crate::drbg); no table lookup on secret data.

Structs

HmacDrbg

HMAC_DRBG internal state (SP 800-90A §10.1.2.1): (K, V) each outlen octets, plus the reseed_counter. K and V are secret.