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Message digest and TLS PRF

Algorithm​

This module groups HMAC, HKDF (RFC 5869), and TLS 1.2 PRF / Finished helpers used when implementing or testing TLS key schedules outside the main Connection API.

Purpose​

HMAC, HKDF (SHA-256/384), TLS 1.2 PRF, Finished verify_data, and transcript helpers.

Rust API​

  • Crate: noxtls-crypto
  • Module path (conceptual): noxtls_crypto::hash
  • Primary symbols:
    • noxtls_hmac_sha256
    • noxtls_hmac_sha384
    • noxtls_hmac_sha512
    • noxtls_hkdf_extract_sha256
    • noxtls_hkdf_expand_sha256
    • noxtls_hkdf_extract_sha384
    • noxtls_hkdf_expand_sha384
    • noxtls_tls12_prf_sha256
    • noxtls_tls12_prf_sha384
    • noxtls_tls12_finished_verify_data_sha256
    • noxtls_tls12_finished_verify_data_sha384
    • TlsTranscriptSha256
    • TlsTranscriptSha384

Functions and types:

  • noxtls_hmac_sha256 / noxtls_hmac_sha384 / noxtls_hmac_sha512 — Keyed MAC over a message; fixed tag sizes.
  • noxtls_hkdf_extract_sha256 / noxtls_hkdf_expand_sha256 / noxtls_hkdf_extract_sha384 / noxtls_hkdf_expand_sha384 — Extract then expand key material with domain separation.
  • noxtls_tls12_prf_sha256 / noxtls_tls12_prf_sha384 — TLS 1.2 PRF over secret, label, and seed.
  • noxtls_tls12_finished_verify_data_sha256 / noxtls_tls12_finished_verify_data_sha384 - Parameters: master secret, Finished label, and handshake transcript bytes. Behavior: derives TLS 1.2 Finished-message verify data for handshake validation. Returns: 12-byte verify data output.
  • TlsTranscriptSha256 / TlsTranscriptSha384 — Rolling handshake transcript hashes.

Feature flags and policy​

SHA-384 HKDF/PRF variants are used when the negotiated TLS profile uses SHA-384.

Examples​

HKDF (SHA-256)​

use noxtls_crypto::{noxtls_hkdf_extract_sha256, noxtls_hkdf_expand_sha256};

let salt = b"";
let ikm = b"input key material";
let prk = noxtls_hkdf_extract_sha256(salt, ikm);
let okm = noxtls_hkdf_expand_sha256(&prk, b"my-app-context-v1", 32)?;
assert_eq!(okm.len(), 32);
# Ok::<(), noxtls_core::Error>(())

TLS 1.2 PRF​

use noxtls_crypto::noxtls_tls12_prf_sha256;

let secret = b"master-secret-bytes";
let label = b"key expansion";
let seed = b"client_randomserver_random";
let key_block = noxtls_tls12_prf_sha256(secret, label, seed, 64)?;
# Ok::<(), noxtls_core::Error>(())

Security and compatibility​

Keep HKDF info and TLS labels distinct per protocol version; never reuse PRK across unrelated protocols.