Skip to main content
Version: 0.2.11

Crypto API: DRBG

NoxTLS uses HmacDrbgSha256 as the deterministic random source for key generation, nonce material, and handshake randomness.

Type​

  • HmacDrbgSha256

Constructor and reseed APIs​

HmacDrbgSha256::new​

pub fn new(entropy: &[u8], nonce: &[u8], personalization: &[u8]) -> Result<Self>
  • entropy: seed entropy; must be at least 16 bytes.
  • nonce: instance nonce.
  • personalization: deployment/application domain separation.

HmacDrbgSha256::reseed​

pub fn reseed(&mut self, entropy: &[u8], additional_input: &[u8]) -> Result<()>
  • entropy: fresh entropy (>=16 bytes).
  • additional_input: optional mixed-in context.
  • Resets reseed counter and internal state.

Output API​

HmacDrbgSha256::generate​

pub fn generate(&mut self, out_len: usize, additional_input: &[u8]) -> Result<Vec<u8>>
  • out_len: number of pseudorandom bytes requested.
  • additional_input: optional per-call context.
  • Returns Error::StateError when reseed is required by counter policy.

Typical call sites​

  • TLS randomness: Connection::send_client_hello_auto.
  • PKC keygen helpers: noxtls_p256_generate_private_key_auto, noxtls_ed25519_generate_private_key_auto, RSA PSS salt generation.

Operational guidance​

  • Keep DRBG state per-security-domain (do not share one instance across unrelated tenants).
  • Reseed after boot entropy refresh, hardware TRNG events, or long-lived sessions.
  • Persisting DRBG state is generally avoided on embedded devices; reseed on startup instead.