Struct KeyHasher 

pub struct KeyHasher { /* private fields */ }

Derives opaque subject keys using HMAC-SHA-256.

Each derivation is domain-separated by the exact policy and scope identifiers. The same normalized subject therefore yields unrelated keys in different policy scopes.

Applications should keep one stable secret per deployment. Rotating it deliberately starts new counters because all derived subject keys change.

The raw secret is not retained after construction. Instead, the hasher caches key-equivalent, precomputed HMAC state. Cloning a hasher copies that state; each copy zeroizes its SHA-256 state and buffered input when dropped. Treat a live KeyHasher as secret material. Debug never exposes its state.

Implementations

impl KeyHasher

pub const MINIMUM_SECRET_LENGTH: usize = 32

Minimum accepted secret length in bytes.

pub fn new(secret: impl AsRef<[u8]>) -> Result<Self, KeyHasherError>

Constructs a hasher by precomputing zeroizing keyed HMAC state.

The supplied raw secret is borrowed only for construction and is not retained by the returned hasher.

Errors

Returns KeyHasherError::SecretTooShort unless the secret contains at least 32 bytes.

pub fn hash( &self, policy_id: &PolicyId, scope_id: &ScopeId, subject: impl AsRef<[u8]>, ) -> SubjectKey

Hashes a normalized subject within an explicit policy and scope.

Normalization is application-owned: two byte strings are treated as distinct subjects even if an application considers them equivalent.

pub fn hash_for<P: RateLimitPolicy + ?Sized>( &self, policy: &P, subject: impl AsRef<[u8]>, ) -> SubjectKey

Hashes a normalized subject in a rate-limit policy’s namespace.

Trait Implementations

impl Clone for KeyHasher

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for KeyHasher

fn fmt(&self, formatter: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.