Module hashing 

Secret hashing, key providers, domain separation, and key versioning (RFC-004).

Every persisted secret (code, session, form token) is stored only as a keyed HMAC LookupKey, never in plaintext (INV-1). Lookup keys are domain-separated so the same plaintext used in two roles derives two different keys, and every derivation is tagged with the KeyVersion of the key that produced it so keys can be rotated without an all-or-nothing migration (RFC-004 §12.2).

Derivation scheme (prefixing — RFC-004 §9.1 recommendation)

message = "codlet/v1/lookup" || 0x00 || domain_label || 0x00 || secret_bytes
LookupKey = lowercase_hex( HMAC-SHA256(key_bytes, message) )

The fixed context string and 0x00 separators make the label and secret unambiguous, so distinct domains cannot collide. This is intentionally not the zinnias-ciao derivation (HMAC(pepper, value) with no domain or prefix); the migration adapter (RFC-014) supplies a legacy mode for existing rows.

Structs

HmacKeyRef

A borrowed HMAC key plus the version that identifies it.

KeyVersion

Identifier of the key version that produced a LookupKey. Stored beside every lookup key (RFC-004 §12.2). Not secret.

LookupKey

A keyed lookup value: the lowercase-hex HMAC of a domain-separated message.

SecretHasher

Derives LookupKeys from secrets using a KeyProvider.

StaticKeyProvider

A key provider holding an active key and zero or more previous keys, in memory. Suitable for production when constructed from real secret material loaded at startup, and for tests/examples.

Enums

SecretDomain

The role a secret plays. Part of the HMAC message, so it cross-namespaces lookup keys (RFC-004 §12.1).

Traits

KeyProvider

Supplies HMAC key material. Synchronous, so key lookup does not couple to a web/runtime async model (RFC-004 §3.3). No fallback key exists: missing material is an error (INV-2, SR-29).