Enum MessageKeyGenerator 

pub enum MessageKeyGenerator {
    Seed(([u8; 32], u32)),
    Serialized(MessageKey),
}

Lazy message key generator that defers key derivation and avoids re-serialization.

This enum enables two optimizations:

1. Lazy derivation: Keys are only derived from seed when actually needed for encryption
2. Zero-cost round-trip: Keys loaded from protobuf are kept in serialized form and returned as-is when saving, avoiding unnecessary deserialization and re-serialization

Variants

Seed(([u8; 32], u32))

Seed for lazy derivation - keys derived on demand

Serialized(MessageKey)

Original protobuf - zero-cost pass-through on save

Implementations

impl MessageKeyGenerator

pub fn new_from_seed(seed: &[u8; 32], counter: u32) -> Self

pub fn generate_keys(self) -> MessageKeys

Generate the actual MessageKeys, deriving them if necessary. This is called when keys are needed for actual encryption/decryption.

pub fn into_pb(self) -> MessageKey

Convert to protobuf format for storage. Zero-cost for Serialized variant (pass-through), allocates for others.

The seed is persisted next to the keys it derives: the derivation is one-way, so a record that kept only the derived keys could never be projected back into a seed-based external format.

pub fn from_pb(pb: MessageKey) -> Result<Self, &'static str>

Load from protobuf without parsing - keeps original bytes for zero-cost round-trip.

pub fn counter(&self) -> u32

Get the counter/index without fully parsing the keys.