Function encryption_keypair 

pub fn encryption_keypair(
    record_topic: RecordTopic,
    secret_rotation_function: &RotationHandle,
    initial_secret_hash: [u8; 32],
    unix_minute: u64,
) -> SigningKey

Derive Ed25519 key for HPKE encryption/decryption.

Incorporates the secret rotation strategy for time-slot isolation.

Example

let topic = RecordTopic::from_str("my-topic")?;
let rotation = RotationHandle::default();
let enc_key = encryption_keypair(topic, &rotation, initial_hash, 0);