Module challenge 

Constants

MAX_MESSAGES

Fixed number of message ID entries to return in privacy-preserving fetch

Functions

decrypt_message_id

Symmetric decryption for message IDs using ChaCha20-Poly1305

derive_challenge_key

Derive symmetric key used for ChaCha20-Poly1305 challenge encryption

encrypt_message_id

Symmetric encryption for message IDs using ChaCha20-Poly1305