protocol.md

QKD-KEM Protocol Specification

Protocol Flow

Key Generation (Alice)

Alice initiates the protocol by generating the key pair and retrieving initial QKD material:

1. Generates KEM keypair qkd_kem_key_new()
2. Initializes QKD context as initiator via init_qkd_context(true)
3. Retrieves QKD key identifier:
   • ETSI 004: Calls OPEN_CONNECT() to establish session and gets key ID
   • ETSI 014: Calls GET_KEY() to obtain both key and key ID
4. Transmits both public key and QKD key ID to Bob

Encapsulation (Bob)

Bob performs encapsulation upon receiving Alice's public key and QKD key ID:

1. Calls oqs_qkd_kem_encaps()
2. Initializes QKD context as responder via init_qkd_context(false)
3. For ETSI 004:
   • Establishes session with OPEN_CONNECT()
   • Retrieves QKD key using GET_KEY(key_id)
4. For ETSI 014:
   • Retrieves QKD key using GET_KEY_WITH_IDS()
5. Performs PQ encapsulation via oqs_qs_kem_encaps_keyslot()

Decapsulation (Alice)

Alice performs decapsulation upon receiving Bob's ciphertext:

1. Calls oqs_qkd_kem_decaps()
2. For ETSI 004: Retrieves QKD key using GET_KEY(key_id)
3. Recovers PQ shared secret via oqs_qs_kem_decaps_keyslot()