Post-Quantum Optical Handshake

Given

Alice has PQ sign keypair (sign_pubA, sign_secA), PQ encrypt keypair (enc_pubA, enc_secA), ECC contact keypair (ecc_pubA, ecc_secA) and userhash hashA. Bob has PQ sign keypair (sign_pubB, sign_secB), PQ encrypt keypair (enc_pubB, enc_secB), ECC contact keypair (ecc_pubB, ecc_secB) and userhash hashB.

Optical Handshake

Alice and Bob exchange public ECC keys (ecc_pubA, ecc_pubB) and random nonces (nonceA, nonceB).

Alice signs nonceB with secret key (ecc_secA) and sends it to Bob. Alice also sends hashA and signs of hashA + nonceB with Alice’s secret key. Bob verifies nonceB with Alice’s public key. -> Confirms Alice has ECC key she claims. Bob recieves unencrypted hashA and verifies the signature of hashA + nonceB with Alice’s public key. -> Confirms Alice claims her user hash is hashA and it was singed right now with Bob nonce and Alice secret key.

Bob does the same symmetrically.

sequenceDiagram
    participant Alice
    participant Bob
    
    Note over Alice, Bob: 1) Each side creates a fresh nonce
    Alice->>Alice: Generate nonceA
    Bob->>Bob: Generate nonceB
    
    Note over Alice, Bob: 2) Exchange ECC public keys + nonces
    Alice->>Bob: ecc_pubA, nonceA
    Bob->>Alice: ecc_pubB, nonceB
    
    Note over Alice, Bob: 3) Alice proves key ownership and hash claim
    Note right of Alice: Sign nonceB with ecc_secA
    Note right of Alice: Sign (hashA + nonceB) with ecc_secA
    Alice->>Bob: Sig(nonceB), hashA, Sig(hashA + nonceB)
    
    Note right of Bob: Verify Sig(nonceB) with ecc_pubA
    Note right of Bob: Confirms Alice owns ecc_pubA
    Note right of Bob: Verify Sig(hashA + nonceB) with ecc_pubA
    Note right of Bob: Confirms hashA claim is fresh (bound to nonceB)
    
    Note over Alice, Bob: 4) Bob does the same symmetrically
    Note left of Bob: Sign nonceA with ecc_secB
    Note left of Bob: Sign (hashB + nonceA) with ecc_secB
    Bob->>Alice: Sig(nonceA), hashB, Sig(hashB + nonceA)
    
    Note left of Alice: Verify Sig(nonceA) with ecc_pubB
    Note left of Alice: Verify Sig(hashB + nonceA) with ecc_pubB
    Note left of Alice: Confirms Bob owns ecc_pubB and claims hashB

ContactCandidate

Alice saves hashB and ecc_pubB. When Alice discovers Usercard that has hashB, she checks that Usercard has ecc_pubB. And (optionally) checks ucercard contact_cert (which is a signature of ecc_pubB with Alice sign_secA). ContactCandidate becomes (trusted?) Contact

Bob does the same symmetrically.

sequenceDiagram
    participant Alice
    participant Bob
    
    Note over Alice, Bob: Pre-requisite: Optical Handshake Complete
    Note over Alice, Bob: Each side already stored peer hash + peer ecc_pub
    
    Note over Alice: Stored candidate: (hashB, ecc_pubB)
    Note over Alice: Discovers Usercard(hashB, ecc_pubB, contact_cert?)
    Note over Alice: Check Usercard hashB has matching ecc_pubB
    Note over Alice: Optional check: verify contact_cert
    
    Note over Alice: Promote ContactCandidate -> Trusted Contact
    
    Note over Bob: Symmetric process with (hashA, ecc_pubA)
    Note over Bob: Discover Usercard(hashA, ecc_pubA, contact_cert?)
    Note over Bob: Check hashA and ecc_pubA match stored candidate
    Note over Bob: Optional check: verify contact_cert
    Note over Bob: Promote ContactCandidate -> Trusted Contact