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0.1.9 - hybridKEM(kyber + X25519)

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@Cryptophobia Cryptophobia released this 27 Dec 18:18
· 1 commit to main since this release
0.1.9
8eb47fe

[0.1.9] - 2025-12-27

Added

Hybrid KEM (Kyber + X25519)

  • Defense-in-depth cryptography: Shared secret remains secure if at least one of Kyber or X25519 remains secure
  • Robust combiner: SS_hybrid = HKDF(SS_pq || SS_ecdh, "Dice52-Hybrid-SS")
  • Updated RFC specification: Section 3.1 now specifies hybrid KEM construction

New X25519 Functions (All Languages)

Language Key Generation Shared Secret
Go GenerateX25519Keypair() X25519SharedSecret()
Rust generate_x25519_keypair() x25519_shared_secret()
Python generate_x25519_keypair() x25519_shared_secret()
Java Handshake.generateX25519Keypair() Handshake.x25519SharedSecret()

Hybrid Encapsulation API (All Languages)

Language Initiator Responder
Go InitiatorHybridEncapsulate() ResponderHybridDecapsulate()
Rust initiator_hybrid_encapsulate() responder_hybrid_decapsulate()
Python initiator_hybrid_encapsulate() responder_hybrid_decapsulate()
Java Handshake.initiatorHybridEncapsulate() Handshake.responderHybridDecapsulate()

Session X25519 Fields

  • Go: ECDHPub, ECDHPriv, PeerECDHPub fields in Session struct
  • Rust: new_with_ecdh() constructor for explicit X25519 keys
  • Python: ecdh_pub, ecdh_priv, peer_ecdh_pub optional constructor parameters
  • Java: New constructor overload accepting X25519PublicKeyParameters and X25519PrivateKeyParameters

Changed

Hybrid Handshake (Section 6)

  • Initiator now generates ephemeral X25519 key pair alongside Kyber encapsulation
  • Signature covers both Kyber ciphertext and X25519 public key: Sign(SigContext || KyberCT || ECDHPub)
  • HandshakeMessage includes ECDHPub field

Hybrid Ratchet (Section 12)

  • Ratchet initiator generates both Kyber and X25519 key pairs
  • RatchetMessage includes ECDHPub field for X25519 public key
  • Signature covers both Kyber public key and X25519 public key
  • Chain key assignment now correctly swaps for initiator vs responder

Documentation

  • Updated README with hybrid KEM examples for Go and Rust
  • Updated all demo files to demonstrate hybrid encapsulation flow
  • RFC Section 3.1 updated to specify hybrid KEM algorithm
  • RFC Section 15 updated with hybrid KEM security properties

Dependencies

Language New Dependency Purpose
Go github.com/cloudflare/circl/dh/x25519 X25519 ECDH
Rust x25519-dalek = "2.0" X25519 ECDH
Python cryptography X25519 via pyca/cryptography
Java (Bouncy Castle already includes) X25519 via BC
Assets 2
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