Cryptographic Architecture

KyberChat is built to survive the transition into the quantum computing era. Traditional encryption standards (like RSA, ECC, and ECDH) rely on mathematical complexities that could be cracked in seconds by a sufficiently powerful quantum computer. KyberChat implements a zero-knowledge relay model, ensuring that the server never holds, reads, or exposes your messages, contacts, or encryption keys.

Our core cryptographic shield implements ML-KEM-768 (FIPS 203), a lattice-based post-quantum key agreement algorithm. By layering ML-KEM on top of existing ECDH protocols, we prevent "Harvest Now, Decrypt Later" threats—where state-sponsored entities collect encrypted internet traffic today to decrypt it once quantum hardware matures.

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  Security Reserve: If either ECDH or ML-KEM is mathematically compromised in the future, your communications remain completely secure as long as the other algorithm holds.
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  NIST Standardization: Built strictly in conformance with modern security practices and peer-reviewed quantum standards.

BIP39 Identity

Your identity is not linked to sensitive personal info like phone numbers or emails. Instead, it is a 24-word seed phrase. This master entropy source is generated locally on your device and enables complete account recovery without central databases.

CSPRNG (256 bits) -> BIP39 Mnemonic (24 words)
Seed = PBKDF2-HMAC-SHA512(Mnemonic, salt="mnemonic", 2048 iters)

Deterministic Derivation

Every key used in our chat protocol is deterministically derived from your master seed using HKDF-SHA256, separating security domains clearly:

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  kyberchat-uuid: Generates your persistent User UUID.
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  kyberchat-identity-key: Derives your X25519 Identity Keypair.
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  kyberchat-signing-key: Derives your Ed25519 Signing Keypair.
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  kyberchat-kem-seed: Derives the 64-byte private seed for ML-KEM-768.

To establish secure sessions without an online third party, KyberChat executes a customized Extended Triple Diffie-Hellman (X3DH) handshake, hybridized with post-quantum key encapsulation:

Where:

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  DH1...DH3 represent ECDH operations between Identity, Signed Pre-Keys, and Ephemeral Keys.
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  DH4 is an optional ECDH step using a One-Time Pre-Key (OTPK) to provide forward secrecy.
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  KEM_SS is the 32-byte shared secret generated via ML-KEM-768 encapsulation against the recipient's public key.

Once the initial session key (SK) is established, the Double Ratchet protocol rotates keys for every message, ensuring perfect forward secrecy and cryptographic self-healing:

Diffie-Hellman Ratchet

Every response triggers an ECDH exchange, constantly introducing new, un-predictable entropy to heal the connection if any previous keys were compromised.

Symmetric Ratchet

Separate message keys are derived for sending and receiving using HMAC-SHA256, and are immediately deleted from device memory once a message is processed:

MessageKey = HMAC-SHA256(ChainKey, 0x01)
NextChainKey = HMAC-SHA256(ChainKey, 0x02)

Authenticated GCM Encryption: Plaintexts are encrypted using AES-256-GCM, providing tamper-resistant, authenticated confidentiality.

Traffic Analysis Defense: To defeat network-level pattern and length matching, every encrypted frame is padded to exactly 1024 Bytes before transmitting. An eavesdropper watching the network sees only a uniform stream of identical packets—protecting your communication profile from traffic metadata analyses.