Post-Quantum Encryption in PHP

A production-grade hybrid post-quantum encryption example using ML-KEM-768 (FIPS 203, formerly Kyber) and AES-256-GCM, implemented in PHP via liboqs FFI bindings.

Why Post-Quantum?

RSA and elliptic-curve cryptography (ECDH, ECDSA) can be broken by a sufficiently powerful quantum computer running Shor's algorithm. ML-KEM is the NIST-standardized replacement for key exchange, designed to resist both classical and quantum attacks.

This project demonstrates how to use ML-KEM in PHP today.

How It Works

The encryption follows a hybrid KEM + symmetric pattern, which is the standard approach for post-quantum encryption:

┌─────────────────────────────────────────────────────────┐
│                    SENDER                                │
│                                                         │
│  1. ML-KEM-768 Encapsulate(publicKey)                   │
│     → sharedSecret (32 bytes)                           │
│     → kemCiphertext (1088 bytes)                        │
│                                                         │
│  2. AES-256-GCM Encrypt(plaintext, sha256(sharedSecret))│
│     → aesCiphertext + iv + tag                          │
│                                                         │
│  3. Output: kemCiphertext || iv || tag || aesCiphertext  │
└─────────────────────────────────────────────────────────┘

┌─────────────────────────────────────────────────────────┐
│                    RECEIVER                              │
│                                                         │
│  1. ML-KEM-768 Decapsulate(kemCiphertext, secretKey)    │
│     → sharedSecret (32 bytes)                           │
│                                                         │
│  2. AES-256-GCM Decrypt(aesCiphertext, sha256(secret))  │
│     → plaintext                                         │
└─────────────────────────────────────────────────────────┘

Algorithm Details

Component	Algorithm	Purpose
Key Encapsulation	ML-KEM-768 (NIST Level 3)	Quantum-resistant key exchange
Symmetric Encryption	AES-256-GCM	Authenticated encryption of message data
Key Derivation	SHA-256	Derive AES key from KEM shared secret

ML-KEM-768 Parameters

Parameter	Size
Public Key	1,184 bytes
Secret Key	2,400 bytes
KEM Ciphertext	1,088 bytes
Shared Secret	32 bytes

Quick Start

Run with Docker

docker build -t pqc-php .
docker run --rm pqc-php

Example Output

Post-Quantum Encryption (Production)
==================================================
Algorithm:       ML-KEM-768
NIST Level:      3
Public Key:      1184 bytes
Secret Key:      2400 bytes
KEM Ciphertext:  1088 bytes
Shared Secret:   32 bytes
==================================================

Keypair generated.
Encrypted "hello world" -> 1127 bytes
Payload (hex):
5afc9c0178118bb27c280bc1dae51efc4c3a16560c6042fae3b0d8deb3924fe8...

Decrypted: "hello world"
Match:     YES

API Usage

$pqc = new PostQuantumEncryption();

// Generate a keypair
$keys = $pqc->generateKeypair();
// $keys['publicKey'] - share this with the sender
// $keys['secretKey'] - keep this private

// Encrypt (sender side)
$encrypted = $pqc->encrypt('secret message', $keys['publicKey']);

// Decrypt (receiver side)
$decrypted = $pqc->decrypt($encrypted, $keys['secretKey']);

Security Features

• NIST-standardized algorithm: ML-KEM-768 (FIPS 203), not an experimental or deprecated scheme
• Battle-tested implementation: Uses liboqs (Open Quantum Safe), a widely reviewed C library
• Authenticated encryption: AES-256-GCM provides both confidentiality and integrity
• Key material zeroisation: Shared secrets and derived keys are wiped from memory via FFI::memset and sodium_memzero in finally blocks, guaranteeing cleanup on all exit paths
• No custom cryptography: All crypto primitives come from liboqs and OpenSSL

Payload Format

The encrypted output is a single binary string:

[ KEM Ciphertext (1088 bytes) ][ IV (12 bytes) ][ GCM Tag (16 bytes) ][ AES Ciphertext ]

Requirements

• PHP 8.3+ with FFI and OpenSSL extensions
• liboqs 0.12.0+ (built automatically by the Dockerfile)
• libsodium (for sodium_memzero, included in PHP by default)

Project Structure

.
├── Dockerfile            # Builds PHP + liboqs environment
├── pqc_encryption.php    # PostQuantumEncryption class + demo
└── README.md

License

MIT