KeyDerivationExtensions

Namespace: WvdS.System.Security.Cryptography.KeyDerivation

Static class for Key Derivation Functions with Post-Quantum support. Supports HKDF, PBKDF2 and Argon2id.

Supported KDF algorithms:

Derives keys from a shared secret (HKDF-Extract-then-Expand).

// ML-KEM Shared Secret from Key Exchange
byte[] sharedSecret = session.SharedSecret;
 
// Standard derivation (SHA-256)
byte[] aesKey = KeyDerivationExtensions.DeriveKey(
    sharedSecret,
    outputLength: 32);  // 256 bit
 
// With salt and context info
byte[] salt = RandomNumberGenerator.GetBytes(32);
byte[] info = Encoding.UTF8.GetBytes("MyApp-Session-Key");
 
byte[] sessionKey = KeyDerivationExtensions.DeriveKey(
    sharedSecret,
    outputLength: 32,
    salt: salt,
    info: info,
    hashAlgorithm: HashAlgorithmName.SHA384);  // Optional

Extracts PRK (Pseudorandom Key) from Input Key Material.

byte[] inputKeyMaterial = GetSharedSecret();
byte[] salt = RandomNumberGenerator.GetBytes(32);
 
byte[] prk = KeyDerivationExtensions.HkdfExtract(
    inputKeyMaterial,
    salt: salt,
    hashAlgorithm: HashAlgorithmName.SHA256);
 
// PRK has same length as hash output (32 bytes for SHA-256)

Expands PRK to Output Key Material.

byte[] prk = GetPrk();
 
// Encryption Key
byte[] encKey = KeyDerivationExtensions.HkdfExpand(
    prk,
    outputLength: 32,
    info: Encoding.UTF8.GetBytes("encryption"));
 
// MAC Key
byte[] macKey = KeyDerivationExtensions.HkdfExpand(
    prk,
    outputLength: 32,
    info: Encoding.UTF8.GetBytes("mac"));

Combines classical (ECDH/DH) and PQ (ML-KEM) shared secrets.

byte[] ecdhSecret = GetEcdhSharedSecret();
byte[] mlKemSecret = GetMlKemSharedSecret();
 
// Hybrid mode: Both secrets are combined
byte[] hybridKey = KeyDerivationExtensions.DeriveHybridKey(
    classicSecret: ecdhSecret,
    pqSecret: mlKemSecret,
    outputLength: 32,
    mode: CryptoMode.Hybrid);
 
// Classic only
byte[] classicKey = KeyDerivationExtensions.DeriveHybridKey(
    classicSecret: ecdhSecret,
    pqSecret: null,
    outputLength: 32,
    mode: CryptoMode.Classic);
 
// Post-Quantum only
byte[] pqKey = KeyDerivationExtensions.DeriveHybridKey(
    classicSecret: null,
    pqSecret: mlKemSecret,
    outputLength: 32,
    mode: CryptoMode.PostQuantum);
 
// Custom Info
byte[] customKey = KeyDerivationExtensions.DeriveHybridKey(
    classicSecret: ecdhSecret,
    pqSecret: mlKemSecret,
    outputLength: 64,
    mode: CryptoMode.Hybrid,
    info: Encoding.UTF8.GetBytes("MyProtocol-v1"));

Key combination:

Hybrid Mode:
  IKM = classicSecret || pqSecret
  Key = HKDF-SHA256(IKM, info="WvdS-Hybrid-Key")

Derives multiple keys for different purposes.

using HybridKeyMaterial keyMaterial = KeyDerivationExtensions.DeriveHybridKeyMaterial(
    classicSecret: ecdhSecret,
    pqSecret: mlKemSecret,
    mode: CryptoMode.Hybrid);
 
// Usage
byte[] encKey = keyMaterial.EncryptionKey;  // 32 bytes
byte[] macKey = keyMaterial.MacKey;         // 32 bytes
byte[] iv = keyMaterial.Iv;                 // 16 bytes
byte[] authKey = keyMaterial.AuthKey;       // 32 bytes
 
// IDisposable: Keys are securely erased

string password = "SecurePassword123!";
byte[] salt = RandomNumberGenerator.GetBytes(32);
 
// Standard PBKDF2
byte[] key = KeyDerivationExtensions.Pbkdf2(
    password,
    salt,
    iterations: 100000,
    outputLength: 32);
 
// With PQ entropy (additional protection)
byte[] pqEntropy = GetPqEntropy();
 
byte[] enhancedKey = KeyDerivationExtensions.Pbkdf2(
    password,
    salt,
    iterations: 100000,
    outputLength: 32,
    pqEntropy: pqEntropy,  // Combined with salt
    hashAlgorithm: HashAlgorithmName.SHA512);

PBKDF2 with PQ-enhanced salt (public key is included in salt calculation).

string password = "UserPassword";
byte[] baseSalt = RandomNumberGenerator.GetBytes(16);
byte[] mlKemPublicKey = GetRecipientPublicKey();
 
// Salt = SHA256(baseSalt || pqPublicKey)
byte[] key = KeyDerivationExtensions.Pbkdf2WithPqSalt(
    password,
    baseSalt,
    mlKemPublicKey,
    iterations: 100000,
    outputLength: 32);

Argon2id via OpenSSL 3.6 - resistant against GPU/ASIC attacks.

byte[] password = Encoding.UTF8.GetBytes("SecurePassword");
byte[] salt = RandomNumberGenerator.GetBytes(16);  // Minimum 16 bytes
 
byte[] key = KeyDerivationExtensions.Argon2id(
    password,
    salt,
    outputLength: 32,     // Key length
    iterations: 3,        // Time cost (t)
    memoryKiB: 65536,     // Memory: 64 MB
    parallelism: 4);      // Threads (p)

string password = "UserPassword123";
byte[] salt = RandomNumberGenerator.GetBytes(16);
 
byte[] key = KeyDerivationExtensions.Argon2id(
    password,
    salt,
    outputLength: 32,
    iterations: 3,
    memoryKiB: 65536,
    parallelism: 4);

Recommended parameters:

byte[] preMasterSecret = GetPreMasterSecret();
byte[] clientRandom = GetClientRandom();
byte[] serverRandom = GetServerRandom();
 
using TlsKeyMaterial keys = KeyDerivationExtensions.DeriveTlsKeys(
    preMasterSecret,
    clientRandom,
    serverRandom,
    mode: CryptoMode.Hybrid);
 
// Usage
var clientKey = keys.ClientWriteKey;   // 32 bytes
var serverKey = keys.ServerWriteKey;   // 32 bytes
var clientIv = keys.ClientWriteIv;     // 12 bytes
var serverIv = keys.ServerWriteIv;     // 12 bytes

TLS 1.3 compatible key schedule.

byte[]? pskSecret = null;  // Pre-Shared Key (optional)
byte[] ecdhSecret = GetEcdhSecret();
byte[] pqSecret = GetMlKemSecret();
byte[] clientHello = GetClientHelloBytes();
byte[] serverHello = GetServerHelloBytes();
 
using Tls13KeySchedule schedule = KeyDerivationExtensions.DeriveTls13Keys(
    pskSecret,
    ecdhSecret,
    pqSecret,
    clientHello,
    serverHello,
    mode: CryptoMode.Hybrid);
 
// Handshake Traffic Secrets
var clientHsSecret = schedule.ClientHandshakeTrafficSecret;
var serverHsSecret = schedule.ServerHandshakeTrafficSecret;
 
// Application Traffic Secrets
var clientAppSecret = schedule.ClientApplicationTrafficSecret;
var serverAppSecret = schedule.ServerApplicationTrafficSecret;
 
// Resumption Secret
var resumptionSecret = schedule.ResumptionMasterSecret;

Container for derived keys with secure memory cleanup.

using HybridKeyMaterial keys = DeriveKeys();
 
// Keys are securely erased on Dispose()
// (CryptographicOperations.ZeroMemory)

TLS 1.2 style key material.

TLS 1.3 key schedule.

using WvdS.System.Security.Cryptography;
using WvdS.System.Security.Cryptography.KeyDerivation;
using WvdS.System.Security.Cryptography.KeyExchange;
 
// 1. Perform key exchange
using var session = new KeyExchangeService();
await session.InitiateKeyExchangeAsync(recipientPublicKey, CryptoMode.Hybrid);
 
// 2. Derive hybrid key material
using HybridKeyMaterial keys = KeyDerivationExtensions.DeriveHybridKeyMaterial(
    classicSecret: session.ClassicSharedSecret,
    pqSecret: session.PqSharedSecret,
    mode: CryptoMode.Hybrid);
 
// 3. Use the keys
using var aes = Aes.Create();
aes.Key = keys.EncryptionKey;
 
using var hmac = new HMACSHA256(keys.MacKey);
 
// 4. Perform encryption
// ...
 
// 5. Keys are automatically securely erased

• KeyDerivation Namespace
• HybridKeyMaterial
• TlsKeyMaterial
• Tls13KeySchedule
• KeyExchange Namespace
• Encryption Namespace
• ML-KEM Algorithm

Wolfgang van der Stille @ EMSR DATA d.o.o. - Post-Quantum Cryptography Professional