====== KeyDerivationExtensions ======

**Namespace:** ''WvdS.System.Security.Cryptography.KeyDerivation''

Classe statica per la derivazione delle chiavi (Key Derivation Functions) con supporto Post-Quantum. Supporta HKDF, PBKDF2 e Argon2id.

===== Panoramica =====

Algoritmi KDF supportati:

^ KDF ^ Standard ^ Utilizzo ^
| HKDF | RFC 5869 | Chiavi di sessione da Shared Secrets |
| PBKDF2 | RFC 8018 | Chiavi basate su password |
| Argon2id | RFC 9106 | KDF memory-hard (password) |

===== HKDF - Hash-based Key Derivation =====

==== DeriveKey ====

Deriva chiavi da un Shared Secret (HKDF-Extract-then-Expand).

<code csharp>
// ML-KEM Shared Secret da Key Exchange
byte[] sharedSecret = session.SharedSecret;

// Derivazione standard (SHA-256)
byte[] aesKey = KeyDerivationExtensions.DeriveKey(
    sharedSecret,
    outputLength: 32);  // 256 Bit

// Con Salt e 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);  // Opzionale
</code>

==== HkdfExtract ====

Estrae PRK (Pseudorandom Key) da Input Key Material.

<code csharp>
byte[] inputKeyMaterial = GetSharedSecret();
byte[] salt = RandomNumberGenerator.GetBytes(32);

byte[] prk = KeyDerivationExtensions.HkdfExtract(
    inputKeyMaterial,
    salt: salt,
    hashAlgorithm: HashAlgorithmName.SHA256);

// PRK ha la stessa lunghezza dell'output Hash (32 Bytes per SHA-256)
</code>

==== HkdfExpand ====

Espande PRK a Output Key Material.

<code csharp>
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"));
</code>

===== Hybrid Key Derivation =====

Combina Shared Secrets classici (ECDH/DH) e PQ (ML-KEM).

==== DeriveHybridKey ====

<code csharp>
byte[] ecdhSecret = GetEcdhSharedSecret();
byte[] mlKemSecret = GetMlKemSharedSecret();

// Modalita ibrida: entrambi i secrets vengono combinati
byte[] hybridKey = KeyDerivationExtensions.DeriveHybridKey(
    classicSecret: ecdhSecret,
    pqSecret: mlKemSecret,
    outputLength: 32,
    mode: CryptoMode.Hybrid);

// Solo classico
byte[] classicKey = KeyDerivationExtensions.DeriveHybridKey(
    classicSecret: ecdhSecret,
    pqSecret: null,
    outputLength: 32,
    mode: CryptoMode.Classic);

// Solo Post-Quantum
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"));
</code>

**Combinazione chiavi:**

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

==== DeriveHybridKeyMaterial ====

Deriva piu chiavi per scopi diversi.

<code csharp>
using HybridKeyMaterial keyMaterial = KeyDerivationExtensions.DeriveHybridKeyMaterial(
    classicSecret: ecdhSecret,
    pqSecret: mlKemSecret,
    mode: CryptoMode.Hybrid);

// Utilizzo
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: le chiavi vengono cancellate in modo sicuro
</code>

===== PBKDF2 - Derivazione basata su password =====

==== Pbkdf2 ====

<code csharp>
string password = "SecurePassword123!";
byte[] salt = RandomNumberGenerator.GetBytes(32);

// PBKDF2 standard
byte[] key = KeyDerivationExtensions.Pbkdf2(
    password,
    salt,
    iterations: 100000,
    outputLength: 32);

// Con PQ-Entropy (protezione aggiuntiva)
byte[] pqEntropy = GetPqEntropy();

byte[] enhancedKey = KeyDerivationExtensions.Pbkdf2(
    password,
    salt,
    iterations: 100000,
    outputLength: 32,
    pqEntropy: pqEntropy,  // Viene combinato con Salt
    hashAlgorithm: HashAlgorithmName.SHA512);
</code>

==== Pbkdf2WithPqSalt ====

PBKDF2 con Salt rinforzato PQ (la chiave pubblica viene inclusa nel calcolo del Salt).

<code csharp>
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);
</code>

<note tip>
**Vantaggio:** Anche con password e Base-Salt identici, si ottiene una chiave diversa per ogni destinatario (chiave pubblica PQ diversa).
</note>

===== Argon2id - Memory-Hard KDF =====

Argon2id via OpenSSL 3.6 - resistente agli attacchi GPU/ASIC.

==== Argon2id (Byte-Array) ====

<code csharp>
byte[] password = Encoding.UTF8.GetBytes("SecurePassword");
byte[] salt = RandomNumberGenerator.GetBytes(16);  // Minimo 16 Bytes

byte[] key = KeyDerivationExtensions.Argon2id(
    password,
    salt,
    outputLength: 32,     // Lunghezza chiave
    iterations: 3,        // Costo temporale (t)
    memoryKiB: 65536,     // Memoria: 64 MB
    parallelism: 4);      // Thread (p)
</code>

==== Argon2id (String) ====

<code csharp>
string password = "UserPassword123";
byte[] salt = RandomNumberGenerator.GetBytes(16);

byte[] key = KeyDerivationExtensions.Argon2id(
    password,
    salt,
    outputLength: 32,
    iterations: 3,
    memoryKiB: 65536,
    parallelism: 4);
</code>

**Parametri raccomandati:**

^ Applicazione ^ Iterations (t) ^ Memory (m) ^ Parallelism (p) ^
| Hashing password | 3 | 64 MB | 4 |
| Alta sicurezza | 4 | 256 MB | 4 |
| Low-Memory | 4 | 16 MB | 4 |

===== TLS Key Derivation =====

==== DeriveTlsKeys (stile TLS 1.2) ====

<code csharp>
byte[] preMasterSecret = GetPreMasterSecret();
byte[] clientRandom = GetClientRandom();
byte[] serverRandom = GetServerRandom();

using TlsKeyMaterial keys = KeyDerivationExtensions.DeriveTlsKeys(
    preMasterSecret,
    clientRandom,
    serverRandom,
    mode: CryptoMode.Hybrid);

// Utilizzo
var clientKey = keys.ClientWriteKey;   // 32 Bytes
var serverKey = keys.ServerWriteKey;   // 32 Bytes
var clientIv = keys.ClientWriteIv;     // 12 Bytes
var serverIv = keys.ServerWriteIv;     // 12 Bytes
</code>

==== DeriveTls13Keys ====

Key Schedule compatibile TLS 1.3.

<code csharp>
byte[]? pskSecret = null;  // Pre-Shared Key (opzionale)
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;
</code>

===== Classi dati =====

==== HybridKeyMaterial ====

Contenitore per chiavi derivate con pulizia sicura della memoria.

^ Proprieta ^ Tipo ^ Lunghezza ^ Descrizione ^
| ''EncryptionKey'' | byte[] | 32 | Chiave AES |
| ''MacKey'' | byte[] | 32 | Chiave HMAC |
| ''Iv'' | byte[] | 16 | Vettore di inizializzazione |
| ''AuthKey'' | byte[] | 32 | Chiave di autenticazione |

<code csharp>
using HybridKeyMaterial keys = DeriveKeys();

// Le chiavi vengono cancellate in modo sicuro con Dispose()
// (CryptographicOperations.ZeroMemory)
</code>

==== TlsKeyMaterial ====

Materiale chiavi stile TLS 1.2.

^ Proprieta ^ Tipo ^ Descrizione ^
| ''MasterSecret'' | byte[] | Master Secret 48 Bytes |
| ''ClientWriteKey'' | byte[] | Chiave di crittografia lato client |
| ''ServerWriteKey'' | byte[] | Chiave di crittografia lato server |
| ''ClientWriteIv'' | byte[] | IV lato client |
| ''ServerWriteIv'' | byte[] | IV lato server |
| ''ClientWriteMacKey'' | byte[] | MAC Key client (vuoto per GCM) |
| ''ServerWriteMacKey'' | byte[] | MAC Key server (vuoto per GCM) |

==== Tls13KeySchedule ====

TLS 1.3 Key Schedule.

^ Proprieta ^ Tipo ^ Descrizione ^
| ''ClientHandshakeTrafficSecret'' | byte[]? | Client Handshake Traffic Secret |
| ''ServerHandshakeTrafficSecret'' | byte[]? | Server Handshake Traffic Secret |
| ''ClientApplicationTrafficSecret'' | byte[]? | Client Application Traffic Secret |
| ''ServerApplicationTrafficSecret'' | byte[]? | Server Application Traffic Secret |
| ''ResumptionMasterSecret'' | byte[]? | Session Resumption Secret |

===== Panoramica metodi =====

==== HKDF ====

^ Metodo ^ Parametri ^ Ritorno ^
| ''DeriveKey'' | byte[] sharedSecret, int outputLength, byte[]? salt, byte[]? info, HashAlgorithmName? | byte[] |
| ''HkdfExtract'' | byte[] ikm, byte[]? salt, HashAlgorithmName? | byte[] |
| ''HkdfExpand'' | byte[] prk, int outputLength, byte[]? info, HashAlgorithmName? | byte[] |

==== Hybrid ====

^ Metodo ^ Parametri ^ Ritorno ^
| ''DeriveHybridKey'' | byte[]? classicSecret, byte[]? pqSecret, int outputLength, CryptoMode, byte[]? info | byte[] |
| ''DeriveHybridKeyMaterial'' | byte[]? classicSecret, byte[]? pqSecret, CryptoMode | HybridKeyMaterial |

==== PBKDF2 ====

^ Metodo ^ Parametri ^ Ritorno ^
| ''Pbkdf2'' | string password, byte[] salt, int iterations, int outputLength, byte[]? pqEntropy, HashAlgorithmName? | byte[] |
| ''Pbkdf2WithPqSalt'' | string password, byte[] baseSalt, byte[] pqPublicKey, int iterations, int outputLength | byte[] |

==== Argon2id ====

^ Metodo ^ Parametri ^ Ritorno ^
| ''Argon2id'' | byte[] password, byte[] salt, int outputLength, int iterations, int memoryKiB, int parallelism | byte[] |
| ''Argon2id'' | string password, byte[] salt, int outputLength, int iterations, int memoryKiB, int parallelism | byte[] |

==== TLS ====

^ Metodo ^ Parametri ^ Ritorno ^
| ''DeriveTlsKeys'' | byte[] preMasterSecret, byte[] clientRandom, byte[] serverRandom, CryptoMode | TlsKeyMaterial |
| ''DeriveTls13Keys'' | byte[]? psk, byte[]? ecdh, byte[]? pq, byte[] clientHello, byte[] serverHello, CryptoMode | Tls13KeySchedule |

===== Esempio completo =====

<code csharp>
using WvdS.System.Security.Cryptography;
using WvdS.System.Security.Cryptography.KeyDerivation;
using WvdS.System.Security.Cryptography.KeyExchange;

// 1. Eseguire Key Exchange
using var session = new KeyExchangeService();
await session.InitiateKeyExchangeAsync(recipientPublicKey, CryptoMode.Hybrid);

// 2. Derivare Hybrid Key Material
using HybridKeyMaterial keys = KeyDerivationExtensions.DeriveHybridKeyMaterial(
    classicSecret: session.ClassicSharedSecret,
    pqSecret: session.PqSharedSecret,
    mode: CryptoMode.Hybrid);

// 3. Utilizzare le chiavi
using var aes = Aes.Create();
aes.Key = keys.EncryptionKey;

using var hmac = new HMACSHA256(keys.MacKey);

// 4. Eseguire crittografia
// ...

// 5. Le chiavi vengono cancellate automaticamente in modo sicuro
</code>

===== Note di sicurezza =====

<note warning>
  * Tutte le classi ''IDisposable'' implementano ''CryptographicOperations.ZeroMemory''
  * Argon2id richiede OpenSSL 3.6 (non disponibile in .NET BCL)
  * PBKDF2 con meno di 100.000 iterazioni non e raccomandato
  * Il Salt deve essere sempre casuale e sufficientemente lungo per PBKDF2/Argon2id (min. 16 Bytes)
</note>

<note tip>
**Sicurezza modalita ibrida:**

In modalita ibrida la chiave finale viene compromessa solo se ENTRAMBI i secrets (classico E PQ) vengono violati. Questo fornisce protezione sia contro attacchi classici che quantistici.
</note>

===== Vedi anche =====

  * [[.:start|Namespace KeyDerivation]]
  * [[.:hybridkeymaterial|HybridKeyMaterial]]
  * [[.:tlskeymaterial|TlsKeyMaterial]]
  * [[.:tls13keyschedule|Tls13KeySchedule]]
  * [[..:keyexchange:start|Namespace KeyExchange]]
  * [[..:encryption:start|Namespace Encryption]]
  * [[it:int:pqcrypt:konzepte:algorithmen:ml-kem|Algoritmo ML-KEM]]

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