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

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

Statička klasa za derivaciju ključeva (Key Derivation Functions) s Post-Quantum podrškom. Podržava HKDF, PBKDF2 i Argon2id.

===== Pregled =====

Podržani KDF algoritmi:

^ KDF ^ Standard ^ Uporaba ^
| HKDF | RFC 5869 | Sesijski ključevi iz dijeljenih tajnih ključeva |
| PBKDF2 | RFC 8018 | Ključevi temeljeni na lozinci |
| Argon2id | RFC 9106 | Memorijski zahtjevan KDF (lozinke) |

===== HKDF - Hash-bazirana derivacija ključeva =====

==== DeriveKey ====

Derivira ključeve iz dijeljenog tajnog ključa (HKDF-Extract-then-Expand).

<code csharp>
// ML-KEM dijeljeni tajni ključ iz Key Exchange
byte[] sharedSecret = session.SharedSecret;

// Standardna derivacija (SHA-256)
byte[] aesKey = KeyDerivationExtensions.DeriveKey(
    sharedSecret,
    outputLength: 32);  // 256 bita

// Sa salt i kontekst informacijom
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);  // Opcionalno
</code>

==== HkdfExtract ====

Ekstrahira PRK (Pseudorandom Key) iz ulaznog ključnog materijala.

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

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

// PRK ima istu duljinu kao hash izlaz (32 bajta za SHA-256)
</code>

==== HkdfExpand ====

Proširuje PRK na izlazni ključni materijal.

<code csharp>
byte[] prk = GetPrk();

// Ključ za šifriranje
byte[] encKey = KeyDerivationExtensions.HkdfExpand(
    prk,
    outputLength: 32,
    info: Encoding.UTF8.GetBytes("encryption"));

// MAC ključ
byte[] macKey = KeyDerivationExtensions.HkdfExpand(
    prk,
    outputLength: 32,
    info: Encoding.UTF8.GetBytes("mac"));
</code>

===== Hibridna derivacija ključeva =====

Kombinira klasične (ECDH/DH) i PQ (ML-KEM) dijeljene tajne ključeve.

==== DeriveHybridKey ====

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

// Hibridni način: Oba tajni ključa se kombiniraju
byte[] hybridKey = KeyDerivationExtensions.DeriveHybridKey(
    classicSecret: ecdhSecret,
    pqSecret: mlKemSecret,
    outputLength: 32,
    mode: CryptoMode.Hybrid);

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

// Samo Post-Quantum
byte[] pqKey = KeyDerivationExtensions.DeriveHybridKey(
    classicSecret: null,
    pqSecret: mlKemSecret,
    outputLength: 32,
    mode: CryptoMode.PostQuantum);

// Prilagođeni info
byte[] customKey = KeyDerivationExtensions.DeriveHybridKey(
    classicSecret: ecdhSecret,
    pqSecret: mlKemSecret,
    outputLength: 64,
    mode: CryptoMode.Hybrid,
    info: Encoding.UTF8.GetBytes("MyProtocol-v1"));
</code>

**Kombinacija ključeva:**

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

==== DeriveHybridKeyMaterial ====

Derivira više ključeva za različite namjene.

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

// Uporaba
byte[] encKey = keyMaterial.EncryptionKey;  // 32 bajta
byte[] macKey = keyMaterial.MacKey;         // 32 bajta
byte[] iv = keyMaterial.Iv;                 // 16 bajtova
byte[] authKey = keyMaterial.AuthKey;       // 32 bajta

// IDisposable: Ključevi se sigurno brišu
</code>

===== PBKDF2 - Derivacija temeljena na lozinci =====

==== Pbkdf2 ====

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

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

// S PQ-entropijom (dodatna zaštita)
byte[] pqEntropy = GetPqEntropy();

byte[] enhancedKey = KeyDerivationExtensions.Pbkdf2(
    password,
    salt,
    iterations: 100000,
    outputLength: 32,
    pqEntropy: pqEntropy,  // Kombinira se sa salt
    hashAlgorithm: HashAlgorithmName.SHA512);
</code>

==== Pbkdf2WithPqSalt ====

PBKDF2 s PQ-pojačanim salt (javni ključ uključen je u izračun 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>
**Prednost:** Čak i s identičnom lozinkom i baznim salt, za svakog primatelja (različiti PQ javni ključ) dobiva se drugačiji ključ.
</note>

===== Argon2id - Memorijski zahtjevan KDF =====

Argon2id putem OpenSSL 3.6 - otporan na GPU/ASIC napade.

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

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

byte[] key = KeyDerivationExtensions.Argon2id(
    password,
    salt,
    outputLength: 32,     // Duljina ključa
    iterations: 3,        // Vremenski trošak (t)
    memoryKiB: 65536,     // Memorija: 64 MB
    parallelism: 4);      // Niti (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>

**Preporučeni parametri:**

^ Primjena ^ Iteracije (t) ^ Memorija (m) ^ Paralelizam (p) ^
| Hashiranje lozinki | 3 | 64 MB | 4 |
| Visoka sigurnost | 4 | 256 MB | 4 |
| Niska memorija | 4 | 16 MB | 4 |

===== TLS derivacija ključeva =====

==== DeriveTlsKeys (TLS 1.2 stil) ====

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

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

// Uporaba
var clientKey = keys.ClientWriteKey;   // 32 bajta
var serverKey = keys.ServerWriteKey;   // 32 bajta
var clientIv = keys.ClientWriteIv;     // 12 bajtova
var serverIv = keys.ServerWriteIv;     // 12 bajtova
</code>

==== DeriveTls13Keys ====

TLS 1.3 kompatibilan raspored ključeva.

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

===== Klase podataka =====

==== HybridKeyMaterial ====

Kontejner za derivirane ključeve sa sigurnim čišćenjem memorije.

^ Svojstvo ^ Tip ^ Duljina ^ Opis ^
| ''EncryptionKey'' | byte[] | 32 | AES ključ |
| ''MacKey'' | byte[] | 32 | HMAC ključ |
| ''Iv'' | byte[] | 16 | Inicijalizacijski vektor |
| ''AuthKey'' | byte[] | 32 | Autentifikacijski ključ |

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

// Ključevi se sigurno brišu pri Dispose()
// (CryptographicOperations.ZeroMemory)
</code>

==== TlsKeyMaterial ====

TLS 1.2 stil ključni materijal.

^ Svojstvo ^ Tip ^ Opis ^
| ''MasterSecret'' | byte[] | 48 bajtova Master Secret |
| ''ClientWriteKey'' | byte[] | Ključ za šifriranje na klijentskoj strani |
| ''ServerWriteKey'' | byte[] | Ključ za šifriranje na serverskoj strani |
| ''ClientWriteIv'' | byte[] | IV na klijentskoj strani |
| ''ServerWriteIv'' | byte[] | IV na serverskoj strani |
| ''ClientWriteMacKey'' | byte[] | Klijentov MAC ključ (prazan za GCM) |
| ''ServerWriteMacKey'' | byte[] | Serverov MAC ključ (prazan za GCM) |

==== Tls13KeySchedule ====

TLS 1.3 raspored ključeva.

^ Svojstvo ^ Tip ^ Opis ^
| ''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 |

===== Pregled metoda =====

==== HKDF ====

^ Metoda ^ Parametri ^ Povratni tip ^
| ''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[] |

==== Hibridni ====

^ Metoda ^ Parametri ^ Povratni tip ^
| ''DeriveHybridKey'' | byte[]? classicSecret, byte[]? pqSecret, int outputLength, CryptoMode, byte[]? info | byte[] |
| ''DeriveHybridKeyMaterial'' | byte[]? classicSecret, byte[]? pqSecret, CryptoMode | HybridKeyMaterial |

==== PBKDF2 ====

^ Metoda ^ Parametri ^ Povratni tip ^
| ''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 ====

^ Metoda ^ Parametri ^ Povratni tip ^
| ''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 ====

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

===== Potpuni primjer =====

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

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

// 2. Derivirati hibridni ključni materijal
using HybridKeyMaterial keys = KeyDerivationExtensions.DeriveHybridKeyMaterial(
    classicSecret: session.ClassicSharedSecret,
    pqSecret: session.PqSharedSecret,
    mode: CryptoMode.Hybrid);

// 3. Koristiti ključeve
using var aes = Aes.Create();
aes.Key = keys.EncryptionKey;

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

// 4. Izvršiti šifriranje
// ...

// 5. Ključevi se automatski sigurno brišu
</code>

===== Sigurnosne napomene =====

<note warning>
  * Sve ''IDisposable'' klase implementiraju ''CryptographicOperations.ZeroMemory''
  * Argon2id zahtijeva OpenSSL 3.6 (nije dostupan u .NET BCL)
  * PBKDF2 s manje od 100.000 iteracija se ne preporučuje
  * Salt mora uvijek biti nasumičan i dovoljno dugačak za PBKDF2/Argon2id (min. 16 bajtova)
</note>

<note tip>
**Sigurnost hibridnog načina:**

U hibridnom načinu konačni ključ je kompromitiran samo ako su OBA tajna ključa (klasični I PQ) probijena. To pruža zaštitu i od klasičnih i od kvantnih napada.
</note>

===== Vidi također =====

  * [[.:start|KeyDerivation prostor imena]]
  * [[.:hybridkeymaterial|HybridKeyMaterial]]
  * [[.:tlskeymaterial|TlsKeyMaterial]]
  * [[.:tls13keyschedule|Tls13KeySchedule]]
  * [[..:keyexchange:start|KeyExchange prostor imena]]
  * [[..:encryption:start|Encryption prostor imena]]
  * [[hr:int:pqcrypt:konzepte:algorithmen:ml-kem|ML-KEM algoritam]]

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