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This Dart repository implements the HMAC-based Key Derivation Function (HKDF) as defined in RFC 5869. HKDF is a key derivation mechanism used to generate strong cryptographic keys from weaker input key material (IKM), suitable for a wide range of cryptographic applications.

HKDF combines a hash-based message authentication code (HMAC) with an extraction and expansion process, ensuring the generation of strong, high-entropy keys. It's highly adaptable and secure, making it an excellent choice for various key derivation needs.

• Robust Security: Resistant to common cryptographic attacks, ensuring the generation of secure keys.
• Flexibility: Suitable for a variety of applications, offering customizable key derivation.
• Configurable Hash Function: Can be used with different hash functions to fit specific security requirements.

• Utilize a cryptographically strong hash function.
• Employ a non-empty salt for improved security, particularly when the quality of the input key material is in question.

HKDF, as standardized in RFC 5869, is a straightforward yet effective tool for cryptographic key derivation, built on the principles of HMAC-based extraction and expansion of keys.

RFC 5869 details the implementation, usage, and security considerations for HKDF, promoting its consistent and secure application in cryptographic systems.

Scenario: Generating a strong encryption key from a password.

import 'dart:typed_data';
import 'package:hkdf/hkdf.dart';

Uint8List password = ...; // User-provided password
Uint8List salt = ...; // A unique salt
Uint8List info = ...; // Optional application-specific information

// Extract phase
Uint8List prk = HKDF.extract(sha256, password, salt);

// Expand phase
Uint8List strongKey = HKDF.expand(sha256, prk, 32, info);

// Use strongKey for cryptographic purposes

Scenario: Deriving keys for secure communication in a client-server model.

import 'dart:typed_data';
import 'package:hkdf/hkdf.dart';

Uint8List sharedSecret = ...; // Shared secret from a key exchange protocol
Uint8List salt = ...; // A unique salt
Uint8List info = ...; // Optional application-specific information

// Extract phase
Uint8List prk = HKDF.extract(sha256, sharedSecret, salt);

// Expand phase to derive specific keys
Uint8List encryptionKey = HKDF.expand(sha256, prk, 32, info);

// Use encryptionKey for encrypting communication

Contributions to improve the implementation, enhance security, and extend functionality are welcome. If you find any issues or have suggestions, please feel free to open an issue or submit a pull request.