encryption.h

#ifndef ENCRYPTION_H
#define ENCRYPTION_H

#include <stddef.h>   // for size_t
#include <stdint.h>   // for uint8_t

// --- Function Declarations ---

// Generate a key-based pseudo keystream
void generate_keystream(uint8_t *keystream, size_t len, const uint8_t *key, size_t keylen);

// Generate key-based permutation using Fisher–Yates shuffle
void generate_permutation(size_t *perm, size_t len, const uint8_t *key, size_t keylen);

// Invert permutation (used during decryption)
void invert_permutation(size_t *inv, const size_t *perm, size_t len);

// Encrypt plaintext into cipher using XOR + substitution + transposition
void hybrid_encrypt(const uint8_t *plaintext, uint8_t *cipher, size_t len,
                    const uint8_t *key, size_t keylen);

// Decrypt cipher back into plaintext (reverse of encryption)
void hybrid_decrypt(const uint8_t *cipher, uint8_t *plaintext, size_t len,
                    const uint8_t *key, size_t keylen);

#endif  // ENCRYPTION_H