/**
 * @file    crypto.h
 * @brief   Lightweight AES-128-CBC + HMAC-SHA256 for STM32G474
 *
 * Uses STM32G474 hardware AES (CRYP peripheral) for acceleration.
 * HMAC-SHA256 uses software implementation (mbedTLS or built-in).
 *
 * Hardware AES on G474: ~28 cycles/block vs ~300 cycles/block software.
 * 128KB firmware decrypt: ~15ms (HW AES) vs ~500ms (SW AES).
 */

#ifndef _CRYPTO_H_
#define _CRYPTO_H_

#include <stdint.h>
#include <stddef.h>
#include <stdbool.h>

/* ==================== AES-128-CBC (Hardware CRYP) ==================== */

/**
 * @brief Initialize CRYP peripheral for AES-128-CBC decryption
 * @param key  AES-128 key (16 bytes)
 */
void CRYPTO_AES_Init(const uint8_t *key);

/**
 * @brief Deinitialize CRYP peripheral (power save)
 */
void CRYPTO_AES_Deinit(void);

/**
 * @brief AES-128-CBC decrypt a data buffer in-place
 *
 * Decrypts data in-place. First 16 bytes are the IV.
 * PKCS7 padding is NOT removed by this function.
 *
 * @param data    Input: IV(16) + ciphertext. Output: plaintext.
 * @param len     Total length (must be multiple of 16, >= 32)
 * @return true on success, false on error
 */
bool CRYPTO_AES_CBC_Decrypt(uint8_t *data, uint32_t len);

/* ==================== HMAC-SHA256 (Software) ==================== */

/**
 * @brief Compute HMAC-SHA256
 *
 * @param key       HMAC key
 * @param key_len   Key length in bytes
 * @param data      Input data
 * @param data_len  Data length
 * @param mac       Output buffer (32 bytes)
 */
void CRYPTO_HMAC_SHA256(const uint8_t *key, uint32_t key_len,
                        const uint8_t *data, uint32_t data_len,
                        uint8_t *mac);

/**
 * @brief Verify HMAC-SHA256 tag (constant-time comparison)
 *
 * @param key       HMAC key
 * @param key_len   Key length
 * @param data      Data that was authenticated
 * @param data_len  Data length
 * @param tag       Expected MAC tag (32 bytes)
 * @return true if match, false otherwise
 */
bool CRYPTO_HMAC_Verify(const uint8_t *key, uint32_t key_len,
                        const uint8_t *data, uint32_t data_len,
                        const uint8_t *tag);

/* ==================== High-level OTA Helpers ==================== */

/**
 * @brief OTA firmware packet structure for decryption
 *
 * Firmware encrypted format (from PC tool):
 * +-----------+--------------------+------------+
 * | IV (16B)  | AES-CBC ciphertext | HMAC (32B) |
 * +-----------+--------------------+------------+
 */
#define OTA_ENC_IV_SIZE         16
#define OTA_ENC_HMAC_SIZE       32
#define OTA_ENC_OVERHEAD        (OTA_ENC_IV_SIZE + OTA_ENC_HMAC_SIZE)

/**
 * @brief Decrypt and verify OTA firmware buffer
 *
 * Verifies HMAC first (before decryption), then AES-CBC decrypts.
 *
 * @param enc_buf     Encrypted buffer (IV + ciphertext + HMAC)
 * @param enc_len     Total encrypted data length
 * @param aes_key     AES-128 key (16 bytes)
 * @param hmac_key    HMAC key (32 bytes)
 * @param out_buf     Output buffer for plaintext firmware (must be large enough)
 * @param out_len     Output plaintext length (written by function)
 * @return true on success, false on HMAC mismatch or decrypt error
 */
bool CRYPTO_OTA_DecryptFirmware(const uint8_t *enc_buf, uint32_t enc_len,
                                const uint8_t *aes_key, const uint8_t *hmac_key,
                                uint8_t *out_buf, uint32_t *out_len);

#endif /* _CRYPTO_H_ */