# Crypto Utils Component
## ASF Sensor Hub (Sub-Hub) Embedded System

**Component ID:** C-CRYPTO-001  
**Version:** 1.0  
**Date:** 2025-02-01  
**Location:** `application_layer/utils/crypto_utils/`  
**Platform:** ESP32-S3, ESP-IDF v5.4

---

## 1. Component Overview

The Crypto Utils component provides cryptographic utility functions including hash computation, encryption/decryption, digital signatures, secure random number generation, and key derivation. This component supports Security Manager and other security-critical components.

**Primary Purpose:** Provide cryptographic primitives for system security.

---

## 2. Responsibilities

### 2.1 In-Scope

- Hash function computation (SHA-256, SHA-512)
- Symmetric encryption/decryption (AES-128, AES-256)
- Digital signature verification (RSA, ECDSA)
- Secure random number generation
- Key derivation functions (PBKDF2, HKDF)
- Message authentication codes (HMAC)

### 2.2 Out-of-Scope

- Key storage (handled by Security Manager)
- Certificate management (handled by Security Manager)
- Secure boot (handled by ESP-IDF)

---

## 3. Provided Interfaces

### 3.1 Hash Functions

```c
/**
 * @brief Compute SHA-256 hash
 * @param data Input data
 * @param data_len Data length
 * @param hash Output hash (32 bytes)
 * @return true on success
 */
bool crypto_hash_sha256(const uint8_t* data, size_t data_len, uint8_t* hash);

/**
 * @brief Compute SHA-512 hash
 * @param data Input data
 * @param data_len Data length
 * @param hash Output hash (64 bytes)
 * @return true on success
 */
bool crypto_hash_sha512(const uint8_t* data, size_t data_len, uint8_t* hash);
```

### 3.2 Encryption Functions

```c
/**
 * @brief Encrypt data using AES-256
 * @param plaintext Input plaintext
 * @param plaintext_len Plaintext length
 * @param key Encryption key (32 bytes)
 * @param iv Initialization vector (16 bytes)
 * @param ciphertext Output ciphertext
 * @return true on success
 */
bool crypto_encrypt_aes256(const uint8_t* plaintext, size_t plaintext_len,
                           const uint8_t* key, const uint8_t* iv,
                           uint8_t* ciphertext, size_t* ciphertext_len);
```

### 3.3 Random Number Generation

```c
/**
 * @brief Generate secure random bytes
 * @param buffer Output buffer
 * @param length Number of bytes to generate
 * @return true on success
 */
bool crypto_random_bytes(uint8_t* buffer, size_t length);
```

---

## 4. ESP-IDF Integration

### 4.1 ESP-IDF Services Used

- `mbedtls/sha256.h` - SHA-256 computation
- `mbedtls/aes.h` - AES encryption
- `mbedtls/rsa.h` - RSA operations
- `esp_random.h` - Secure random number generation
- Hardware acceleration (ESP32-S3 crypto peripherals)

### 4.2 Hardware Acceleration

- AES encryption/decryption (hardware-accelerated)
- SHA computation (hardware-accelerated)
- Random number generation (hardware RNG)

---

## 5. Traceability

### 11.1 Software Requirements

- **SWR-SEC-022:** Secure random number generation
- **SWR-SEC-023:** Key derivation functions
- **SWR-OTA-007:** Firmware integrity validation (SHA-256)

---

**Document Status:** Complete  
**Next Review:** Before implementation