crypto.c

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//
//  crypto.c
//  crypto_test
//
//  Created by stoffer on 21/06/2016.
//  Copyright © 2016 stoffer. All rights reserved.
//

#include <esp8266.h>
#include <string.h>
#include "crypto/crypto.h"
#include "crypto/aes.h"
#include "crypto/sha256.h"
#include "crypto/hmac-sha256.h"
#include "user_config.h"

// variables passed to crypto library have to be int32_t aligned becouse they are casted and accessed as such
uint8_t sha256_hash[SHA256_DIGEST_LENGTH];
uint8_t aes_key[16];
uint8_t hmac_sha256_key[16];

void init_aes_hmac_combined(uint8_t *key) {
#ifdef DEBUG
    unsigned int i;
#endif
    _align_32_bit uint8_t master_key[16];
    
    memcpy(master_key, key, 16);
    
#ifdef DEBUG
    system_soft_wdt_stop();
    printf("master key: ");
    for (i = 0; i < 16; i++) {
        printf("%02x", key[i]);
    }
    printf("\n");
    system_soft_wdt_restart();
#endif  
    // generate aes_key and hmac_sha256_key from master_key
    memset(sha256_hash, 0, sizeof(sha256_hash));
    
    sha256_raw(master_key, 16, sha256_hash);
    
    // first 16 bytes is aes key
    memcpy(aes_key, sha256_hash, sizeof(aes_key));
    // last 16 bytes is hmac sha256 key
    memcpy(hmac_sha256_key, sha256_hash + sizeof(aes_key), sizeof(hmac_sha256_key));
    
#ifdef DEBUG
    system_soft_wdt_stop();
    // print keys
    printf("aes key: ");
    for (i = 0; i < 16; i++) {
        printf("%02x", aes_key[i]);
    }
    printf("\n");
    
    printf("hmac sha256 key: ");
    for (i = 0; i < 16; i++) {
        printf("%02x", hmac_sha256_key[i]);
    }
    printf("\n");
    system_soft_wdt_restart();
#endif
}

ICACHE_FLASH_ATTR
size_t encrypt_aes_hmac_combined(uint8_t *dst, uint8_t *topic, size_t topic_l, uint8_t *message, size_t message_l) {
    hmac_sha256_ctx_t hctx;
    int return_l;

    // encrypt
    memset(dst, 0, sizeof(dst));
    // get random iv in first 16 bytes of mqtt_message
    os_get_random(dst + SHA256_DIGEST_LENGTH, 16);

    // calculate blocks needed for encrypted string
    return_l = message_l;
    if (return_l % 16) {
        return_l = (return_l / 16) * 16 + 16;
    }
    else {
        return_l = (return_l / 16) * 16;
    }
    
    AES128_CBC_encrypt_buffer(dst + SHA256_DIGEST_LENGTH + 16, message, return_l, aes_key, dst + SHA256_DIGEST_LENGTH); // first 32 bytes of mqtt_message contains hmac sha256, next 16 bytes contains IV
    return_l += SHA256_DIGEST_LENGTH + 16;
    
    // hmac sha256
    hmac_sha256_init(&hctx, hmac_sha256_key, sizeof(hmac_sha256_key));
    hmac_sha256_update(&hctx, topic, topic_l);
    hmac_sha256_update(&hctx, dst + SHA256_DIGEST_LENGTH, return_l - SHA256_DIGEST_LENGTH);
    hmac_sha256_final(&hctx, dst);
    
    return return_l;
}

ICACHE_FLASH_ATTR
size_t decrypt_aes_hmac_combined(uint8_t *dst, uint8_t *topic, size_t topic_l, uint8_t *message, size_t message_l) {
    hmac_sha256_ctx_t hctx;
    uint8_t calculated_hmac_sha256[SHA256_DIGEST_LENGTH];

    // hmac sha256
    hmac_sha256_init(&hctx, hmac_sha256_key, sizeof(hmac_sha256_key));
    hmac_sha256_update(&hctx, topic, topic_l);
    hmac_sha256_update(&hctx, message + SHA256_DIGEST_LENGTH, message_l - SHA256_DIGEST_LENGTH);
    hmac_sha256_final(&hctx, calculated_hmac_sha256);

    if (memcmp(calculated_hmac_sha256, message, SHA256_DIGEST_LENGTH) == 0) {
        // hmac sha256 matches
        
        AES128_CBC_decrypt_buffer(dst + 0, message + SHA256_DIGEST_LENGTH + 16, message_l, aes_key, message + SHA256_DIGEST_LENGTH);
        return strlen(dst);
    }
    else {
        return 0;
    }
}