HMAC.c

#include <stdio.h>
#include <string.h>
#include <openssl/hmac.h>

unsigned char* generate_hmac(unsigned char *key, unsigned char *data) {
    unsigned char* hmac;
    hmac = HMAC(EVP_sha256(), key, strlen((const char *)key), data, strlen((const char *)data), NULL, NULL);
    return hmac;
}

int compare_hmac(unsigned char *key, unsigned char *data, unsigned char *hmac) {
    unsigned char* new_hmac;
    new_hmac = generate_hmac(key, data);

    for(int i = 0; i < 32; i++) {
        if (hmac[i] != new_hmac[i]){
            return 0;
        }
    }

    return 1;
}

// int main() {
//     // Secret key
//     char key[] = "012345678";
    
//     // Encrypted data to be hashed using HMAC
//     char data[] = "hello world";

//     unsigned char *hmac = (unsigned char*)malloc(sizeof(char) * 32);
//     unsigned char *old_hmac = (unsigned char*)malloc(sizeof(char) * 32);

//     hmac = generate_hmac((unsigned char *)key, (unsigned char *)data);

//     //char mdString[32];
//     //for(int i = 0; i < 32; i++)
//     //     sprintf(&mdString[i*2], "%02x", (unsigned int)hmac[i]);
//     //printf("HMAC: %s\n", mdString);

//     // Compare HMAC
//     memcpy(old_hmac, hmac, 32);
//     char fkey[] = "000000000";
//     char fdata[] = "world hello";

//     if(compare_hmac((unsigned char *)key, (unsigned char *)data, old_hmac)){
//         printf("CORRECT \n");
//     } else {
//         printf("WRONG\n");
//     }

//     if(compare_hmac((unsigned char *)fkey, (unsigned char *)data, old_hmac)){
//         printf("WRONG\n");
//     } else {
//         printf("CORRECT\n");
//     }

//     if(compare_hmac((unsigned char *)key, (unsigned char *)fdata, old_hmac)){
//         printf("WRONG\n");
//     } else {
//         printf("CORRECT\n");
//     }

//     if(compare_hmac((unsigned char *)fkey, (unsigned char *)fdata, old_hmac)){
//         printf("WRONG\n");
//     } else {
//         printf("CORRECT\n");
//     }
//     return 0;
// }