LibTomCrypt를 이용한 AES – CFB 모드 복호화 테스트

MinGW 에서.. crypt 라이브러리를 뭐로.. 쓸까.. 이리저리 기웃거리다..
LibTomCrypt를 사용하기로 결정하였음. 다른 라이브러리를 사용하여..
암호화된 파일을 LibTomCrypt를 사용하여 복호화를 해봄.

코드를 보면.. base64 디코드를 한후 복호화를 하는데..
AES로 암호화후 base64로 인코딩을 해놓은 데이타라 그런것임.

 

참고로 LibTomCrypt 는 msys2 에서 바로 설치 가능.

pacman -S mingw-w64-x86_64-libtomcrypt

아래의 코드를 만들기 위해 참고한 코드: modes_test.c

#include <tomcrypt.h>
  
int errno;
 
static void *
read_file (const char *fname, size_t *r_length)
{
    FILE *fp;
    struct stat st;
    char *buf;
    size_t buflen;
 
    fp = fopen (fname, "rb");
    if (!fp)
    {
        printf ("can't open `%s': %s\n", fname, strerror (errno));
        return NULL;
    }
 
    if (fstat (fileno(fp), &st))
    {
        printf ("can't stat `%s': %s\n", fname, strerror (errno));
        fclose (fp);
        return NULL;
    }
 
    buflen = st.st_size;
    buf = malloc (buflen+1);
    if (fread (buf, buflen, 1, fp) != 1)
    {
        printf ("error reading `%s': %s\n", fname, strerror (errno));
        fclose (fp);
        free (buf);
        return NULL;
    }
    fclose (fp);
 
    if (r_length)
        *r_length = buflen;
    return buf;
}
 
int main(void)
{
    unsigned char *base64dec;
    unsigned long base64dec_len;
    {
        size_t file_length;
        unsigned char *base64enc = read_file("a.b64", &file_length);
        base64dec = malloc(file_length);
        base64dec_len = file_length;
        base64_decode(base64enc, file_length, base64dec, &base64dec_len);
    }
 
    {
        register_cipher(&aes_desc);
 
        unsigned char key[16], iv[16];
        symmetric_CFB cfb;
        int cipher_idx;
 
        cipher_idx = find_cipher("aes");
        if (cipher_idx == -1) {
            printf("Invalid cipher entered on command line.\n");
            exit(-1);
        }
 
        sprintf(iv, "%s", "1234567812345678");
        sprintf(key, "%s", "1234567890123456");
 
        char *decrypt = malloc(base64dec_len+1);
        cfb_start(cipher_idx, iv, key, 16, 0, &cfb);
        cfb_setiv(iv, 16, &cfb);
        cfb_decrypt(base64dec, decrypt, base64dec_len, &cfb);
 
        fprintf(stdout, "%s\n", decrypt);
        fflush(stdout);
 
        free(decrypt);
    }
 
    return 0;
}