Cipher Mode GCM-SIV

[NickBrighten]

I´ve implement the source and I get the following result from the AES-128-GCM-SIV with the following params in gcm_siv_memory()

Params (all in UTF-8):
INPUT: 0123456789abcdef
KEY : 0123456789abcdef
IV / NONCE : 0123456789abcdef (will be truncated to the length of 12-Bytes)
AAD : 0123456789abcdef

Results (base64-encoded):
Encrypt : cciPtpnmA7hGR3WBK1j4lQ==
TAG : vnomxFopChLQEkDlWFU77Q==

When i want to decrypt with the encrypted string and the tag with the params below, it doesn't decrypt the encrypted string.

Don´t know why - encryption should be correct, but decryption???
Can you explain it?

[karel-m]

This code seems to work:

#include <tomcrypt.h>

static void print_b64(const unsigned char *buf, unsigned long len)
{
   char out[64];
   unsigned long olen = sizeof(out);
   base64_encode(buf, len, out, &olen);
   printf("%s\n", out);
}

int main(void)
{
   unsigned char key[16], nonce[16], aad[16], pt[16], ct[16], tag[16], dec[16];
   unsigned long taglen;
   int cipher, err;

   register_cipher(&aes_desc);
   cipher = find_cipher("aes");

   XMEMCPY(key,   "0123456789abcdef", 16);
   XMEMCPY(nonce, "0123456789ab", 12);
   XMEMCPY(aad,   "0123456789abcdef", 16);
   XMEMCPY(pt,    "0123456789abcdef", 16);

   taglen = 16;
   err = gcm_siv_memory(cipher, key, 16, nonce, 12, aad, 16, pt, 16, ct, tag, &taglen, LTC_ENCRYPT);
   printf("   encrypt: %s\n", error_to_string(err));
   printf("   CT : "); print_b64(ct, 16);
   printf("   TAG: "), print_b64(tag, taglen);

   taglen = 16;
   err = gcm_siv_memory(cipher, key, 16, nonce, 12, aad, 16, ct, 16, dec, tag, &taglen, LTC_DECRYPT);
   printf("   decrypt: %s\n", error_to_string(err));
   printf("   XMEM_NEQ: %d\n", XMEM_NEQ(dec, pt, 16));

   return 0;
}

output:

   encrypt: CRYPT_OK
   CT : cciPtpnmA7hGR3WBK1j4lQ==
   TAG: vnomxFopChLQEkDlWFU77Q==
   decrypt: CRYPT_OK
   XMEM_NEQ: 0