core/lib/libtomcrypt/src/encauth/chachapoly/chacha20poly1305_setiv_rfc7905.c

// SPDX-License-Identifier: BSD-2-Clause
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
 *
 * LibTomCrypt is a library that provides various cryptographic
 * algorithms in a highly modular and flexible manner.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 */

#include "tomcrypt_private.h"

#ifdef LTC_CHACHA20POLY1305_MODE

/**
  Set IV + counter data (with RFC7905-magic) to the ChaCha20Poly1305 state and reset the context
  @param st     The ChaCha20Poly1305 state
  @param iv     The IV data to add
  @param ivlen  The length of the IV (must be 12 or 8)
  @param sequence_number   64bit sequence number which is incorporated into IV as described in RFC7905
  @return CRYPT_OK on success
 */
int chacha20poly1305_setiv_rfc7905(chacha20poly1305_state *st, const unsigned char *iv, unsigned long ivlen, ulong64 sequence_number)
{
   int i;
   unsigned char combined_iv[12] = { 0 };

   LTC_ARGCHK(st != NULL);
   LTC_ARGCHK(iv != NULL);
   LTC_ARGCHK(ivlen == 12);

   STORE64L(sequence_number, combined_iv + 4);
   for (i = 0; i < 12; i++) combined_iv[i] = iv[i] ^ combined_iv[i];
   return chacha20poly1305_setiv(st, combined_iv, 12);
}

#endif

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