/* 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.

 */

/* The implementation is based on:

 * chacha-ref.c version 20080118

 * Public domain from D. J. Bernstein

 */

#include "tomcrypt.h"

#ifdef LTC_CHACHA

static const char * const sigma = "expand 32-byte k";

static const char * const tau   = "expand 16-byte k";

/**

   Initialize an ChaCha context (only the key)

   @param st        [out] The destination of the ChaCha state

   @param key       The secret key

   @param keylen    The length of the secret key (octets)

   @param rounds    Number of rounds (e.g. 20 for ChaCha20)

   @return CRYPT_OK if successful

*/

int chacha_setup(chacha_state *st, const unsigned char *key, unsigned long keylen, int rounds)

{

   const char *constants;

   LTC_ARGCHK(st  != NULL);

   LTC_ARGCHK(key != NULL);

   LTC_ARGCHK(keylen == 32 || keylen == 16);

   if (rounds == 0) rounds = 20;

   LOAD32L(st->input[4], key + 0);

   LOAD32L(st->input[5], key + 4);

   LOAD32L(st->input[6], key + 8);

   LOAD32L(st->input[7], key + 12);

   if (keylen == 32) { /* 256bit */

      key += 16;

      constants = sigma;

   } else { /* 128bit */

      constants = tau;

   }

   LOAD32L(st->input[8],  key + 0);

   LOAD32L(st->input[9],  key + 4);

   LOAD32L(st->input[10], key + 8);

   LOAD32L(st->input[11], key + 12);

   LOAD32L(st->input[0],  constants + 0);

   LOAD32L(st->input[1],  constants + 4);

   LOAD32L(st->input[2],  constants + 8);

   LOAD32L(st->input[3],  constants + 12);

   st->rounds = rounds; /* e.g. 20 for chacha20 */

   st->ivlen = 0; /* will be set later by chacha_ivctr(32|64) */

   return CRYPT_OK;

}

#endif

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