Add Chacha20-Poly1305, AES128-GCM and AES256-GCM support (#93) * Add Chacha20-Poly1305 authenticated encryption * Add general AEAD approach. * Add [email protected] algo using LibTomCrypt chacha and poly1305 routines. Chacha20-Poly1305 is generally faster than AES256 on CPU w/o dedicated AES instructions, having the same key size. Compiling in will add ~5,5kB to binary size on x86-64. function old new delta chacha_crypt - 1397 +1397 _poly1305_block - 608 +608 poly1305_done - 595 +595 dropbear_chachapoly_crypt - 457 +457 .rodata 26976 27392 +416 poly1305_process - 290 +290 poly1305_init - 221 +221 chacha_setup - 218 +218 encrypt_packet 1068 1270 +202 dropbear_chachapoly_getlength - 147 +147 decrypt_packet 756 897 +141 chacha_ivctr64 - 137 +137 read_packet 543 637 +94 dropbear_chachapoly_start - 94 +94 read_kex_algos 792 880 +88 chacha_keystream - 69 +69 dropbear_mode_chachapoly - 48 +48 sshciphers 280 320 +40 dropbear_mode_none 24 48 +24 dropbear_mode_ctr 24 48 +24 dropbear_mode_cbc 24 48 +24 dropbear_chachapoly_mac - 24 +24 dropbear_chachapoly - 24 +24 gen_new_keys 848 854 +6 ------------------------------------------------------------------------------ (add/remove: 14/0 grow/shrink: 10/0 up/down: 5388/0) Total: 5388 bytes * Add AES128-GCM and AES256-GCM authenticated encryption * Add general AES-GCM mode. * Add [email protected] and [email protected] algo using LibTomCrypt gcm routines. AES-GCM is combination of AES CTR mode and GHASH, slower than AES-CTR on CPU w/o dedicated AES/GHASH instructions therefore disabled by default. Compiling in will add ~6kB to binary size on x86-64. function old new delta gcm_process - 1060 +1060 .rodata 26976 27808 +832 gcm_gf_mult - 820 +820 gcm_add_aad - 660 +660 gcm_shift_table - 512 +512 gcm_done - 471 +471 gcm_add_iv - 384 +384 gcm_init - 347 +347 dropbear_gcm_crypt - 309 +309 encrypt_packet 1068 1270 +202 decrypt_packet 756 897 +141 gcm_reset - 118 +118 read_packet 543 637 +94 read_kex_algos 792 880 +88 sshciphers 280 360 +80 gcm_mult_h - 80 +80 dropbear_gcm_start - 62 +62 dropbear_mode_gcm - 48 +48 dropbear_mode_none 24 48 +24 dropbear_mode_ctr 24 48 +24 dropbear_mode_cbc 24 48 +24 dropbear_ghash - 24 +24 dropbear_gcm_getlength - 24 +24 gen_new_keys 848 854 +6 ------------------------------------------------------------------------------ (add/remove: 14/0 grow/shrink: 10/0 up/down: 6434/0) Total: 6434 bytes

#include "tommath_private.h"
#ifdef BN_MP_DIV_D_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
 *
 * LibTomMath is a library that provides multiple-precision
 * integer arithmetic as well as number theoretic functionality.
 *
 * The library was designed directly after the MPI library by
 * Michael Fromberger but has been written from scratch with
 * additional optimizations in place.
 *
 * SPDX-License-Identifier: Unlicense
 */

static int s_is_power_of_two(mp_digit b, int *p)
{
   int x;

   /* fast return if no power of two */
   if ((b == 0u) || ((b & (b-1u)) != 0u)) {
      return 0;
   }

   for (x = 0; x < DIGIT_BIT; x++) {
      if (b == ((mp_digit)1<<(mp_digit)x)) {
         *p = x;
         return 1;
      }
   }
   return 0;
}

/* single digit division (based on routine from MPI) */
int mp_div_d(const mp_int *a, mp_digit b, mp_int *c, mp_digit *d)
{
   mp_int  q;
   mp_word w;
   mp_digit t;
   int     res, ix;

   /* cannot divide by zero */
   if (b == 0u) {
      return MP_VAL;
   }

   /* quick outs */
   if ((b == 1u) || (mp_iszero(a) == MP_YES)) {
      if (d != NULL) {
         *d = 0;
      }
      if (c != NULL) {
         return mp_copy(a, c);
      }
      return MP_OKAY;
   }

   /* power of two ? */
   if (s_is_power_of_two(b, &ix) == 1) {
      if (d != NULL) {
         *d = a->dp[0] & (((mp_digit)1<<(mp_digit)ix) - 1uL);
      }
      if (c != NULL) {
         return mp_div_2d(a, ix, c, NULL);
      }
      return MP_OKAY;
   }

#ifdef BN_MP_DIV_3_C
   /* three? */
   if (b == 3u) {
      return mp_div_3(a, c, d);
   }
#endif

   /* no easy answer [c'est la vie].  Just division */
   if ((res = mp_init_size(&q, a->used)) != MP_OKAY) {
      return res;
   }

   q.used = a->used;
   q.sign = a->sign;
   w = 0;
   for (ix = a->used - 1; ix >= 0; ix--) {
      w = (w << (mp_word)DIGIT_BIT) | (mp_word)a->dp[ix];

      if (w >= b) {
         t = (mp_digit)(w / b);
         w -= (mp_word)t * (mp_word)b;
      } else {
         t = 0;
      }
      q.dp[ix] = t;
   }

   if (d != NULL) {
      *d = (mp_digit)w;
   }

   if (c != NULL) {
      mp_clamp(&q);
      mp_exch(&q, c);
   }
   mp_clear(&q);

   return res;
}

#endif

/* ref:         HEAD -> master, tag: v1.1.0 */
/* git commit:  08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */
/* commit time: 2019-01-28 20:32:32 +0100 */