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_2D_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
 */

/* shift right by a certain bit count (store quotient in c, optional remainder in d) */
int mp_div_2d(const mp_int *a, int b, mp_int *c, mp_int *d)
{
   mp_digit D, r, rr;
   int     x, res;

   /* if the shift count is <= 0 then we do no work */
   if (b <= 0) {
      res = mp_copy(a, c);
      if (d != NULL) {
         mp_zero(d);
      }
      return res;
   }

   /* copy */
   if ((res = mp_copy(a, c)) != MP_OKAY) {
      return res;
   }
   /* 'a' should not be used after here - it might be the same as d */

   /* get the remainder */
   if (d != NULL) {
      if ((res = mp_mod_2d(a, b, d)) != MP_OKAY) {
         return res;
      }
   }

   /* shift by as many digits in the bit count */
   if (b >= DIGIT_BIT) {
      mp_rshd(c, b / DIGIT_BIT);
   }

   /* shift any bit count < DIGIT_BIT */
   D = (mp_digit)(b % DIGIT_BIT);
   if (D != 0u) {
      mp_digit *tmpc, mask, shift;

      /* mask */
      mask = ((mp_digit)1 << D) - 1uL;

      /* shift for lsb */
      shift = (mp_digit)DIGIT_BIT - D;

      /* alias */
      tmpc = c->dp + (c->used - 1);

      /* carry */
      r = 0;
      for (x = c->used - 1; x >= 0; x--) {
         /* get the lower  bits of this word in a temp */
         rr = *tmpc & mask;

         /* shift the current word and mix in the carry bits from the previous word */
         *tmpc = (*tmpc >> D) | (r << shift);
         --tmpc;

         /* set the carry to the carry bits of the current word found above */
         r = rr;
      }
   }
   mp_clamp(c);
   return MP_OKAY;
}
#endif

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