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boringssl/crypto/curve25519/x25519-x86_64.c
David Benjamin 17cf2cb1d2 Work around language and compiler bug in memcpy, etc. 
Most C standard library functions are undefined if passed NULL, even
when the corresponding length is zero. This gives them (and, in turn,
all functions which call them) surprising behavior on empty arrays.
Some compilers will miscompile code due to this rule. See also
https://www.imperialviolet.org/2016/06/26/nonnull.html

Add OPENSSL_memcpy, etc., wrappers which avoid this problem.

BUG=23

Change-Id: I95f42b23e92945af0e681264fffaf578e7f8465e
Reviewed-on: https://boringssl-review.googlesource.com/12928
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
2016-12-21 20:34:47 +00:00

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/* Copyright (c) 2015, Google Inc.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
/* This code is mostly taken from the ref10 version of Ed25519 in SUPERCOP
* 20141124 (http://bench.cr.yp.to/supercop.html). That code is released as
* public domain but this file has the ISC license just to keep licencing
* simple.
*
* The field functions are shared by Ed25519 and X25519 where possible. */
#include <openssl/curve25519.h>
#include <string.h>
#include "../internal.h"
#include "internal.h"
#if defined(BORINGSSL_X25519_X86_64)
typedef struct { uint64_t v[5]; } fe25519;
/* These functions are defined in asm/x25519-x86_64.S */
void x25519_x86_64_work_cswap(fe25519 *, uint64_t);
void x25519_x86_64_mul(fe25519 *out, const fe25519 *a, const fe25519 *b);
void x25519_x86_64_square(fe25519 *out, const fe25519 *a);
void x25519_x86_64_freeze(fe25519 *);
void x25519_x86_64_ladderstep(fe25519 *work);
static void fe25519_setint(fe25519 *r, unsigned v) {
r->v[0] = v;
r->v[1] = 0;
r->v[2] = 0;
r->v[3] = 0;
r->v[4] = 0;
}
/* Assumes input x being reduced below 2^255 */
static void fe25519_pack(unsigned char r[32], const fe25519 *x) {
fe25519 t;
t = *x;
x25519_x86_64_freeze(&t);
r[0] = (uint8_t)(t.v[0] & 0xff);
r[1] = (uint8_t)((t.v[0] >> 8) & 0xff);
r[2] = (uint8_t)((t.v[0] >> 16) & 0xff);
r[3] = (uint8_t)((t.v[0] >> 24) & 0xff);
r[4] = (uint8_t)((t.v[0] >> 32) & 0xff);
r[5] = (uint8_t)((t.v[0] >> 40) & 0xff);
r[6] = (uint8_t)((t.v[0] >> 48));
r[6] ^= (uint8_t)((t.v[1] << 3) & 0xf8);
r[7] = (uint8_t)((t.v[1] >> 5) & 0xff);
r[8] = (uint8_t)((t.v[1] >> 13) & 0xff);
r[9] = (uint8_t)((t.v[1] >> 21) & 0xff);
r[10] = (uint8_t)((t.v[1] >> 29) & 0xff);
r[11] = (uint8_t)((t.v[1] >> 37) & 0xff);
r[12] = (uint8_t)((t.v[1] >> 45));
r[12] ^= (uint8_t)((t.v[2] << 6) & 0xc0);
r[13] = (uint8_t)((t.v[2] >> 2) & 0xff);
r[14] = (uint8_t)((t.v[2] >> 10) & 0xff);
r[15] = (uint8_t)((t.v[2] >> 18) & 0xff);
r[16] = (uint8_t)((t.v[2] >> 26) & 0xff);
r[17] = (uint8_t)((t.v[2] >> 34) & 0xff);
r[18] = (uint8_t)((t.v[2] >> 42) & 0xff);
r[19] = (uint8_t)((t.v[2] >> 50));
r[19] ^= (uint8_t)((t.v[3] << 1) & 0xfe);
r[20] = (uint8_t)((t.v[3] >> 7) & 0xff);
r[21] = (uint8_t)((t.v[3] >> 15) & 0xff);
r[22] = (uint8_t)((t.v[3] >> 23) & 0xff);
r[23] = (uint8_t)((t.v[3] >> 31) & 0xff);
r[24] = (uint8_t)((t.v[3] >> 39) & 0xff);
r[25] = (uint8_t)((t.v[3] >> 47));
r[25] ^= (uint8_t)((t.v[4] << 4) & 0xf0);
r[26] = (uint8_t)((t.v[4] >> 4) & 0xff);
r[27] = (uint8_t)((t.v[4] >> 12) & 0xff);
r[28] = (uint8_t)((t.v[4] >> 20) & 0xff);
r[29] = (uint8_t)((t.v[4] >> 28) & 0xff);
r[30] = (uint8_t)((t.v[4] >> 36) & 0xff);
r[31] = (uint8_t)((t.v[4] >> 44));
}
static void fe25519_unpack(fe25519 *r, const uint8_t x[32]) {
r->v[0] = x[0];
r->v[0] += (uint64_t)x[1] << 8;
r->v[0] += (uint64_t)x[2] << 16;
r->v[0] += (uint64_t)x[3] << 24;
r->v[0] += (uint64_t)x[4] << 32;
r->v[0] += (uint64_t)x[5] << 40;
r->v[0] += ((uint64_t)x[6] & 7) << 48;
r->v[1] = x[6] >> 3;
r->v[1] += (uint64_t)x[7] << 5;
r->v[1] += (uint64_t)x[8] << 13;
r->v[1] += (uint64_t)x[9] << 21;
r->v[1] += (uint64_t)x[10] << 29;
r->v[1] += (uint64_t)x[11] << 37;
r->v[1] += ((uint64_t)x[12] & 63) << 45;
r->v[2] = x[12] >> 6;
r->v[2] += (uint64_t)x[13] << 2;
r->v[2] += (uint64_t)x[14] << 10;
r->v[2] += (uint64_t)x[15] << 18;
r->v[2] += (uint64_t)x[16] << 26;
r->v[2] += (uint64_t)x[17] << 34;
r->v[2] += (uint64_t)x[18] << 42;
r->v[2] += ((uint64_t)x[19] & 1) << 50;
r->v[3] = x[19] >> 1;
r->v[3] += (uint64_t)x[20] << 7;
r->v[3] += (uint64_t)x[21] << 15;
r->v[3] += (uint64_t)x[22] << 23;
r->v[3] += (uint64_t)x[23] << 31;
r->v[3] += (uint64_t)x[24] << 39;
r->v[3] += ((uint64_t)x[25] & 15) << 47;
r->v[4] = x[25] >> 4;
r->v[4] += (uint64_t)x[26] << 4;
r->v[4] += (uint64_t)x[27] << 12;
r->v[4] += (uint64_t)x[28] << 20;
r->v[4] += (uint64_t)x[29] << 28;
r->v[4] += (uint64_t)x[30] << 36;
r->v[4] += ((uint64_t)x[31] & 127) << 44;
}
static void fe25519_invert(fe25519 *r, const fe25519 *x) {
fe25519 z2;
fe25519 z9;
fe25519 z11;
fe25519 z2_5_0;
fe25519 z2_10_0;
fe25519 z2_20_0;
fe25519 z2_50_0;
fe25519 z2_100_0;
fe25519 t;
int i;
/* 2 */ x25519_x86_64_square(&z2, x);
/* 4 */ x25519_x86_64_square(&t, &z2);
/* 8 */ x25519_x86_64_square(&t, &t);
/* 9 */ x25519_x86_64_mul(&z9, &t, x);
/* 11 */ x25519_x86_64_mul(&z11, &z9, &z2);
/* 22 */ x25519_x86_64_square(&t, &z11);
/* 2^5 - 2^0 = 31 */ x25519_x86_64_mul(&z2_5_0, &t, &z9);
/* 2^6 - 2^1 */ x25519_x86_64_square(&t, &z2_5_0);
/* 2^20 - 2^10 */ for (i = 1; i < 5; i++) { x25519_x86_64_square(&t, &t); }
/* 2^10 - 2^0 */ x25519_x86_64_mul(&z2_10_0, &t, &z2_5_0);
/* 2^11 - 2^1 */ x25519_x86_64_square(&t, &z2_10_0);
/* 2^20 - 2^10 */ for (i = 1; i < 10; i++) { x25519_x86_64_square(&t, &t); }
/* 2^20 - 2^0 */ x25519_x86_64_mul(&z2_20_0, &t, &z2_10_0);
/* 2^21 - 2^1 */ x25519_x86_64_square(&t, &z2_20_0);
/* 2^40 - 2^20 */ for (i = 1; i < 20; i++) { x25519_x86_64_square(&t, &t); }
/* 2^40 - 2^0 */ x25519_x86_64_mul(&t, &t, &z2_20_0);
/* 2^41 - 2^1 */ x25519_x86_64_square(&t, &t);
/* 2^50 - 2^10 */ for (i = 1; i < 10; i++) { x25519_x86_64_square(&t, &t); }
/* 2^50 - 2^0 */ x25519_x86_64_mul(&z2_50_0, &t, &z2_10_0);
/* 2^51 - 2^1 */ x25519_x86_64_square(&t, &z2_50_0);
/* 2^100 - 2^50 */ for (i = 1; i < 50; i++) { x25519_x86_64_square(&t, &t); }
/* 2^100 - 2^0 */ x25519_x86_64_mul(&z2_100_0, &t, &z2_50_0);
/* 2^101 - 2^1 */ x25519_x86_64_square(&t, &z2_100_0);
/* 2^200 - 2^100 */ for (i = 1; i < 100; i++) {
x25519_x86_64_square(&t, &t);
}
/* 2^200 - 2^0 */ x25519_x86_64_mul(&t, &t, &z2_100_0);
/* 2^201 - 2^1 */ x25519_x86_64_square(&t, &t);
/* 2^250 - 2^50 */ for (i = 1; i < 50; i++) { x25519_x86_64_square(&t, &t); }
/* 2^250 - 2^0 */ x25519_x86_64_mul(&t, &t, &z2_50_0);
/* 2^251 - 2^1 */ x25519_x86_64_square(&t, &t);
/* 2^252 - 2^2 */ x25519_x86_64_square(&t, &t);
/* 2^253 - 2^3 */ x25519_x86_64_square(&t, &t);
/* 2^254 - 2^4 */ x25519_x86_64_square(&t, &t);
/* 2^255 - 2^5 */ x25519_x86_64_square(&t, &t);
/* 2^255 - 21 */ x25519_x86_64_mul(r, &t, &z11);
}
static void mladder(fe25519 *xr, fe25519 *zr, const uint8_t s[32]) {
fe25519 work[5];
work[0] = *xr;
fe25519_setint(work + 1, 1);
fe25519_setint(work + 2, 0);
work[3] = *xr;
fe25519_setint(work + 4, 1);
int i, j;
uint8_t prevbit = 0;
j = 6;
for (i = 31; i >= 0; i--) {
while (j >= 0) {
const uint8_t bit = 1 & (s[i] >> j);
const uint64_t swap = bit ^ prevbit;
prevbit = bit;
x25519_x86_64_work_cswap(work + 1, swap);
x25519_x86_64_ladderstep(work);
j -= 1;
}
j = 7;
}
*xr = work[1];
*zr = work[2];
}
void x25519_x86_64(uint8_t out[32], const uint8_t scalar[32],
const uint8_t point[32]) {
uint8_t e[32];
OPENSSL_memcpy(e, scalar, sizeof(e));
e[0] &= 248;
e[31] &= 127;
e[31] |= 64;
fe25519 t;
fe25519 z;
fe25519_unpack(&t, point);
mladder(&t, &z, e);
fe25519_invert(&z, &z);
x25519_x86_64_mul(&t, &t, &z);
fe25519_pack(out, &t);
}
#endif /* BORINGSSL_X25519_X86_64 */
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