2 * Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.
3 * Copyright 2015-2016 Cryptography Research, Inc.
5 * Licensed under the OpenSSL license (the "License"). You may not use
6 * this file except in compliance with the License. You can obtain a copy
7 * in the file LICENSE in the source distribution or at
8 * https://www.openssl.org/source/license.html
10 * Originally written by Mike Hamburg
14 static const gf MODULUS = {FIELD_LITERAL(
15 0xffffffffffffff, 0xffffffffffffff, 0xffffffffffffff, 0xffffffffffffff, 0xfffffffffffffe, 0xffffffffffffff, 0xffffffffffffff, 0xffffffffffffff
18 /** Serialize to wire format. */
19 void gf_serialize (uint8_t serial[SER_BYTES], const gf x, int with_hibit) {
20 unsigned int j=0, fill=0;
26 gf_strong_reduce(red);
27 if (!with_hibit) { assert(gf_hibit(red) == 0); }
29 UNROLL for (i=0; i<(with_hibit ? X_SER_BYTES : SER_BYTES); i++) {
30 if (fill < 8 && j < NLIMBS) {
31 buffer |= ((dword_t)red->limb[LIMBPERM(j)]) << fill;
32 fill += LIMB_PLACE_VALUE(LIMBPERM(j));
41 /** Return high bit of x = low bit of 2x mod p */
42 mask_t gf_hibit(const gf x) {
46 return -(y->limb[0]&1);
49 /** Return high bit of x = low bit of 2x mod p */
50 mask_t gf_lobit(const gf x) {
54 return -(y->limb[0]&1);
57 /** Deserialize from wire format; return -1 on success and 0 on failure. */
58 mask_t gf_deserialize (gf x, const uint8_t serial[SER_BYTES], int with_hibit, uint8_t hi_nmask) {
59 unsigned int j=0, fill=0;
62 const unsigned nbytes = with_hibit ? X_SER_BYTES : SER_BYTES;
66 UNROLL for (i=0; i<NLIMBS; i++) {
67 UNROLL while (fill < LIMB_PLACE_VALUE(LIMBPERM(i)) && j < nbytes) {
68 uint8_t sj = serial[j];
69 if (j==nbytes-1) sj &= ~hi_nmask;
70 buffer |= ((dword_t)sj) << fill;
74 x->limb[LIMBPERM(i)] = (i<NLIMBS-1) ? buffer & LIMB_MASK(LIMBPERM(i)) : buffer;
75 fill -= LIMB_PLACE_VALUE(LIMBPERM(i));
76 buffer >>= LIMB_PLACE_VALUE(LIMBPERM(i));
77 scarry = (scarry + x->limb[LIMBPERM(i)] - MODULUS->limb[LIMBPERM(i)]) >> (8*sizeof(word_t));
79 succ = with_hibit ? -(mask_t)1 : ~gf_hibit(x);
80 return succ & word_is_zero(buffer) & ~word_is_zero(scarry);
83 /** Reduce to canonical form. */
84 void gf_strong_reduce (gf a) {
90 /* first, clear high */
91 gf_weak_reduce(a); /* Determined to have negligible perf impact. */
93 /* now the total is less than 2p */
95 /* compute total_value - p. No need to reduce mod p. */
97 for (i=0; i<NLIMBS; i++) {
98 scarry = scarry + a->limb[LIMBPERM(i)] - MODULUS->limb[LIMBPERM(i)];
99 a->limb[LIMBPERM(i)] = scarry & LIMB_MASK(LIMBPERM(i));
100 scarry >>= LIMB_PLACE_VALUE(LIMBPERM(i));
103 /* uncommon case: it was >= p, so now scarry = 0 and this = x
104 * common case: it was < p, so now scarry = -1 and this = x - p + 2^255
105 * so let's add back in p. will carry back off the top for 2^255.
107 assert(word_is_zero(scarry) | word_is_zero(scarry+1));
112 for (i=0; i<NLIMBS; i++) {
113 carry = carry + a->limb[LIMBPERM(i)] + (scarry_0 & MODULUS->limb[LIMBPERM(i)]);
114 a->limb[LIMBPERM(i)] = carry & LIMB_MASK(LIMBPERM(i));
115 carry >>= LIMB_PLACE_VALUE(LIMBPERM(i));
118 assert(word_is_zero(carry + scarry_0));
121 /** Subtract two gf elements d=a-b */
122 void gf_sub (gf d, const gf a, const gf b) {
123 gf_sub_RAW ( d, a, b );
125 gf_weak_reduce ( d );
128 /** Add two field elements d = a+b */
129 void gf_add (gf d, const gf a, const gf b) {
130 gf_add_RAW ( d, a, b );
131 gf_weak_reduce ( d );
135 mask_t gf_eq(const gf a, const gf b) {
143 for (i=0; i<NLIMBS; i++) {
144 ret |= c->limb[LIMBPERM(i)];
147 return word_is_zero(ret);