X-Git-Url: https://www.bearssl.org/gitweb//home/git/?p=BearSSL;a=blobdiff_plain;f=src%2Fec%2Fec_c25519_i15.c;fp=src%2Fec%2Fec_c25519_i15.c;h=79560ae9f6197be721501c22670e197a86f887d6;hp=0000000000000000000000000000000000000000;hb=2f9c953af45299f8546df8984d5262e767a7d943;hpb=ef318ef83a3a58b0a9e036676b84d11261ed7bb4 diff --git a/src/ec/ec_c25519_i15.c b/src/ec/ec_c25519_i15.c new file mode 100644 index 0000000..79560ae --- /dev/null +++ b/src/ec/ec_c25519_i15.c @@ -0,0 +1,303 @@ +/* + * Copyright (c) 2017 Thomas Pornin + * + * Permission is hereby granted, free of charge, to any person obtaining + * a copy of this software and associated documentation files (the + * "Software"), to deal in the Software without restriction, including + * without limitation the rights to use, copy, modify, merge, publish, + * distribute, sublicense, and/or sell copies of the Software, and to + * permit persons to whom the Software is furnished to do so, subject to + * the following conditions: + * + * The above copyright notice and this permission notice shall be + * included in all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND + * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS + * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN + * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN + * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE + * SOFTWARE. + */ + +#include "inner.h" + +/* + * Parameters for the field: + * - field modulus p = 2^255-19 + * - R^2 mod p (R = 2^(15k) for the smallest k such that R >= p) + */ + +static const uint16_t C255_P[] = { + 0x0110, + 0x7FED, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, + 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, 0x7FFF, + 0x7FFF +}; + +#define P0I 0x4A1B + +static const uint16_t C255_R2[] = { + 0x0110, + 0x0169, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, + 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, + 0x0000 +}; + +static const uint16_t C255_A24[] = { + 0x0110, + 0x45D3, 0x0046, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, + 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, + 0x0000 +}; + +static const unsigned char GEN[] = { + 0x09, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 +}; + +static const unsigned char ORDER[] = { + 0x10, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, + 0x14, 0xDE, 0xF9, 0xDE, 0xA2, 0xF7, 0x9C, 0xD6, + 0x58, 0x12, 0x63, 0x1A, 0x5C, 0xF5, 0xD3, 0xED +}; + +static const unsigned char * +api_generator(int curve, size_t *len) +{ + (void)curve; + *len = 32; + return GEN; +} + +static const unsigned char * +api_order(int curve, size_t *len) +{ + (void)curve; + *len = 32; + return ORDER; +} + +static void +cswap(uint16_t *a, uint16_t *b, uint32_t ctl) +{ + int i; + + ctl = -ctl; + for (i = 0; i < 18; i ++) { + uint32_t aw, bw, tw; + + aw = a[i]; + bw = b[i]; + tw = ctl & (aw ^ bw); + a[i] = aw ^ tw; + b[i] = bw ^ tw; + } +} + +static void +c255_add(uint16_t *d, const uint16_t *a, const uint16_t *b) +{ + uint32_t ctl; + uint16_t t[18]; + + memcpy(t, a, sizeof t); + ctl = br_i15_add(t, b, 1); + ctl |= NOT(br_i15_sub(t, C255_P, 0)); + br_i15_sub(t, C255_P, ctl); + memcpy(d, t, sizeof t); +} + +static void +c255_sub(uint16_t *d, const uint16_t *a, const uint16_t *b) +{ + uint16_t t[18]; + + memcpy(t, a, sizeof t); + br_i15_add(t, C255_P, br_i15_sub(t, b, 1)); + memcpy(d, t, sizeof t); +} + +static void +c255_mul(uint16_t *d, const uint16_t *a, const uint16_t *b) +{ + uint16_t t[18]; + + br_i15_montymul(t, a, b, C255_P, P0I); + memcpy(d, t, sizeof t); +} + +static void +byteswap(unsigned char *G) +{ + int i; + + for (i = 0; i < 16; i ++) { + unsigned char t; + + t = G[i]; + G[i] = G[31 - i]; + G[31 - i] = t; + } +} + +static uint32_t +api_mul(unsigned char *G, size_t Glen, + const unsigned char *kb, size_t kblen, int curve) +{ + uint16_t x1[18], x2[18], x3[18], z2[18], z3[18]; + uint16_t a[18], aa[18], b[18], bb[18]; + uint16_t c[18], d[18], e[18], da[18], cb[18]; + unsigned char k[32]; + uint32_t swap; + int i; + + (void)curve; + + /* + * Points are encoded over exactly 32 bytes. Multipliers must fit + * in 32 bytes as well. + * RFC 7748 mandates that the high bit of the last point byte must + * be ignored/cleared. + */ + if (Glen != 32 || kblen > 32) { + return 0; + } + G[31] &= 0x7F; + + /* + * Byteswap the point encoding, because it uses little-endian, and + * the generic decoding routine uses big-endian. + */ + byteswap(G); + + /* + * Initialise variables x1, x2, z2, x3 and z3. We set all of them + * into Montgomery representation. + */ + br_i15_decode_reduce(a, G, 32, C255_P); + br_i15_montymul(x1, a, C255_R2, C255_P, P0I); + memcpy(x3, x1, sizeof x1); + br_i15_zero(z2, C255_P[0]); + memcpy(x2, z2, sizeof z2); + x2[1] = 19; + memcpy(z3, x2, sizeof x2); + + memcpy(k, kb, kblen); + memset(k + kblen, 0, (sizeof k) - kblen); + k[0] &= 0xF8; + k[31] &= 0x7F; + k[31] |= 0x40; + + swap = 0; + for (i = 254; i >= 0; i --) { + uint32_t kt; + + kt = (k[i >> 3] >> (i & 7)) & 1; + swap ^= kt; + cswap(x2, x3, swap); + cswap(z2, z3, swap); + swap = kt; + + c255_add(a, x2, z2); + c255_mul(aa, a, a); + c255_sub(b, x2, z2); + c255_mul(bb, b, b); + c255_sub(e, aa, bb); + c255_add(c, x3, z3); + c255_sub(d, x3, z3); + c255_mul(da, d, a); + c255_mul(cb, c, b); + c255_add(x3, da, cb); + c255_mul(x3, x3, x3); + c255_sub(z3, da, cb); + c255_mul(z3, z3, z3); + c255_mul(z3, z3, x1); + c255_mul(x2, aa, bb); + c255_mul(z2, C255_A24, e); + c255_add(z2, z2, aa); + c255_mul(z2, e, z2); + } + cswap(x2, x3, swap); + cswap(z2, z3, swap); + + /* + * Inverse z2 with a modular exponentiation. This is a simple + * square-and-multiply algorithm; we mutualise most non-squarings + * since the exponent contains almost only ones. + */ + memcpy(a, z2, sizeof z2); + for (i = 0; i < 15; i ++) { + c255_mul(a, a, a); + c255_mul(a, a, z2); + } + memcpy(b, a, sizeof a); + for (i = 0; i < 14; i ++) { + int j; + + for (j = 0; j < 16; j ++) { + c255_mul(b, b, b); + } + c255_mul(b, b, a); + } + for (i = 14; i >= 0; i --) { + c255_mul(b, b, b); + if ((0xFFEB >> i) & 1) { + c255_mul(b, z2, b); + } + } + c255_mul(x2, x2, b); + br_i15_from_monty(x2, C255_P, P0I); + br_i15_encode(G, 32, x2); + byteswap(G); + return 1; +} + +static size_t +api_mulgen(unsigned char *R, + const unsigned char *x, size_t xlen, int curve) +{ + const unsigned char *G; + size_t Glen; + + G = api_generator(curve, &Glen); + memcpy(R, G, Glen); + api_mul(R, Glen, x, xlen, curve); + return Glen; +} + +static uint32_t +api_muladd(unsigned char *A, const unsigned char *B, size_t len, + const unsigned char *x, size_t xlen, + const unsigned char *y, size_t ylen, int curve) +{ + /* + * We don't implement this method, since it is used for ECDSA + * only, and there is no ECDSA over Curve25519 (which instead + * uses EdDSA). + */ + (void)A; + (void)B; + (void)len; + (void)x; + (void)xlen; + (void)y; + (void)ylen; + (void)curve; + return 0; +} + +/* see bearssl_ec.h */ +const br_ec_impl br_ec_c25519_i15 = { + (uint32_t)0x20000000, + &api_generator, + &api_order, + &api_mul, + &api_mulgen, + &api_muladd +};