/* 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. */ /* A 64-bit implementation of the NIST P-256 elliptic curve point * multiplication * * OpenSSL integration was taken from Emilia Kasper's work in ecp_nistp224.c. * Otherwise based on Emilia's P224 work, which was inspired by my curve25519 * work which got its smarts from Daniel J. Bernstein's work on the same. */ #include #if defined(OPENSSL_64_BIT) && !defined(OPENSSL_WINDOWS) #include #include #include #include #include #include "internal.h" #include "../internal.h" typedef uint8_t u8; typedef uint64_t u64; typedef int64_t s64; /* The underlying field. P256 operates over GF(2^256-2^224+2^192+2^96-1). We * can serialise an element of this field into 32 bytes. We call this an * felem_bytearray. */ typedef u8 felem_bytearray[32]; /* The representation of field elements. * ------------------------------------ * * We represent field elements with either four 128-bit values, eight 128-bit * values, or four 64-bit values. The field element represented is: * v[0]*2^0 + v[1]*2^64 + v[2]*2^128 + v[3]*2^192 (mod p) * or: * v[0]*2^0 + v[1]*2^64 + v[2]*2^128 + ... + v[8]*2^512 (mod p) * * 128-bit values are called 'limbs'. Since the limbs are spaced only 64 bits * apart, but are 128-bits wide, the most significant bits of each limb overlap * with the least significant bits of the next. * * A field element with four limbs is an 'felem'. One with eight limbs is a * 'longfelem' * * A field element with four, 64-bit values is called a 'smallfelem'. Small * values are used as intermediate values before multiplication. */ #define NLIMBS 4 typedef uint128_t limb; typedef limb felem[NLIMBS]; typedef limb longfelem[NLIMBS * 2]; typedef u64 smallfelem[NLIMBS]; /* This is the value of the prime as four 64-bit words, little-endian. */ static const u64 kPrime[4] = {0xfffffffffffffffful, 0xffffffff, 0, 0xffffffff00000001ul}; static const u64 bottom63bits = 0x7ffffffffffffffful; /* bin32_to_felem takes a little-endian byte array and converts it into felem * form. This assumes that the CPU is little-endian. */ static void bin32_to_felem(felem out, const u8 in[32]) { out[0] = *((const u64 *)&in[0]); out[1] = *((const u64 *)&in[8]); out[2] = *((const u64 *)&in[16]); out[3] = *((const u64 *)&in[24]); } /* smallfelem_to_bin32 takes a smallfelem and serialises into a little endian, * 32 byte array. This assumes that the CPU is little-endian. */ static void smallfelem_to_bin32(u8 out[32], const smallfelem in) { *((u64 *)&out[0]) = in[0]; *((u64 *)&out[8]) = in[1]; *((u64 *)&out[16]) = in[2]; *((u64 *)&out[24]) = in[3]; } /* To preserve endianness when using BN_bn2bin and BN_bin2bn. */ static void flip_endian(u8 *out, const u8 *in, size_t len) { for (size_t i = 0; i < len; ++i) { out[i] = in[len - 1 - i]; } } /* BN_to_felem converts an OpenSSL BIGNUM into an felem. */ static int BN_to_felem(felem out, const BIGNUM *bn) { if (BN_is_negative(bn)) { OPENSSL_PUT_ERROR(EC, EC_R_BIGNUM_OUT_OF_RANGE); return 0; } felem_bytearray b_out; /* BN_bn2bin eats leading zeroes */ OPENSSL_memset(b_out, 0, sizeof(b_out)); size_t num_bytes = BN_num_bytes(bn); if (num_bytes > sizeof(b_out)) { OPENSSL_PUT_ERROR(EC, EC_R_BIGNUM_OUT_OF_RANGE); return 0; } felem_bytearray b_in; num_bytes = BN_bn2bin(bn, b_in); flip_endian(b_out, b_in, num_bytes); bin32_to_felem(out, b_out); return 1; } /* felem_to_BN converts an felem into an OpenSSL BIGNUM. */ static BIGNUM *smallfelem_to_BN(BIGNUM *out, const smallfelem in) { felem_bytearray b_in, b_out; smallfelem_to_bin32(b_in, in); flip_endian(b_out, b_in, sizeof(b_out)); return BN_bin2bn(b_out, sizeof(b_out), out); } /* Field operations. */ static void felem_assign(felem out, const felem in) { out[0] = in[0]; out[1] = in[1]; out[2] = in[2]; out[3] = in[3]; } /* felem_sum sets out = out + in. */ static void felem_sum(felem out, const felem in) { out[0] += in[0]; out[1] += in[1]; out[2] += in[2]; out[3] += in[3]; } /* felem_small_sum sets out = out + in. */ static void felem_small_sum(felem out, const smallfelem in) { out[0] += in[0]; out[1] += in[1]; out[2] += in[2]; out[3] += in[3]; } /* felem_scalar sets out = out * scalar */ static void felem_scalar(felem out, const u64 scalar) { out[0] *= scalar; out[1] *= scalar; out[2] *= scalar; out[3] *= scalar; } /* longfelem_scalar sets out = out * scalar */ static void longfelem_scalar(longfelem out, const u64 scalar) { out[0] *= scalar; out[1] *= scalar; out[2] *= scalar; out[3] *= scalar; out[4] *= scalar; out[5] *= scalar; out[6] *= scalar; out[7] *= scalar; } #define two105m41m9 ((((limb)1) << 105) - (((limb)1) << 41) - (((limb)1) << 9)) #define two105 (((limb)1) << 105) #define two105m41p9 ((((limb)1) << 105) - (((limb)1) << 41) + (((limb)1) << 9)) /* zero105 is 0 mod p */ static const felem zero105 = {two105m41m9, two105, two105m41p9, two105m41p9}; /* smallfelem_neg sets |out| to |-small| * On exit: * out[i] < out[i] + 2^105 */ static void smallfelem_neg(felem out, const smallfelem small) { /* In order to prevent underflow, we subtract from 0 mod p. */ out[0] = zero105[0] - small[0]; out[1] = zero105[1] - small[1]; out[2] = zero105[2] - small[2]; out[3] = zero105[3] - small[3]; } /* felem_diff subtracts |in| from |out| * On entry: * in[i] < 2^104 * On exit: * out[i] < out[i] + 2^105. */ static void felem_diff(felem out, const felem in) { /* In order to prevent underflow, we add 0 mod p before subtracting. */ out[0] += zero105[0]; out[1] += zero105[1]; out[2] += zero105[2]; out[3] += zero105[3]; out[0] -= in[0]; out[1] -= in[1]; out[2] -= in[2]; out[3] -= in[3]; } #define two107m43m11 \ ((((limb)1) << 107) - (((limb)1) << 43) - (((limb)1) << 11)) #define two107 (((limb)1) << 107) #define two107m43p11 \ ((((limb)1) << 107) - (((limb)1) << 43) + (((limb)1) << 11)) /* zero107 is 0 mod p */ static const felem zero107 = {two107m43m11, two107, two107m43p11, two107m43p11}; /* An alternative felem_diff for larger inputs |in| * felem_diff_zero107 subtracts |in| from |out| * On entry: * in[i] < 2^106 * On exit: * out[i] < out[i] + 2^107. */ static void felem_diff_zero107(felem out, const felem in) { /* In order to prevent underflow, we add 0 mod p before subtracting. */ out[0] += zero107[0]; out[1] += zero107[1]; out[2] += zero107[2]; out[3] += zero107[3]; out[0] -= in[0]; out[1] -= in[1]; out[2] -= in[2]; out[3] -= in[3]; } /* longfelem_diff subtracts |in| from |out| * On entry: * in[i] < 7*2^67 * On exit: * out[i] < out[i] + 2^70 + 2^40. */ static void longfelem_diff(longfelem out, const longfelem in) { static const limb two70m8p6 = (((limb)1) << 70) - (((limb)1) << 8) + (((limb)1) << 6); static const limb two70p40 = (((limb)1) << 70) + (((limb)1) << 40); static const limb two70 = (((limb)1) << 70); static const limb two70m40m38p6 = (((limb)1) << 70) - (((limb)1) << 40) - (((limb)1) << 38) + (((limb)1) << 6); static const limb two70m6 = (((limb)1) << 70) - (((limb)1) << 6); /* add 0 mod p to avoid underflow */ out[0] += two70m8p6; out[1] += two70p40; out[2] += two70; out[3] += two70m40m38p6; out[4] += two70m6; out[5] += two70m6; out[6] += two70m6; out[7] += two70m6; /* in[i] < 7*2^67 < 2^70 - 2^40 - 2^38 + 2^6 */ out[0] -= in[0]; out[1] -= in[1]; out[2] -= in[2]; out[3] -= in[3]; out[4] -= in[4]; out[5] -= in[5]; out[6] -= in[6]; out[7] -= in[7]; } #define two64m0 ((((limb)1) << 64) - 1) #define two110p32m0 ((((limb)1) << 110) + (((limb)1) << 32) - 1) #define two64m46 ((((limb)1) << 64) - (((limb)1) << 46)) #define two64m32 ((((limb)1) << 64) - (((limb)1) << 32)) /* zero110 is 0 mod p. */ static const felem zero110 = {two64m0, two110p32m0, two64m46, two64m32}; /* felem_shrink converts an felem into a smallfelem. The result isn't quite * minimal as the value may be greater than p. * * On entry: * in[i] < 2^109 * On exit: * out[i] < 2^64. */ static void felem_shrink(smallfelem out, const felem in) { felem tmp; u64 a, b, mask; s64 high, low; static const u64 kPrime3Test = 0x7fffffff00000001ul; /* 2^63 - 2^32 + 1 */ /* Carry 2->3 */ tmp[3] = zero110[3] + in[3] + ((u64)(in[2] >> 64)); /* tmp[3] < 2^110 */ tmp[2] = zero110[2] + (u64)in[2]; tmp[0] = zero110[0] + in[0]; tmp[1] = zero110[1] + in[1]; /* tmp[0] < 2**110, tmp[1] < 2^111, tmp[2] < 2**65 */ /* We perform two partial reductions where we eliminate the high-word of * tmp[3]. We don't update the other words till the end. */ a = tmp[3] >> 64; /* a < 2^46 */ tmp[3] = (u64)tmp[3]; tmp[3] -= a; tmp[3] += ((limb)a) << 32; /* tmp[3] < 2^79 */ b = a; a = tmp[3] >> 64; /* a < 2^15 */ b += a; /* b < 2^46 + 2^15 < 2^47 */ tmp[3] = (u64)tmp[3]; tmp[3] -= a; tmp[3] += ((limb)a) << 32; /* tmp[3] < 2^64 + 2^47 */ /* This adjusts the other two words to complete the two partial * reductions. */ tmp[0] += b; tmp[1] -= (((limb)b) << 32); /* In order to make space in tmp[3] for the carry from 2 -> 3, we * conditionally subtract kPrime if tmp[3] is large enough. */ high = tmp[3] >> 64; /* As tmp[3] < 2^65, high is either 1 or 0 */ high = ~(high - 1); /* high is: * all ones if the high word of tmp[3] is 1 * all zeros if the high word of tmp[3] if 0 */ low = tmp[3]; mask = low >> 63; /* mask is: * all ones if the MSB of low is 1 * all zeros if the MSB of low if 0 */ low &= bottom63bits; low -= kPrime3Test; /* if low was greater than kPrime3Test then the MSB is zero */ low = ~low; low >>= 63; /* low is: * all ones if low was > kPrime3Test * all zeros if low was <= kPrime3Test */ mask = (mask & low) | high; tmp[0] -= mask & kPrime[0]; tmp[1] -= mask & kPrime[1]; /* kPrime[2] is zero, so omitted */ tmp[3] -= mask & kPrime[3]; /* tmp[3] < 2**64 - 2**32 + 1 */ tmp[1] += ((u64)(tmp[0] >> 64)); tmp[0] = (u64)tmp[0]; tmp[2] += ((u64)(tmp[1] >> 64)); tmp[1] = (u64)tmp[1]; tmp[3] += ((u64)(tmp[2] >> 64)); tmp[2] = (u64)tmp[2]; /* tmp[i] < 2^64 */ out[0] = tmp[0]; out[1] = tmp[1]; out[2] = tmp[2]; out[3] = tmp[3]; } /* smallfelem_expand converts a smallfelem to an felem */ static void smallfelem_expand(felem out, const smallfelem in) { out[0] = in[0]; out[1] = in[1]; out[2] = in[2]; out[3] = in[3]; } /* smallfelem_square sets |out| = |small|^2 * On entry: * small[i] < 2^64 * On exit: * out[i] < 7 * 2^64 < 2^67 */ static void smallfelem_square(longfelem out, const smallfelem small) { limb a; u64 high, low; a = ((uint128_t)small[0]) * small[0]; low = a; high = a >> 64; out[0] = low; out[1] = high; a = ((uint128_t)small[0]) * small[1]; low = a; high = a >> 64; out[1] += low; out[1] += low; out[2] = high; a = ((uint128_t)small[0]) * small[2]; low = a; high = a >> 64; out[2] += low; out[2] *= 2; out[3] = high; a = ((uint128_t)small[0]) * small[3]; low = a; high = a >> 64; out[3] += low; out[4] = high; a = ((uint128_t)small[1]) * small[2]; low = a; high = a >> 64; out[3] += low; out[3] *= 2; out[4] += high; a = ((uint128_t)small[1]) * small[1]; low = a; high = a >> 64; out[2] += low; out[3] += high; a = ((uint128_t)small[1]) * small[3]; low = a; high = a >> 64; out[4] += low; out[4] *= 2; out[5] = high; a = ((uint128_t)small[2]) * small[3]; low = a; high = a >> 64; out[5] += low; out[5] *= 2; out[6] = high; out[6] += high; a = ((uint128_t)small[2]) * small[2]; low = a; high = a >> 64; out[4] += low; out[5] += high; a = ((uint128_t)small[3]) * small[3]; low = a; high = a >> 64; out[6] += low; out[7] = high; } /*felem_square sets |out| = |in|^2 * On entry: * in[i] < 2^109 * On exit: * out[i] < 7 * 2^64 < 2^67. */ static void felem_square(longfelem out, const felem in) { u64 small[4]; felem_shrink(small, in); smallfelem_square(out, small); } /* smallfelem_mul sets |out| = |small1| * |small2| * On entry: * small1[i] < 2^64 * small2[i] < 2^64 * On exit: * out[i] < 7 * 2^64 < 2^67. */ static void smallfelem_mul(longfelem out, const smallfelem small1, const smallfelem small2) { limb a; u64 high, low; a = ((uint128_t)small1[0]) * small2[0]; low = a; high = a >> 64; out[0] = low; out[1] = high; a = ((uint128_t)small1[0]) * small2[1]; low = a; high = a >> 64; out[1] += low; out[2] = high; a = ((uint128_t)small1[1]) * small2[0]; low = a; high = a >> 64; out[1] += low; out[2] += high; a = ((uint128_t)small1[0]) * small2[2]; low = a; high = a >> 64; out[2] += low; out[3] = high; a = ((uint128_t)small1[1]) * small2[1]; low = a; high = a >> 64; out[2] += low; out[3] += high; a = ((uint128_t)small1[2]) * small2[0]; low = a; high = a >> 64; out[2] += low; out[3] += high; a = ((uint128_t)small1[0]) * small2[3]; low = a; high = a >> 64; out[3] += low; out[4] = high; a = ((uint128_t)small1[1]) * small2[2]; low = a; high = a >> 64; out[3] += low; out[4] += high; a = ((uint128_t)small1[2]) * small2[1]; low = a; high = a >> 64; out[3] += low; out[4] += high; a = ((uint128_t)small1[3]) * small2[0]; low = a; high = a >> 64; out[3] += low; out[4] += high; a = ((uint128_t)small1[1]) * small2[3]; low = a; high = a >> 64; out[4] += low; out[5] = high; a = ((uint128_t)small1[2]) * small2[2]; low = a; high = a >> 64; out[4] += low; out[5] += high; a = ((uint128_t)small1[3]) * small2[1]; low = a; high = a >> 64; out[4] += low; out[5] += high; a = ((uint128_t)small1[2]) * small2[3]; low = a; high = a >> 64; out[5] += low; out[6] = high; a = ((uint128_t)small1[3]) * small2[2]; low = a; high = a >> 64; out[5] += low; out[6] += high; a = ((uint128_t)small1[3]) * small2[3]; low = a; high = a >> 64; out[6] += low; out[7] = high; } /* felem_mul sets |out| = |in1| * |in2| * On entry: * in1[i] < 2^109 * in2[i] < 2^109 * On exit: * out[i] < 7 * 2^64 < 2^67 */ static void felem_mul(longfelem out, const felem in1, const felem in2) { smallfelem small1, small2; felem_shrink(small1, in1); felem_shrink(small2, in2); smallfelem_mul(out, small1, small2); } /* felem_small_mul sets |out| = |small1| * |in2| * On entry: * small1[i] < 2^64 * in2[i] < 2^109 * On exit: * out[i] < 7 * 2^64 < 2^67 */ static void felem_small_mul(longfelem out, const smallfelem small1, const felem in2) { smallfelem small2; felem_shrink(small2, in2); smallfelem_mul(out, small1, small2); } #define two100m36m4 ((((limb)1) << 100) - (((limb)1) << 36) - (((limb)1) << 4)) #define two100 (((limb)1) << 100) #define two100m36p4 ((((limb)1) << 100) - (((limb)1) << 36) + (((limb)1) << 4)) /* zero100 is 0 mod p */ static const felem zero100 = {two100m36m4, two100, two100m36p4, two100m36p4}; /* Internal function for the different flavours of felem_reduce. * felem_reduce_ reduces the higher coefficients in[4]-in[7]. * On entry: * out[0] >= in[6] + 2^32*in[6] + in[7] + 2^32*in[7] * out[1] >= in[7] + 2^32*in[4] * out[2] >= in[5] + 2^32*in[5] * out[3] >= in[4] + 2^32*in[5] + 2^32*in[6] * On exit: * out[0] <= out[0] + in[4] + 2^32*in[5] * out[1] <= out[1] + in[5] + 2^33*in[6] * out[2] <= out[2] + in[7] + 2*in[6] + 2^33*in[7] * out[3] <= out[3] + 2^32*in[4] + 3*in[7] */ static void felem_reduce_(felem out, const longfelem in) { int128_t c; /* combine common terms from below */ c = in[4] + (in[5] << 32); out[0] += c; out[3] -= c; c = in[5] - in[7]; out[1] += c; out[2] -= c; /* the remaining terms */ /* 256: [(0,1),(96,-1),(192,-1),(224,1)] */ out[1] -= (in[4] << 32); out[3] += (in[4] << 32); /* 320: [(32,1),(64,1),(128,-1),(160,-1),(224,-1)] */ out[2] -= (in[5] << 32); /* 384: [(0,-1),(32,-1),(96,2),(128,2),(224,-1)] */ out[0] -= in[6]; out[0] -= (in[6] << 32); out[1] += (in[6] << 33); out[2] += (in[6] * 2); out[3] -= (in[6] << 32); /* 448: [(0,-1),(32,-1),(64,-1),(128,1),(160,2),(192,3)] */ out[0] -= in[7]; out[0] -= (in[7] << 32); out[2] += (in[7] << 33); out[3] += (in[7] * 3); } /* felem_reduce converts a longfelem into an felem. * To be called directly after felem_square or felem_mul. * On entry: * in[0] < 2^64, in[1] < 3*2^64, in[2] < 5*2^64, in[3] < 7*2^64 * in[4] < 7*2^64, in[5] < 5*2^64, in[6] < 3*2^64, in[7] < 2*64 * On exit: * out[i] < 2^101 */ static void felem_reduce(felem out, const longfelem in) { out[0] = zero100[0] + in[0]; out[1] = zero100[1] + in[1]; out[2] = zero100[2] + in[2]; out[3] = zero100[3] + in[3]; felem_reduce_(out, in); /* out[0] > 2^100 - 2^36 - 2^4 - 3*2^64 - 3*2^96 - 2^64 - 2^96 > 0 * out[1] > 2^100 - 2^64 - 7*2^96 > 0 * out[2] > 2^100 - 2^36 + 2^4 - 5*2^64 - 5*2^96 > 0 * out[3] > 2^100 - 2^36 + 2^4 - 7*2^64 - 5*2^96 - 3*2^96 > 0 * * out[0] < 2^100 + 2^64 + 7*2^64 + 5*2^96 < 2^101 * out[1] < 2^100 + 3*2^64 + 5*2^64 + 3*2^97 < 2^101 * out[2] < 2^100 + 5*2^64 + 2^64 + 3*2^65 + 2^97 < 2^101 * out[3] < 2^100 + 7*2^64 + 7*2^96 + 3*2^64 < 2^101 */ } /* felem_reduce_zero105 converts a larger longfelem into an felem. * On entry: * in[0] < 2^71 * On exit: * out[i] < 2^106 */ static void felem_reduce_zero105(felem out, const longfelem in) { out[0] = zero105[0] + in[0]; out[1] = zero105[1] + in[1]; out[2] = zero105[2] + in[2]; out[3] = zero105[3] + in[3]; felem_reduce_(out, in); /* out[0] > 2^105 - 2^41 - 2^9 - 2^71 - 2^103 - 2^71 - 2^103 > 0 * out[1] > 2^105 - 2^71 - 2^103 > 0 * out[2] > 2^105 - 2^41 + 2^9 - 2^71 - 2^103 > 0 * out[3] > 2^105 - 2^41 + 2^9 - 2^71 - 2^103 - 2^103 > 0 * * out[0] < 2^105 + 2^71 + 2^71 + 2^103 < 2^106 * out[1] < 2^105 + 2^71 + 2^71 + 2^103 < 2^106 * out[2] < 2^105 + 2^71 + 2^71 + 2^71 + 2^103 < 2^106 * out[3] < 2^105 + 2^71 + 2^103 + 2^71 < 2^106 */ } /* subtract_u64 sets *result = *result - v and *carry to one if the * subtraction underflowed. */ static void subtract_u64(u64 *result, u64 *carry, u64 v) { uint128_t r = *result; r -= v; *carry = (r >> 64) & 1; *result = (u64)r; } /* felem_contract converts |in| to its unique, minimal representation. On * entry: in[i] < 2^109. */ static void felem_contract(smallfelem out, const felem in) { u64 all_equal_so_far = 0, result = 0; felem_shrink(out, in); /* small is minimal except that the value might be > p */ all_equal_so_far--; /* We are doing a constant time test if out >= kPrime. We need to compare * each u64, from most-significant to least significant. For each one, if * all words so far have been equal (m is all ones) then a non-equal * result is the answer. Otherwise we continue. */ for (size_t i = 3; i < 4; i--) { u64 equal; uint128_t a = ((uint128_t)kPrime[i]) - out[i]; /* if out[i] > kPrime[i] then a will underflow and the high 64-bits * will all be set. */ result |= all_equal_so_far & ((u64)(a >> 64)); /* if kPrime[i] == out[i] then |equal| will be all zeros and the * decrement will make it all ones. */ equal = kPrime[i] ^ out[i]; equal--; equal &= equal << 32; equal &= equal << 16; equal &= equal << 8; equal &= equal << 4; equal &= equal << 2; equal &= equal << 1; equal = ((s64)equal) >> 63; all_equal_so_far &= equal; } /* if all_equal_so_far is still all ones then the two values are equal * and so out >= kPrime is true. */ result |= all_equal_so_far; /* if out >= kPrime then we subtract kPrime. */ u64 carry; subtract_u64(&out[0], &carry, result & kPrime[0]); subtract_u64(&out[1], &carry, carry); subtract_u64(&out[2], &carry, carry); subtract_u64(&out[3], &carry, carry); subtract_u64(&out[1], &carry, result & kPrime[1]); subtract_u64(&out[2], &carry, carry); subtract_u64(&out[3], &carry, carry); subtract_u64(&out[2], &carry, result & kPrime[2]); subtract_u64(&out[3], &carry, carry); subtract_u64(&out[3], &carry, result & kPrime[3]); } /* felem_is_zero returns a limb with all bits set if |in| == 0 (mod p) and 0 * otherwise. * On entry: * small[i] < 2^64 */ static limb smallfelem_is_zero(const smallfelem small) { limb result; u64 is_p; u64 is_zero = small[0] | small[1] | small[2] | small[3]; is_zero--; is_zero &= is_zero << 32; is_zero &= is_zero << 16; is_zero &= is_zero << 8; is_zero &= is_zero << 4; is_zero &= is_zero << 2; is_zero &= is_zero << 1; is_zero = ((s64)is_zero) >> 63; is_p = (small[0] ^ kPrime[0]) | (small[1] ^ kPrime[1]) | (small[2] ^ kPrime[2]) | (small[3] ^ kPrime[3]); is_p--; is_p &= is_p << 32; is_p &= is_p << 16; is_p &= is_p << 8; is_p &= is_p << 4; is_p &= is_p << 2; is_p &= is_p << 1; is_p = ((s64)is_p) >> 63; is_zero |= is_p; result = is_zero; result |= ((limb)is_zero) << 64; return result; } /* felem_inv calculates |out| = |in|^{-1} * * Based on Fermat's Little Theorem: * a^p = a (mod p) * a^{p-1} = 1 (mod p) * a^{p-2} = a^{-1} (mod p) */ static void felem_inv(felem out, const felem in) { felem ftmp, ftmp2; /* each e_I will hold |in|^{2^I - 1} */ felem e2, e4, e8, e16, e32, e64; longfelem tmp; felem_square(tmp, in); felem_reduce(ftmp, tmp); /* 2^1 */ felem_mul(tmp, in, ftmp); felem_reduce(ftmp, tmp); /* 2^2 - 2^0 */ felem_assign(e2, ftmp); felem_square(tmp, ftmp); felem_reduce(ftmp, tmp); /* 2^3 - 2^1 */ felem_square(tmp, ftmp); felem_reduce(ftmp, tmp); /* 2^4 - 2^2 */ felem_mul(tmp, ftmp, e2); felem_reduce(ftmp, tmp); /* 2^4 - 2^0 */ felem_assign(e4, ftmp); felem_square(tmp, ftmp); felem_reduce(ftmp, tmp); /* 2^5 - 2^1 */ felem_square(tmp, ftmp); felem_reduce(ftmp, tmp); /* 2^6 - 2^2 */ felem_square(tmp, ftmp); felem_reduce(ftmp, tmp); /* 2^7 - 2^3 */ felem_square(tmp, ftmp); felem_reduce(ftmp, tmp); /* 2^8 - 2^4 */ felem_mul(tmp, ftmp, e4); felem_reduce(ftmp, tmp); /* 2^8 - 2^0 */ felem_assign(e8, ftmp); for (size_t i = 0; i < 8; i++) { felem_square(tmp, ftmp); felem_reduce(ftmp, tmp); } /* 2^16 - 2^8 */ felem_mul(tmp, ftmp, e8); felem_reduce(ftmp, tmp); /* 2^16 - 2^0 */ felem_assign(e16, ftmp); for (size_t i = 0; i < 16; i++) { felem_square(tmp, ftmp); felem_reduce(ftmp, tmp); } /* 2^32 - 2^16 */ felem_mul(tmp, ftmp, e16); felem_reduce(ftmp, tmp); /* 2^32 - 2^0 */ felem_assign(e32, ftmp); for (size_t i = 0; i < 32; i++) { felem_square(tmp, ftmp); felem_reduce(ftmp, tmp); } /* 2^64 - 2^32 */ felem_assign(e64, ftmp); felem_mul(tmp, ftmp, in); felem_reduce(ftmp, tmp); /* 2^64 - 2^32 + 2^0 */ for (size_t i = 0; i < 192; i++) { felem_square(tmp, ftmp); felem_reduce(ftmp, tmp); } /* 2^256 - 2^224 + 2^192 */ felem_mul(tmp, e64, e32); felem_reduce(ftmp2, tmp); /* 2^64 - 2^0 */ for (size_t i = 0; i < 16; i++) { felem_square(tmp, ftmp2); felem_reduce(ftmp2, tmp); } /* 2^80 - 2^16 */ felem_mul(tmp, ftmp2, e16); felem_reduce(ftmp2, tmp); /* 2^80 - 2^0 */ for (size_t i = 0; i < 8; i++) { felem_square(tmp, ftmp2); felem_reduce(ftmp2, tmp); } /* 2^88 - 2^8 */ felem_mul(tmp, ftmp2, e8); felem_reduce(ftmp2, tmp); /* 2^88 - 2^0 */ for (size_t i = 0; i < 4; i++) { felem_square(tmp, ftmp2); felem_reduce(ftmp2, tmp); } /* 2^92 - 2^4 */ felem_mul(tmp, ftmp2, e4); felem_reduce(ftmp2, tmp); /* 2^92 - 2^0 */ felem_square(tmp, ftmp2); felem_reduce(ftmp2, tmp); /* 2^93 - 2^1 */ felem_square(tmp, ftmp2); felem_reduce(ftmp2, tmp); /* 2^94 - 2^2 */ felem_mul(tmp, ftmp2, e2); felem_reduce(ftmp2, tmp); /* 2^94 - 2^0 */ felem_square(tmp, ftmp2); felem_reduce(ftmp2, tmp); /* 2^95 - 2^1 */ felem_square(tmp, ftmp2); felem_reduce(ftmp2, tmp); /* 2^96 - 2^2 */ felem_mul(tmp, ftmp2, in); felem_reduce(ftmp2, tmp); /* 2^96 - 3 */ felem_mul(tmp, ftmp2, ftmp); felem_reduce(out, tmp); /* 2^256 - 2^224 + 2^192 + 2^96 - 3 */ } /* Group operations * ---------------- * * Building on top of the field operations we have the operations on the * elliptic curve group itself. Points on the curve are represented in Jacobian * coordinates. */ /* point_double calculates 2*(x_in, y_in, z_in) * * The method is taken from: * http://hyperelliptic.org/EFD/g1p/auto-shortw-jacobian-3.html#doubling-dbl-2001-b * * Outputs can equal corresponding inputs, i.e., x_out == x_in is allowed. * while x_out == y_in is not (maybe this works, but it's not tested). */ static void point_double(felem x_out, felem y_out, felem z_out, const felem x_in, const felem y_in, const felem z_in) { longfelem tmp, tmp2; felem delta, gamma, beta, alpha, ftmp, ftmp2; smallfelem small1, small2; felem_assign(ftmp, x_in); /* ftmp[i] < 2^106 */ felem_assign(ftmp2, x_in); /* ftmp2[i] < 2^106 */ /* delta = z^2 */ felem_square(tmp, z_in); felem_reduce(delta, tmp); /* delta[i] < 2^101 */ /* gamma = y^2 */ felem_square(tmp, y_in); felem_reduce(gamma, tmp); /* gamma[i] < 2^101 */ felem_shrink(small1, gamma); /* beta = x*gamma */ felem_small_mul(tmp, small1, x_in); felem_reduce(beta, tmp); /* beta[i] < 2^101 */ /* alpha = 3*(x-delta)*(x+delta) */ felem_diff(ftmp, delta); /* ftmp[i] < 2^105 + 2^106 < 2^107 */ felem_sum(ftmp2, delta); /* ftmp2[i] < 2^105 + 2^106 < 2^107 */ felem_scalar(ftmp2, 3); /* ftmp2[i] < 3 * 2^107 < 2^109 */ felem_mul(tmp, ftmp, ftmp2); felem_reduce(alpha, tmp); /* alpha[i] < 2^101 */ felem_shrink(small2, alpha); /* x' = alpha^2 - 8*beta */ smallfelem_square(tmp, small2); felem_reduce(x_out, tmp); felem_assign(ftmp, beta); felem_scalar(ftmp, 8); /* ftmp[i] < 8 * 2^101 = 2^104 */ felem_diff(x_out, ftmp); /* x_out[i] < 2^105 + 2^101 < 2^106 */ /* z' = (y + z)^2 - gamma - delta */ felem_sum(delta, gamma); /* delta[i] < 2^101 + 2^101 = 2^102 */ felem_assign(ftmp, y_in); felem_sum(ftmp, z_in); /* ftmp[i] < 2^106 + 2^106 = 2^107 */ felem_square(tmp, ftmp); felem_reduce(z_out, tmp); felem_diff(z_out, delta); /* z_out[i] < 2^105 + 2^101 < 2^106 */ /* y' = alpha*(4*beta - x') - 8*gamma^2 */ felem_scalar(beta, 4); /* beta[i] < 4 * 2^101 = 2^103 */ felem_diff_zero107(beta, x_out); /* beta[i] < 2^107 + 2^103 < 2^108 */ felem_small_mul(tmp, small2, beta); /* tmp[i] < 7 * 2^64 < 2^67 */ smallfelem_square(tmp2, small1); /* tmp2[i] < 7 * 2^64 */ longfelem_scalar(tmp2, 8); /* tmp2[i] < 8 * 7 * 2^64 = 7 * 2^67 */ longfelem_diff(tmp, tmp2); /* tmp[i] < 2^67 + 2^70 + 2^40 < 2^71 */ felem_reduce_zero105(y_out, tmp); /* y_out[i] < 2^106 */ } /* point_double_small is the same as point_double, except that it operates on * smallfelems. */ static void point_double_small(smallfelem x_out, smallfelem y_out, smallfelem z_out, const smallfelem x_in, const smallfelem y_in, const smallfelem z_in) { felem felem_x_out, felem_y_out, felem_z_out; felem felem_x_in, felem_y_in, felem_z_in; smallfelem_expand(felem_x_in, x_in); smallfelem_expand(felem_y_in, y_in); smallfelem_expand(felem_z_in, z_in); point_double(felem_x_out, felem_y_out, felem_z_out, felem_x_in, felem_y_in, felem_z_in); felem_shrink(x_out, felem_x_out); felem_shrink(y_out, felem_y_out); felem_shrink(z_out, felem_z_out); } /* copy_conditional copies in to out iff mask is all ones. */ static void copy_conditional(felem out, const felem in, limb mask) { for (size_t i = 0; i < NLIMBS; ++i) { const limb tmp = mask & (in[i] ^ out[i]); out[i] ^= tmp; } } /* copy_small_conditional copies in to out iff mask is all ones. */ static void copy_small_conditional(felem out, const smallfelem in, limb mask) { const u64 mask64 = mask; for (size_t i = 0; i < NLIMBS; ++i) { out[i] = ((limb)(in[i] & mask64)) | (out[i] & ~mask); } } /* point_add calcuates (x1, y1, z1) + (x2, y2, z2) * * The method is taken from: * http://hyperelliptic.org/EFD/g1p/auto-shortw-jacobian-3.html#addition-add-2007-bl, * adapted for mixed addition (z2 = 1, or z2 = 0 for the point at infinity). * * This function includes a branch for checking whether the two input points * are equal, (while not equal to the point at infinity). This case never * happens during single point multiplication, so there is no timing leak for * ECDH or ECDSA signing. */ static void point_add(felem x3, felem y3, felem z3, const felem x1, const felem y1, const felem z1, const int mixed, const smallfelem x2, const smallfelem y2, const smallfelem z2) { felem ftmp, ftmp2, ftmp3, ftmp4, ftmp5, ftmp6, x_out, y_out, z_out; longfelem tmp, tmp2; smallfelem small1, small2, small3, small4, small5; limb x_equal, y_equal, z1_is_zero, z2_is_zero; felem_shrink(small3, z1); z1_is_zero = smallfelem_is_zero(small3); z2_is_zero = smallfelem_is_zero(z2); /* ftmp = z1z1 = z1**2 */ smallfelem_square(tmp, small3); felem_reduce(ftmp, tmp); /* ftmp[i] < 2^101 */ felem_shrink(small1, ftmp); if (!mixed) { /* ftmp2 = z2z2 = z2**2 */ smallfelem_square(tmp, z2); felem_reduce(ftmp2, tmp); /* ftmp2[i] < 2^101 */ felem_shrink(small2, ftmp2); felem_shrink(small5, x1); /* u1 = ftmp3 = x1*z2z2 */ smallfelem_mul(tmp, small5, small2); felem_reduce(ftmp3, tmp); /* ftmp3[i] < 2^101 */ /* ftmp5 = z1 + z2 */ felem_assign(ftmp5, z1); felem_small_sum(ftmp5, z2); /* ftmp5[i] < 2^107 */ /* ftmp5 = (z1 + z2)**2 - (z1z1 + z2z2) = 2z1z2 */ felem_square(tmp, ftmp5); felem_reduce(ftmp5, tmp); /* ftmp2 = z2z2 + z1z1 */ felem_sum(ftmp2, ftmp); /* ftmp2[i] < 2^101 + 2^101 = 2^102 */ felem_diff(ftmp5, ftmp2); /* ftmp5[i] < 2^105 + 2^101 < 2^106 */ /* ftmp2 = z2 * z2z2 */ smallfelem_mul(tmp, small2, z2); felem_reduce(ftmp2, tmp); /* s1 = ftmp2 = y1 * z2**3 */ felem_mul(tmp, y1, ftmp2); felem_reduce(ftmp6, tmp); /* ftmp6[i] < 2^101 */ } else { /* We'll assume z2 = 1 (special case z2 = 0 is handled later). */ /* u1 = ftmp3 = x1*z2z2 */ felem_assign(ftmp3, x1); /* ftmp3[i] < 2^106 */ /* ftmp5 = 2z1z2 */ felem_assign(ftmp5, z1); felem_scalar(ftmp5, 2); /* ftmp5[i] < 2*2^106 = 2^107 */ /* s1 = ftmp2 = y1 * z2**3 */ felem_assign(ftmp6, y1); /* ftmp6[i] < 2^106 */ } /* u2 = x2*z1z1 */ smallfelem_mul(tmp, x2, small1); felem_reduce(ftmp4, tmp); /* h = ftmp4 = u2 - u1 */ felem_diff_zero107(ftmp4, ftmp3); /* ftmp4[i] < 2^107 + 2^101 < 2^108 */ felem_shrink(small4, ftmp4); x_equal = smallfelem_is_zero(small4); /* z_out = ftmp5 * h */ felem_small_mul(tmp, small4, ftmp5); felem_reduce(z_out, tmp); /* z_out[i] < 2^101 */ /* ftmp = z1 * z1z1 */ smallfelem_mul(tmp, small1, small3); felem_reduce(ftmp, tmp); /* s2 = tmp = y2 * z1**3 */ felem_small_mul(tmp, y2, ftmp); felem_reduce(ftmp5, tmp); /* r = ftmp5 = (s2 - s1)*2 */ felem_diff_zero107(ftmp5, ftmp6); /* ftmp5[i] < 2^107 + 2^107 = 2^108 */ felem_scalar(ftmp5, 2); /* ftmp5[i] < 2^109 */ felem_shrink(small1, ftmp5); y_equal = smallfelem_is_zero(small1); if (x_equal && y_equal && !z1_is_zero && !z2_is_zero) { point_double(x3, y3, z3, x1, y1, z1); return; } /* I = ftmp = (2h)**2 */ felem_assign(ftmp, ftmp4); felem_scalar(ftmp, 2); /* ftmp[i] < 2*2^108 = 2^109 */ felem_square(tmp, ftmp); felem_reduce(ftmp, tmp); /* J = ftmp2 = h * I */ felem_mul(tmp, ftmp4, ftmp); felem_reduce(ftmp2, tmp); /* V = ftmp4 = U1 * I */ felem_mul(tmp, ftmp3, ftmp); felem_reduce(ftmp4, tmp); /* x_out = r**2 - J - 2V */ smallfelem_square(tmp, small1); felem_reduce(x_out, tmp); felem_assign(ftmp3, ftmp4); felem_scalar(ftmp4, 2); felem_sum(ftmp4, ftmp2); /* ftmp4[i] < 2*2^101 + 2^101 < 2^103 */ felem_diff(x_out, ftmp4); /* x_out[i] < 2^105 + 2^101 */ /* y_out = r(V-x_out) - 2 * s1 * J */ felem_diff_zero107(ftmp3, x_out); /* ftmp3[i] < 2^107 + 2^101 < 2^108 */ felem_small_mul(tmp, small1, ftmp3); felem_mul(tmp2, ftmp6, ftmp2); longfelem_scalar(tmp2, 2); /* tmp2[i] < 2*2^67 = 2^68 */ longfelem_diff(tmp, tmp2); /* tmp[i] < 2^67 + 2^70 + 2^40 < 2^71 */ felem_reduce_zero105(y_out, tmp); /* y_out[i] < 2^106 */ copy_small_conditional(x_out, x2, z1_is_zero); copy_conditional(x_out, x1, z2_is_zero); copy_small_conditional(y_out, y2, z1_is_zero); copy_conditional(y_out, y1, z2_is_zero); copy_small_conditional(z_out, z2, z1_is_zero); copy_conditional(z_out, z1, z2_is_zero); felem_assign(x3, x_out); felem_assign(y3, y_out); felem_assign(z3, z_out); } /* point_add_small is the same as point_add, except that it operates on * smallfelems. */ static void point_add_small(smallfelem x3, smallfelem y3, smallfelem z3, smallfelem x1, smallfelem y1, smallfelem z1, smallfelem x2, smallfelem y2, smallfelem z2) { felem felem_x3, felem_y3, felem_z3; felem felem_x1, felem_y1, felem_z1; smallfelem_expand(felem_x1, x1); smallfelem_expand(felem_y1, y1); smallfelem_expand(felem_z1, z1); point_add(felem_x3, felem_y3, felem_z3, felem_x1, felem_y1, felem_z1, 0, x2, y2, z2); felem_shrink(x3, felem_x3); felem_shrink(y3, felem_y3); felem_shrink(z3, felem_z3); } /* Base point pre computation * -------------------------- * * Two different sorts of precomputed tables are used in the following code. * Each contain various points on the curve, where each point is three field * elements (x, y, z). * * For the base point table, z is usually 1 (0 for the point at infinity). * This table has 2 * 16 elements, starting with the following: * index | bits | point * ------+---------+------------------------------ * 0 | 0 0 0 0 | 0G * 1 | 0 0 0 1 | 1G * 2 | 0 0 1 0 | 2^64G * 3 | 0 0 1 1 | (2^64 + 1)G * 4 | 0 1 0 0 | 2^128G * 5 | 0 1 0 1 | (2^128 + 1)G * 6 | 0 1 1 0 | (2^128 + 2^64)G * 7 | 0 1 1 1 | (2^128 + 2^64 + 1)G * 8 | 1 0 0 0 | 2^192G * 9 | 1 0 0 1 | (2^192 + 1)G * 10 | 1 0 1 0 | (2^192 + 2^64)G * 11 | 1 0 1 1 | (2^192 + 2^64 + 1)G * 12 | 1 1 0 0 | (2^192 + 2^128)G * 13 | 1 1 0 1 | (2^192 + 2^128 + 1)G * 14 | 1 1 1 0 | (2^192 + 2^128 + 2^64)G * 15 | 1 1 1 1 | (2^192 + 2^128 + 2^64 + 1)G * followed by a copy of this with each element multiplied by 2^32. * * The reason for this is so that we can clock bits into four different * locations when doing simple scalar multiplies against the base point, * and then another four locations using the second 16 elements. * * Tables for other points have table[i] = iG for i in 0 .. 16. */ /* g_pre_comp is the table of precomputed base points */ static const smallfelem g_pre_comp[2][16][3] = { {{{0, 0, 0, 0}, {0, 0, 0, 0}, {0, 0, 0, 0}}, {{0xf4a13945d898c296, 0x77037d812deb33a0, 0xf8bce6e563a440f2, 0x6b17d1f2e12c4247}, {0xcbb6406837bf51f5, 0x2bce33576b315ece, 0x8ee7eb4a7c0f9e16, 0x4fe342e2fe1a7f9b}, {1, 0, 0, 0}}, {{0x90e75cb48e14db63, 0x29493baaad651f7e, 0x8492592e326e25de, 0x0fa822bc2811aaa5}, {0xe41124545f462ee7, 0x34b1a65050fe82f5, 0x6f4ad4bcb3df188b, 0xbff44ae8f5dba80d}, {1, 0, 0, 0}}, {{0x93391ce2097992af, 0xe96c98fd0d35f1fa, 0xb257c0de95e02789, 0x300a4bbc89d6726f}, {0xaa54a291c08127a0, 0x5bb1eeada9d806a5, 0x7f1ddb25ff1e3c6f, 0x72aac7e0d09b4644}, {1, 0, 0, 0}}, {{0x57c84fc9d789bd85, 0xfc35ff7dc297eac3, 0xfb982fd588c6766e, 0x447d739beedb5e67}, {0x0c7e33c972e25b32, 0x3d349b95a7fae500, 0xe12e9d953a4aaff7, 0x2d4825ab834131ee}, {1, 0, 0, 0}}, {{0x13949c932a1d367f, 0xef7fbd2b1a0a11b7, 0xddc6068bb91dfc60, 0xef9519328a9c72ff}, {0x196035a77376d8a8, 0x23183b0895ca1740, 0xc1ee9807022c219c, 0x611e9fc37dbb2c9b}, {1, 0, 0, 0}}, {{0xcae2b1920b57f4bc, 0x2936df5ec6c9bc36, 0x7dea6482e11238bf, 0x550663797b51f5d8}, {0x44ffe216348a964c, 0x9fb3d576dbdefbe1, 0x0afa40018d9d50e5, 0x157164848aecb851}, {1, 0, 0, 0}}, {{0xe48ecafffc5cde01, 0x7ccd84e70d715f26, 0xa2e8f483f43e4391, 0xeb5d7745b21141ea}, {0xcac917e2731a3479, 0x85f22cfe2844b645, 0x0990e6a158006cee, 0xeafd72ebdbecc17b}, {1, 0, 0, 0}}, {{0x6cf20ffb313728be, 0x96439591a3c6b94a, 0x2736ff8344315fc5, 0xa6d39677a7849276}, {0xf2bab833c357f5f4, 0x824a920c2284059b, 0x66b8babd2d27ecdf, 0x674f84749b0b8816}, {1, 0, 0, 0}}, {{0x2df48c04677c8a3e, 0x74e02f080203a56b, 0x31855f7db8c7fedb, 0x4e769e7672c9ddad}, {0xa4c36165b824bbb0, 0xfb9ae16f3b9122a5, 0x1ec0057206947281, 0x42b99082de830663}, {1, 0, 0, 0}}, {{0x6ef95150dda868b9, 0xd1f89e799c0ce131, 0x7fdc1ca008a1c478, 0x78878ef61c6ce04d}, {0x9c62b9121fe0d976, 0x6ace570ebde08d4f, 0xde53142c12309def, 0xb6cb3f5d7b72c321}, {1, 0, 0, 0}}, {{0x7f991ed2c31a3573, 0x5b82dd5bd54fb496, 0x595c5220812ffcae, 0x0c88bc4d716b1287}, {0x3a57bf635f48aca8, 0x7c8181f4df2564f3, 0x18d1b5b39c04e6aa, 0xdd5ddea3f3901dc6}, {1, 0, 0, 0}}, {{0xe96a79fb3e72ad0c, 0x43a0a28c42ba792f, 0xefe0a423083e49f3, 0x68f344af6b317466}, {0xcdfe17db3fb24d4a, 0x668bfc2271f5c626, 0x604ed93c24d67ff3, 0x31b9c405f8540a20}, {1, 0, 0, 0}}, {{0xd36b4789a2582e7f, 0x0d1a10144ec39c28, 0x663c62c3edbad7a0, 0x4052bf4b6f461db9}, {0x235a27c3188d25eb, 0xe724f33999bfcc5b, 0x862be6bd71d70cc8, 0xfecf4d5190b0fc61}, {1, 0, 0, 0}}, {{0x74346c10a1d4cfac, 0xafdf5cc08526a7a4, 0x123202a8f62bff7a, 0x1eddbae2c802e41a}, {0x8fa0af2dd603f844, 0x36e06b7e4c701917, 0x0c45f45273db33a0, 0x43104d86560ebcfc}, {1, 0, 0, 0}}, {{0x9615b5110d1d78e5, 0x66b0de3225c4744b, 0x0a4a46fb6aaf363a, 0xb48e26b484f7a21c}, {0x06ebb0f621a01b2d, 0xc004e4048b7b0f98, 0x64131bcdfed6f668, 0xfac015404d4d3dab}, {1, 0, 0, 0}}}, {{{0, 0, 0, 0}, {0, 0, 0, 0}, {0, 0, 0, 0}}, {{0x3a5a9e22185a5943, 0x1ab919365c65dfb6, 0x21656b32262c71da, 0x7fe36b40af22af89}, {0xd50d152c699ca101, 0x74b3d5867b8af212, 0x9f09f40407dca6f1, 0xe697d45825b63624}, {1, 0, 0, 0}}, {{0xa84aa9397512218e, 0xe9a521b074ca0141, 0x57880b3a18a2e902, 0x4a5b506612a677a6}, {0x0beada7a4c4f3840, 0x626db15419e26d9d, 0xc42604fbe1627d40, 0xeb13461ceac089f1}, {1, 0, 0, 0}}, {{0xf9faed0927a43281, 0x5e52c4144103ecbc, 0xc342967aa815c857, 0x0781b8291c6a220a}, {0x5a8343ceeac55f80, 0x88f80eeee54a05e3, 0x97b2a14f12916434, 0x690cde8df0151593}, {1, 0, 0, 0}}, {{0xaee9c75df7f82f2a, 0x9e4c35874afdf43a, 0xf5622df437371326, 0x8a535f566ec73617}, {0xc5f9a0ac223094b7, 0xcde533864c8c7669, 0x37e02819085a92bf, 0x0455c08468b08bd7}, {1, 0, 0, 0}}, {{0x0c0a6e2c9477b5d9, 0xf9a4bf62876dc444, 0x5050a949b6cdc279, 0x06bada7ab77f8276}, {0xc8b4aed1ea48dac9, 0xdebd8a4b7ea1070f, 0x427d49101366eb70, 0x5b476dfd0e6cb18a}, {1, 0, 0, 0}}, {{0x7c5c3e44278c340a, 0x4d54606812d66f3b, 0x29a751b1ae23c5d8, 0x3e29864e8a2ec908}, {0x142d2a6626dbb850, 0xad1744c4765bd780, 0x1f150e68e322d1ed, 0x239b90ea3dc31e7e}, {1, 0, 0, 0}}, {{0x78c416527a53322a, 0x305dde6709776f8e, 0xdbcab759f8862ed4, 0x820f4dd949f72ff7}, {0x6cc544a62b5debd4, 0x75be5d937b4e8cc4, 0x1b481b1b215c14d3, 0x140406ec783a05ec}, {1, 0, 0, 0}}, {{0x6a703f10e895df07, 0xfd75f3fa01876bd8, 0xeb5b06e70ce08ffe, 0x68f6b8542783dfee}, {0x90c76f8a78712655, 0xcf5293d2f310bf7f, 0xfbc8044dfda45028, 0xcbe1feba92e40ce6}, {1, 0, 0, 0}}, {{0xe998ceea4396e4c1, 0xfc82ef0b6acea274, 0x230f729f2250e927, 0xd0b2f94d2f420109}, {0x4305adddb38d4966, 0x10b838f8624c3b45, 0x7db2636658954e7a, 0x971459828b0719e5}, {1, 0, 0, 0}}, {{0x4bd6b72623369fc9, 0x57f2929e53d0b876, 0xc2d5cba4f2340687, 0x961610004a866aba}, {0x49997bcd2e407a5e, 0x69ab197d92ddcb24, 0x2cf1f2438fe5131c, 0x7acb9fadcee75e44}, {1, 0, 0, 0}}, {{0x254e839423d2d4c0, 0xf57f0c917aea685b, 0xa60d880f6f75aaea, 0x24eb9acca333bf5b}, {0xe3de4ccb1cda5dea, 0xfeef9341c51a6b4f, 0x743125f88bac4c4d, 0x69f891c5acd079cc}, {1, 0, 0, 0}}, {{0xeee44b35702476b5, 0x7ed031a0e45c2258, 0xb422d1e7bd6f8514, 0xe51f547c5972a107}, {0xa25bcd6fc9cf343d, 0x8ca922ee097c184e, 0xa62f98b3a9fe9a06, 0x1c309a2b25bb1387}, {1, 0, 0, 0}}, {{0x9295dbeb1967c459, 0xb00148833472c98e, 0xc504977708011828, 0x20b87b8aa2c4e503}, {0x3063175de057c277, 0x1bd539338fe582dd, 0x0d11adef5f69a044, 0xf5c6fa49919776be}, {1, 0, 0, 0}}, {{0x8c944e760fd59e11, 0x3876cba1102fad5f, 0xa454c3fad83faa56, 0x1ed7d1b9332010b9}, {0xa1011a270024b889, 0x05e4d0dcac0cd344, 0x52b520f0eb6a2a24, 0x3a2b03f03217257a}, {1, 0, 0, 0}}, {{0xf20fc2afdf1d043d, 0xf330240db58d5a62, 0xfc7d229ca0058c3b, 0x15fee545c78dd9f6}, {0x501e82885bc98cda, 0x41ef80e5d046ac04, 0x557d9f49461210fb, 0x4ab5b6b2b8753f81}, {1, 0, 0, 0}}}}; /* select_point selects the |idx|th point from a precomputation table and * copies it to out. */ static void select_point(const u64 idx, size_t size, const smallfelem pre_comp[/*size*/][3], smallfelem out[3]) { u64 *outlimbs = &out[0][0]; OPENSSL_memset(outlimbs, 0, 3 * sizeof(smallfelem)); for (size_t i = 0; i < size; i++) { const u64 *inlimbs = (const u64 *)&pre_comp[i][0][0]; u64 mask = i ^ idx; mask |= mask >> 4; mask |= mask >> 2; mask |= mask >> 1; mask &= 1; mask--; for (size_t j = 0; j < NLIMBS * 3; j++) { outlimbs[j] |= inlimbs[j] & mask; } } } /* get_bit returns the |i|th bit in |in| */ static char get_bit(const felem_bytearray in, int i) { if (i < 0 || i >= 256) { return 0; } return (in[i >> 3] >> (i & 7)) & 1; } /* Interleaved point multiplication using precomputed point multiples: The * small point multiples 0*P, 1*P, ..., 17*P are in pre_comp[], the scalars * in scalars[]. If g_scalar is non-NULL, we also add this multiple of the * generator, using certain (large) precomputed multiples in g_pre_comp. * Output point (X, Y, Z) is stored in x_out, y_out, z_out. */ static void batch_mul(felem x_out, felem y_out, felem z_out, const felem_bytearray scalars[], const size_t num_points, const u8 *g_scalar, const smallfelem pre_comp[][17][3]) { felem nq[3], ftmp; smallfelem tmp[3]; u64 bits; u8 sign, digit; /* set nq to the point at infinity */ OPENSSL_memset(nq, 0, 3 * sizeof(felem)); /* Loop over all scalars msb-to-lsb, interleaving additions of multiples * of the generator (two in each of the last 32 rounds) and additions of * other points multiples (every 5th round). */ int skip = 1; /* save two point operations in the first round */ size_t i = num_points != 0 ? 255 : 31; for (;;) { /* double */ if (!skip) { point_double(nq[0], nq[1], nq[2], nq[0], nq[1], nq[2]); } /* add multiples of the generator */ if (g_scalar != NULL && i <= 31) { /* first, look 32 bits upwards */ bits = get_bit(g_scalar, i + 224) << 3; bits |= get_bit(g_scalar, i + 160) << 2; bits |= get_bit(g_scalar, i + 96) << 1; bits |= get_bit(g_scalar, i + 32); /* select the point to add, in constant time */ select_point(bits, 16, g_pre_comp[1], tmp); if (!skip) { point_add(nq[0], nq[1], nq[2], nq[0], nq[1], nq[2], 1 /* mixed */, tmp[0], tmp[1], tmp[2]); } else { smallfelem_expand(nq[0], tmp[0]); smallfelem_expand(nq[1], tmp[1]); smallfelem_expand(nq[2], tmp[2]); skip = 0; } /* second, look at the current position */ bits = get_bit(g_scalar, i + 192) << 3; bits |= get_bit(g_scalar, i + 128) << 2; bits |= get_bit(g_scalar, i + 64) << 1; bits |= get_bit(g_scalar, i); /* select the point to add, in constant time */ select_point(bits, 16, g_pre_comp[0], tmp); point_add(nq[0], nq[1], nq[2], nq[0], nq[1], nq[2], 1 /* mixed */, tmp[0], tmp[1], tmp[2]); } /* do other additions every 5 doublings */ if (num_points != 0 && i % 5 == 0) { /* loop over all scalars */ size_t num; for (num = 0; num < num_points; ++num) { bits = get_bit(scalars[num], i + 4) << 5; bits |= get_bit(scalars[num], i + 3) << 4; bits |= get_bit(scalars[num], i + 2) << 3; bits |= get_bit(scalars[num], i + 1) << 2; bits |= get_bit(scalars[num], i) << 1; bits |= get_bit(scalars[num], i - 1); ec_GFp_nistp_recode_scalar_bits(&sign, &digit, bits); /* select the point to add or subtract, in constant time. */ select_point(digit, 17, pre_comp[num], tmp); smallfelem_neg(ftmp, tmp[1]); /* (X, -Y, Z) is the negative * point */ copy_small_conditional(ftmp, tmp[1], (((limb)sign) - 1)); felem_contract(tmp[1], ftmp); if (!skip) { point_add(nq[0], nq[1], nq[2], nq[0], nq[1], nq[2], 0 /* mixed */, tmp[0], tmp[1], tmp[2]); } else { smallfelem_expand(nq[0], tmp[0]); smallfelem_expand(nq[1], tmp[1]); smallfelem_expand(nq[2], tmp[2]); skip = 0; } } } if (i == 0) { break; } --i; } felem_assign(x_out, nq[0]); felem_assign(y_out, nq[1]); felem_assign(z_out, nq[2]); } /******************************************************************************/ /* * OPENSSL EC_METHOD FUNCTIONS */ /* Takes the Jacobian coordinates (X, Y, Z) of a point and returns (X', Y') = * (X/Z^2, Y/Z^3). */ static int ec_GFp_nistp256_point_get_affine_coordinates(const EC_GROUP *group, const EC_POINT *point, BIGNUM *x, BIGNUM *y, BN_CTX *ctx) { felem z1, z2, x_in, y_in; smallfelem x_out, y_out; longfelem tmp; if (EC_POINT_is_at_infinity(group, point)) { OPENSSL_PUT_ERROR(EC, EC_R_POINT_AT_INFINITY); return 0; } if (!BN_to_felem(x_in, &point->X) || !BN_to_felem(y_in, &point->Y) || !BN_to_felem(z1, &point->Z)) { return 0; } felem_inv(z2, z1); felem_square(tmp, z2); felem_reduce(z1, tmp); if (x != NULL) { felem_mul(tmp, x_in, z1); felem_reduce(x_in, tmp); felem_contract(x_out, x_in); if (!smallfelem_to_BN(x, x_out)) { OPENSSL_PUT_ERROR(EC, ERR_R_BN_LIB); return 0; } } if (y != NULL) { felem_mul(tmp, z1, z2); felem_reduce(z1, tmp); felem_mul(tmp, y_in, z1); felem_reduce(y_in, tmp); felem_contract(y_out, y_in); if (!smallfelem_to_BN(y, y_out)) { OPENSSL_PUT_ERROR(EC, ERR_R_BN_LIB); return 0; } } return 1; } static int ec_GFp_nistp256_points_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *g_scalar, const EC_POINT *p_, const BIGNUM *p_scalar_, BN_CTX *ctx) { /* TODO: This function used to take |points| and |scalars| as arrays of * |num| elements. The code below should be simplified to work in terms of |p| * and |p_scalar|. */ size_t num = p_ != NULL ? 1 : 0; const EC_POINT **points = p_ != NULL ? &p_ : NULL; BIGNUM const *const *scalars = p_ != NULL ? &p_scalar_ : NULL; int ret = 0; BN_CTX *new_ctx = NULL; BIGNUM *x, *y, *z, *tmp_scalar; felem_bytearray g_secret; felem_bytearray *secrets = NULL; smallfelem(*pre_comp)[17][3] = NULL; felem_bytearray tmp; size_t num_points = num; smallfelem x_in, y_in, z_in; felem x_out, y_out, z_out; const EC_POINT *p = NULL; const BIGNUM *p_scalar = NULL; if (ctx == NULL) { ctx = new_ctx = BN_CTX_new(); if (ctx == NULL) { return 0; } } BN_CTX_start(ctx); if ((x = BN_CTX_get(ctx)) == NULL || (y = BN_CTX_get(ctx)) == NULL || (z = BN_CTX_get(ctx)) == NULL || (tmp_scalar = BN_CTX_get(ctx)) == NULL) { goto err; } if (num_points > 0) { secrets = OPENSSL_malloc(num_points * sizeof(felem_bytearray)); pre_comp = OPENSSL_malloc(num_points * sizeof(smallfelem[17][3])); if (secrets == NULL || pre_comp == NULL) { OPENSSL_PUT_ERROR(EC, ERR_R_MALLOC_FAILURE); goto err; } /* we treat NULL scalars as 0, and NULL points as points at infinity, * i.e., they contribute nothing to the linear combination. */ OPENSSL_memset(secrets, 0, num_points * sizeof(felem_bytearray)); OPENSSL_memset(pre_comp, 0, num_points * 17 * 3 * sizeof(smallfelem)); for (size_t i = 0; i < num_points; ++i) { if (i == num) { /* we didn't have a valid precomputation, so we pick the generator. */ p = EC_GROUP_get0_generator(group); p_scalar = g_scalar; } else { /* the i^th point */ p = points[i]; p_scalar = scalars[i]; } if (p_scalar != NULL && p != NULL) { size_t num_bytes; /* reduce g_scalar to 0 <= g_scalar < 2^256 */ if (BN_num_bits(p_scalar) > 256 || BN_is_negative(p_scalar)) { /* this is an unusual input, and we don't guarantee * constant-timeness. */ if (!BN_nnmod(tmp_scalar, p_scalar, &group->order, ctx)) { OPENSSL_PUT_ERROR(EC, ERR_R_BN_LIB); goto err; } num_bytes = BN_bn2bin(tmp_scalar, tmp); } else { num_bytes = BN_bn2bin(p_scalar, tmp); } flip_endian(secrets[i], tmp, num_bytes); /* precompute multiples */ if (!BN_to_felem(x_out, &p->X) || !BN_to_felem(y_out, &p->Y) || !BN_to_felem(z_out, &p->Z)) { goto err; } felem_shrink(pre_comp[i][1][0], x_out); felem_shrink(pre_comp[i][1][1], y_out); felem_shrink(pre_comp[i][1][2], z_out); for (size_t j = 2; j <= 16; ++j) { if (j & 1) { point_add_small(pre_comp[i][j][0], pre_comp[i][j][1], pre_comp[i][j][2], pre_comp[i][1][0], pre_comp[i][1][1], pre_comp[i][1][2], pre_comp[i][j - 1][0], pre_comp[i][j - 1][1], pre_comp[i][j - 1][2]); } else { point_double_small(pre_comp[i][j][0], pre_comp[i][j][1], pre_comp[i][j][2], pre_comp[i][j / 2][0], pre_comp[i][j / 2][1], pre_comp[i][j / 2][2]); } } } } } if (g_scalar != NULL) { size_t num_bytes; OPENSSL_memset(g_secret, 0, sizeof(g_secret)); /* reduce g_scalar to 0 <= g_scalar < 2^256 */ if (BN_num_bits(g_scalar) > 256 || BN_is_negative(g_scalar)) { /* this is an unusual input, and we don't guarantee * constant-timeness. */ if (!BN_nnmod(tmp_scalar, g_scalar, &group->order, ctx)) { OPENSSL_PUT_ERROR(EC, ERR_R_BN_LIB); goto err; } num_bytes = BN_bn2bin(tmp_scalar, tmp); } else { num_bytes = BN_bn2bin(g_scalar, tmp); } flip_endian(g_secret, tmp, num_bytes); } batch_mul(x_out, y_out, z_out, (const felem_bytearray(*))secrets, num_points, g_scalar != NULL ? g_secret : NULL, (const smallfelem(*)[17][3])pre_comp); /* reduce the output to its unique minimal representation */ felem_contract(x_in, x_out); felem_contract(y_in, y_out); felem_contract(z_in, z_out); if (!smallfelem_to_BN(x, x_in) || !smallfelem_to_BN(y, y_in) || !smallfelem_to_BN(z, z_in)) { OPENSSL_PUT_ERROR(EC, ERR_R_BN_LIB); goto err; } ret = ec_point_set_Jprojective_coordinates_GFp(group, r, x, y, z, ctx); err: BN_CTX_end(ctx); BN_CTX_free(new_ctx); OPENSSL_free(secrets); OPENSSL_free(pre_comp); return ret; } const EC_METHOD EC_GFp_nistp256_method = { ec_GFp_simple_group_init, ec_GFp_simple_group_finish, ec_GFp_simple_group_copy, ec_GFp_simple_group_set_curve, ec_GFp_nistp256_point_get_affine_coordinates, ec_GFp_nistp256_points_mul, ec_GFp_simple_field_mul, ec_GFp_simple_field_sqr, NULL /* field_encode */, NULL /* field_decode */, }; #endif /* 64_BIT && !WINDOWS */