Small Issues & Maintenance

-=-=-=-=-=-=-=-=-=-=-=-=-=

-Begin work on Navigation Meshes (simple pathfinding for now, will improve soon)
-More doc on theme overriding
-Upgraded OpenSSL to version without bugs
-Misc bugfixes

1 files changed, 2171 insertions, 0 deletions

diff --git a/drivers/builtin_openssl2/crypto/ec/ecp_nistp256.c b/drivers/builtin_openssl2/crypto/ec/ecp_nistp256.c
new file mode 100644
index 0000000000..4bc0f5dce0
--- /dev/null
+++ b/drivers/builtin_openssl2/crypto/ec/ecp_nistp256.c
@@ -0,0 +1,2171 @@
+/* crypto/ec/ecp_nistp256.c */
+/*
+ * Written by Adam Langley (Google) for the OpenSSL project
+ */
+/* Copyright 2011 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ *
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+/*
+ * 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 <openssl/opensslconf.h>
+#ifndef OPENSSL_NO_EC_NISTP_64_GCC_128
+
+#ifndef OPENSSL_SYS_VMS
+#include <stdint.h>
+#else
+#include <inttypes.h>
+#endif
+
+#include <string.h>
+#include <openssl/err.h>
+#include "ec_lcl.h"
+
+#if defined(__GNUC__) && (__GNUC__ > 3 || (__GNUC__ == 3 && __GNUC_MINOR__ >= 1))
+  /* even with gcc, the typedef won't work for 32-bit platforms */
+  typedef __uint128_t uint128_t; /* nonstandard; implemented by gcc on 64-bit platforms */
+  typedef __int128_t int128_t;
+#else
+  #error "Need GCC 3.1 or later to define type uint128_t"
+#endif
+
+typedef uint8_t u8;
+typedef uint32_t u32;
+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];
+
+/* These are the parameters of P256, taken from FIPS 186-3, page 86. These
+ * values are big-endian. */
+static const felem_bytearray nistp256_curve_params[5] = {
+	{0xff, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x01,       /* p */
+	 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff,
+	 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff},
+	{0xff, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00, 0x01,       /* a = -3 */
+	 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	 0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff,
+	 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xfc},      /* b */
+	{0x5a, 0xc6, 0x35, 0xd8, 0xaa, 0x3a, 0x93, 0xe7,
+	 0xb3, 0xeb, 0xbd, 0x55, 0x76, 0x98, 0x86, 0xbc,
+	 0x65, 0x1d, 0x06, 0xb0, 0xcc, 0x53, 0xb0, 0xf6,
+	 0x3b, 0xce, 0x3c, 0x3e, 0x27, 0xd2, 0x60, 0x4b},
+	{0x6b, 0x17, 0xd1, 0xf2, 0xe1, 0x2c, 0x42, 0x47,       /* x */
+	 0xf8, 0xbc, 0xe6, 0xe5, 0x63, 0xa4, 0x40, 0xf2,
+	 0x77, 0x03, 0x7d, 0x81, 0x2d, 0xeb, 0x33, 0xa0,
+	 0xf4, 0xa1, 0x39, 0x45, 0xd8, 0x98, 0xc2, 0x96},
+	{0x4f, 0xe3, 0x42, 0xe2, 0xfe, 0x1a, 0x7f, 0x9b,       /* y */
+	 0x8e, 0xe7, 0xeb, 0x4a, 0x7c, 0x0f, 0x9e, 0x16,
+	 0x2b, 0xce, 0x33, 0x57, 0x6b, 0x31, 0x5e, 0xce,
+	 0xcb, 0xb6, 0x40, 0x68, 0x37, 0xbf, 0x51, 0xf5}
+};
+
+/* 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 limb bottom32bits = 0xffffffff;
+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] = *((u64*) &in[0]);
+	out[1] = *((u64*) &in[8]);
+	out[2] = *((u64*) &in[16]);
+	out[3] = *((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, unsigned len)
+	{
+	unsigned i;
+	for (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)
+	{
+	felem_bytearray b_in;
+	felem_bytearray b_out;
+	unsigned num_bytes;
+
+	/* BN_bn2bin eats leading zeroes */
+	memset(b_out, 0, sizeof b_out);
+	num_bytes = BN_num_bytes(bn);
+	if (num_bytes > sizeof b_out)
+		{
+		ECerr(EC_F_BN_TO_FELEM, EC_R_BIGNUM_OUT_OF_RANGE);
+		return 0;
+		}
+	if (BN_is_negative(bn))
+		{
+		ECerr(EC_F_BN_TO_FELEM, EC_R_BIGNUM_OUT_OF_RANGE);
+		return 0;
+		}
+	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 smallfelem_one(smallfelem out)
+	{
+	out[0] = 1;
+	out[1] = 0;
+	out[2] = 0;
+	out[3] = 0;
+	}
+
+static void smallfelem_assign(smallfelem out, const smallfelem in)
+	{
+	out[0] = in[0];
+	out[1] = in[1];
+	out[2] = in[2];
+	out[3] = in[3];
+	}
+
+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 <<= 63;
+	high >>= 63;
+	/* 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)
+	{
+	unsigned i;
+	u64 all_equal_so_far = 0, result = 0, carry;
+
+	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 (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. */
+	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]);
+	}
+
+static void smallfelem_square_contract(smallfelem out, const smallfelem in)
+	{
+	longfelem longtmp;
+	felem tmp;
+
+	smallfelem_square(longtmp, in);
+	felem_reduce(tmp, longtmp);
+	felem_contract(out, tmp);
+	}
+
+static void smallfelem_mul_contract(smallfelem out, const smallfelem in1, const smallfelem in2)
+	{
+	longfelem longtmp;
+	felem tmp;
+
+	smallfelem_mul(longtmp, in1, in2);
+	felem_reduce(tmp, longtmp);
+	felem_contract(out, tmp);
+	}
+
+/* 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;
+	}
+
+static int smallfelem_is_zero_int(const smallfelem small)
+	{
+	return (int) (smallfelem_is_zero(small) & ((limb)1));
+	}
+
+/* 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;
+	unsigned i;
+
+	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 (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 (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 (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 (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 (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 (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 (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 */
+	}
+
+static void smallfelem_inv_contract(smallfelem out, const smallfelem in)
+	{
+	felem tmp;
+
+	smallfelem_expand(tmp, in);
+	felem_inv(tmp, tmp);
+	felem_contract(out, tmp);
+	}
+
+/* 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)
+	{
+	unsigned i;
+	for (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)
+	{
+	unsigned i;
+	const u64 mask64 = mask;
+	for (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. */
+
+/* gmul is the table of precomputed base points */
+static const smallfelem gmul[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, unsigned int size, const smallfelem pre_comp[16][3], smallfelem out[3])
+	{
+	unsigned i, j;
+	u64 *outlimbs = &out[0][0];
+	memset(outlimbs, 0, 3 * sizeof(smallfelem));
+
+	for (i = 0; i < size; i++)
+		{
+		const u64 *inlimbs = (u64*) &pre_comp[i][0][0];
+		u64 mask = i ^ idx;
+		mask |= mask >> 4;
+		mask |= mask >> 2;
+		mask |= mask >> 1;
+		mask &= 1;
+		mask--;
+		for (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 unsigned num_points, const u8 *g_scalar,
+	const int mixed, const smallfelem pre_comp[][17][3], const smallfelem g_pre_comp[2][16][3])
+	{
+	int i, skip;
+	unsigned num, gen_mul = (g_scalar != NULL);
+	felem nq[3], ftmp;
+	smallfelem tmp[3];
+	u64 bits;
+	u8 sign, digit;
+
+	/* set nq to the point at infinity */
+	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).
+	 */
+	skip = 1; /* save two point operations in the first round */
+	for (i = (num_points ? 255 : 31); i >= 0; --i)
+		{
+		/* double */
+		if (!skip)
+			point_double(nq[0], nq[1], nq[2], nq[0], nq[1], nq[2]);
+
+		/* add multiples of the generator */
+		if (gen_mul && (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 && (i % 5 == 0))
+			{
+			/* loop over all scalars */
+			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],
+						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;
+					}
+				}
+			}
+		}
+	felem_assign(x_out, nq[0]);
+	felem_assign(y_out, nq[1]);
+	felem_assign(z_out, nq[2]);
+	}
+
+/* Precomputation for the group generator. */
+typedef struct {
+	smallfelem g_pre_comp[2][16][3];
+	int references;
+} NISTP256_PRE_COMP;
+
+const EC_METHOD *EC_GFp_nistp256_method(void)
+	{
+	static const EC_METHOD ret = {
+		EC_FLAGS_DEFAULT_OCT,
+		NID_X9_62_prime_field,
+		ec_GFp_nistp256_group_init,
+		ec_GFp_simple_group_finish,
+		ec_GFp_simple_group_clear_finish,
+		ec_GFp_nist_group_copy,
+		ec_GFp_nistp256_group_set_curve,
+		ec_GFp_simple_group_get_curve,
+		ec_GFp_simple_group_get_degree,
+		ec_GFp_simple_group_check_discriminant,
+		ec_GFp_simple_point_init,
+		ec_GFp_simple_point_finish,
+		ec_GFp_simple_point_clear_finish,
+		ec_GFp_simple_point_copy,
+		ec_GFp_simple_point_set_to_infinity,
+		ec_GFp_simple_set_Jprojective_coordinates_GFp,
+		ec_GFp_simple_get_Jprojective_coordinates_GFp,
+		ec_GFp_simple_point_set_affine_coordinates,
+		ec_GFp_nistp256_point_get_affine_coordinates,
+		0 /* point_set_compressed_coordinates */,
+		0 /* point2oct */,
+		0 /* oct2point */,
+		ec_GFp_simple_add,
+		ec_GFp_simple_dbl,
+		ec_GFp_simple_invert,
+		ec_GFp_simple_is_at_infinity,
+		ec_GFp_simple_is_on_curve,
+		ec_GFp_simple_cmp,
+		ec_GFp_simple_make_affine,
+		ec_GFp_simple_points_make_affine,
+		ec_GFp_nistp256_points_mul,
+		ec_GFp_nistp256_precompute_mult,
+		ec_GFp_nistp256_have_precompute_mult,
+		ec_GFp_nist_field_mul,
+		ec_GFp_nist_field_sqr,
+		0 /* field_div */,
+		0 /* field_encode */,
+		0 /* field_decode */,
+		0 /* field_set_to_one */ };
+
+	return &ret;
+	}
+
+/******************************************************************************/
+/*		       FUNCTIONS TO MANAGE PRECOMPUTATION
+ */
+
+static NISTP256_PRE_COMP *nistp256_pre_comp_new()
+	{
+	NISTP256_PRE_COMP *ret = NULL;
+	ret = (NISTP256_PRE_COMP *) OPENSSL_malloc(sizeof *ret);
+	if (!ret)
+		{
+		ECerr(EC_F_NISTP256_PRE_COMP_NEW, ERR_R_MALLOC_FAILURE);
+		return ret;
+		}
+	memset(ret->g_pre_comp, 0, sizeof(ret->g_pre_comp));
+	ret->references = 1;
+	return ret;
+	}
+
+static void *nistp256_pre_comp_dup(void *src_)
+	{
+	NISTP256_PRE_COMP *src = src_;
+
+	/* no need to actually copy, these objects never change! */
+	CRYPTO_add(&src->references, 1, CRYPTO_LOCK_EC_PRE_COMP);
+
+	return src_;
+	}
+
+static void nistp256_pre_comp_free(void *pre_)
+	{
+	int i;
+	NISTP256_PRE_COMP *pre = pre_;
+
+	if (!pre)
+		return;
+
+	i = CRYPTO_add(&pre->references, -1, CRYPTO_LOCK_EC_PRE_COMP);
+	if (i > 0)
+		return;
+
+	OPENSSL_free(pre);
+	}
+
+static void nistp256_pre_comp_clear_free(void *pre_)
+	{
+	int i;
+	NISTP256_PRE_COMP *pre = pre_;
+
+	if (!pre)
+		return;
+
+	i = CRYPTO_add(&pre->references, -1, CRYPTO_LOCK_EC_PRE_COMP);
+	if (i > 0)
+		return;
+
+	OPENSSL_cleanse(pre, sizeof *pre);
+	OPENSSL_free(pre);
+	}
+
+/******************************************************************************/
+/*			   OPENSSL EC_METHOD FUNCTIONS
+ */
+
+int ec_GFp_nistp256_group_init(EC_GROUP *group)
+	{
+	int ret;
+	ret = ec_GFp_simple_group_init(group);
+	group->a_is_minus3 = 1;
+	return ret;
+	}
+
+int ec_GFp_nistp256_group_set_curve(EC_GROUP *group, const BIGNUM *p,
+	const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx)
+	{
+	int ret = 0;
+	BN_CTX *new_ctx = NULL;
+	BIGNUM *curve_p, *curve_a, *curve_b;
+
+	if (ctx == NULL)
+		if ((ctx = new_ctx = BN_CTX_new()) == NULL) return 0;
+	BN_CTX_start(ctx);
+	if (((curve_p = BN_CTX_get(ctx)) == NULL) ||
+		((curve_a = BN_CTX_get(ctx)) == NULL) ||
+		((curve_b = BN_CTX_get(ctx)) == NULL)) goto err;
+	BN_bin2bn(nistp256_curve_params[0], sizeof(felem_bytearray), curve_p);
+	BN_bin2bn(nistp256_curve_params[1], sizeof(felem_bytearray), curve_a);
+	BN_bin2bn(nistp256_curve_params[2], sizeof(felem_bytearray), curve_b);
+	if ((BN_cmp(curve_p, p)) || (BN_cmp(curve_a, a)) ||
+		(BN_cmp(curve_b, b)))
+		{
+		ECerr(EC_F_EC_GFP_NISTP256_GROUP_SET_CURVE,
+			EC_R_WRONG_CURVE_PARAMETERS);
+		goto err;
+		}
+	group->field_mod_func = BN_nist_mod_256;
+	ret = ec_GFp_simple_group_set_curve(group, p, a, b, ctx);
+err:
+	BN_CTX_end(ctx);
+	if (new_ctx != NULL)
+		BN_CTX_free(new_ctx);
+	return ret;
+	}
+
+/* Takes the Jacobian coordinates (X, Y, Z) of a point and returns
+ * (X', Y') = (X/Z^2, Y/Z^3) */
+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))
+		{
+		ECerr(EC_F_EC_GFP_NISTP256_POINT_GET_AFFINE_COORDINATES,
+			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);
+	felem_mul(tmp, x_in, z1); felem_reduce(x_in, tmp);
+	felem_contract(x_out, x_in);
+	if (x != NULL)
+		{
+		if (!smallfelem_to_BN(x, x_out)) {
+		ECerr(EC_F_EC_GFP_NISTP256_POINT_GET_AFFINE_COORDINATES,
+			ERR_R_BN_LIB);
+		return 0;
+		}
+		}
+	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 (y != NULL)
+		{
+		if (!smallfelem_to_BN(y, y_out))
+			{
+			ECerr(EC_F_EC_GFP_NISTP256_POINT_GET_AFFINE_COORDINATES,
+				ERR_R_BN_LIB);
+			return 0;
+			}
+		}
+	return 1;
+	}
+
+static void make_points_affine(size_t num, smallfelem points[/* num */][3], smallfelem tmp_smallfelems[/* num+1 */])
+	{
+	/* Runs in constant time, unless an input is the point at infinity
+	 * (which normally shouldn't happen). */
+	ec_GFp_nistp_points_make_affine_internal(
+		num,
+		points,
+		sizeof(smallfelem),
+		tmp_smallfelems,
+		(void (*)(void *)) smallfelem_one,
+		(int (*)(const void *)) smallfelem_is_zero_int,
+		(void (*)(void *, const void *)) smallfelem_assign,
+		(void (*)(void *, const void *)) smallfelem_square_contract,
+		(void (*)(void *, const void *, const void *)) smallfelem_mul_contract,
+		(void (*)(void *, const void *)) smallfelem_inv_contract,
+		(void (*)(void *, const void *)) smallfelem_assign /* nothing to contract */);
+	}
+
+/* Computes scalar*generator + \sum scalars[i]*points[i], ignoring NULL values
+ * Result is stored in r (r can equal one of the inputs). */
+int ec_GFp_nistp256_points_mul(const EC_GROUP *group, EC_POINT *r,
+	const BIGNUM *scalar, size_t num, const EC_POINT *points[],
+	const BIGNUM *scalars[], BN_CTX *ctx)
+	{
+	int ret = 0;
+	int j;
+	int mixed = 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;
+	smallfelem *tmp_smallfelems = NULL;
+	felem_bytearray tmp;
+	unsigned i, num_bytes;
+	int have_pre_comp = 0;
+	size_t num_points = num;
+	smallfelem x_in, y_in, z_in;
+	felem x_out, y_out, z_out;
+	NISTP256_PRE_COMP *pre = NULL;
+	const smallfelem (*g_pre_comp)[16][3] = NULL;
+	EC_POINT *generator = NULL;
+	const EC_POINT *p = NULL;
+	const BIGNUM *p_scalar = NULL;
+
+	if (ctx == NULL)
+		if ((ctx = new_ctx = BN_CTX_new()) == 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 (scalar != NULL)
+		{
+		pre = EC_EX_DATA_get_data(group->extra_data,
+			nistp256_pre_comp_dup, nistp256_pre_comp_free,
+			nistp256_pre_comp_clear_free);
+		if (pre)
+			/* we have precomputation, try to use it */
+			g_pre_comp = (const smallfelem (*)[16][3]) pre->g_pre_comp;
+		else
+			/* try to use the standard precomputation */
+			g_pre_comp = &gmul[0];
+		generator = EC_POINT_new(group);
+		if (generator == NULL)
+			goto err;
+		/* get the generator from precomputation */
+		if (!smallfelem_to_BN(x, g_pre_comp[0][1][0]) ||
+			!smallfelem_to_BN(y, g_pre_comp[0][1][1]) ||
+			!smallfelem_to_BN(z, g_pre_comp[0][1][2]))
+			{
+			ECerr(EC_F_EC_GFP_NISTP256_POINTS_MUL, ERR_R_BN_LIB);
+			goto err;
+			}
+		if (!EC_POINT_set_Jprojective_coordinates_GFp(group,
+				generator, x, y, z, ctx))
+			goto err;
+		if (0 == EC_POINT_cmp(group, generator, group->generator, ctx))
+			/* precomputation matches generator */
+			have_pre_comp = 1;
+		else
+			/* we don't have valid precomputation:
+			 * treat the generator as a random point */
+			num_points++;
+		}
+	if (num_points > 0)
+		{
+		if (num_points >= 3)
+			{
+			/* unless we precompute multiples for just one or two points,
+			 * converting those into affine form is time well spent  */
+			mixed = 1;
+			}
+		secrets = OPENSSL_malloc(num_points * sizeof(felem_bytearray));
+		pre_comp = OPENSSL_malloc(num_points * 17 * 3 * sizeof(smallfelem));
+		if (mixed)
+			tmp_smallfelems = OPENSSL_malloc((num_points * 17 + 1) * sizeof(smallfelem));
+		if ((secrets == NULL) || (pre_comp == NULL) || (mixed && (tmp_smallfelems == NULL)))
+			{
+			ECerr(EC_F_EC_GFP_NISTP256_POINTS_MUL, 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 */
+		memset(secrets, 0, num_points * sizeof(felem_bytearray));
+		memset(pre_comp, 0, num_points * 17 * 3 * sizeof(smallfelem));
+		for (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 = scalar;
+				}
+			else
+				/* the i^th point */
+				{
+				p = points[i];
+				p_scalar = scalars[i];
+				}
+			if ((p_scalar != NULL) && (p != NULL))
+				{
+				/* reduce scalar to 0 <= 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))
+						{
+						ECerr(EC_F_EC_GFP_NISTP256_POINTS_MUL, 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 (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 (mixed)
+			make_points_affine(num_points * 17, pre_comp[0], tmp_smallfelems);
+		}
+
+	/* the scalar for the generator */
+	if ((scalar != NULL) && (have_pre_comp))
+		{
+		memset(g_secret, 0, sizeof(g_secret));
+		/* reduce scalar to 0 <= scalar < 2^256 */
+		if ((BN_num_bits(scalar) > 256) || (BN_is_negative(scalar)))
+			{
+			/* this is an unusual input, and we don't guarantee
+			 * constant-timeness */
+			if (!BN_nnmod(tmp_scalar, scalar, &group->order, ctx))
+				{
+				ECerr(EC_F_EC_GFP_NISTP256_POINTS_MUL, ERR_R_BN_LIB);
+				goto err;
+				}
+			num_bytes = BN_bn2bin(tmp_scalar, tmp);
+			}
+		else
+			num_bytes = BN_bn2bin(scalar, tmp);
+		flip_endian(g_secret, tmp, num_bytes);
+		/* do the multiplication with generator precomputation*/
+		batch_mul(x_out, y_out, z_out,
+			(const felem_bytearray (*)) secrets, num_points,
+			g_secret,
+			mixed, (const smallfelem (*)[17][3]) pre_comp,
+			g_pre_comp);
+		}
+	else
+		/* do the multiplication without generator precomputation */
+		batch_mul(x_out, y_out, z_out,
+			(const felem_bytearray (*)) secrets, num_points,
+			NULL, mixed, (const smallfelem (*)[17][3]) pre_comp, NULL);
+	/* 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)))
+		{
+		ECerr(EC_F_EC_GFP_NISTP256_POINTS_MUL, ERR_R_BN_LIB);
+		goto err;
+		}
+	ret = EC_POINT_set_Jprojective_coordinates_GFp(group, r, x, y, z, ctx);
+
+err:
+	BN_CTX_end(ctx);
+	if (generator != NULL)
+		EC_POINT_free(generator);
+	if (new_ctx != NULL)
+		BN_CTX_free(new_ctx);
+	if (secrets != NULL)
+		OPENSSL_free(secrets);
+	if (pre_comp != NULL)
+		OPENSSL_free(pre_comp);
+	if (tmp_smallfelems != NULL)
+		OPENSSL_free(tmp_smallfelems);
+	return ret;
+	}
+
+int ec_GFp_nistp256_precompute_mult(EC_GROUP *group, BN_CTX *ctx)
+	{
+	int ret = 0;
+	NISTP256_PRE_COMP *pre = NULL;
+	int i, j;
+	BN_CTX *new_ctx = NULL;
+	BIGNUM *x, *y;
+	EC_POINT *generator = NULL;
+	smallfelem tmp_smallfelems[32];
+	felem x_tmp, y_tmp, z_tmp;
+
+	/* throw away old precomputation */
+	EC_EX_DATA_free_data(&group->extra_data, nistp256_pre_comp_dup,
+		nistp256_pre_comp_free, nistp256_pre_comp_clear_free);
+	if (ctx == NULL)
+		if ((ctx = new_ctx = BN_CTX_new()) == NULL) return 0;
+	BN_CTX_start(ctx);
+	if (((x = BN_CTX_get(ctx)) == NULL) ||
+		((y = BN_CTX_get(ctx)) == NULL))
+		goto err;
+	/* get the generator */
+	if (group->generator == NULL) goto err;
+	generator = EC_POINT_new(group);
+	if (generator == NULL)
+		goto err;
+	BN_bin2bn(nistp256_curve_params[3], sizeof (felem_bytearray), x);
+	BN_bin2bn(nistp256_curve_params[4], sizeof (felem_bytearray), y);
+	if (!EC_POINT_set_affine_coordinates_GFp(group, generator, x, y, ctx))
+		goto err;
+	if ((pre = nistp256_pre_comp_new()) == NULL)
+		goto err;
+	/* if the generator is the standard one, use built-in precomputation */
+	if (0 == EC_POINT_cmp(group, generator, group->generator, ctx))
+		{
+		memcpy(pre->g_pre_comp, gmul, sizeof(pre->g_pre_comp));
+		ret = 1;
+		goto err;
+		}
+	if ((!BN_to_felem(x_tmp, &group->generator->X)) ||
+		(!BN_to_felem(y_tmp, &group->generator->Y)) ||
+		(!BN_to_felem(z_tmp, &group->generator->Z)))
+		goto err;
+	felem_shrink(pre->g_pre_comp[0][1][0], x_tmp);
+	felem_shrink(pre->g_pre_comp[0][1][1], y_tmp);
+	felem_shrink(pre->g_pre_comp[0][1][2], z_tmp);
+	/* compute 2^64*G, 2^128*G, 2^192*G for the first table,
+	 * 2^32*G, 2^96*G, 2^160*G, 2^224*G for the second one
+	 */
+	for (i = 1; i <= 8; i <<= 1)
+		{
+		point_double_small(
+			pre->g_pre_comp[1][i][0], pre->g_pre_comp[1][i][1], pre->g_pre_comp[1][i][2],
+			pre->g_pre_comp[0][i][0], pre->g_pre_comp[0][i][1], pre->g_pre_comp[0][i][2]);
+		for (j = 0; j < 31; ++j)
+			{
+			point_double_small(
+				pre->g_pre_comp[1][i][0], pre->g_pre_comp[1][i][1], pre->g_pre_comp[1][i][2],
+				pre->g_pre_comp[1][i][0], pre->g_pre_comp[1][i][1], pre->g_pre_comp[1][i][2]);
+			}
+		if (i == 8)
+			break;
+		point_double_small(
+			pre->g_pre_comp[0][2*i][0], pre->g_pre_comp[0][2*i][1], pre->g_pre_comp[0][2*i][2],
+			pre->g_pre_comp[1][i][0], pre->g_pre_comp[1][i][1], pre->g_pre_comp[1][i][2]);
+		for (j = 0; j < 31; ++j)
+			{
+			point_double_small(
+				pre->g_pre_comp[0][2*i][0], pre->g_pre_comp[0][2*i][1], pre->g_pre_comp[0][2*i][2],
+				pre->g_pre_comp[0][2*i][0], pre->g_pre_comp[0][2*i][1], pre->g_pre_comp[0][2*i][2]);
+			}
+		}
+	for (i = 0; i < 2; i++)
+		{
+		/* g_pre_comp[i][0] is the point at infinity */
+		memset(pre->g_pre_comp[i][0], 0, sizeof(pre->g_pre_comp[i][0]));
+		/* the remaining multiples */
+		/* 2^64*G + 2^128*G resp. 2^96*G + 2^160*G */
+		point_add_small(
+			pre->g_pre_comp[i][6][0], pre->g_pre_comp[i][6][1], pre->g_pre_comp[i][6][2],
+			pre->g_pre_comp[i][4][0], pre->g_pre_comp[i][4][1], pre->g_pre_comp[i][4][2],
+			pre->g_pre_comp[i][2][0], pre->g_pre_comp[i][2][1], pre->g_pre_comp[i][2][2]);
+		/* 2^64*G + 2^192*G resp. 2^96*G + 2^224*G */
+		point_add_small(
+			pre->g_pre_comp[i][10][0], pre->g_pre_comp[i][10][1], pre->g_pre_comp[i][10][2],
+			pre->g_pre_comp[i][8][0], pre->g_pre_comp[i][8][1], pre->g_pre_comp[i][8][2],
+			pre->g_pre_comp[i][2][0], pre->g_pre_comp[i][2][1], pre->g_pre_comp[i][2][2]);
+		/* 2^128*G + 2^192*G resp. 2^160*G + 2^224*G */
+		point_add_small(
+			pre->g_pre_comp[i][12][0], pre->g_pre_comp[i][12][1], pre->g_pre_comp[i][12][2],
+			pre->g_pre_comp[i][8][0], pre->g_pre_comp[i][8][1], pre->g_pre_comp[i][8][2],
+			pre->g_pre_comp[i][4][0], pre->g_pre_comp[i][4][1], pre->g_pre_comp[i][4][2]);
+		/* 2^64*G + 2^128*G + 2^192*G resp. 2^96*G + 2^160*G + 2^224*G */
+		point_add_small(
+			pre->g_pre_comp[i][14][0], pre->g_pre_comp[i][14][1], pre->g_pre_comp[i][14][2],
+			pre->g_pre_comp[i][12][0], pre->g_pre_comp[i][12][1], pre->g_pre_comp[i][12][2],
+			pre->g_pre_comp[i][2][0], pre->g_pre_comp[i][2][1], pre->g_pre_comp[i][2][2]);
+		for (j = 1; j < 8; ++j)
+			{
+			/* odd multiples: add G resp. 2^32*G */
+			point_add_small(
+				pre->g_pre_comp[i][2*j+1][0], pre->g_pre_comp[i][2*j+1][1], pre->g_pre_comp[i][2*j+1][2],
+				pre->g_pre_comp[i][2*j][0], pre->g_pre_comp[i][2*j][1], pre->g_pre_comp[i][2*j][2],
+				pre->g_pre_comp[i][1][0], pre->g_pre_comp[i][1][1], pre->g_pre_comp[i][1][2]);
+			}
+		}
+	make_points_affine(31, &(pre->g_pre_comp[0][1]), tmp_smallfelems);
+
+	if (!EC_EX_DATA_set_data(&group->extra_data, pre, nistp256_pre_comp_dup,
+			nistp256_pre_comp_free, nistp256_pre_comp_clear_free))
+		goto err;
+	ret = 1;
+	pre = NULL;
+ err:
+	BN_CTX_end(ctx);
+	if (generator != NULL)
+		EC_POINT_free(generator);
+	if (new_ctx != NULL)
+		BN_CTX_free(new_ctx);
+	if (pre)
+		nistp256_pre_comp_free(pre);
+	return ret;
+	}
+
+int ec_GFp_nistp256_have_precompute_mult(const EC_GROUP *group)
+	{
+	if (EC_EX_DATA_get_data(group->extra_data, nistp256_pre_comp_dup,
+			nistp256_pre_comp_free, nistp256_pre_comp_clear_free)
+		!= NULL)
+		return 1;
+	else
+		return 0;
+	}
+#else
+static void *dummy=&dummy;
+#endif