mirror of
https://github.com/servalproject/serval-dna.git
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bf9710fd5a
This only affects build_android, if nacl-gcc-prep is run then build/`uname -s` will be created.
478 lines
14 KiB
C
478 lines
14 KiB
C
/* Copyright 2008, Google Inc.
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* All rights reserved.
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*
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* Code released into the public domain.
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*
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* curve25519-donna: Curve25519 elliptic curve, public key function
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*
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* http://code.google.com/p/curve25519-donna/
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*
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* Adam Langley <agl@imperialviolet.org>
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*
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* Derived from public domain C code by Daniel J. Bernstein <djb@cr.yp.to>
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*
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* More information about curve25519 can be found here
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* http://cr.yp.to/ecdh.html
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*
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* djb's sample implementation of curve25519 is written in a special assembly
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* language called qhasm and uses the floating point registers.
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*
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* This is, almost, a clean room reimplementation from the curve25519 paper. It
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* uses many of the tricks described therein. Only the crecip function is taken
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* from the sample implementation.
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*/
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#include <string.h>
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#include <stdint.h>
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#include "crypto_scalarmult.h"
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typedef uint8_t u8;
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typedef uint64_t felem;
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// This is a special gcc mode for 128-bit integers. It's implemented on 64-bit
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// platforms only as far as I know.
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typedef unsigned uint128_t __attribute__((mode(TI)));
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/* Sum two numbers: output += in */
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static void fsum(felem *output, const felem *in) {
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unsigned i;
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for (i = 0; i < 5; ++i) output[i] += in[i];
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}
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/* Find the difference of two numbers: output = in - output
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* (note the order of the arguments!)
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*/
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static void fdifference_backwards(felem *ioutput, const felem *iin) {
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static const int64_t twotothe51 = (1l << 51);
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const int64_t *in = (const int64_t *) iin;
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int64_t *out = (int64_t *) ioutput;
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out[0] = in[0] - out[0];
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out[1] = in[1] - out[1];
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out[2] = in[2] - out[2];
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out[3] = in[3] - out[3];
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out[4] = in[4] - out[4];
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// An arithmetic shift right of 63 places turns a positive number to 0 and a
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// negative number to all 1's. This gives us a bitmask that lets us avoid
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// side-channel prone branches.
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int64_t t;
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#define NEGCHAIN(a,b) \
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t = out[a] >> 63; \
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out[a] += twotothe51 & t; \
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out[b] -= 1 & t;
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#define NEGCHAIN19(a,b) \
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t = out[a] >> 63; \
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out[a] += twotothe51 & t; \
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out[b] -= 19 & t;
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NEGCHAIN(0, 1);
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NEGCHAIN(1, 2);
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NEGCHAIN(2, 3);
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NEGCHAIN(3, 4);
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NEGCHAIN19(4, 0);
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NEGCHAIN(0, 1);
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NEGCHAIN(1, 2);
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NEGCHAIN(2, 3);
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NEGCHAIN(3, 4);
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}
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/* Multiply a number by a scalar: output = in * scalar */
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static void fscalar_product(felem *output, const felem *in, const felem scalar) {
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uint128_t a;
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a = ((uint128_t) in[0]) * scalar;
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output[0] = a & 0x7ffffffffffff;
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a = ((uint128_t) in[1]) * scalar + (a >> 51);
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output[1] = a & 0x7ffffffffffff;
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a = ((uint128_t) in[2]) * scalar + (a >> 51);
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output[2] = a & 0x7ffffffffffff;
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a = ((uint128_t) in[3]) * scalar + (a >> 51);
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output[3] = a & 0x7ffffffffffff;
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a = ((uint128_t) in[4]) * scalar + (a >> 51);
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output[4] = a & 0x7ffffffffffff;
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output[0] += (a >> 51) * 19;
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}
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/* Multiply two numbers: output = in2 * in
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*
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* output must be distinct to both inputs. The inputs are reduced coefficient
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* form, the output is not.
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*/
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static void fmul(felem *output, const felem *in2, const felem *in) {
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uint128_t t[9];
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t[0] = ((uint128_t) in[0]) * in2[0];
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t[1] = ((uint128_t) in[0]) * in2[1] +
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((uint128_t) in[1]) * in2[0];
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t[2] = ((uint128_t) in[0]) * in2[2] +
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((uint128_t) in[2]) * in2[0] +
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((uint128_t) in[1]) * in2[1];
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t[3] = ((uint128_t) in[0]) * in2[3] +
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((uint128_t) in[3]) * in2[0] +
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((uint128_t) in[1]) * in2[2] +
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((uint128_t) in[2]) * in2[1];
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t[4] = ((uint128_t) in[0]) * in2[4] +
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((uint128_t) in[4]) * in2[0] +
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((uint128_t) in[3]) * in2[1] +
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((uint128_t) in[1]) * in2[3] +
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((uint128_t) in[2]) * in2[2];
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t[5] = ((uint128_t) in[4]) * in2[1] +
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((uint128_t) in[1]) * in2[4] +
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((uint128_t) in[2]) * in2[3] +
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((uint128_t) in[3]) * in2[2];
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t[6] = ((uint128_t) in[4]) * in2[2] +
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((uint128_t) in[2]) * in2[4] +
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((uint128_t) in[3]) * in2[3];
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t[7] = ((uint128_t) in[3]) * in2[4] +
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((uint128_t) in[4]) * in2[3];
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t[8] = ((uint128_t) in[4]) * in2[4];
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t[0] += t[5] * 19;
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t[1] += t[6] * 19;
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t[2] += t[7] * 19;
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t[3] += t[8] * 19;
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t[1] += t[0] >> 51;
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t[0] &= 0x7ffffffffffff;
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t[2] += t[1] >> 51;
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t[1] &= 0x7ffffffffffff;
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t[3] += t[2] >> 51;
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t[2] &= 0x7ffffffffffff;
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t[4] += t[3] >> 51;
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t[3] &= 0x7ffffffffffff;
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t[0] += 19 * (t[4] >> 51);
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t[4] &= 0x7ffffffffffff;
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t[1] += t[0] >> 51;
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t[0] &= 0x7ffffffffffff;
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t[2] += t[1] >> 51;
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t[1] &= 0x7ffffffffffff;
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output[0] = t[0];
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output[1] = t[1];
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output[2] = t[2];
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output[3] = t[3];
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output[4] = t[4];
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}
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static void
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fsquare(felem *output, const felem *in) {
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uint128_t t[9];
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t[0] = ((uint128_t) in[0]) * in[0];
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t[1] = ((uint128_t) in[0]) * in[1] * 2;
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t[2] = ((uint128_t) in[0]) * in[2] * 2 +
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((uint128_t) in[1]) * in[1];
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t[3] = ((uint128_t) in[0]) * in[3] * 2 +
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((uint128_t) in[1]) * in[2] * 2;
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t[4] = ((uint128_t) in[0]) * in[4] * 2 +
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((uint128_t) in[3]) * in[1] * 2 +
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((uint128_t) in[2]) * in[2];
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t[5] = ((uint128_t) in[4]) * in[1] * 2 +
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((uint128_t) in[2]) * in[3] * 2;
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t[6] = ((uint128_t) in[4]) * in[2] * 2 +
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((uint128_t) in[3]) * in[3];
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t[7] = ((uint128_t) in[3]) * in[4] * 2;
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t[8] = ((uint128_t) in[4]) * in[4];
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t[0] += t[5] * 19;
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t[1] += t[6] * 19;
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t[2] += t[7] * 19;
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t[3] += t[8] * 19;
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t[1] += t[0] >> 51;
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t[0] &= 0x7ffffffffffff;
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t[2] += t[1] >> 51;
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t[1] &= 0x7ffffffffffff;
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t[3] += t[2] >> 51;
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t[2] &= 0x7ffffffffffff;
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t[4] += t[3] >> 51;
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t[3] &= 0x7ffffffffffff;
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t[0] += 19 * (t[4] >> 51);
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t[4] &= 0x7ffffffffffff;
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t[1] += t[0] >> 51;
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t[0] &= 0x7ffffffffffff;
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output[0] = t[0];
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output[1] = t[1];
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output[2] = t[2];
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output[3] = t[3];
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output[4] = t[4];
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}
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/* Take a little-endian, 32-byte number and expand it into polynomial form */
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static void
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fexpand(felem *output, const u8 *in) {
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output[0] = *((const uint64_t *)(in)) & 0x7ffffffffffff;
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output[1] = (*((const uint64_t *)(in+6)) >> 3) & 0x7ffffffffffff;
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output[2] = (*((const uint64_t *)(in+12)) >> 6) & 0x7ffffffffffff;
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output[3] = (*((const uint64_t *)(in+19)) >> 1) & 0x7ffffffffffff;
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output[4] = (*((const uint64_t *)(in+25)) >> 4) & 0x7ffffffffffff;
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}
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/* Take a fully reduced polynomial form number and contract it into a
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* little-endian, 32-byte array
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*/
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static void
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fcontract(u8 *output, const felem *input) {
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uint128_t t[5];
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t[0] = input[0];
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t[1] = input[1];
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t[2] = input[2];
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t[3] = input[3];
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t[4] = input[4];
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t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
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t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
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t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
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t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
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t[0] += 19 * (t[4] >> 51); t[4] &= 0x7ffffffffffff;
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t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
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t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
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t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
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t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
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t[0] += 19 * (t[4] >> 51); t[4] &= 0x7ffffffffffff;
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/* now t is between 0 and 2^255-1, properly carried. */
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/* case 1: between 0 and 2^255-20. case 2: between 2^255-19 and 2^255-1. */
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t[0] += 19;
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t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
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t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
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t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
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t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
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t[0] += 19 * (t[4] >> 51); t[4] &= 0x7ffffffffffff;
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/* now between 19 and 2^255-1 in both cases, and offset by 19. */
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t[0] += 0x8000000000000 - 19;
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t[1] += 0x8000000000000 - 1;
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t[2] += 0x8000000000000 - 1;
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t[3] += 0x8000000000000 - 1;
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t[4] += 0x8000000000000 - 1;
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/* now between 2^255 and 2^256-20, and offset by 2^255. */
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t[1] += t[0] >> 51; t[0] &= 0x7ffffffffffff;
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t[2] += t[1] >> 51; t[1] &= 0x7ffffffffffff;
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t[3] += t[2] >> 51; t[2] &= 0x7ffffffffffff;
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t[4] += t[3] >> 51; t[3] &= 0x7ffffffffffff;
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t[4] &= 0x7ffffffffffff;
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*((uint64_t *)(output)) = t[0] | (t[1] << 51);
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*((uint64_t *)(output+8)) = (t[1] >> 13) | (t[2] << 38);
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*((uint64_t *)(output+16)) = (t[2] >> 26) | (t[3] << 25);
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*((uint64_t *)(output+24)) = (t[3] >> 39) | (t[4] << 12);
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}
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/* Input: Q, Q', Q-Q'
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* Output: 2Q, Q+Q'
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*
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* x2 z3: long form
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* x3 z3: long form
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* x z: short form, destroyed
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* xprime zprime: short form, destroyed
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* qmqp: short form, preserved
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*/
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static void
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fmonty(felem *x2, felem *z2, /* output 2Q */
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felem *x3, felem *z3, /* output Q + Q' */
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felem *x, felem *z, /* input Q */
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felem *xprime, felem *zprime, /* input Q' */
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const felem *qmqp /* input Q - Q' */) {
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felem origx[5], origxprime[5], zzz[5], xx[5], zz[5], xxprime[5],
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zzprime[5], zzzprime[5];
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memcpy(origx, x, 5 * sizeof(felem));
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fsum(x, z);
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fdifference_backwards(z, origx); // does x - z
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memcpy(origxprime, xprime, sizeof(felem) * 5);
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fsum(xprime, zprime);
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fdifference_backwards(zprime, origxprime);
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fmul(xxprime, xprime, z);
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fmul(zzprime, x, zprime);
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memcpy(origxprime, xxprime, sizeof(felem) * 5);
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fsum(xxprime, zzprime);
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fdifference_backwards(zzprime, origxprime);
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fsquare(x3, xxprime);
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fsquare(zzzprime, zzprime);
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fmul(z3, zzzprime, qmqp);
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fsquare(xx, x);
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fsquare(zz, z);
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fmul(x2, xx, zz);
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fdifference_backwards(zz, xx); // does zz = xx - zz
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fscalar_product(zzz, zz, 121665);
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fsum(zzz, xx);
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fmul(z2, zz, zzz);
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}
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// -----------------------------------------------------------------------------
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// Maybe swap the contents of two felem arrays (@a and @b), each @len elements
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// long. Perform the swap iff @swap is non-zero.
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//
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// This function performs the swap without leaking any side-channel
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// information.
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// -----------------------------------------------------------------------------
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static void
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swap_conditional(felem *a, felem *b, unsigned len, felem iswap) {
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unsigned i;
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const felem swap = -iswap;
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for (i = 0; i < len; ++i) {
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const felem x = swap & (a[i] ^ b[i]);
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a[i] ^= x;
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b[i] ^= x;
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}
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}
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/* Calculates nQ where Q is the x-coordinate of a point on the curve
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*
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* resultx/resultz: the x coordinate of the resulting curve point (short form)
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* n: a little endian, 32-byte number
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* q: a point of the curve (short form)
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*/
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static void
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cmult(felem *resultx, felem *resultz, const u8 *n, const felem *q) {
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felem a[5] = {0}, b[5] = {1}, c[5] = {1}, d[5] = {0};
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felem *nqpqx = a, *nqpqz = b, *nqx = c, *nqz = d, *t;
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felem e[5] = {0}, f[5] = {1}, g[5] = {0}, h[5] = {1};
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felem *nqpqx2 = e, *nqpqz2 = f, *nqx2 = g, *nqz2 = h;
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unsigned i, j;
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memcpy(nqpqx, q, sizeof(felem) * 5);
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for (i = 0; i < 32; ++i) {
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u8 byte = n[31 - i];
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for (j = 0; j < 8; ++j) {
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const felem bit = byte >> 7;
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swap_conditional(nqx, nqpqx, 5, bit);
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swap_conditional(nqz, nqpqz, 5, bit);
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fmonty(nqx2, nqz2,
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nqpqx2, nqpqz2,
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nqx, nqz,
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nqpqx, nqpqz,
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q);
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swap_conditional(nqx2, nqpqx2, 5, bit);
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swap_conditional(nqz2, nqpqz2, 5, bit);
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t = nqx;
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nqx = nqx2;
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nqx2 = t;
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t = nqz;
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nqz = nqz2;
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nqz2 = t;
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t = nqpqx;
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nqpqx = nqpqx2;
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nqpqx2 = t;
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t = nqpqz;
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nqpqz = nqpqz2;
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nqpqz2 = t;
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byte <<= 1;
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}
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}
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memcpy(resultx, nqx, sizeof(felem) * 5);
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memcpy(resultz, nqz, sizeof(felem) * 5);
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}
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// -----------------------------------------------------------------------------
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// Shamelessly copied from djb's code
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// -----------------------------------------------------------------------------
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static void
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crecip(felem *out, const felem *z) {
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felem z2[5];
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felem z9[5];
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felem z11[5];
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felem z2_5_0[5];
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felem z2_10_0[5];
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felem z2_20_0[5];
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felem z2_50_0[5];
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felem z2_100_0[5];
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felem t0[5];
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felem t1[5];
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int i;
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/* 2 */ fsquare(z2,z);
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/* 4 */ fsquare(t1,z2);
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/* 8 */ fsquare(t0,t1);
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/* 9 */ fmul(z9,t0,z);
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/* 11 */ fmul(z11,z9,z2);
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/* 22 */ fsquare(t0,z11);
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/* 2^5 - 2^0 = 31 */ fmul(z2_5_0,t0,z9);
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/* 2^6 - 2^1 */ fsquare(t0,z2_5_0);
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/* 2^7 - 2^2 */ fsquare(t1,t0);
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/* 2^8 - 2^3 */ fsquare(t0,t1);
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/* 2^9 - 2^4 */ fsquare(t1,t0);
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/* 2^10 - 2^5 */ fsquare(t0,t1);
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/* 2^10 - 2^0 */ fmul(z2_10_0,t0,z2_5_0);
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/* 2^11 - 2^1 */ fsquare(t0,z2_10_0);
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/* 2^12 - 2^2 */ fsquare(t1,t0);
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/* 2^20 - 2^10 */ for (i = 2;i < 10;i += 2) { fsquare(t0,t1); fsquare(t1,t0); }
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/* 2^20 - 2^0 */ fmul(z2_20_0,t1,z2_10_0);
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/* 2^21 - 2^1 */ fsquare(t0,z2_20_0);
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/* 2^22 - 2^2 */ fsquare(t1,t0);
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/* 2^40 - 2^20 */ for (i = 2;i < 20;i += 2) { fsquare(t0,t1); fsquare(t1,t0); }
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/* 2^40 - 2^0 */ fmul(t0,t1,z2_20_0);
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/* 2^41 - 2^1 */ fsquare(t1,t0);
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/* 2^42 - 2^2 */ fsquare(t0,t1);
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/* 2^50 - 2^10 */ for (i = 2;i < 10;i += 2) { fsquare(t1,t0); fsquare(t0,t1); }
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/* 2^50 - 2^0 */ fmul(z2_50_0,t0,z2_10_0);
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/* 2^51 - 2^1 */ fsquare(t0,z2_50_0);
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/* 2^52 - 2^2 */ fsquare(t1,t0);
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/* 2^100 - 2^50 */ for (i = 2;i < 50;i += 2) { fsquare(t0,t1); fsquare(t1,t0); }
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/* 2^100 - 2^0 */ fmul(z2_100_0,t1,z2_50_0);
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/* 2^101 - 2^1 */ fsquare(t1,z2_100_0);
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/* 2^102 - 2^2 */ fsquare(t0,t1);
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/* 2^200 - 2^100 */ for (i = 2;i < 100;i += 2) { fsquare(t1,t0); fsquare(t0,t1); }
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/* 2^200 - 2^0 */ fmul(t1,t0,z2_100_0);
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/* 2^201 - 2^1 */ fsquare(t0,t1);
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/* 2^202 - 2^2 */ fsquare(t1,t0);
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/* 2^250 - 2^50 */ for (i = 2;i < 50;i += 2) { fsquare(t0,t1); fsquare(t1,t0); }
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/* 2^250 - 2^0 */ fmul(t0,t1,z2_50_0);
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/* 2^251 - 2^1 */ fsquare(t1,t0);
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/* 2^252 - 2^2 */ fsquare(t0,t1);
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/* 2^253 - 2^3 */ fsquare(t1,t0);
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/* 2^254 - 2^4 */ fsquare(t0,t1);
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/* 2^255 - 2^5 */ fsquare(t1,t0);
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/* 2^255 - 21 */ fmul(out,t1,z11);
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}
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int
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crypto_scalarmult(u8 *mypublic, const u8 *secret, const u8 *basepoint) {
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felem bp[5], x[5], z[5], zmone[5];
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unsigned char e[32];
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int i;
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for (i = 0;i < 32;++i) e[i] = secret[i];
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e[0] &= 248;
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e[31] &= 127;
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e[31] |= 64;
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fexpand(bp, basepoint);
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cmult(x, z, e, bp);
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crecip(zmone, z);
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fmul(z, x, zmone);
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fcontract(mypublic, z);
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return 0;
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}
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