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n2n/src/curve25519.c
Logan oos Even e686b9592c
(C) update (#965)
2022-03-12 10:22:42 +01:00

357 lines
8.4 KiB
C
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/**
* (C) 2007-22 - ntop.org and contributors
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not see see <http://www.gnu.org/licenses/>
*
*/
/**
* version 20081011
* Matthew Dempsky
* Public domain.
* Derived from public domain code by D. J. Bernstein.
* 20140216 tweak: Mask top bit of point input.
*
*/
static void add (unsigned int out[32], const unsigned int a[32], const unsigned int b[32]) {
unsigned int j;
unsigned int u;
u = 0;
for(j = 0; j < 31; ++j) {
u += a[j] + b[j];
out[j] = u & 255;
u >>= 8;
}
u += a[31] + b[31];
out[31] = u;
}
static void sub (unsigned int out[32], const unsigned int a[32], const unsigned int b[32]) {
unsigned int j;
unsigned int u;
u = 218;
for(j = 0; j < 31; ++j) {
u += a[j] + 65280 - b[j];
out[j] = u & 255;
u >>= 8;
}
u += a[31] - b[31];
out[31] = u;
}
static void squeeze (unsigned int a[32]) {
unsigned int j;
unsigned int u;
u = 0;
for(j = 0; j < 31; ++j) {
u += a[j];
a[j] = u & 255;
u >>= 8;
}
u += a[31];
a[31] = u & 127;
u = 19 * (u >> 7);
for(j = 0; j < 31; ++j) {
u += a[j];
a[j] = u & 255;
u >>= 8;
}
u += a[31];
a[31] = u;
}
static const unsigned int minusp[32] = { 19, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 128 };
static void freeze (unsigned int a[32]) {
unsigned int aorig[32];
unsigned int j;
unsigned int negative;
for(j = 0; j < 32; ++j)
aorig[j] = a[j];
add(a, a, minusp);
negative = -((a[31] >> 7) & 1);
for(j = 0; j < 32; ++j)
a[j] ^= negative & (aorig[j] ^ a[j]);
}
static void mult (unsigned int out[32], const unsigned int a[32], const unsigned int b[32]) {
unsigned int i;
unsigned int j;
unsigned int u;
for(i = 0; i < 32; ++i) {
u = 0;
for(j = 0; j <= i; ++j)
u += a[j] * b[i - j];
for(j = i + 1; j < 32; ++j)
u += 38 * a[j] * b[i + 32 - j];
out[i] = u;
}
squeeze(out);
}
static void mult121665 (unsigned int out[32], const unsigned int a[32]) {
unsigned int j;
unsigned int u;
u = 0;
for(j = 0; j < 31; ++j) {
u += 121665 * a[j];
out[j] = u & 255;
u >>= 8;
}
u += 121665 * a[31];
out[31] = u & 127;
u = 19 * (u >> 7);
for(j = 0; j < 31; ++j) {
u += out[j];
out[j] = u & 255;
u >>= 8;
}
u += out[j];
out[j] = u;
}
static void square (unsigned int out[32], const unsigned int a[32]) {
unsigned int i;
unsigned int j;
unsigned int u;
for(i = 0; i < 32; ++i) {
u = 0;
for(j = 0; j < i - j; ++j)
u += a[j] * a[i - j];
for(j = i + 1; j < i + 32 - j; ++j)
u += 38 * a[j] * a[i + 32 - j];
u *= 2;
if((i & 1) == 0) {
u += a[i / 2] * a[i / 2];
u += 38 * a[i / 2 + 16] * a[i / 2 + 16];
}
out[i] = u;
}
squeeze(out);
}
static void select (unsigned int p[64], unsigned int q[64], const unsigned int r[64],
const unsigned int s[64], unsigned int b) {
unsigned int j;
unsigned int t;
unsigned int bminus1;
bminus1 = b - 1;
for(j = 0; j < 64; ++j) {
t = bminus1 & (r[j] ^ s[j]);
p[j] = s[j] ^ t;
q[j] = r[j] ^ t;
}
}
static void mainloop (unsigned int work[64], const unsigned char e[32]) {
unsigned int xzm1[64];
unsigned int xzm[64];
unsigned int xzmb[64];
unsigned int xzm1b[64];
unsigned int xznb[64];
unsigned int xzn1b[64];
unsigned int a0[64];
unsigned int a1[64];
unsigned int b0[64];
unsigned int b1[64];
unsigned int c1[64];
unsigned int r[32];
unsigned int s[32];
unsigned int t[32];
unsigned int u[32];
unsigned int j;
unsigned int b;
int pos;
for(j = 0; j < 32; ++j)
xzm1[j] = work[j];
xzm1[32] = 1;
for(j = 33; j < 64; ++j)
xzm1[j] = 0;
xzm[0] = 1;
for(j = 1; j < 64; ++j)
xzm[j] = 0;
for(pos = 254; pos >= 0; --pos) {
b = e[pos / 8] >> (pos & 7);
b &= 1;
select(xzmb, xzm1b, xzm, xzm1, b);
add(a0, xzmb, xzmb + 32);
sub(a0 + 32, xzmb, xzmb + 32);
add (a1, xzm1b, xzm1b + 32);
sub(a1 + 32, xzm1b, xzm1b + 32);
square(b0, a0);
square(b0 + 32, a0 + 32);
mult(b1, a1, a0 + 32);
mult(b1 + 32, a1 + 32, a0);
add(c1, b1, b1 + 32);
sub(c1 + 32, b1, b1 + 32);
square(r, c1 + 32);
sub(s, b0, b0 + 32);
mult121665 (t, s);
add(u, t, b0);
mult(xznb, b0, b0 + 32);
mult(xznb + 32, s, u);
square(xzn1b, c1);
mult(xzn1b + 32, r, work);
select(xzm, xzm1, xznb, xzn1b, b);
}
for(j = 0; j < 64; ++j)
work[j] = xzm[j];
}
static void recip (unsigned int out[32], const unsigned int z[32]) {
unsigned int z2[32];
unsigned int z9[32];
unsigned int z11[32];
unsigned int z2_5_0[32];
unsigned int z2_10_0[32];
unsigned int z2_20_0[32];
unsigned int z2_50_0[32];
unsigned int z2_100_0[32];
unsigned int t0[32];
unsigned int t1[32];
int i;
/* 2 */ square(z2, z);
/* 4 */ square(t1, z2);
/* 8 */ square(t0, t1);
/* 9 */ mult(z9, t0, z);
/* 11 */ mult(z11, z9, z2);
/* 22 */ square(t0, z11);
/* 2^5 - 2^0 = 31 */ mult(z2_5_0, t0, z9);
/* 2^6 - 2^1 */ square(t0, z2_5_0);
/* 2^7 - 2^2 */ square(t1, t0);
/* 2^8 - 2^3 */ square(t0, t1);
/* 2^9 - 2^4 */ square(t1, t0);
/* 2^10 - 2^5 */ square(t0, t1);
/* 2^10 - 2^0 */ mult(z2_10_0, t0, z2_5_0);
/* 2^11 - 2^1 */ square(t0, z2_10_0);
/* 2^12 - 2^2 */ square(t1, t0);
/* 2^20 - 2^10 */ for(i = 2; i < 10; i += 2) {
square(t0, t1);
square(t1, t0);
}
/* 2^20 - 2^0 */ mult(z2_20_0, t1, z2_10_0);
/* 2^21 - 2^1 */ square(t0, z2_20_0);
/* 2^22 - 2^2 */ square(t1, t0);
/* 2^40 - 2^20 */ for(i = 2; i < 20; i += 2) {
square(t0, t1);
square(t1, t0);
}
/* 2^40 - 2^0 */ mult(t0, t1, z2_20_0);
/* 2^41 - 2^1 */ square(t1, t0);
/* 2^42 - 2^2 */ square(t0, t1);
/* 2^50 - 2^10 */ for(i = 2; i < 10; i += 2) {
square(t1, t0);
square(t0, t1);
}
/* 2^50 - 2^0 */ mult(z2_50_0, t0, z2_10_0);
/* 2^51 - 2^1 */ square(t0, z2_50_0);
/* 2^52 - 2^2 */ square(t1, t0);
/* 2^100 - 2^50 */ for(i = 2; i < 50; i += 2) {
square(t0, t1);
square(t1, t0);
}
/* 2^100 - 2^0 */ mult(z2_100_0, t1, z2_50_0);
/* 2^101 - 2^1 */ square(t1, z2_100_0);
/* 2^102 - 2^2 */ square(t0, t1);
/* 2^200 - 2^100 */ for(i = 2; i < 100; i += 2) {
square(t1, t0);
square(t0, t1);
}
/* 2^200 - 2^0 */ mult(t1, t0, z2_100_0);
/* 2^201 - 2^1 */ square(t0, t1);
/* 2^202 - 2^2 */ square(t1, t0);
/* 2^250 - 2^50 */ for(i = 2; i < 50; i += 2) {
square(t0, t1);
square(t1, t0);
}
/* 2^250 - 2^0 */ mult(t0, t1, z2_50_0);
/* 2^251 - 2^1 */ square(t1, t0);
/* 2^252 - 2^2 */ square(t0, t1);
/* 2^253 - 2^3 */ square(t1, t0);
/* 2^254 - 2^4 */ square(t0, t1);
/* 2^255 - 2^5 */ square(t1, t0);
/* 2^255 - 21 */ mult(out, t1, z11);
}
void curve25519 (unsigned char *q, const unsigned char *n, const unsigned char *p) {
unsigned int work[96];
unsigned char e[32];
unsigned int i;
for (i = 0; i < 32; ++i)
e[i] = n[i];
e[0] &= 248;
e[31] &= 127;
e[31] |= 64;
for (i = 0; i < 32; ++i)
work[i] = p[i];
work[31] &= 127;
mainloop(work, e);
recip(work + 32, work + 32);
mult(work + 64, work, work + 32);
freeze(work + 64);
for(i = 0; i < 32; ++i)
q[i] = work[64 + i];
}
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