athena/src/bn.cpp

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// Copyright 2007,2008 Segher Boessenkool <segher@kernel.crashing.org>
// Licensed under the terms of the GNU GPL, version 2
// http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt
#include <string.h>
#include <stdio.h>
#include "bn.h"
static void bn_zero(Uint8 *d, Uint32 n)
{
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memset(d, 0, n);
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}
static void bn_copy(Uint8 *d, Uint8 *a, Uint32 n)
{
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memcpy(d, a, n);
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}
int bn_compare(Uint8 *a, Uint8 *b, Uint32 n)
{
Uint32 i;
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for (i = 0; i < n; i++) {
if (a[i] < b[i])
return -1;
if (a[i] > b[i])
return 1;
}
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return 0;
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}
void bn_sub_modulus(Uint8 *a, Uint8 *N, Uint32 n)
{
Uint32 i;
Uint32 dig;
Uint8 c;
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c = 0;
for (i = n - 1; i < n; i--) {
dig = N[i] + c;
c = (a[i] < dig);
a[i] -= dig;
}
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}
void bn_add(Uint8 *d, Uint8 *a, Uint8 *b, Uint8 *N, Uint32 n)
{
Uint32 i;
Uint32 dig;
Uint8 c;
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c = 0;
for (i = n - 1; i < n; i--) {
dig = a[i] + b[i] + c;
c = (dig >= 0x100);
d[i] = dig;
}
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if (c)
bn_sub_modulus(d, N, n);
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if (bn_compare(d, N, n) >= 0)
bn_sub_modulus(d, N, n);
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}
void bn_mul(Uint8 *d, Uint8 *a, Uint8 *b, Uint8 *N, Uint32 n)
{
Uint32 i;
Uint8 mask;
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bn_zero(d, n);
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for (i = 0; i < n; i++)
for (mask = 0x80; mask != 0; mask >>= 1) {
bn_add(d, d, d, N, n);
if ((a[i] & mask) != 0)
bn_add(d, d, b, N, n);
}
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}
void bn_exp(Uint8 *d, Uint8 *a, Uint8 *N, Uint32 n, Uint8 *e, Uint32 en)
{
Uint8 t[512];
Uint32 i;
Uint8 mask;
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bn_zero(d, n);
d[n-1] = 1;
for (i = 0; i < en; i++)
for (mask = 0x80; mask != 0; mask >>= 1) {
bn_mul(t, d, d, N, n);
if ((e[i] & mask) != 0)
bn_mul(d, t, a, N, n);
else
bn_copy(d, t, n);
}
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}
// only for prime N -- stupid but lazy, see if I care
void bn_inv(Uint8 *d, Uint8 *a, Uint8 *N, Uint32 n)
{
Uint8 t[512], s[512];
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bn_copy(t, N, n);
bn_zero(s, n);
s[n-1] = 2;
bn_sub_modulus(t, s, n);
bn_exp(d, a, N, n, t, n);
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}