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b9dd94b9b2
The loops relied on unsigned integer overflow, which is not immediately obvious. Replace them with less clever variants that are clearer. Also implement bn_compare using std::memcmp.
98 lines
1.8 KiB
C++
98 lines
1.8 KiB
C++
// Copyright 2007,2008 Segher Boessenkool <segher@kernel.crashing.org>
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// Licensed under the terms of the GNU GPL, version 2
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// http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt
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#include <cstdio>
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#include <cstring>
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#include "Common/CommonTypes.h"
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#include "Common/Crypto/bn.h"
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static void bn_zero(u8* d, int n)
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{
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std::memset(d, 0, n);
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}
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static void bn_copy(u8* d, const u8* a, int n)
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{
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std::memcpy(d, a, n);
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}
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int bn_compare(const u8* a, const u8* b, int n)
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{
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return std::memcmp(a, b, n);
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}
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void bn_sub_modulus(u8* a, const u8* N, int n)
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{
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u8 c = 0;
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for (int i = n - 1; i >= 0; --i)
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{
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u32 dig = N[i] + c;
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c = (a[i] < dig);
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a[i] -= dig;
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}
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}
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void bn_add(u8* d, const u8* a, const u8* b, const u8* N, int n)
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{
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u8 c = 0;
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for (int i = n - 1; i >= 0; --i)
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{
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u32 dig = a[i] + b[i] + c;
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c = (dig >= 0x100);
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d[i] = dig;
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}
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if (c)
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bn_sub_modulus(d, N, n);
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if (bn_compare(d, N, n) >= 0)
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bn_sub_modulus(d, N, n);
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}
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void bn_mul(u8* d, const u8* a, const u8* b, const u8* N, int n)
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{
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bn_zero(d, n);
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for (int i = 0; i < n; i++)
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{
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for (u8 mask = 0x80; mask != 0; mask >>= 1)
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{
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bn_add(d, d, d, N, n);
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if ((a[i] & mask) != 0)
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bn_add(d, d, b, N, n);
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}
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}
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}
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void bn_exp(u8* d, const u8* a, const u8* N, int n, const u8* e, int en)
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{
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u8 t[512];
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bn_zero(d, n);
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d[n - 1] = 1;
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for (int i = 0; i < en; i++)
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{
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for (u8 mask = 0x80; mask != 0; mask >>= 1)
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{
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bn_mul(t, d, d, N, n);
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if ((e[i] & mask) != 0)
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bn_mul(d, t, a, N, n);
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else
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bn_copy(d, t, n);
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}
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}
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}
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// only for prime N -- stupid but lazy, see if I care
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void bn_inv(u8* d, const u8* a, const u8* N, int n)
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{
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u8 t[512], s[512];
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bn_copy(t, N, n);
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bn_zero(s, n);
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s[n - 1] = 2;
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bn_sub_modulus(t, s, n);
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bn_exp(d, a, N, n, t, n);
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}
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