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Fix for constant time (step 4)

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NIIBE Yutaka 2014-01-21 14:13:36 +09:00
parent df8434db59
commit 0e7078bacb
2 changed files with 45 additions and 22 deletions
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7
ChangeLog
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@ -1,5 +1,12 @@
2014-01-21 Niibe Yutaka <gniibe@fsij.org>
* src/modp256.c (modp256_add, modp256_sub, modp256_reduce)
(modp256_shift): Fix for constant time.
(modp256_inv): Likewise (not fully constant time, yet).
* src/mod.c (mod_reduce): Fix for constant time.
(mod_inv): Likewise (not fully constant time, yet).
* src/bn.h (bn256, bn512): words -> word.
* src/ec_p256.h (naf4_257): Likewise.

60
src/modp256.c
View File

@ -1,7 +1,7 @@
/*
* modp256.c -- modulo P256 arithmetic
*
* Copyright (C) 2011, 2013 Free Software Initiative of Japan
* Copyright (C) 2011, 2013, 2014 Free Software Initiative of Japan
* Author: NIIBE Yutaka <gniibe@fsij.org>
*
* This file is a part of Gnuk, a GnuPG USB Token implementation.
@ -52,11 +52,14 @@ const bn256 p256 = { {0xffffffff, 0xffffffff, 0xffffffff, 0x00000000,
void
modp256_add (bn256 *X, const bn256 *A, const bn256 *B)
{
int carry;
uint32_t carry;
bn256 tmp[1];
carry = bn256_add (X, A, B);
if (carry)
bn256_sub (X, X, P256);
else
bn256_sub (tmp, X, P256);
}
/**
@ -65,11 +68,14 @@ modp256_add (bn256 *X, const bn256 *A, const bn256 *B)
void
modp256_sub (bn256 *X, const bn256 *A, const bn256 *B)
{
int borrow;
uint32_t borrow;
bn256 tmp[1];
borrow = bn256_sub (X, A, B);
if (borrow)
bn256_add (X, X, P256);
else
bn256_add (tmp, X, P256);
}
/**
@ -79,6 +85,7 @@ void
modp256_reduce (bn256 *X, const bn512 *A)
{
bn256 tmp[1];
uint32_t borrow;
#define S1 X
#define S2 tmp
@ -181,8 +188,11 @@ modp256_reduce (bn256 *X, const bn512 *A)
/* X -= S9 */
modp256_sub (X, X, S9);
if (bn256_is_ge (X, P256))
bn256_sub (X, X, P256);
borrow = bn256_sub (tmp, X, P256);
if (borrow)
memcpy (tmp, X, sizeof (bn256));
else
memcpy (X, tmp, sizeof (bn256));
}
/**
@ -218,8 +228,10 @@ modp256_sqr (bn256 *X, const bn256 *A)
int
modp256_inv (bn256 *C, const bn256 *a)
{
bn256 u[1], v[1];
bn256 u[1], v[1], tmp[1];
bn256 A[1] = { { { 1, 0, 0, 0, 0, 0, 0, 0 } } };
uint32_t carry;
#define borrow carry
if (bn256_is_zero (a))
return -1;
@ -234,30 +246,30 @@ modp256_inv (bn256 *C, const bn256 *a)
{
bn256_shift (u, u, -1);
if (bn256_is_even (A))
bn256_shift (A, A, -1);
else
{
int carry = bn256_add (A, A, P256);
bn256_shift (A, A, -1);
if (carry)
A->word[7] |= 0x80000000;
bn256_add (tmp, A, P256);
carry = 0;
}
else
carry = bn256_add (A, A, P256);
bn256_shift (A, A, -1);
A->word[7] |= carry * 0x80000000;
}
while (bn256_is_even (v))
{
bn256_shift (v, v, -1);
if (bn256_is_even (C))
bn256_shift (C, C, -1);
else
{
int carry = bn256_add (C, C, P256);
bn256_shift (C, C, -1);
if (carry)
C->word[7] |= 0x80000000;
bn256_add (tmp, C, P256);
carry = 0;
}
else
carry = bn256_add (C, C, P256);
bn256_shift (C, C, -1);
C->word[7] |= carry * 0x80000000;
}
if (bn256_is_ge (u, v))
@ -283,6 +295,7 @@ void
modp256_shift (bn256 *X, const bn256 *A, int shift)
{
uint32_t carry;
#define borrow carry
bn256 tmp[1];
carry = bn256_shift (X, A, shift);
@ -300,6 +313,9 @@ modp256_shift (bn256 *X, const bn256 *A, int shift)
tmp->word[3] = carry;
modp256_sub (X, X, tmp);
if (bn256_is_ge (X, P256))
bn256_sub (X, X, P256);
borrow = bn256_sub (tmp, X, P256);
if (borrow)
memcpy (tmp, X, sizeof (bn256));
else
memcpy (X, tmp, sizeof (bn256));
}