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Fix for constant time (step 4)
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@ -1,5 +1,12 @@
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2014-01-21 Niibe Yutaka <gniibe@fsij.org>
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* src/modp256.c (modp256_add, modp256_sub, modp256_reduce)
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(modp256_shift): Fix for constant time.
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(modp256_inv): Likewise (not fully constant time, yet).
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* src/mod.c (mod_reduce): Fix for constant time.
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(mod_inv): Likewise (not fully constant time, yet).
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* src/bn.h (bn256, bn512): words -> word.
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* src/ec_p256.h (naf4_257): Likewise.
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@ -1,7 +1,7 @@
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/*
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* modp256.c -- modulo P256 arithmetic
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*
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* Copyright (C) 2011, 2013 Free Software Initiative of Japan
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* Copyright (C) 2011, 2013, 2014 Free Software Initiative of Japan
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* Author: NIIBE Yutaka <gniibe@fsij.org>
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*
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* This file is a part of Gnuk, a GnuPG USB Token implementation.
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@ -52,11 +52,14 @@ const bn256 p256 = { {0xffffffff, 0xffffffff, 0xffffffff, 0x00000000,
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void
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modp256_add (bn256 *X, const bn256 *A, const bn256 *B)
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{
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int carry;
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uint32_t carry;
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bn256 tmp[1];
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carry = bn256_add (X, A, B);
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if (carry)
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bn256_sub (X, X, P256);
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else
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bn256_sub (tmp, X, P256);
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}
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/**
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@ -65,11 +68,14 @@ modp256_add (bn256 *X, const bn256 *A, const bn256 *B)
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void
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modp256_sub (bn256 *X, const bn256 *A, const bn256 *B)
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{
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int borrow;
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uint32_t borrow;
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bn256 tmp[1];
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borrow = bn256_sub (X, A, B);
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if (borrow)
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bn256_add (X, X, P256);
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else
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bn256_add (tmp, X, P256);
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}
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/**
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@ -79,6 +85,7 @@ void
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modp256_reduce (bn256 *X, const bn512 *A)
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{
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bn256 tmp[1];
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uint32_t borrow;
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#define S1 X
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#define S2 tmp
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@ -181,8 +188,11 @@ modp256_reduce (bn256 *X, const bn512 *A)
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/* X -= S9 */
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modp256_sub (X, X, S9);
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if (bn256_is_ge (X, P256))
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bn256_sub (X, X, P256);
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borrow = bn256_sub (tmp, X, P256);
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if (borrow)
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memcpy (tmp, X, sizeof (bn256));
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else
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memcpy (X, tmp, sizeof (bn256));
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}
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/**
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@ -218,8 +228,10 @@ modp256_sqr (bn256 *X, const bn256 *A)
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int
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modp256_inv (bn256 *C, const bn256 *a)
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{
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bn256 u[1], v[1];
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bn256 u[1], v[1], tmp[1];
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bn256 A[1] = { { { 1, 0, 0, 0, 0, 0, 0, 0 } } };
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uint32_t carry;
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#define borrow carry
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if (bn256_is_zero (a))
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return -1;
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@ -234,30 +246,30 @@ modp256_inv (bn256 *C, const bn256 *a)
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{
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bn256_shift (u, u, -1);
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if (bn256_is_even (A))
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bn256_shift (A, A, -1);
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else
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{
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int carry = bn256_add (A, A, P256);
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bn256_add (tmp, A, P256);
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carry = 0;
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}
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else
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carry = bn256_add (A, A, P256);
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bn256_shift (A, A, -1);
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if (carry)
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A->word[7] |= 0x80000000;
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}
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A->word[7] |= carry * 0x80000000;
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}
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while (bn256_is_even (v))
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{
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bn256_shift (v, v, -1);
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if (bn256_is_even (C))
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bn256_shift (C, C, -1);
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else
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{
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int carry = bn256_add (C, C, P256);
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bn256_add (tmp, C, P256);
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carry = 0;
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}
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else
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carry = bn256_add (C, C, P256);
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bn256_shift (C, C, -1);
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if (carry)
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C->word[7] |= 0x80000000;
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}
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C->word[7] |= carry * 0x80000000;
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}
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if (bn256_is_ge (u, v))
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@ -283,6 +295,7 @@ void
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modp256_shift (bn256 *X, const bn256 *A, int shift)
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{
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uint32_t carry;
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#define borrow carry
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bn256 tmp[1];
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carry = bn256_shift (X, A, shift);
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@ -300,6 +313,9 @@ modp256_shift (bn256 *X, const bn256 *A, int shift)
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tmp->word[3] = carry;
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modp256_sub (X, X, tmp);
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if (bn256_is_ge (X, P256))
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bn256_sub (X, X, P256);
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borrow = bn256_sub (tmp, X, P256);
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if (borrow)
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memcpy (tmp, X, sizeof (bn256));
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else
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memcpy (X, tmp, sizeof (bn256));
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}
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