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Added more constant-time code and removed biases in the prime number generation routines.

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This commit is contained in:
Pascal Junod 2015-03-11 16:49:45 +01:00
parent 02ba5785bf
commit b99183dfc6
2 changed files with 32 additions and 19 deletions
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41
library/bignum.c
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@ -223,8 +223,8 @@ int mpi_safe_cond_assign( mpi *X, const mpi *Y, unsigned char assign )
int ret = 0;
size_t i;
/* make sure assign is 0 or 1 */
assign = ( assign != 0 );
/* make sure assign is 0 or 1 in a time-constant manner */
assign = (assign | (unsigned char)-assign) >> 7;
MPI_CHK( mpi_grow( X, Y->n ) );
@ -255,8 +255,8 @@ int mpi_safe_cond_swap( mpi *X, mpi *Y, unsigned char swap )
if( X == Y )
return( 0 );
/* make sure swap is 0 or 1 */
swap = ( swap != 0 );
/* make sure swap is 0 or 1 in a time-constant manner */
swap = (swap | (unsigned char)-swap) >> 7;
MPI_CHK( mpi_grow( X, Y->n ) );
MPI_CHK( mpi_grow( Y, X->n ) );
@ -1958,8 +1958,8 @@ static int mpi_miller_rabin( const mpi *X,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret;
size_t i, j, n, s;
int ret, count;
size_t i, j, k, n, s;
mpi W, R, T, A, RR;
mpi_init( &W ); mpi_init( &R ); mpi_init( &T ); mpi_init( &A );
@ -1987,14 +1987,23 @@ static int mpi_miller_rabin( const mpi *X,
/*
* pick a random A, 1 < A < |X| - 1
*/
count = 0;
do {
MPI_CHK( mpi_fill_random( &A, X->n * ciL, f_rng, p_rng ) );
if( mpi_cmp_mpi( &A, &W ) >= 0 )
{
j = mpi_msb( &A ) - mpi_msb( &W );
MPI_CHK( mpi_shift_r( &A, j + 1 ) );
j = mpi_msb( &A );
k = mpi_msb( &W );
if (j > k) {
MPI_CHK( mpi_shift_r( &A, j - k ) );
}
A.p[0] |= 3;
if (count++ > 30) {
return POLARSSL_ERR_MPI_NOT_ACCEPTABLE;
}
} while ( (mpi_cmp_mpi( &A, &W ) >= 0) ||
(mpi_cmp_int( &A, 1 ) <= 0) );
/*
* A = A^R mod |X|
@ -2092,10 +2101,11 @@ int mpi_gen_prime( mpi *X, size_t nbits, int dh_flag,
MPI_CHK( mpi_fill_random( X, n * ciL, f_rng, p_rng ) );
k = mpi_msb( X );
if( k < nbits ) MPI_CHK( mpi_shift_l( X, nbits - k ) );
if( k > nbits ) MPI_CHK( mpi_shift_r( X, k - nbits ) );
if( k > nbits ) MPI_CHK( mpi_shift_r( X, k - nbits + 1 ) );
X->p[0] |= 3;
mpi_set_bit( X, nbits-1, 1 );
X->p[0] |= 1;
if( dh_flag == 0 )
{
@ -2114,6 +2124,9 @@ int mpi_gen_prime( mpi *X, size_t nbits, int dh_flag,
* is X = 2 mod 3 (which is equivalent to Y = 2 mod 3).
* Make sure it is satisfied, while keeping X = 3 mod 4
*/
X->p[0] |= 2;
MPI_CHK( mpi_mod_int( &r, X, 3 ) );
if( r == 0 )
MPI_CHK( mpi_add_int( X, X, 8 ) );

6
library/rsa.c
View File

@ -761,7 +761,7 @@ int rsa_rsaes_oaep_decrypt( rsa_context *ctx,
for( i = 0; i < ilen - 2 * hlen - 2; i++ )
{
pad_done |= p[i];
pad_len += ( pad_done == 0 );
pad_len += ((pad_done | (unsigned char)-pad_done) >> 7) ^ 1;
}
p += pad_len;
@ -835,8 +835,8 @@ int rsa_rsaes_pkcs1_v15_decrypt( rsa_context *ctx,
* (minus one, for the 00 byte) */
for( i = 0; i < ilen - 3; i++ )
{
pad_done |= ( p[i] == 0 );
pad_count += ( pad_done == 0 );
pad_done |= ((p[i] | (unsigned char)-p[i]) >> 7) ^ 1;
pad_count += ((pad_done | (unsigned char)-pad_done) >> 7) ^ 1;
}
p += pad_count;