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Tighten ecp_mul() validity checks

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Manuel Pégourié-Gonnard 2013-11-21 09:28:03 +01:00
parent 09ceaf49d0
commit ff27b7c968
4 changed files with 42 additions and 43 deletions
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15
include/polarssl/ecp.h
View File

@ -459,22 +459,19 @@ int ecp_sub( const ecp_group *grp, ecp_point *R,
* \param p_rng RNG parameter
*
* \return 0 if successful,
* POLARSSL_ERR_ECP_INVALID_KEY if m is not a valid privkey
* or P is not a valid pubkey,
* POLARSSL_ERR_MPI_MALLOC_FAILED if memory allocation failed
* POLARSSL_ERR_ECP_BAD_INPUT_DATA if m < 0 of m has greater
* bit length than N, the number of points in the group.
*
* \note In order to prevent simple timing attacks, this function
* executes a constant number of operations (that is, point
* doubling and addition of distinct points) for random m in
* the allowed range.
*
* \note If f_rng is not NULL, it is used to randomize projective
* coordinates of indermediate results, in order to prevent
* more elaborate timing attacks relying on intermediate
* operations. (This is a prophylactic measure since no such
* attack has been published yet.) Since this contermeasure
* has very low overhead, it is recommended to always provide
* a non-NULL f_rng parameter when using secret inputs.
* \note If f_rng is not NULL, it is used to randomize intermediate
* results in order to prevent potential attacks targetting
* these results. It is recommended to always provide a
* non-NULL f_rng (the overhead is negligible).
*/
int ecp_mul( ecp_group *grp, ecp_point *R,
const mpi *m, const ecp_point *P,

30
library/ecp.c
View File

@ -1440,21 +1440,24 @@ int ecp_mul( ecp_group *grp, ecp_point *R,
ecp_point Q, *T = NULL, S[2];
mpi M;
if( mpi_cmp_int( m, 0 ) < 0 || mpi_msb( m ) > grp->nbits )
return( POLARSSL_ERR_ECP_BAD_INPUT_DATA );
/*
* Sanity checks (before we even initialize anything)
*/
if( ( ret = ecp_check_privkey( grp, m ) ) != 0 )
return( ret );
/* We'll need this later, but do it now to possibly avoid cheking P */
p_eq_g = ( mpi_cmp_int( &P->Z, 1 ) == 0 &&
mpi_cmp_mpi( &P->Y, &grp->G.Y ) == 0 &&
mpi_cmp_mpi( &P->X, &grp->G.X ) == 0 );
if( ! p_eq_g && ( ret = ecp_check_pubkey( grp, P ) ) != 0 )
return( ret );
mpi_init( &M );
ecp_point_init( &Q );
ecp_point_init( &S[0] );
ecp_point_init( &S[1] );
/*
* Check if P == G
*/
p_eq_g = ( mpi_cmp_int( &P->Z, 1 ) == 0 &&
mpi_cmp_mpi( &P->Y, &grp->G.Y ) == 0 &&
mpi_cmp_mpi( &P->X, &grp->G.X ) == 0 );
/*
* Minimize the number of multiplications, that is minimize
* 10 * d * w + 18 * 2^(w-1) + 11 * d + 7 * w
@ -2061,13 +2064,12 @@ int ecp_self_test( int verbose )
/* exponents especially adapted for secp192r1 */
const char *exponents[] =
{
"000000000000000000000000000000000000000000000000", /* zero */
"000000000000000000000000000000000000000000000001", /* one */
"FFFFFFFFFFFFFFFFFFFFFFFF99DEF836146BC9B1B4D22831", /* N */
"FFFFFFFFFFFFFFFFFFFFFFFF99DEF836146BC9B1B4D22830", /* N - 1 */
"5EA6F389A38B8BC81E767753B15AA5569E1782E30ABE7D25", /* random */
"400000000000000000000000000000000000000000000000",
"7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF",
"555555555555555555555555555555555555555555555555",
"400000000000000000000000000000000000000000000000", /* one and zeros */
"7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF", /* all ones */
"555555555555555555555555555555555555555555555555", /* 101010... */
};
ecp_group_init( &grp );

14
tests/suites/test_suite_ecp.data
View File

@ -50,10 +50,10 @@ ECP small subtraction #9
ecp_small_sub:0:"14":"11":0:"14":"36":0:27:30
ECP small multiplication negative
ecp_small_mul:-1:0:0:0:POLARSSL_ERR_ECP_BAD_INPUT_DATA
ecp_small_mul:-1:0:0:0:POLARSSL_ERR_ECP_INVALID_KEY
ECP small multiplication #0
ecp_small_mul:0:1:0:0:0
ecp_small_mul:0:1:0:0:POLARSSL_ERR_ECP_INVALID_KEY
ECP small multiplication #1
ecp_small_mul:1:0:17:42:0
@ -92,16 +92,10 @@ ECP small multiplication #12
ecp_small_mul:12:0:17:05:0
ECP small multiplication #13
ecp_small_mul:13:1:0:0:0
ecp_small_mul:13:1:0:0:POLARSSL_ERR_ECP_INVALID_KEY
ECP small multiplication #14
ecp_small_mul:1:0:17:42:0
ECP small multiplication #15
ecp_small_mul:2:0:20:01:0
ECP small multiplication too big
ecp_small_mul:-1:0:0:0:POLARSSL_ERR_ECP_BAD_INPUT_DATA
ecp_small_mul:14:0:17:42:POLARSSL_ERR_ECP_INVALID_KEY
ECP small check pubkey #1
ecp_small_check_pub:1:1:0:POLARSSL_ERR_ECP_INVALID_KEY

26
tests/suites/test_suite_ecp.function
View File

@ -115,12 +115,15 @@ void ecp_small_mul( int m_str, int r_zero, int x_r, int y_r, int ret )
TEST_ASSERT( ecp_mul( &grp, &R, &m, &grp.G, NULL, NULL ) == ret );
if( r_zero )
TEST_ASSERT( mpi_cmp_int( &R.Z, 0 ) == 0 );
else
if( ret == 0 )
{
TEST_ASSERT( mpi_cmp_int( &R.X, x_r ) == 0 );
TEST_ASSERT( mpi_cmp_int( &R.Y, y_r ) == 0 );
if( r_zero )
TEST_ASSERT( mpi_cmp_int( &R.Z, 0 ) == 0 );
else
{
TEST_ASSERT( mpi_cmp_int( &R.X, x_r ) == 0 );
TEST_ASSERT( mpi_cmp_int( &R.Y, y_r ) == 0 );
}
}
/* try again with randomization */
@ -129,12 +132,15 @@ void ecp_small_mul( int m_str, int r_zero, int x_r, int y_r, int ret )
TEST_ASSERT( ecp_mul( &grp, &R, &m, &grp.G,
&rnd_pseudo_rand, &rnd_info ) == ret );
if( r_zero )
TEST_ASSERT( mpi_cmp_int( &R.Z, 0 ) == 0 );
else
if( ret == 0 )
{
TEST_ASSERT( mpi_cmp_int( &R.X, x_r ) == 0 );
TEST_ASSERT( mpi_cmp_int( &R.Y, y_r ) == 0 );
if( r_zero )
TEST_ASSERT( mpi_cmp_int( &R.Z, 0 ) == 0 );
else
{
TEST_ASSERT( mpi_cmp_int( &R.X, x_r ) == 0 );
TEST_ASSERT( mpi_cmp_int( &R.Y, y_r ) == 0 );
}
}
ecp_group_free( &grp );