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mbedtls_ecp_gen_privkey_sw: generalize to mbedtls_mpi_random

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Rename mbedtls_ecp_gen_privkey_sw to mbedtls_mpi_random since it has
no particular connection to elliptic curves beyond the fact that its
operation is defined by the deterministic ECDSA specification. This is
a generic function that generates a random MPI between 1 inclusive and
N exclusive.

Slightly generalize the function to accept a different lower bound,
which adds a negligible amount of complexity.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2021-03-29 21:53:58 +02:00
parent 7888073147
commit 8cfffb30b3
4 changed files with 119 additions and 99 deletions
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23
tests/suites/test_suite_ecp.function
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@ -1324,7 +1324,7 @@ exit:
/* END_CASE */
/* BEGIN_CASE depends_on:MBEDTLS_TEST_HOOKS:MBEDTLS_ECP_SHORT_WEIERSTRASS_ENABLED */
void genkey_sw_many( data_t *bound_bytes, int iterations )
void mpi_random_many( int min, data_t *bound_bytes, int iterations )
{
/* Generate numbers in the range 1..bound-1. Do it iterations times.
* This function assumes that the value of bound is at least 2 and
@ -1332,11 +1332,11 @@ void genkey_sw_many( data_t *bound_bytes, int iterations )
* effectively never occurs.
*/
mbedtls_mpi bound;
mbedtls_mpi upper_bound;
size_t n_bits;
mbedtls_mpi result;
size_t b;
/* If bound is small, stats[b] is the number of times the value b
/* If upper_bound is small, stats[b] is the number of times the value b
* has been generated. Otherwise stats[b] is the number of times a
* value with bit b set has been generated. */
size_t *stats = NULL;
@ -1344,12 +1344,12 @@ void genkey_sw_many( data_t *bound_bytes, int iterations )
int full_stats;
size_t i;
mbedtls_mpi_init( &bound );
mbedtls_mpi_init( &upper_bound );
mbedtls_mpi_init( &result );
TEST_EQUAL( 0, mbedtls_mpi_read_binary( &bound,
TEST_EQUAL( 0, mbedtls_mpi_read_binary( &upper_bound,
bound_bytes->x, bound_bytes->len ) );
n_bits = mbedtls_mpi_bitlen( &bound );
n_bits = mbedtls_mpi_bitlen( &upper_bound );
/* Consider a bound "small" if it's less than 2^5. This value is chosen
* to be small enough that the probability of missing one value is
* negligible given the number of iterations. It must be less than
@ -1370,12 +1370,11 @@ void genkey_sw_many( data_t *bound_bytes, int iterations )
for( i = 0; i < (size_t) iterations; i++ )
{
mbedtls_test_set_step( i );
TEST_EQUAL( 0, mbedtls_ecp_gen_privkey_sw(
&bound, n_bits, &result,
mbedtls_test_rnd_std_rand, NULL ) );
TEST_EQUAL( 0, mbedtls_mpi_random( &result, min, &upper_bound,
mbedtls_test_rnd_std_rand, NULL ) );
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &result, &bound ) < 0 );
TEST_ASSERT( mbedtls_mpi_cmp_int( &result, 1 ) >= 0 );
TEST_ASSERT( mbedtls_mpi_cmp_mpi( &result, &upper_bound ) < 0 );
TEST_ASSERT( mbedtls_mpi_cmp_int( &result, min ) >= 0 );
if( full_stats )
{
uint8_t value;
@ -1425,7 +1424,7 @@ void genkey_sw_many( data_t *bound_bytes, int iterations )
}
exit:
mbedtls_mpi_free( &bound );
mbedtls_mpi_free( &upper_bound );
mbedtls_mpi_free( &result );
mbedtls_free( stats );
}