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HMAC_DRBG entropy usage: test the exact amount of consumed entropy

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This commit is contained in:
Gilles Peskine 2019-10-22 19:10:33 +02:00
parent 58b56ce444
commit 4d2d4ff9b0
1 changed files with 22 additions and 13 deletions
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35
tests/suites/test_suite_hmac_drbg.function
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@ -37,7 +37,9 @@ void hmac_drbg_entropy_usage( int md_alg )
const mbedtls_md_info_t *md_info;
mbedtls_hmac_drbg_context ctx;
entropy_ctx entropy;
size_t last_len, i, reps = 10;
size_t i, reps = 10;
size_t default_entropy_len;
size_t expected_consumed_entropy = 0;
mbedtls_hmac_drbg_init( &ctx );
memset( buf, 0, sizeof( buf ) );
@ -48,23 +50,29 @@ void hmac_drbg_entropy_usage( int md_alg )
md_info = mbedtls_md_info_from_type( md_alg );
TEST_ASSERT( md_info != NULL );
if( mbedtls_md_get_size( md_info ) <= 20 )
default_entropy_len = 16;
else if( mbedtls_md_get_size( md_info ) <= 28 )
default_entropy_len = 24;
else
default_entropy_len = 32;
/* Init must use entropy */
last_len = entropy.len;
TEST_ASSERT( mbedtls_hmac_drbg_seed( &ctx, md_info, mbedtls_test_entropy_func, &entropy,
NULL, 0 ) == 0 );
TEST_ASSERT( entropy.len < last_len );
/* default_entropy_len of entropy, plus half as much for the nonce */
expected_consumed_entropy += default_entropy_len * 3 / 2;
TEST_EQUAL( sizeof( buf ) - entropy.len, expected_consumed_entropy );
/* By default, PR is off and reseed_interval is large,
* so the next few calls should not use entropy */
last_len = entropy.len;
for( i = 0; i < reps; i++ )
{
TEST_ASSERT( mbedtls_hmac_drbg_random( &ctx, out, sizeof( out ) - 4 ) == 0 );
TEST_ASSERT( mbedtls_hmac_drbg_random_with_add( &ctx, out, sizeof( out ) - 4,
buf, 16 ) == 0 );
}
TEST_ASSERT( entropy.len == last_len );
TEST_EQUAL( sizeof( buf ) - entropy.len, expected_consumed_entropy );
/* While at it, make sure we didn't write past the requested length */
TEST_ASSERT( out[sizeof( out ) - 4] == 0 );
@ -76,33 +84,34 @@ void hmac_drbg_entropy_usage( int md_alg )
* so the next call should reseed */
mbedtls_hmac_drbg_set_reseed_interval( &ctx, 2 * reps );
TEST_ASSERT( mbedtls_hmac_drbg_random( &ctx, out, sizeof( out ) ) == 0 );
TEST_ASSERT( entropy.len < last_len );
expected_consumed_entropy += default_entropy_len;
TEST_EQUAL( sizeof( buf ) - entropy.len, expected_consumed_entropy );
/* The new few calls should not reseed */
last_len = entropy.len;
for( i = 0; i < reps / 2; i++ )
{
TEST_ASSERT( mbedtls_hmac_drbg_random( &ctx, out, sizeof( out ) ) == 0 );
TEST_ASSERT( mbedtls_hmac_drbg_random_with_add( &ctx, out, sizeof( out ) ,
buf, 16 ) == 0 );
}
TEST_ASSERT( entropy.len == last_len );
TEST_EQUAL( sizeof( buf ) - entropy.len, expected_consumed_entropy );
/* Now enable PR, so the next few calls should all reseed */
mbedtls_hmac_drbg_set_prediction_resistance( &ctx, MBEDTLS_HMAC_DRBG_PR_ON );
TEST_ASSERT( mbedtls_hmac_drbg_random( &ctx, out, sizeof( out ) ) == 0 );
TEST_ASSERT( entropy.len < last_len );
expected_consumed_entropy += default_entropy_len;
TEST_EQUAL( sizeof( buf ) - entropy.len, expected_consumed_entropy );
/* Finally, check setting entropy_len */
mbedtls_hmac_drbg_set_entropy_len( &ctx, 42 );
last_len = entropy.len;
TEST_ASSERT( mbedtls_hmac_drbg_random( &ctx, out, sizeof( out ) ) == 0 );
TEST_ASSERT( (int) last_len - entropy.len == 42 );
expected_consumed_entropy += 42;
TEST_EQUAL( sizeof( buf ) - entropy.len, expected_consumed_entropy );
mbedtls_hmac_drbg_set_entropy_len( &ctx, 13 );
last_len = entropy.len;
TEST_ASSERT( mbedtls_hmac_drbg_random( &ctx, out, sizeof( out ) ) == 0 );
TEST_ASSERT( (int) last_len - entropy.len == 13 );
expected_consumed_entropy += 13;
TEST_EQUAL( sizeof( buf ) - entropy.len, expected_consumed_entropy );
exit:
mbedtls_hmac_drbg_free( &ctx );