CTR_DRBG: explicitly set entropy_nonce_len=0 when desired

No behavior change. Prepare for a future version that will set the
entropy nonce length to a nonzero value by default.

Author: gilles-peskine-arm

library/ctr_drbg.c

@@ -732,6 +732,7 @@ int mbedtls_ctr_drbg_self_test( int verbose )
 
     test_offset = 0;
     mbedtls_ctr_drbg_set_entropy_len( &ctx, 32 );
+    mbedtls_ctr_drbg_set_nonce_len( &ctx, 0 );
     CHK( mbedtls_ctr_drbg_seed( &ctx,
                                 ctr_drbg_self_test_entropy,
                                 (void *) entropy_source_pr,
@@ -756,6 +757,7 @@ int mbedtls_ctr_drbg_self_test( int verbose )
 
     test_offset = 0;
     mbedtls_ctr_drbg_set_entropy_len( &ctx, 32 );
+    mbedtls_ctr_drbg_set_nonce_len( &ctx, 0 );
     CHK( mbedtls_ctr_drbg_seed( &ctx,
                                 ctr_drbg_self_test_entropy,
                                 (void *) entropy_source_nopr,

tests/suites/test_suite_ctr_drbg.function

@@ -45,6 +45,7 @@ static void ctr_drbg_validate_internal( int reseed_mode, data_t * nonce,
     /* CTR_DRBG_Instantiate(entropy[:entropy->len], nonce, perso, <ignored>)
      * where nonce||perso = nonce[nonce->len] */
     mbedtls_ctr_drbg_set_entropy_len( &ctx, entropy_chunk_len );
+    mbedtls_ctr_drbg_set_nonce_len( &ctx, 0 );
     TEST_ASSERT( mbedtls_ctr_drbg_seed(
                      &ctx,
                      mbedtls_test_entropy_func, entropy->x,