SSL test programs: abstract CTR_DRBG away

In ssl_client2 and ssl_server2, to generate random data, go through a
level of indirection provided by ssl_test_lib. This way the programs
don't depend on a particular choice of RNG implementation, and only
ssl_test_lib.{h,c} explicitly reference CTR_DRBG.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

programs/ssl/ssl_client2.c

@@ -1880,7 +1880,7 @@ int main( int argc, char *argv[] )
 #endif
 #endif
     }
-    mbedtls_ssl_conf_rng( &conf, mbedtls_ctr_drbg_random, &rng.drbg );
+    mbedtls_ssl_conf_rng( &conf, rng_get, &rng );
     mbedtls_ssl_conf_dbg( &conf, my_debug, stdout );
 
     mbedtls_ssl_conf_read_timeout( &conf, opt.read_timeout );

programs/ssl/ssl_server2.c

@@ -2682,7 +2682,7 @@ int main( int argc, char *argv[] )
 #endif
 #endif
     }
-    mbedtls_ssl_conf_rng( &conf, mbedtls_ctr_drbg_random, &rng.drbg );
+    mbedtls_ssl_conf_rng( &conf, rng_get, &rng );
     mbedtls_ssl_conf_dbg( &conf, my_debug, stdout );
 
 #if defined(MBEDTLS_SSL_CACHE_C)
@@ -2701,7 +2701,7 @@ int main( int argc, char *argv[] )
     if( opt.tickets == MBEDTLS_SSL_SESSION_TICKETS_ENABLED )
     {
         if( ( ret = mbedtls_ssl_ticket_setup( &ticket_ctx,
-                        mbedtls_ctr_drbg_random, &rng.drbg,
+                        rng_get, &rng,
                         MBEDTLS_CIPHER_AES_256_GCM,
                         opt.ticket_timeout ) ) != 0 )
         {
@@ -2723,7 +2723,7 @@ int main( int argc, char *argv[] )
         if( opt.cookies > 0 )
         {
             if( ( ret = mbedtls_ssl_cookie_setup( &cookie_ctx,
-                                          mbedtls_ctr_drbg_random, &rng.drbg ) ) != 0 )
+                                                  rng_get, &rng ) ) != 0 )
             {
                 mbedtls_printf( " failed\n  ! mbedtls_ssl_cookie_setup returned %d\n\n", ret );
                 goto exit;
@@ -2875,8 +2875,8 @@ int main( int argc, char *argv[] )
         ssl_async_keys.inject_error = ( opt.async_private_error < 0 ?
                                         - opt.async_private_error :
                                         opt.async_private_error );
-        ssl_async_keys.f_rng = mbedtls_ctr_drbg_random;
+        ssl_async_keys.f_rng = rng_get;
-        ssl_async_keys.p_rng = &rng.drbg;
+        ssl_async_keys.p_rng = &rng;
         mbedtls_ssl_conf_async_private_cb( &conf,
                                            sign,
                                            decrypt,

programs/ssl/ssl_test_lib.c

@@ -95,6 +95,12 @@ void rng_free( rng_context_t *rng )
     mbedtls_entropy_free( &rng->entropy );
 }
 
+int rng_get( void *p_rng, unsigned char *output, size_t output_len )
+{
+    rng_context_t *rng = p_rng;
+    return( mbedtls_ctr_drbg_random( &rng->drbg, output, output_len ) );
+}
+
 #if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
 int ca_callback( void *data, mbedtls_x509_crt const *child,
                  mbedtls_x509_crt **candidates )

programs/ssl/ssl_test_lib.h

@@ -164,6 +164,21 @@ int rng_seed( rng_context_t *rng, int reproducible, const char *pers );
  */
 void rng_free( rng_context_t *rng );
 
+/** Generate random data.
+ *
+ * This function is suitable for use as the \c f_rng argument to Mbed TLS
+ * library functions.
+ *
+ * \param p_rng         The CTR_DRBG context. This must be a pointer to a
+ *                      #rng_context_t structure.
+ * \param output        The buffer to fill.
+ * \param output_len    The length of the buffer in bytes.
+ *
+ * \return              \c 0 on success.
+ * \return              An Mbed TLS error code on error.
+ */
+int rng_get( void *p_rng, unsigned char *output, size_t output_len );
+
 #if defined(MBEDTLS_X509_TRUSTED_CERTIFICATE_CALLBACK)
 int ca_callback( void *data, mbedtls_x509_crt const *child,
                  mbedtls_x509_crt **candidates );