DHM: new functions to query the length of the modulus

Add two functions mbedtls_dhm_get_len() and mbedtls_dhm_get_bitlen() to
query the length of the modulus in bytes or bits.

Remove the len field: the cost of calling mbedtls_dhm_get_len() each time
it's needed is negligible, and this improves the abstraction of the DHM
module.

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

2 files changed, 6 insertions, 5 deletions

diff --git a/programs/pkey/dh_client.c b/programs/pkey/dh_client.c
index 101b0bb..d68dc24 100644
--- a/programs/pkey/dh_client.c
+++ b/programs/pkey/dh_client.c
@@ -192,7 +192,8 @@ int main( void )
         goto exit;
     }
 
-    if( dhm.MBEDTLS_PRIVATE(len) < 64 || dhm.MBEDTLS_PRIVATE(len) > 512 )
+    n = mbedtls_dhm_get_len( &dhm );
+    if( n < 64 || n > 512 )
     {
         mbedtls_printf( " failed\n  ! Invalid DHM modulus size\n\n" );
         goto exit;
@@ -232,8 +233,8 @@ int main( void )
     mbedtls_printf( "\n  . Sending own public value to server" );
     fflush( stdout );
 
-    n = dhm.MBEDTLS_PRIVATE(len);
-    if( ( ret = mbedtls_dhm_make_public( &dhm, (int) dhm.MBEDTLS_PRIVATE(len), buf, n,
+    n = mbedtls_dhm_get_len( &dhm );
+    if( ( ret = mbedtls_dhm_make_public( &dhm, (int) n, buf, n,
                                  mbedtls_ctr_drbg_random, &ctr_drbg ) ) != 0 )
     {
         mbedtls_printf( " failed\n  ! mbedtls_dhm_make_public returned %d\n\n", ret );
diff --git a/programs/pkey/dh_server.c b/programs/pkey/dh_server.c
index 745e68a..9d51c14 100644
--- a/programs/pkey/dh_server.c
+++ b/programs/pkey/dh_server.c
@@ -254,14 +254,14 @@ int main( void )
 
     memset( buf, 0, sizeof( buf ) );
 
-    n = dhm.MBEDTLS_PRIVATE(len);
+    n = mbedtls_dhm_get_len( &dhm );
     if( ( ret = mbedtls_net_recv( &client_fd, buf, n ) ) != (int) n )
     {
         mbedtls_printf( " failed\n  ! mbedtls_net_recv returned %d\n\n", ret );
         goto exit;
     }
 
-    if( ( ret = mbedtls_dhm_read_public( &dhm, buf, dhm.MBEDTLS_PRIVATE(len) ) ) != 0 )
+    if( ( ret = mbedtls_dhm_read_public( &dhm, buf, n ) ) != 0 )
     {
         mbedtls_printf( " failed\n  ! mbedtls_dhm_read_public returned %d\n\n", ret );
         goto exit;