New function mbedtls_rsa_get_bitlen

Add a new function mbedtls_rsa_get_bitlen which returns the RSA key
size, i.e. the bit size of the modulus. In the pk module, call
mbedtls_rsa_get_bitlen instead of mbedtls_rsa_get_len, which gave the
wrong result for key sizes that are not a multiple of 8.

This commit adds one non-regression test in the pk suite. More tests
are needed for RSA key sizes that are a multiple of 8.

This commit does not address RSA alternative implementations, which
only provide an interface that return the modulus size in bytes.

include/mbedtls/rsa.h

@@ -403,6 +403,16 @@ void mbedtls_rsa_set_padding( mbedtls_rsa_context *ctx, int padding,
  */
 size_t mbedtls_rsa_get_len( const mbedtls_rsa_context *ctx );
 
+/**
+ * \brief This function retrieves the length of the RSA modulus in bits.
+ *
+ * \param ctx The initialized RSA context.
+ *
+ * \return The length of the RSA modulus in bits.
+ *
+ */
+size_t mbedtls_rsa_get_bitlen( const mbedtls_rsa_context *ctx );
+
 /**
  * \brief This function generates an RSA keypair.
  *

library/pk_wrap.c

@@ -66,7 +66,7 @@ static int rsa_can_do( mbedtls_pk_type_t type )
 static size_t rsa_get_bitlen( const void *ctx )
 {
  const mbedtls_rsa_context * rsa = (const mbedtls_rsa_context *) ctx;
- return( 8 * mbedtls_rsa_get_len( rsa ) );
+ return( mbedtls_rsa_get_bitlen( rsa ) );
 }
 
 static int rsa_verify_wrap( void *ctx, mbedtls_md_type_t md_alg,

library/rsa.c

@@ -480,12 +480,19 @@ void mbedtls_rsa_set_padding( mbedtls_rsa_context *ctx, int padding, int hash_id
 /*
  * Get length in bytes of RSA modulus
  */
-
 size_t mbedtls_rsa_get_len( const mbedtls_rsa_context *ctx )
 {
  return( ctx->len );
 }
 
+/*
+ * Get length in bits of RSA modulus
+ */
+size_t mbedtls_rsa_get_bitlen( const mbedtls_rsa_context *ctx )
+{
+ return( mbedtls_mpi_bitlen( &ctx->N ) );
+}
+
 
 #if defined(MBEDTLS_GENPRIME)
 

tests/suites/test_suite_pk.data

@@ -1,7 +1,16 @@
-PK utils: RSA
+PK utils: RSA, 512 bits
 depends_on:MBEDTLS_RSA_C:MBEDTLS_GENPRIME
 pk_utils:MBEDTLS_PK_RSA:512:64:"RSA"
 
+## RSA key generation only supports even bit sizes
+#PK utils: RSA, 511 bits
+#depends_on:MBEDTLS_RSA_C:MBEDTLS_GENPRIME
+#pk_utils:MBEDTLS_PK_RSA:511:64:"RSA"
+#
+PK utils: RSA, 510 bits
+depends_on:MBEDTLS_RSA_C:MBEDTLS_GENPRIME
+pk_utils:MBEDTLS_PK_RSA:510:64:"RSA"
+
 PK utils: ECKEY
 depends_on:MBEDTLS_ECP_C:MBEDTLS_ECP_DP_SECP192R1_ENABLED
 pk_utils:MBEDTLS_PK_ECKEY:192:24:"EC"

tests/suites/test_suite_pk.function

@@ -13,22 +13,49 @@ static int rnd_std_rand( void *rng_state, unsigned char *output, size_t len );
 #define RSA_KEY_SIZE 512
 #define RSA_KEY_LEN 64
 
-static int pk_genkey( mbedtls_pk_context *pk )
+static int pk_genkey( mbedtls_pk_context *pk, int size )
 {
  ((void) pk);
 
 #if defined(MBEDTLS_RSA_C) && defined(MBEDTLS_GENPRIME)
  if( mbedtls_pk_get_type( pk ) == MBEDTLS_PK_RSA )
- return mbedtls_rsa_gen_key( mbedtls_pk_rsa( *pk ), rnd_std_rand, NULL, RSA_KEY_SIZE, 3 );
+ {
+ if( size == 0 )
+ size = RSA_KEY_SIZE;
+ return( mbedtls_rsa_gen_key( mbedtls_pk_rsa( *pk ),
+ rnd_std_rand, NULL, size, 3 ) );
+ }
 #endif
 #if defined(MBEDTLS_ECP_C)
  if( mbedtls_pk_get_type( pk ) == MBEDTLS_PK_ECKEY ||
  mbedtls_pk_get_type( pk ) == MBEDTLS_PK_ECKEY_DH ||
  mbedtls_pk_get_type( pk ) == MBEDTLS_PK_ECDSA )
  {
  int ret;
+ mbedtls_ecp_group_id curve;
+ switch( size )
+ {
+ case 0:
+ case 192:
+ curve = MBEDTLS_ECP_DP_SECP192R1;
+ break;
+ case 224:
+ curve = MBEDTLS_ECP_DP_SECP224R1;
+ break;
+ case 256:
+ curve = MBEDTLS_ECP_DP_SECP256R1;
+ break;
+ case 384:
+ curve = MBEDTLS_ECP_DP_SECP384R1;
+ break;
+ case 521:
+ curve = MBEDTLS_ECP_DP_SECP521R1;
+ break;
+ default:
+ return( -1 );
+ }
  if( ( ret = mbedtls_ecp_group_load( &mbedtls_pk_ec( *pk )->grp,
- MBEDTLS_ECP_DP_SECP192R1 ) ) != 0 )
+  curve ) ) != 0 )
  return( ret );
 
  return mbedtls_ecp_gen_keypair( &mbedtls_pk_ec( *pk )->grp, &mbedtls_pk_ec( *pk )->d,
@@ -77,7 +104,7 @@ void pk_utils( int type, int size, int len, char * name )
  mbedtls_pk_init( &pk );
 
  TEST_ASSERT( mbedtls_pk_setup( &pk, mbedtls_pk_info_from_type( type ) ) == 0 );
- TEST_ASSERT( pk_genkey( &pk ) == 0 );
+ TEST_ASSERT( pk_genkey( &pk, size ) == 0 );
 
  TEST_ASSERT( (int) mbedtls_pk_get_type( &pk ) == type );
  TEST_ASSERT( mbedtls_pk_can_do( &pk, type ) );
@@ -252,7 +279,7 @@ void pk_sign_verify( int type, int sign_ret, int verify_ret )
  memset( sig, 0, sizeof sig );
 
  TEST_ASSERT( mbedtls_pk_setup( &pk, mbedtls_pk_info_from_type( type ) ) == 0 );
- TEST_ASSERT( pk_genkey( &pk ) == 0 );
+ TEST_ASSERT( pk_genkey( &pk, 0 ) == 0 );
 
  TEST_ASSERT( mbedtls_pk_sign( &pk, MBEDTLS_MD_SHA256, hash, sizeof hash,
  sig, &sig_len, rnd_std_rand, NULL ) == sign_ret );
@@ -447,7 +474,7 @@ void pk_rsa_alt( )
  /* Initiliaze PK RSA context with random key */
  TEST_ASSERT( mbedtls_pk_setup( &rsa,
  mbedtls_pk_info_from_type( MBEDTLS_PK_RSA ) ) == 0 );
- TEST_ASSERT( pk_genkey( &rsa ) == 0 );
+ TEST_ASSERT( pk_genkey( &rsa, RSA_KEY_SIZE ) == 0 );
 
  /* Extract key to the raw rsa context */
  TEST_ASSERT( mbedtls_rsa_copy( &raw, mbedtls_pk_rsa( rsa ) ) == 0 );

tests/suites/test_suite_rsa.function

@@ -44,7 +44,8 @@ void mbedtls_rsa_pkcs1_sign( data_t * message_str, int padding_mode,
  TEST_ASSERT( mbedtls_mpi_read_string( &E, radix_E, input_E ) == 0 );
 
  TEST_ASSERT( mbedtls_rsa_import( &ctx, &N, &P, &Q, NULL, &E ) == 0 );
- TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod / 8 ) );
+ TEST_ASSERT( mbedtls_rsa_get_bitlen( &ctx ) == (size_t) mod );
+ TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod + 7 ) / 8 );
  TEST_ASSERT( mbedtls_rsa_complete( &ctx ) == 0 );
  TEST_ASSERT( mbedtls_rsa_check_privkey( &ctx ) == 0 );
 
@@ -86,7 +87,8 @@ void mbedtls_rsa_pkcs1_verify( data_t * message_str, int padding_mode,
  TEST_ASSERT( mbedtls_mpi_read_string( &N, radix_N, input_N ) == 0 );
  TEST_ASSERT( mbedtls_mpi_read_string( &E, radix_E, input_E ) == 0 );
  TEST_ASSERT( mbedtls_rsa_import( &ctx, &N, NULL, NULL, NULL, &E ) == 0 );
- TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod / 8 ) );
+ TEST_ASSERT( mbedtls_rsa_get_bitlen( &ctx ) == (size_t) mod );
+ TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod + 7 ) / 8 );
  TEST_ASSERT( mbedtls_rsa_check_pubkey( &ctx ) == 0 );
 
 
@@ -127,7 +129,8 @@ void rsa_pkcs1_sign_raw( data_t * hash_result,
  TEST_ASSERT( mbedtls_mpi_read_string( &E, radix_E, input_E ) == 0 );
 
  TEST_ASSERT( mbedtls_rsa_import( &ctx, &N, &P, &Q, NULL, &E ) == 0 );
- TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod / 8 ) );
+ TEST_ASSERT( mbedtls_rsa_get_bitlen( &ctx ) == (size_t) mod );
+ TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod + 7 ) / 8 );
  TEST_ASSERT( mbedtls_rsa_complete( &ctx ) == 0 );
  TEST_ASSERT( mbedtls_rsa_check_privkey( &ctx ) == 0 );
 
@@ -192,7 +195,8 @@ void rsa_pkcs1_verify_raw( data_t * hash_result,
  TEST_ASSERT( mbedtls_mpi_read_string( &E, radix_E, input_E ) == 0 );
 
  TEST_ASSERT( mbedtls_rsa_import( &ctx, &N, NULL, NULL, NULL, &E ) == 0 );
- TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod / 8 ) );
+ TEST_ASSERT( mbedtls_rsa_get_bitlen( &ctx ) == (size_t) mod );
+ TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod + 7 ) / 8 );
  TEST_ASSERT( mbedtls_rsa_check_pubkey( &ctx ) == 0 );
 
 
@@ -256,7 +260,8 @@ void mbedtls_rsa_pkcs1_encrypt( data_t * message_str, int padding_mode,
  TEST_ASSERT( mbedtls_mpi_read_string( &E, radix_E, input_E ) == 0 );
 
  TEST_ASSERT( mbedtls_rsa_import( &ctx, &N, NULL, NULL, NULL, &E ) == 0 );
- TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod / 8 ) );
+ TEST_ASSERT( mbedtls_rsa_get_bitlen( &ctx ) == (size_t) mod );
+ TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod + 7 ) / 8 );
  TEST_ASSERT( mbedtls_rsa_check_pubkey( &ctx ) == 0 );
 
 
@@ -294,7 +299,8 @@ void rsa_pkcs1_encrypt_bad_rng( data_t * message_str, int padding_mode,
  TEST_ASSERT( mbedtls_mpi_read_string( &E, radix_E, input_E ) == 0 );
 
  TEST_ASSERT( mbedtls_rsa_import( &ctx, &N, NULL, NULL, NULL, &E ) == 0 );
- TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod / 8 ) );
+ TEST_ASSERT( mbedtls_rsa_get_bitlen( &ctx ) == (size_t) mod );
+ TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod + 7 ) / 8 );
  TEST_ASSERT( mbedtls_rsa_check_pubkey( &ctx ) == 0 );
 
 
@@ -342,7 +348,8 @@ void mbedtls_rsa_pkcs1_decrypt( data_t * message_str, int padding_mode,
  TEST_ASSERT( mbedtls_mpi_read_string( &E, radix_E, input_E ) == 0 );
 
  TEST_ASSERT( mbedtls_rsa_import( &ctx, &N, &P, &Q, NULL, &E ) == 0 );
- TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod / 8 ) );
+ TEST_ASSERT( mbedtls_rsa_get_bitlen( &ctx ) == (size_t) mod );
+ TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod + 7 ) / 8 );
  TEST_ASSERT( mbedtls_rsa_complete( &ctx ) == 0 );
  TEST_ASSERT( mbedtls_rsa_check_privkey( &ctx ) == 0 );
 
@@ -381,7 +388,8 @@ void mbedtls_rsa_public( data_t * message_str, int mod, int radix_N,
  TEST_ASSERT( mbedtls_mpi_read_string( &E, radix_E, input_E ) == 0 );
 
  TEST_ASSERT( mbedtls_rsa_import( &ctx, &N, NULL, NULL, NULL, &E ) == 0 );
- TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod / 8 ) );
+ TEST_ASSERT( mbedtls_rsa_get_bitlen( &ctx ) == (size_t) mod );
+ TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod + 7 ) / 8 );
  TEST_ASSERT( mbedtls_rsa_check_pubkey( &ctx ) == 0 );
 
 
@@ -440,7 +448,8 @@ void mbedtls_rsa_private( data_t * message_str, int mod, int radix_P,
  TEST_ASSERT( mbedtls_mpi_read_string( &E, radix_E, input_E ) == 0 );
 
  TEST_ASSERT( mbedtls_rsa_import( &ctx, &N, &P, &Q, NULL, &E ) == 0 );
- TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod / 8 ) );
+ TEST_ASSERT( mbedtls_rsa_get_bitlen( &ctx ) == (size_t) mod );
+ TEST_ASSERT( mbedtls_rsa_get_len( &ctx ) == (size_t) ( mod + 7 ) / 8 );
  TEST_ASSERT( mbedtls_rsa_complete( &ctx ) == 0 );
  TEST_ASSERT( mbedtls_rsa_check_privkey( &ctx ) == 0 );