Merge remote-tracking branch 'public/pr/1902' into development

CMakeLists.txt

@@ -36,10 +36,27 @@ set(NULL_ENTROPY_WARNING "${WARNING_BORDER}"
                          "${NULL_ENTROPY_WARN_L3}"
                          "${WARNING_BORDER}")
 
+set(CTR_DRBG_128_BIT_KEY_WARN_L1 "****  WARNING!  MBEDTLS_CTR_DRBG_USE_128_BIT_KEY defined!\n")
+set(CTR_DRBG_128_BIT_KEY_WARN_L2 "****  Using 128-bit keys for CTR_DRBG limits the security of generated\n")
+set(CTR_DRBG_128_BIT_KEY_WARN_L3 "****  keys and operations that use random values generated to 128-bit security\n")
+
+set(CTR_DRBG_128_BIT_KEY_WARNING "${WARNING_BORDER}"
+                         "${CTR_DRBG_128_BIT_KEY_WARN_L1}"
+                         "${CTR_DRBG_128_BIT_KEY_WARN_L2}"
+                         "${CTR_DRBG_128_BIT_KEY_WARN_L3}"
+                         "${WARNING_BORDER}")
+
 find_package(PythonInterp)
 find_package(Perl)
 if(PERL_FOUND)
 
+    # If 128-bit keys are configured for CTR_DRBG, display an appropriate warning
+    execute_process(COMMAND ${PERL_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/scripts/config.pl -f ${CMAKE_CURRENT_SOURCE_DIR}/include/mbedtls/config.h get MBEDTLS_CTR_DRBG_USE_128_BIT_KEY
+                        RESULT_VARIABLE result)
+    if(${result} EQUAL 0)
+        message(WARNING ${CTR_DRBG_128_BIT_KEY_WARNING})
+    endif()
+
     # If NULL Entropy is configured, display an appropriate warning
     execute_process(COMMAND ${PERL_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/scripts/config.pl -f ${CMAKE_CURRENT_SOURCE_DIR}/include/mbedtls/config.h get MBEDTLS_TEST_NULL_ENTROPY
                         RESULT_VARIABLE result)

ChangeLog

@@ -159,6 +159,8 @@ Features
      independently contributed again by Paul Sokolovsky.
    * Add support for key wrapping modes based on AES as defined by
      NIST SP 800-38F algorithms KW and KWP and by RFC 3394 and RFC 5649.
+   * Add support for 128-bit keys in CTR_DRBG. Note that using keys shorter
+     than 256 bits limits the security of generated material to 128 bits.
 
 Bugfix
    * Fix the key_app_writer example which was writing a leading zero byte which

Makefile

@@ -61,9 +61,21 @@ NULL_ENTROPY_WARN_L3=****  AND IS *NOT* SUITABLE FOR PRODUCTION USE     ****\n
 
 NULL_ENTROPY_WARNING=\n$(WARNING_BORDER)$(NULL_ENTROPY_WARN_L1)$(NULL_ENTROPY_WARN_L2)$(NULL_ENTROPY_WARN_L3)$(WARNING_BORDER)
 
+WARNING_BORDER_LONG      =**********************************************************************************\n
+CTR_DRBG_128_BIT_KEY_WARN_L1=****  WARNING!  MBEDTLS_CTR_DRBG_USE_128_BIT_KEY defined!                      ****\n
+CTR_DRBG_128_BIT_KEY_WARN_L2=****  Using 128-bit keys for CTR_DRBG limits the security of generated         ****\n
+CTR_DRBG_128_BIT_KEY_WARN_L3=****  keys and operations that use random values generated to 128-bit security ****\n
+
+CTR_DRBG_128_BIT_KEY_WARNING=\n$(WARNING_BORDER_LONG)$(CTR_DRBG_128_BIT_KEY_WARN_L1)$(CTR_DRBG_128_BIT_KEY_WARN_L2)$(CTR_DRBG_128_BIT_KEY_WARN_L3)$(WARNING_BORDER_LONG)
+
 # Post build steps
 post_build:
 ifndef WINDOWS
+
+	# If 128-bit keys are configured for CTR_DRBG, display an appropriate warning
+	-scripts/config.pl get MBEDTLS_CTR_DRBG_USE_128_BIT_KEY && ([ $$? -eq 0 ]) && \
+	    echo '$(CTR_DRBG_128_BIT_KEY_WARNING)'
+
 	# If NULL Entropy is configured, display an appropriate warning
 	-scripts/config.pl get MBEDTLS_TEST_NULL_ENTROPY && ([ $$? -eq 0 ]) && \
 	    echo '$(NULL_ENTROPY_WARNING)'

include/mbedtls/config.h

@@ -2047,14 +2047,16 @@
 /**
  * \def MBEDTLS_CTR_DRBG_C
  *
- * Enable the CTR_DRBG AES-256-based random generator.
+ * Enable the CTR_DRBG AES-based random generator.
+ * The CTR_DRBG generator uses AES-256 by default.
+ * To use AES-128 instead, enable MBEDTLS_CTR_DRBG_USE_128_BIT_KEY below.
  *
  * Module:  library/ctr_drbg.c
  * Caller:
  *
  * Requires: MBEDTLS_AES_C
  *
- * This module provides the CTR_DRBG AES-256 random number generator.
+ * This module provides the CTR_DRBG AES random number generator.
  */
 #define MBEDTLS_CTR_DRBG_C
 
@@ -2939,6 +2941,7 @@
 //#define MBEDTLS_CTR_DRBG_MAX_INPUT                256 /**< Maximum number of additional input bytes */
 //#define MBEDTLS_CTR_DRBG_MAX_REQUEST             1024 /**< Maximum number of requested bytes per call */
 //#define MBEDTLS_CTR_DRBG_MAX_SEED_INPUT           384 /**< Maximum size of (re)seed buffer */
+//#define MBEDTLS_CTR_DRBG_USE_128_BIT_KEY              /**< Use 128-bit key for CTR_DRBG - may reduce security (see ctr_drbg.h) */
 
 /* HMAC_DRBG options */
 //#define MBEDTLS_HMAC_DRBG_RESEED_INTERVAL   10000 /**< Interval before reseed is performed by default */

include/mbedtls/ctr_drbg.h

@@ -8,8 +8,11 @@
  * Recommendation for Random Number Generation Using Deterministic Random
  * Bit Generators</em>.
  *
- * The Mbed TLS implementation of CTR_DRBG uses AES-256 as the underlying
+ * The Mbed TLS implementation of CTR_DRBG uses AES-256 (default) or AES-128
- * block cipher.
+ * as the underlying block cipher.
+ *
+ *  \warning Using 128-bit keys for CTR_DRBG limits the security of generated
+ *  keys and operations that use random values generated to 128-bit security.
  */
 /*
  *  Copyright (C) 2006-2018, Arm Limited (or its affiliates), All Rights Reserved
@@ -45,7 +48,13 @@
 #define MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR                -0x003A  /**< Read or write error in file. */
 
 #define MBEDTLS_CTR_DRBG_BLOCKSIZE          16 /**< The block size used by the cipher. */
-#define MBEDTLS_CTR_DRBG_KEYSIZE            32 /**< The key size used by the cipher. */
+
+#if defined(MBEDTLS_CTR_DRBG_USE_128_BIT_KEY)
+#define MBEDTLS_CTR_DRBG_KEYSIZE            16 /**< The key size used by the cipher (compile-time choice: 128 bits). */
+#else
+#define MBEDTLS_CTR_DRBG_KEYSIZE            32 /**< The key size used by the cipher (compile-time choice: 256 bits). */
+#endif
+
 #define MBEDTLS_CTR_DRBG_KEYBITS            ( MBEDTLS_CTR_DRBG_KEYSIZE * 8 ) /**< The key size for the DRBG operation, in bits. */
 #define MBEDTLS_CTR_DRBG_SEEDLEN            ( MBEDTLS_CTR_DRBG_KEYSIZE + MBEDTLS_CTR_DRBG_BLOCKSIZE ) /**< The seed length, calculated as (counter + AES key). */
 

library/ctr_drbg.c

@@ -66,6 +66,18 @@ void mbedtls_ctr_drbg_init( mbedtls_ctr_drbg_context *ctx )
  * Non-public function wrapped by mbedtls_ctr_drbg_seed(). Necessary to allow
  * NIST tests to succeed (which require known length fixed entropy)
  */
+/* CTR_DRBG_Instantiate with derivation function (SP 800-90A §10.2.1.3.2)
+ * mbedtls_ctr_drbg_seed_entropy_len(ctx, f_entropy, p_entropy,
+ *                                   custom, len, entropy_len)
+ * implements
+ * CTR_DRBG_Instantiate(entropy_input, nonce, personalization_string,
+ *                      security_strength) -> initial_working_state
+ * with inputs
+ *   custom[:len] = nonce || personalization_string
+ * where entropy_input comes from f_entropy for entropy_len bytes
+ * and with outputs
+ *   ctx = initial_working_state
+ */
 int mbedtls_ctr_drbg_seed_entropy_len(
                    mbedtls_ctr_drbg_context *ctx,
                    int (*f_entropy)(void *, unsigned char *, size_t),
@@ -256,6 +268,14 @@ exit:
     return( ret );
 }
 
+/* CTR_DRBG_Update (SP 800-90A §10.2.1.2)
+ * ctr_drbg_update_internal(ctx, provided_data)
+ * implements
+ * CTR_DRBG_Update(provided_data, Key, V)
+ * with inputs and outputs
+ *   ctx->aes_ctx = Key
+ *   ctx->counter = V
+ */
 static int ctr_drbg_update_internal( mbedtls_ctr_drbg_context *ctx,
                               const unsigned char data[MBEDTLS_CTR_DRBG_SEEDLEN] )
 {
@@ -301,6 +321,18 @@ static int ctr_drbg_update_internal( mbedtls_ctr_drbg_context *ctx,
     return( 0 );
 }
 
+/* CTR_DRBG_Instantiate with derivation function (SP 800-90A §10.2.1.3.2)
+ * mbedtls_ctr_drbg_update(ctx, additional, add_len)
+ * implements
+ * CTR_DRBG_Instantiate(entropy_input, nonce, personalization_string,
+ *                      security_strength) -> initial_working_state
+ * with inputs
+ *   ctx->counter = all-bits-0
+ *   ctx->aes_ctx = context from all-bits-0 key
+ *   additional[:add_len] = entropy_input || nonce || personalization_string
+ * and with outputs
+ *   ctx = initial_working_state
+ */
 void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
                       const unsigned char *additional, size_t add_len )
 {
@@ -318,6 +350,18 @@ void mbedtls_ctr_drbg_update( mbedtls_ctr_drbg_context *ctx,
     }
 }
 
+/* CTR_DRBG_Reseed with derivation function (SP 800-90A §10.2.1.4.2)
+ * mbedtls_ctr_drbg_reseed(ctx, additional, len)
+ * implements
+ * CTR_DRBG_Reseed(working_state, entropy_input, additional_input)
+ *                -> new_working_state
+ * with inputs
+ *   ctx contains working_state
+ *   additional[:len] = additional_input
+ * and entropy_input comes from calling ctx->f_entropy
+ * and with output
+ *   ctx contains new_working_state
+ */
 int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
                      const unsigned char *additional, size_t len )
 {
@@ -371,6 +415,25 @@ int mbedtls_ctr_drbg_reseed( mbedtls_ctr_drbg_context *ctx,
     return( 0 );
 }
 
+/* CTR_DRBG_Generate with derivation function (SP 800-90A §10.2.1.5.2)
+ * mbedtls_ctr_drbg_random_with_add(ctx, output, output_len, additional, add_len)
+ * implements
+ * CTR_DRBG_Reseed(working_state, entropy_input, additional[:add_len])
+ *                -> working_state_after_reseed
+ *                if required, then
+ * CTR_DRBG_Generate(working_state_after_reseed,
+ *                   requested_number_of_bits, additional_input)
+ *                -> status, returned_bits, new_working_state
+ * with inputs
+ *   ctx contains working_state
+ *   requested_number_of_bits = 8 * output_len
+ *   additional[:add_len] = additional_input
+ * and entropy_input comes from calling ctx->f_entropy
+ * and with outputs
+ *   status = SUCCESS (this function does the reseed internally)
+ *   returned_bits = output[:output_len]
+ *   ctx contains new_working_state
+ */
 int mbedtls_ctr_drbg_random_with_add( void *p_rng,
                               unsigned char *output, size_t output_len,
                               const unsigned char *additional, size_t add_len )

tests/suites/test_suite_ctr_drbg.function

@@ -1,15 +1,97 @@
 /* BEGIN_HEADER */
+#include "mbedtls/entropy.h"
 #include "mbedtls/ctr_drbg.h"
 #include "string.h"
 
-static int test_offset_idx;
+/* Modes for ctr_drbg_validate */
+enum reseed_mode
+{
+    RESEED_NEVER, /* never reseed */
+    RESEED_FIRST, /* instantiate, reseed, generate, generate */
+    RESEED_SECOND, /* instantiate, generate, reseed, generate */
+    RESEED_ALWAYS /* prediction resistance, no explicit reseed */
+};
+
+static size_t test_offset_idx = 0;
+static size_t test_max_idx  = 0;
 static int mbedtls_test_entropy_func( void *data, unsigned char *buf, size_t len )
 {
     const unsigned char *p = (unsigned char *) data;
+    if( test_offset_idx + len > test_max_idx )
+        return( MBEDTLS_ERR_ENTROPY_SOURCE_FAILED );
     memcpy( buf, p + test_offset_idx, len );
     test_offset_idx += len;
     return( 0 );
 }
+
+static void ctr_drbg_validate_internal( int reseed_mode, data_t * nonce,
+                        int entropy_len_arg, data_t * entropy,
+                        data_t * reseed,
+                        data_t * add1, data_t * add2,
+                        data_t * result )
+{
+    mbedtls_ctr_drbg_context ctx;
+    unsigned char buf[64];
+
+    size_t entropy_chunk_len = (size_t) entropy_len_arg;
+
+    TEST_ASSERT( entropy_chunk_len <= sizeof( buf ) );
+
+    test_offset_idx = 0;
+    mbedtls_ctr_drbg_init( &ctx );
+
+    test_max_idx = entropy->len;
+
+    /* CTR_DRBG_Instantiate(entropy[:entropy->len], nonce, perso, <ignored>)
+     * where nonce||perso = nonce[nonce->len] */
+    TEST_ASSERT( mbedtls_ctr_drbg_seed_entropy_len(
+                     &ctx,
+                     mbedtls_test_entropy_func, entropy->x,
+                     nonce->x, nonce->len,
+                     entropy_chunk_len ) == 0 );
+    if( reseed_mode == RESEED_ALWAYS )
+        mbedtls_ctr_drbg_set_prediction_resistance(
+            &ctx,
+            MBEDTLS_CTR_DRBG_PR_ON );
+
+    if( reseed_mode == RESEED_FIRST )
+    {
+        /* CTR_DRBG_Reseed(entropy[idx:idx+entropy->len],
+         *                 reseed[:reseed->len]) */
+        TEST_ASSERT( mbedtls_ctr_drbg_reseed(
+                         &ctx,
+                         reseed->x, reseed->len ) == 0 );
+    }
+
+    /* CTR_DRBG_Generate(result->len * 8 bits, add1[:add1->len]) -> buf */
+    /* Then reseed if prediction resistance is enabled. */
+    TEST_ASSERT( mbedtls_ctr_drbg_random_with_add(
+                     &ctx,
+                     buf, result->len,
+                     add1->x, add1->len ) == 0 );
+
+
+    if( reseed_mode == RESEED_SECOND )
+    {
+        /* CTR_DRBG_Reseed(entropy[idx:idx+entropy->len],
+         *                 reseed[:reseed->len]) */
+        TEST_ASSERT( mbedtls_ctr_drbg_reseed(
+                         &ctx,
+                         reseed->x, reseed->len ) == 0 );
+    }
+
+    /* CTR_DRBG_Generate(result->len * 8 bits, add2->x[:add2->len]) -> buf */
+    /* Then reseed if prediction resistance is enabled. */
+    TEST_ASSERT( mbedtls_ctr_drbg_random_with_add(
+                     &ctx,
+                     buf, result->len,
+                     add2->x, add2->len ) == 0 );
+    TEST_ASSERT( memcmp( buf, result->x, result->len ) == 0 );
+
+exit:
+    mbedtls_ctr_drbg_free( &ctx );
+}
+
 /* END_HEADER */
 
 /* BEGIN_DEPENDENCIES
@@ -18,7 +100,7 @@ static int mbedtls_test_entropy_func( void *data, unsigned char *buf, size_t len
  */
 
 /* BEGIN_CASE */
-void ctr_drbg_special_behaviours(  )
+void ctr_drbg_special_behaviours( )
 {
     mbedtls_ctr_drbg_context ctx;
     unsigned char output[512];
@@ -50,54 +132,63 @@ exit:
 }
 /* END_CASE */
 
+
+/* BEGIN_CASE */
+void ctr_drbg_validate_no_reseed( data_t * add_init, data_t * entropy,
+                                  data_t * add1, data_t * add2,
+                                  data_t * result_string )
+{
+    data_t empty = { 0, 0 };
+    ctr_drbg_validate_internal( RESEED_NEVER, add_init,
+                                entropy->len, entropy,
+                                &empty, add1, add2,
+                                result_string );
+    goto exit; // goto is needed to avoid warning ( no test assertions in func)
+}
+/* END_CASE */
+
 /* BEGIN_CASE */
 void ctr_drbg_validate_pr( data_t * add_init, data_t * entropy,
                            data_t * add1, data_t * add2,
-                           data_t * result_str )
+                           data_t * result_string )
 {
-    mbedtls_ctr_drbg_context ctx;
+    data_t empty = { 0, 0 };
-    unsigned char buf[512];
+    ctr_drbg_validate_internal( RESEED_ALWAYS, add_init,
-
+                                entropy->len / 3, entropy,
-    mbedtls_ctr_drbg_init( &ctx );
+                                &empty, add1, add2,
-
+                                result_string );
-
+    goto exit; // goto is needed to avoid warning ( no test assertions in func)
-    test_offset_idx = 0;
-    TEST_ASSERT( mbedtls_ctr_drbg_seed_entropy_len( &ctx, mbedtls_test_entropy_func, entropy->x, add_init->x, add_init->len, 32 ) == 0 );
-    mbedtls_ctr_drbg_set_prediction_resistance( &ctx, MBEDTLS_CTR_DRBG_PR_ON );
-
-    TEST_ASSERT( mbedtls_ctr_drbg_random_with_add( &ctx, buf, 16, add1->x, add1->len ) == 0 );
-    TEST_ASSERT( mbedtls_ctr_drbg_random_with_add( &ctx, buf, 16, add2->x, add2->len ) == 0 );
-    TEST_ASSERT( hexcmp( buf, result_str->x, 16, result_str->len ) == 0 );
-
-exit:
-    mbedtls_ctr_drbg_free( &ctx );
 }
 /* END_CASE */
 
 /* BEGIN_CASE */
-void ctr_drbg_validate_nopr( data_t * add_init, data_t * entropy,
+void ctr_drbg_validate_reseed_between( data_t * add_init, data_t * entropy,
                              data_t * add1, data_t * add_reseed,
-                             data_t * add2, data_t * result_str )
+                             data_t * add2, data_t * result_string )
 {
-    mbedtls_ctr_drbg_context ctx;
+    ctr_drbg_validate_internal( RESEED_SECOND, add_init,
-    unsigned char buf[512];
+                                entropy->len / 2, entropy,
-
+                                add_reseed, add1, add2,
-    mbedtls_ctr_drbg_init( &ctx );
+                                result_string );
-
+    goto exit; // goto is needed to avoid warning ( no test assertions in func)
-
-    test_offset_idx = 0;
-    TEST_ASSERT( mbedtls_ctr_drbg_seed_entropy_len( &ctx, mbedtls_test_entropy_func, entropy->x, add_init->x, add_init->len, 32 ) == 0 );
-
-    TEST_ASSERT( mbedtls_ctr_drbg_random_with_add( &ctx, buf, 16, add1->x, add1->len ) == 0 );
-    TEST_ASSERT( mbedtls_ctr_drbg_reseed( &ctx, add_reseed->x, add_reseed->len ) == 0 );
-    TEST_ASSERT( mbedtls_ctr_drbg_random_with_add( &ctx, buf, 16, add2->x, add2->len ) == 0 );
-    TEST_ASSERT( hexcmp( buf, result_str->x, 16, result_str->len ) == 0 );
-
-exit:
-    mbedtls_ctr_drbg_free( &ctx );
 }
 /* END_CASE */
 
+/* BEGIN_CASE */
+void ctr_drbg_validate_reseed_first( data_t * add_init, data_t * entropy,
+                             data_t * add1, data_t * add_reseed,
+                             data_t * add2, data_t * result_string )
+{
+    ctr_drbg_validate_internal( RESEED_FIRST, add_init,
+                                entropy->len / 2, entropy,
+                                add_reseed, add1, add2,
+                                result_string );
+    goto exit; // goto is needed to avoid warning ( no test assertions in func)
+}
+/* END_CASE */
+
+
+
 /* BEGIN_CASE */
 void ctr_drbg_entropy_usage(  )
 {
@@ -106,10 +197,11 @@ void ctr_drbg_entropy_usage(  )
     unsigned char entropy[1024];
     mbedtls_ctr_drbg_context ctx;
     size_t i, reps = 10;
-    int last_idx;
+    size_t last_idx;
 
     mbedtls_ctr_drbg_init( &ctx );
     test_offset_idx = 0;
+    test_max_idx = sizeof( entropy );
     memset( entropy, 0, sizeof( entropy ) );
     memset( out, 0, sizeof( out ) );
     memset( add, 0, sizeof( add ) );