library/entropy.c - security/mbedtls - Rivoreo Source Code Repositories

 /*
  *  Entropy accumulator implementation
  *
  *  Copyright (C) 2006-2016, ARM Limited, All Rights Reserved
  *  SPDX-License-Identifier: Apache-2.0
  *
  *  Licensed under the Apache License, Version 2.0 (the "License"); you may
  *  not use this file except in compliance with the License.
  *  You may obtain a copy of the License at
  *
  *  http://www.apache.org/licenses/LICENSE-2.0
  *
  *  Unless required by applicable law or agreed to in writing, software
  *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  *  See the License for the specific language governing permissions and
  *  limitations under the License.
  *
  *  This file is part of mbed TLS (https://tls.mbed.org)
  */

 #if !defined(MBEDTLS_CONFIG_FILE)
 #include "mbedtls/config.h"
 #else
 #include MBEDTLS_CONFIG_FILE
 #endif

 #if defined(MBEDTLS_ENTROPY_C)

 #if defined(MBEDTLS_TEST_NULL_ENTROPY)
 #warning "**** WARNING!  MBEDTLS_TEST_NULL_ENTROPY defined! "
 #warning "**** THIS BUILD HAS NO DEFINED ENTROPY SOURCES "
 #warning "**** THIS BUILD IS *NOT* SUITABLE FOR PRODUCTION USE "
 #endif

 #include "mbedtls/entropy.h"
 #include "mbedtls/entropy_poll.h"
 #include "mbedtls/platform_util.h"

 #include <string.h>

 #if defined(MBEDTLS_FS_IO)
 #include <stdio.h>
 #endif

 #if defined(MBEDTLS_ENTROPY_NV_SEED)
 #include "mbedtls/platform.h"
 #endif

 #if defined(MBEDTLS_SELF_TEST)
 #if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"
 #else
 #include <stdio.h>
 #define mbedtls_printf     printf
 #endif /* MBEDTLS_PLATFORM_C */
 #endif /* MBEDTLS_SELF_TEST */

 #if defined(MBEDTLS_HAVEGE_C)
 #include "mbedtls/havege.h"
 #endif

 #define ENTROPY_MAX_LOOP    256     /**< Maximum amount to loop before error */

 void mbedtls_entropy_init( mbedtls_entropy_context *ctx )
 {
     ctx->source_count = 0;
     memset( ctx->source, 0, sizeof( ctx->source ) );

 #if defined(MBEDTLS_THREADING_C)
     mbedtls_mutex_init( &ctx->mutex );
 #endif

     ctx->accumulator_started = 0;
 #if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
     mbedtls_sha512_init( &ctx->accumulator );
 #else
     mbedtls_sha256_init( &ctx->accumulator );
 #endif
 #if defined(MBEDTLS_HAVEGE_C)
     mbedtls_havege_init( &ctx->havege_data );
 #endif

     /* Reminder: Update ENTROPY_HAVE_STRONG in the test files
      *           when adding more strong entropy sources here. */

 #if defined(MBEDTLS_TEST_NULL_ENTROPY)
     mbedtls_entropy_add_source( ctx, mbedtls_null_entropy_poll, NULL,
                                 1, MBEDTLS_ENTROPY_SOURCE_STRONG );
 #endif

 #if !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES)
 #if !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
     mbedtls_entropy_add_source( ctx, mbedtls_platform_entropy_poll, NULL,
                                 MBEDTLS_ENTROPY_MIN_PLATFORM,
                                 MBEDTLS_ENTROPY_SOURCE_STRONG );
 #endif
 #if defined(MBEDTLS_TIMING_C)
     mbedtls_entropy_add_source( ctx, mbedtls_hardclock_poll, NULL,
                                 MBEDTLS_ENTROPY_MIN_HARDCLOCK,
                                 MBEDTLS_ENTROPY_SOURCE_WEAK );
 #endif
 #if defined(MBEDTLS_HAVEGE_C)
     mbedtls_entropy_add_source( ctx, mbedtls_havege_poll, &ctx->havege_data,
                                 MBEDTLS_ENTROPY_MIN_HAVEGE,
                                 MBEDTLS_ENTROPY_SOURCE_STRONG );
 #endif
 #if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
     mbedtls_entropy_add_source( ctx, mbedtls_hardware_poll, NULL,
                                 MBEDTLS_ENTROPY_MIN_HARDWARE,
                                 MBEDTLS_ENTROPY_SOURCE_STRONG );
 #endif
 #if defined(MBEDTLS_ENTROPY_NV_SEED)
     mbedtls_entropy_add_source( ctx, mbedtls_nv_seed_poll, NULL,
                                 MBEDTLS_ENTROPY_BLOCK_SIZE,
                                 MBEDTLS_ENTROPY_SOURCE_STRONG );
     ctx->initial_entropy_run = 0;
 #endif
 #endif /* MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES */
 }

 void mbedtls_entropy_free( mbedtls_entropy_context *ctx )
 {
 #if defined(MBEDTLS_HAVEGE_C)
     mbedtls_havege_free( &ctx->havege_data );
 #endif
 #if defined(MBEDTLS_THREADING_C)
     mbedtls_mutex_free( &ctx->mutex );
 #endif
 #if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
     mbedtls_sha512_free( &ctx->accumulator );
 #else
     mbedtls_sha256_free( &ctx->accumulator );
 #endif
 #if defined(MBEDTLS_ENTROPY_NV_SEED)
     ctx->initial_entropy_run = 0;
 #endif
     ctx->source_count = 0;
     mbedtls_platform_zeroize( ctx->source, sizeof( ctx->source ) );
     ctx->accumulator_started = 0;
 }

 int mbedtls_entropy_add_source( mbedtls_entropy_context *ctx,
                         mbedtls_entropy_f_source_ptr f_source, void *p_source,
                         size_t threshold, int strong )
 {
     int idx, ret = 0;

 #if defined(MBEDTLS_THREADING_C)
     if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
         return( ret );
 #endif

     idx = ctx->source_count;
     if( idx >= MBEDTLS_ENTROPY_MAX_SOURCES )
     {
         ret = MBEDTLS_ERR_ENTROPY_MAX_SOURCES;
         goto exit;
     }

     ctx->source[idx].f_source  = f_source;
     ctx->source[idx].p_source  = p_source;
     ctx->source[idx].threshold = threshold;
     ctx->source[idx].strong    = strong;

     ctx->source_count++;

 exit:
 #if defined(MBEDTLS_THREADING_C)
     if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
         return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
 #endif

     return( ret );
 }

 /*
  * Entropy accumulator update
  */
 static int entropy_update( mbedtls_entropy_context *ctx, unsigned char source_id,
                            const unsigned char *data, size_t len )
 {
     unsigned char header[2];
     unsigned char tmp[MBEDTLS_ENTROPY_BLOCK_SIZE];
     size_t use_len = len;
     const unsigned char *p = data;
     int ret = 0;

     if( use_len > MBEDTLS_ENTROPY_BLOCK_SIZE )
     {
 #if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
         if( ( ret = mbedtls_sha512_ret( data, len, tmp, 0 ) ) != 0 )
             goto cleanup;
 #else
         if( ( ret = mbedtls_sha256_ret( data, len, tmp, 0 ) ) != 0 )
             goto cleanup;
 #endif
         p = tmp;
         use_len = MBEDTLS_ENTROPY_BLOCK_SIZE;
     }

     header[0] = source_id;
     header[1] = use_len & 0xFF;

     /*
      * Start the accumulator if this has not already happened. Note that
      * it is sufficient to start the accumulator here only because all calls to
      * gather entropy eventually execute this code.
      */
 #if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
     if( ctx->accumulator_started == 0 &&
         ( ret = mbedtls_sha512_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
         goto cleanup;
     else
         ctx->accumulator_started = 1;
     if( ( ret = mbedtls_sha512_update_ret( &ctx->accumulator, header, 2 ) ) != 0 )
         goto cleanup;
     ret = mbedtls_sha512_update_ret( &ctx->accumulator, p, use_len );
 #else
     if( ctx->accumulator_started == 0 &&
         ( ret = mbedtls_sha256_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
         goto cleanup;
     else
         ctx->accumulator_started = 1;
     if( ( ret = mbedtls_sha256_update_ret( &ctx->accumulator, header, 2 ) ) != 0 )
         goto cleanup;
     ret = mbedtls_sha256_update_ret( &ctx->accumulator, p, use_len );
 #endif

 cleanup:
     mbedtls_platform_zeroize( tmp, sizeof( tmp ) );

     return( ret );
 }

 int mbedtls_entropy_update_manual( mbedtls_entropy_context *ctx,
                            const unsigned char *data, size_t len )
 {
     int ret;

 #if defined(MBEDTLS_THREADING_C)
     if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
         return( ret );
 #endif

     ret = entropy_update( ctx, MBEDTLS_ENTROPY_SOURCE_MANUAL, data, len );

 #if defined(MBEDTLS_THREADING_C)
     if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
         return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
 #endif

     return( ret );
 }

 /*
  * Run through the different sources to add entropy to our accumulator
  */
 static int entropy_gather_internal( mbedtls_entropy_context *ctx )
 {
     int ret, i, have_one_strong = 0;
     unsigned char buf[MBEDTLS_ENTROPY_MAX_GATHER];
     size_t olen;

     if( ctx->source_count == 0 )
         return( MBEDTLS_ERR_ENTROPY_NO_SOURCES_DEFINED );

     /*
      * Run through our entropy sources
      */
     for( i = 0; i < ctx->source_count; i++ )
     {
         if( ctx->source[i].strong == MBEDTLS_ENTROPY_SOURCE_STRONG )
             have_one_strong = 1;

         olen = 0;
         if( ( ret = ctx->source[i].f_source( ctx->source[i].p_source,
                         buf, MBEDTLS_ENTROPY_MAX_GATHER, &olen ) ) != 0 )
         {
             goto cleanup;
         }

         /*
          * Add if we actually gathered something
          */
         if( olen > 0 )
         {
             if( ( ret = entropy_update( ctx, (unsigned char) i,
                                         buf, olen ) ) != 0 )
                 return( ret );
             ctx->source[i].size += olen;
         }
     }

     if( have_one_strong == 0 )
         ret = MBEDTLS_ERR_ENTROPY_NO_STRONG_SOURCE;

 cleanup:
     mbedtls_platform_zeroize( buf, sizeof( buf ) );

     return( ret );
 }

 /*
  * Thread-safe wrapper for entropy_gather_internal()
  */
 int mbedtls_entropy_gather( mbedtls_entropy_context *ctx )
 {
     int ret;

 #if defined(MBEDTLS_THREADING_C)
     if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
         return( ret );
 #endif

     ret = entropy_gather_internal( ctx );

 #if defined(MBEDTLS_THREADING_C)
     if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
         return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
 #endif

     return( ret );
 }

 int mbedtls_entropy_func( void *data, unsigned char *output, size_t len )
 {
     int ret, count = 0, i, done;
     mbedtls_entropy_context *ctx = (mbedtls_entropy_context *) data;
     unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];

     if( len > MBEDTLS_ENTROPY_BLOCK_SIZE )
         return( MBEDTLS_ERR_ENTROPY_SOURCE_FAILED );

 #if defined(MBEDTLS_ENTROPY_NV_SEED)
     /* Update the NV entropy seed before generating any entropy for outside
      * use.
      */
     if( ctx->initial_entropy_run == 0 )
     {
         ctx->initial_entropy_run = 1;
         if( ( ret = mbedtls_entropy_update_nv_seed( ctx ) ) != 0 )
             return( ret );
     }
 #endif

 #if defined(MBEDTLS_THREADING_C)
     if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
         return( ret );
 #endif

     /*
      * Always gather extra entropy before a call
      */
     do
     {
         if( count++ > ENTROPY_MAX_LOOP )
         {
             ret = MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
             goto exit;
         }

         if( ( ret = entropy_gather_internal( ctx ) ) != 0 )
             goto exit;

         done = 1;
         for( i = 0; i < ctx->source_count; i++ )
             if( ctx->source[i].size < ctx->source[i].threshold )
                 done = 0;
     }
     while( ! done );

     memset( buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE );

 #if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
     /*
      * Note that at this stage it is assumed that the accumulator was started
      * in a previous call to entropy_update(). If this is not guaranteed, the
      * code below will fail.
      */
     if( ( ret = mbedtls_sha512_finish_ret( &ctx->accumulator, buf ) ) != 0 )
         goto exit;

     /*
      * Reset accumulator and counters and recycle existing entropy
      */
     mbedtls_sha512_free( &ctx->accumulator );
     mbedtls_sha512_init( &ctx->accumulator );
     if( ( ret = mbedtls_sha512_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
         goto exit;
     if( ( ret = mbedtls_sha512_update_ret( &ctx->accumulator, buf,
                                            MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
         goto exit;

     /*
      * Perform second SHA-512 on entropy
      */
     if( ( ret = mbedtls_sha512_ret( buf, MBEDTLS_ENTROPY_BLOCK_SIZE,
                                     buf, 0 ) ) != 0 )
         goto exit;
 #else /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */
     if( ( ret = mbedtls_sha256_finish_ret( &ctx->accumulator, buf ) ) != 0 )
         goto exit;

     /*
      * Reset accumulator and counters and recycle existing entropy
      */
     mbedtls_sha256_free( &ctx->accumulator );
     mbedtls_sha256_init( &ctx->accumulator );
     if( ( ret = mbedtls_sha256_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
         goto exit;
     if( ( ret = mbedtls_sha256_update_ret( &ctx->accumulator, buf,
                                            MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
         goto exit;

     /*
      * Perform second SHA-256 on entropy
      */
     if( ( ret = mbedtls_sha256_ret( buf, MBEDTLS_ENTROPY_BLOCK_SIZE,
                                     buf, 0 ) ) != 0 )
         goto exit;
 #endif /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */

     for( i = 0; i < ctx->source_count; i++ )
         ctx->source[i].size = 0;

     memcpy( output, buf, len );

     ret = 0;

 exit:
     mbedtls_platform_zeroize( buf, sizeof( buf ) );

 #if defined(MBEDTLS_THREADING_C)
     if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
         return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
 #endif

     return( ret );
 }

 #if defined(MBEDTLS_ENTROPY_NV_SEED)
 int mbedtls_entropy_update_nv_seed( mbedtls_entropy_context *ctx )
 {
     int ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
     unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];

     /* Read new seed  and write it to NV */
     if( ( ret = mbedtls_entropy_func( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
         return( ret );

     if( mbedtls_nv_seed_write( buf, MBEDTLS_ENTROPY_BLOCK_SIZE ) < 0 )
         return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );

     /* Manually update the remaining stream with a separator value to diverge */
     memset( buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE );
     ret = mbedtls_entropy_update_manual( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE );

     return( ret );
 }
 #endif /* MBEDTLS_ENTROPY_NV_SEED */

 #if defined(MBEDTLS_FS_IO)
 int mbedtls_entropy_write_seed_file( mbedtls_entropy_context *ctx, const char *path )
 {
     int ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
     FILE *f;
     unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];

     if( ( f = fopen( path, "wb" ) ) == NULL )
         return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );

     if( ( ret = mbedtls_entropy_func( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
         goto exit;

     if( fwrite( buf, 1, MBEDTLS_ENTROPY_BLOCK_SIZE, f ) != MBEDTLS_ENTROPY_BLOCK_SIZE )
     {
         ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
         goto exit;
     }

     ret = 0;

 exit:
     mbedtls_platform_zeroize( buf, sizeof( buf ) );

     fclose( f );
     return( ret );
 }

 int mbedtls_entropy_update_seed_file( mbedtls_entropy_context *ctx, const char *path )
 {
     int ret = 0;
     FILE *f;
     size_t n;
     unsigned char buf[ MBEDTLS_ENTROPY_MAX_SEED_SIZE ];

     if( ( f = fopen( path, "rb" ) ) == NULL )
         return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );

     fseek( f, 0, SEEK_END );
     n = (size_t) ftell( f );
     fseek( f, 0, SEEK_SET );

     if( n > MBEDTLS_ENTROPY_MAX_SEED_SIZE )
         n = MBEDTLS_ENTROPY_MAX_SEED_SIZE;

     if( fread( buf, 1, n, f ) != n )
         ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
     else
         ret = mbedtls_entropy_update_manual( ctx, buf, n );

     fclose( f );

     mbedtls_platform_zeroize( buf, sizeof( buf ) );

     if( ret != 0 )
         return( ret );

     return( mbedtls_entropy_write_seed_file( ctx, path ) );
 }
 #endif /* MBEDTLS_FS_IO */

 #if defined(MBEDTLS_SELF_TEST)
 #if !defined(MBEDTLS_TEST_NULL_ENTROPY)
 /*
  * Dummy source function
  */
 static int entropy_dummy_source( void *data, unsigned char *output,
                                  size_t len, size_t *olen )
 {
     ((void) data);

     memset( output, 0x2a, len );
     *olen = len;

     return( 0 );
 }
 #endif /* !MBEDTLS_TEST_NULL_ENTROPY */

 #if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)

 static int mbedtls_entropy_source_self_test_gather( unsigned char *buf, size_t buf_len )
 {
     int ret = 0;
     size_t entropy_len = 0;
     size_t olen = 0;
     size_t attempts = buf_len;

     while( attempts > 0 && entropy_len < buf_len )
     {
         if( ( ret = mbedtls_hardware_poll( NULL, buf + entropy_len,
             buf_len - entropy_len, &olen ) ) != 0 )
             return( ret );

         entropy_len += olen;
         attempts--;
     }

     if( entropy_len < buf_len )
     {
         ret = 1;
     }

     return( ret );
 }


 static int mbedtls_entropy_source_self_test_check_bits( const unsigned char *buf,
                                                         size_t buf_len )
 {
     unsigned char set= 0xFF;
     unsigned char unset = 0x00;
     size_t i;

     for( i = 0; i < buf_len; i++ )
     {
         set &= buf[i];
         unset |= buf[i];
     }

     return( set == 0xFF || unset == 0x00 );
 }

 /*
  * A test to ensure hat the entropy sources are functioning correctly
  * and there is no obvious failure. The test performs the following checks:
  *  - The entropy source is not providing only 0s (all bits unset) or 1s (all
  *    bits set).
  *  - The entropy source is not providing values in a pattern. Because the
  *    hardware could be providing data in an arbitrary length, this check polls
  *    the hardware entropy source twice and compares the result to ensure they
  *    are not equal.
  *  - The error code returned by the entropy source is not an error.
  */
 int mbedtls_entropy_source_self_test( int verbose )
 {
     int ret = 0;
     unsigned char buf0[2 * sizeof( unsigned long long int )];
     unsigned char buf1[2 * sizeof( unsigned long long int )];

     if( verbose != 0 )
         mbedtls_printf( "  ENTROPY_BIAS test: " );

     memset( buf0, 0x00, sizeof( buf0 ) );
     memset( buf1, 0x00, sizeof( buf1 ) );

     if( ( ret = mbedtls_entropy_source_self_test_gather( buf0, sizeof( buf0 ) ) ) != 0 )
         goto cleanup;
     if( ( ret = mbedtls_entropy_source_self_test_gather( buf1, sizeof( buf1 ) ) ) != 0 )
         goto cleanup;

     /* Make sure that the returned values are not all 0 or 1 */
     if( ( ret = mbedtls_entropy_source_self_test_check_bits( buf0, sizeof( buf0 ) ) ) != 0 )
         goto cleanup;
     if( ( ret = mbedtls_entropy_source_self_test_check_bits( buf1, sizeof( buf1 ) ) ) != 0 )
         goto cleanup;

     /* Make sure that the entropy source is not returning values in a
      * pattern */
     ret = memcmp( buf0, buf1, sizeof( buf0 ) ) == 0;

 cleanup:
     if( verbose != 0 )
     {
         if( ret != 0 )
             mbedtls_printf( "failed\n" );
         else
             mbedtls_printf( "passed\n" );

         mbedtls_printf( "\n" );
     }

     return( ret != 0 );
 }

 #endif /* MBEDTLS_ENTROPY_HARDWARE_ALT */

 /*
  * The actual entropy quality is hard to test, but we can at least
  * test that the functions don't cause errors and write the correct
  * amount of data to buffers.
  */
 int mbedtls_entropy_self_test( int verbose )
 {
     int ret = 1;
 #if !defined(MBEDTLS_TEST_NULL_ENTROPY)
     mbedtls_entropy_context ctx;
     unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
     unsigned char acc[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
     size_t i, j;
 #endif /* !MBEDTLS_TEST_NULL_ENTROPY */

     if( verbose != 0 )
         mbedtls_printf( "  ENTROPY test: " );

 #if !defined(MBEDTLS_TEST_NULL_ENTROPY)
     mbedtls_entropy_init( &ctx );

     /* First do a gather to make sure we have default sources */
     if( ( ret = mbedtls_entropy_gather( &ctx ) ) != 0 )
         goto cleanup;

     ret = mbedtls_entropy_add_source( &ctx, entropy_dummy_source, NULL, 16,
                                       MBEDTLS_ENTROPY_SOURCE_WEAK );
     if( ret != 0 )
         goto cleanup;

     if( ( ret = mbedtls_entropy_update_manual( &ctx, buf, sizeof buf ) ) != 0 )
         goto cleanup;

     /*
      * To test that mbedtls_entropy_func writes correct number of bytes:
      * - use the whole buffer and rely on ASan to detect overruns
      * - collect entropy 8 times and OR the result in an accumulator:
      *   any byte should then be 0 with probably 2^(-64), so requiring
      *   each of the 32 or 64 bytes to be non-zero has a false failure rate
      *   of at most 2^(-58) which is acceptable.
      */
     for( i = 0; i < 8; i++ )
     {
         if( ( ret = mbedtls_entropy_func( &ctx, buf, sizeof( buf ) ) ) != 0 )
             goto cleanup;

         for( j = 0; j < sizeof( buf ); j++ )
             acc[j] |= buf[j];
     }

     for( j = 0; j < sizeof( buf ); j++ )
     {
         if( acc[j] == 0 )
         {
             ret = 1;
             goto cleanup;
         }
     }

 #if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
     if( ( ret = mbedtls_entropy_source_self_test( 0 ) ) != 0 )
         goto cleanup;
 #endif

 cleanup:
     mbedtls_entropy_free( &ctx );
 #endif /* !MBEDTLS_TEST_NULL_ENTROPY */

     if( verbose != 0 )
     {
         if( ret != 0 )
             mbedtls_printf( "failed\n" );
         else
             mbedtls_printf( "passed\n" );

         mbedtls_printf( "\n" );
     }

     return( ret != 0 );
 }
 #endif /* MBEDTLS_SELF_TEST */

 #endif /* MBEDTLS_ENTROPY_C */
	/*
	* Entropy accumulator implementation
	*
	* Copyright (C) 2006-2016, ARM Limited, All Rights Reserved
	* SPDX-License-Identifier: Apache-2.0
	*
	* Licensed under the Apache License, Version 2.0 (the "License"); you may
	* not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
	* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*
	* This file is part of mbed TLS (https://tls.mbed.org)
	*/

	#if !defined(MBEDTLS_CONFIG_FILE)
	#include "mbedtls/config.h"
	#else
	#include MBEDTLS_CONFIG_FILE
	#endif

	#if defined(MBEDTLS_ENTROPY_C)

	#if defined(MBEDTLS_TEST_NULL_ENTROPY)
	#warning "**** WARNING! MBEDTLS_TEST_NULL_ENTROPY defined! "
	#warning "**** THIS BUILD HAS NO DEFINED ENTROPY SOURCES "
	#warning "**** THIS BUILD IS NOT SUITABLE FOR PRODUCTION USE "
	#endif

	#include "mbedtls/entropy.h"
	#include "mbedtls/entropy_poll.h"
	#include "mbedtls/platform_util.h"

	#include <string.h>

	#if defined(MBEDTLS_FS_IO)
	#include <stdio.h>
	#endif

	#if defined(MBEDTLS_ENTROPY_NV_SEED)
	#include "mbedtls/platform.h"
	#endif

	#if defined(MBEDTLS_SELF_TEST)
	#if defined(MBEDTLS_PLATFORM_C)
	#include "mbedtls/platform.h"
	#else
	#include <stdio.h>
	#define mbedtls_printf printf
	#endif /* MBEDTLS_PLATFORM_C */
	#endif /* MBEDTLS_SELF_TEST */

	#if defined(MBEDTLS_HAVEGE_C)
	#include "mbedtls/havege.h"
	#endif

	#define ENTROPY_MAX_LOOP 256 /*< Maximum amount to loop before error /

	void mbedtls_entropy_init( mbedtls_entropy_context *ctx )
	{
	ctx->source_count = 0;
	memset( ctx->source, 0, sizeof( ctx->source ) );

	#if defined(MBEDTLS_THREADING_C)
	mbedtls_mutex_init( &ctx->mutex );
	#endif

	ctx->accumulator_started = 0;
	#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
	mbedtls_sha512_init( &ctx->accumulator );
	#else
	mbedtls_sha256_init( &ctx->accumulator );
	#endif
	#if defined(MBEDTLS_HAVEGE_C)
	mbedtls_havege_init( &ctx->havege_data );
	#endif

	/* Reminder: Update ENTROPY_HAVE_STRONG in the test files
	* when adding more strong entropy sources here. */

	#if defined(MBEDTLS_TEST_NULL_ENTROPY)
	mbedtls_entropy_add_source( ctx, mbedtls_null_entropy_poll, NULL,
	1, MBEDTLS_ENTROPY_SOURCE_STRONG );
	#endif

	#if !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES)
	#if !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
	mbedtls_entropy_add_source( ctx, mbedtls_platform_entropy_poll, NULL,
	MBEDTLS_ENTROPY_MIN_PLATFORM,
	MBEDTLS_ENTROPY_SOURCE_STRONG );
	#endif
	#if defined(MBEDTLS_TIMING_C)
	mbedtls_entropy_add_source( ctx, mbedtls_hardclock_poll, NULL,
	MBEDTLS_ENTROPY_MIN_HARDCLOCK,
	MBEDTLS_ENTROPY_SOURCE_WEAK );
	#endif
	#if defined(MBEDTLS_HAVEGE_C)
	mbedtls_entropy_add_source( ctx, mbedtls_havege_poll, &ctx->havege_data,
	MBEDTLS_ENTROPY_MIN_HAVEGE,
	MBEDTLS_ENTROPY_SOURCE_STRONG );
	#endif
	#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
	mbedtls_entropy_add_source( ctx, mbedtls_hardware_poll, NULL,
	MBEDTLS_ENTROPY_MIN_HARDWARE,
	MBEDTLS_ENTROPY_SOURCE_STRONG );
	#endif
	#if defined(MBEDTLS_ENTROPY_NV_SEED)
	mbedtls_entropy_add_source( ctx, mbedtls_nv_seed_poll, NULL,
	MBEDTLS_ENTROPY_BLOCK_SIZE,
	MBEDTLS_ENTROPY_SOURCE_STRONG );
	ctx->initial_entropy_run = 0;
	#endif
	#endif /* MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES */
	}

	void mbedtls_entropy_free( mbedtls_entropy_context *ctx )
	{
	#if defined(MBEDTLS_HAVEGE_C)
	mbedtls_havege_free( &ctx->havege_data );
	#endif
	#if defined(MBEDTLS_THREADING_C)
	mbedtls_mutex_free( &ctx->mutex );
	#endif
	#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
	mbedtls_sha512_free( &ctx->accumulator );
	#else
	mbedtls_sha256_free( &ctx->accumulator );
	#endif
	#if defined(MBEDTLS_ENTROPY_NV_SEED)
	ctx->initial_entropy_run = 0;
	#endif
	ctx->source_count = 0;
	mbedtls_platform_zeroize( ctx->source, sizeof( ctx->source ) );
	ctx->accumulator_started = 0;
	}

	int mbedtls_entropy_add_source( mbedtls_entropy_context *ctx,
	mbedtls_entropy_f_source_ptr f_source, void *p_source,
	size_t threshold, int strong )
	{
	int idx, ret = 0;

	#if defined(MBEDTLS_THREADING_C)
	if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
	return( ret );
	#endif

	idx = ctx->source_count;
	if( idx >= MBEDTLS_ENTROPY_MAX_SOURCES )
	{
	ret = MBEDTLS_ERR_ENTROPY_MAX_SOURCES;
	goto exit;
	}

	ctx->source[idx].f_source = f_source;
	ctx->source[idx].p_source = p_source;
	ctx->source[idx].threshold = threshold;
	ctx->source[idx].strong = strong;

	ctx->source_count++;

	exit:
	#if defined(MBEDTLS_THREADING_C)
	if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
	return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
	#endif

	return( ret );
	}

	/*
	* Entropy accumulator update
	*/
	static int entropy_update( mbedtls_entropy_context *ctx, unsigned char source_id,
	const unsigned char *data, size_t len )
	{
	unsigned char header[2];
	unsigned char tmp[MBEDTLS_ENTROPY_BLOCK_SIZE];
	size_t use_len = len;
	const unsigned char *p = data;
	int ret = 0;

	if( use_len > MBEDTLS_ENTROPY_BLOCK_SIZE )
	{
	#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
	if( ( ret = mbedtls_sha512_ret( data, len, tmp, 0 ) ) != 0 )
	goto cleanup;
	#else
	if( ( ret = mbedtls_sha256_ret( data, len, tmp, 0 ) ) != 0 )
	goto cleanup;
	#endif
	p = tmp;
	use_len = MBEDTLS_ENTROPY_BLOCK_SIZE;
	}

	header[0] = source_id;
	header[1] = use_len & 0xFF;

	/*
	* Start the accumulator if this has not already happened. Note that
	* it is sufficient to start the accumulator here only because all calls to
	* gather entropy eventually execute this code.
	*/
	#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
	if( ctx->accumulator_started == 0 &&
	( ret = mbedtls_sha512_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
	goto cleanup;
	else
	ctx->accumulator_started = 1;
	if( ( ret = mbedtls_sha512_update_ret( &ctx->accumulator, header, 2 ) ) != 0 )
	goto cleanup;
	ret = mbedtls_sha512_update_ret( &ctx->accumulator, p, use_len );
	#else
	if( ctx->accumulator_started == 0 &&
	( ret = mbedtls_sha256_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
	goto cleanup;
	else
	ctx->accumulator_started = 1;
	if( ( ret = mbedtls_sha256_update_ret( &ctx->accumulator, header, 2 ) ) != 0 )
	goto cleanup;
	ret = mbedtls_sha256_update_ret( &ctx->accumulator, p, use_len );
	#endif

	cleanup:
	mbedtls_platform_zeroize( tmp, sizeof( tmp ) );

	return( ret );
	}

	int mbedtls_entropy_update_manual( mbedtls_entropy_context *ctx,
	const unsigned char *data, size_t len )
	{
	int ret;

	#if defined(MBEDTLS_THREADING_C)
	if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
	return( ret );
	#endif

	ret = entropy_update( ctx, MBEDTLS_ENTROPY_SOURCE_MANUAL, data, len );

	#if defined(MBEDTLS_THREADING_C)
	if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
	return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
	#endif

	return( ret );
	}

	/*
	* Run through the different sources to add entropy to our accumulator
	*/
	static int entropy_gather_internal( mbedtls_entropy_context *ctx )
	{
	int ret, i, have_one_strong = 0;
	unsigned char buf[MBEDTLS_ENTROPY_MAX_GATHER];
	size_t olen;

	if( ctx->source_count == 0 )
	return( MBEDTLS_ERR_ENTROPY_NO_SOURCES_DEFINED );

	/*
	* Run through our entropy sources
	*/
	for( i = 0; i < ctx->source_count; i++ )
	{
	if( ctx->source[i].strong == MBEDTLS_ENTROPY_SOURCE_STRONG )
	have_one_strong = 1;

	olen = 0;
	if( ( ret = ctx->source[i].f_source( ctx->source[i].p_source,
	buf, MBEDTLS_ENTROPY_MAX_GATHER, &olen ) ) != 0 )
	{
	goto cleanup;
	}

	/*
	* Add if we actually gathered something
	*/
	if( olen > 0 )
	{
	if( ( ret = entropy_update( ctx, (unsigned char) i,
	buf, olen ) ) != 0 )
	return( ret );
	ctx->source[i].size += olen;
	}
	}

	if( have_one_strong == 0 )
	ret = MBEDTLS_ERR_ENTROPY_NO_STRONG_SOURCE;

	cleanup:
	mbedtls_platform_zeroize( buf, sizeof( buf ) );

	return( ret );
	}

	/*
	* Thread-safe wrapper for entropy_gather_internal()
	*/
	int mbedtls_entropy_gather( mbedtls_entropy_context *ctx )
	{
	int ret;

	#if defined(MBEDTLS_THREADING_C)
	if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
	return( ret );
	#endif

	ret = entropy_gather_internal( ctx );

	#if defined(MBEDTLS_THREADING_C)
	if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
	return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
	#endif

	return( ret );
	}

	int mbedtls_entropy_func( void data, unsigned char output, size_t len )
	{
	int ret, count = 0, i, done;
	mbedtls_entropy_context ctx = (mbedtls_entropy_context ) data;
	unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];

	if( len > MBEDTLS_ENTROPY_BLOCK_SIZE )
	return( MBEDTLS_ERR_ENTROPY_SOURCE_FAILED );

	#if defined(MBEDTLS_ENTROPY_NV_SEED)
	/* Update the NV entropy seed before generating any entropy for outside
	* use.
	*/
	if( ctx->initial_entropy_run == 0 )
	{
	ctx->initial_entropy_run = 1;
	if( ( ret = mbedtls_entropy_update_nv_seed( ctx ) ) != 0 )
	return( ret );
	}
	#endif

	#if defined(MBEDTLS_THREADING_C)
	if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
	return( ret );
	#endif

	/*
	* Always gather extra entropy before a call
	*/
	do
	{
	if( count++ > ENTROPY_MAX_LOOP )
	{
	ret = MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
	goto exit;
	}

	if( ( ret = entropy_gather_internal( ctx ) ) != 0 )
	goto exit;

	done = 1;
	for( i = 0; i < ctx->source_count; i++ )
	if( ctx->source[i].size < ctx->source[i].threshold )
	done = 0;
	}
	while( ! done );

	memset( buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE );

	#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
	/*
	* Note that at this stage it is assumed that the accumulator was started
	* in a previous call to entropy_update(). If this is not guaranteed, the
	* code below will fail.
	*/
	if( ( ret = mbedtls_sha512_finish_ret( &ctx->accumulator, buf ) ) != 0 )
	goto exit;

	/*
	* Reset accumulator and counters and recycle existing entropy
	*/
	mbedtls_sha512_free( &ctx->accumulator );
	mbedtls_sha512_init( &ctx->accumulator );
	if( ( ret = mbedtls_sha512_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
	goto exit;
	if( ( ret = mbedtls_sha512_update_ret( &ctx->accumulator, buf,
	MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
	goto exit;

	/*
	* Perform second SHA-512 on entropy
	*/
	if( ( ret = mbedtls_sha512_ret( buf, MBEDTLS_ENTROPY_BLOCK_SIZE,
	buf, 0 ) ) != 0 )
	goto exit;
	#else /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */
	if( ( ret = mbedtls_sha256_finish_ret( &ctx->accumulator, buf ) ) != 0 )
	goto exit;

	/*
	* Reset accumulator and counters and recycle existing entropy
	*/
	mbedtls_sha256_free( &ctx->accumulator );
	mbedtls_sha256_init( &ctx->accumulator );
	if( ( ret = mbedtls_sha256_starts_ret( &ctx->accumulator, 0 ) ) != 0 )
	goto exit;
	if( ( ret = mbedtls_sha256_update_ret( &ctx->accumulator, buf,
	MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
	goto exit;

	/*
	* Perform second SHA-256 on entropy
	*/
	if( ( ret = mbedtls_sha256_ret( buf, MBEDTLS_ENTROPY_BLOCK_SIZE,
	buf, 0 ) ) != 0 )
	goto exit;
	#endif /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */

	for( i = 0; i < ctx->source_count; i++ )
	ctx->source[i].size = 0;

	memcpy( output, buf, len );

	ret = 0;

	exit:
	mbedtls_platform_zeroize( buf, sizeof( buf ) );

	#if defined(MBEDTLS_THREADING_C)
	if( mbedtls_mutex_unlock( &ctx->mutex ) != 0 )
	return( MBEDTLS_ERR_THREADING_MUTEX_ERROR );
	#endif

	return( ret );
	}

	#if defined(MBEDTLS_ENTROPY_NV_SEED)
	int mbedtls_entropy_update_nv_seed( mbedtls_entropy_context *ctx )
	{
	int ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
	unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];

	/* Read new seed and write it to NV */
	if( ( ret = mbedtls_entropy_func( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
	return( ret );

	if( mbedtls_nv_seed_write( buf, MBEDTLS_ENTROPY_BLOCK_SIZE ) < 0 )
	return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );

	/* Manually update the remaining stream with a separator value to diverge */
	memset( buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE );
	ret = mbedtls_entropy_update_manual( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE );

	return( ret );
	}
	#endif /* MBEDTLS_ENTROPY_NV_SEED */

	#if defined(MBEDTLS_FS_IO)
	int mbedtls_entropy_write_seed_file( mbedtls_entropy_context ctx, const char path )
	{
	int ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
	FILE *f;
	unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];

	if( ( f = fopen( path, "wb" ) ) == NULL )
	return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );

	if( ( ret = mbedtls_entropy_func( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE ) ) != 0 )
	goto exit;

	if( fwrite( buf, 1, MBEDTLS_ENTROPY_BLOCK_SIZE, f ) != MBEDTLS_ENTROPY_BLOCK_SIZE )
	{
	ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
	goto exit;
	}

	ret = 0;

	exit:
	mbedtls_platform_zeroize( buf, sizeof( buf ) );

	fclose( f );
	return( ret );
	}

	int mbedtls_entropy_update_seed_file( mbedtls_entropy_context ctx, const char path )
	{
	int ret = 0;
	FILE *f;
	size_t n;
	unsigned char buf[ MBEDTLS_ENTROPY_MAX_SEED_SIZE ];

	if( ( f = fopen( path, "rb" ) ) == NULL )
	return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );

	fseek( f, 0, SEEK_END );
	n = (size_t) ftell( f );
	fseek( f, 0, SEEK_SET );

	if( n > MBEDTLS_ENTROPY_MAX_SEED_SIZE )
	n = MBEDTLS_ENTROPY_MAX_SEED_SIZE;

	if( fread( buf, 1, n, f ) != n )
	ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
	else
	ret = mbedtls_entropy_update_manual( ctx, buf, n );

	fclose( f );

	mbedtls_platform_zeroize( buf, sizeof( buf ) );

	if( ret != 0 )
	return( ret );

	return( mbedtls_entropy_write_seed_file( ctx, path ) );
	}
	#endif /* MBEDTLS_FS_IO */

	#if defined(MBEDTLS_SELF_TEST)
	#if !defined(MBEDTLS_TEST_NULL_ENTROPY)
	/*
	* Dummy source function
	*/
	static int entropy_dummy_source( void data, unsigned char output,
	size_t len, size_t *olen )
	{
	((void) data);

	memset( output, 0x2a, len );
	*olen = len;

	return( 0 );
	}
	#endif /* !MBEDTLS_TEST_NULL_ENTROPY */

	#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)

	static int mbedtls_entropy_source_self_test_gather( unsigned char *buf, size_t buf_len )
	{
	int ret = 0;
	size_t entropy_len = 0;
	size_t olen = 0;
	size_t attempts = buf_len;

	while( attempts > 0 && entropy_len < buf_len )
	{
	if( ( ret = mbedtls_hardware_poll( NULL, buf + entropy_len,
	buf_len - entropy_len, &olen ) ) != 0 )
	return( ret );

	entropy_len += olen;
	attempts--;
	}

	if( entropy_len < buf_len )
	{
	ret = 1;
	}

	return( ret );
	}


	static int mbedtls_entropy_source_self_test_check_bits( const unsigned char *buf,
	size_t buf_len )
	{
	unsigned char set= 0xFF;
	unsigned char unset = 0x00;
	size_t i;

	for( i = 0; i < buf_len; i++ )
	{
	set &= buf[i];
	unset \|= buf[i];
	}

	return( set == 0xFF \|\| unset == 0x00 );
	}

	/*
	* A test to ensure hat the entropy sources are functioning correctly
	* and there is no obvious failure. The test performs the following checks:
	* - The entropy source is not providing only 0s (all bits unset) or 1s (all
	* bits set).
	* - The entropy source is not providing values in a pattern. Because the
	* hardware could be providing data in an arbitrary length, this check polls
	* the hardware entropy source twice and compares the result to ensure they
	* are not equal.
	* - The error code returned by the entropy source is not an error.
	*/
	int mbedtls_entropy_source_self_test( int verbose )
	{
	int ret = 0;
	unsigned char buf0[2 * sizeof( unsigned long long int )];
	unsigned char buf1[2 * sizeof( unsigned long long int )];

	if( verbose != 0 )
	mbedtls_printf( " ENTROPY_BIAS test: " );

	memset( buf0, 0x00, sizeof( buf0 ) );
	memset( buf1, 0x00, sizeof( buf1 ) );

	if( ( ret = mbedtls_entropy_source_self_test_gather( buf0, sizeof( buf0 ) ) ) != 0 )
	goto cleanup;
	if( ( ret = mbedtls_entropy_source_self_test_gather( buf1, sizeof( buf1 ) ) ) != 0 )
	goto cleanup;

	/* Make sure that the returned values are not all 0 or 1 */
	if( ( ret = mbedtls_entropy_source_self_test_check_bits( buf0, sizeof( buf0 ) ) ) != 0 )
	goto cleanup;
	if( ( ret = mbedtls_entropy_source_self_test_check_bits( buf1, sizeof( buf1 ) ) ) != 0 )
	goto cleanup;

	/* Make sure that the entropy source is not returning values in a
	* pattern */
	ret = memcmp( buf0, buf1, sizeof( buf0 ) ) == 0;

	cleanup:
	if( verbose != 0 )
	{
	if( ret != 0 )
	mbedtls_printf( "failed\n" );
	else
	mbedtls_printf( "passed\n" );

	mbedtls_printf( "\n" );
	}

	return( ret != 0 );
	}

	#endif /* MBEDTLS_ENTROPY_HARDWARE_ALT */

	/*
	* The actual entropy quality is hard to test, but we can at least
	* test that the functions don't cause errors and write the correct
	* amount of data to buffers.
	*/
	int mbedtls_entropy_self_test( int verbose )
	{
	int ret = 1;
	#if !defined(MBEDTLS_TEST_NULL_ENTROPY)
	mbedtls_entropy_context ctx;
	unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
	unsigned char acc[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
	size_t i, j;
	#endif /* !MBEDTLS_TEST_NULL_ENTROPY */

	if( verbose != 0 )
	mbedtls_printf( " ENTROPY test: " );

	#if !defined(MBEDTLS_TEST_NULL_ENTROPY)
	mbedtls_entropy_init( &ctx );

	/* First do a gather to make sure we have default sources */
	if( ( ret = mbedtls_entropy_gather( &ctx ) ) != 0 )
	goto cleanup;

	ret = mbedtls_entropy_add_source( &ctx, entropy_dummy_source, NULL, 16,
	MBEDTLS_ENTROPY_SOURCE_WEAK );
	if( ret != 0 )
	goto cleanup;

	if( ( ret = mbedtls_entropy_update_manual( &ctx, buf, sizeof buf ) ) != 0 )
	goto cleanup;

	/*
	* To test that mbedtls_entropy_func writes correct number of bytes:
	* - use the whole buffer and rely on ASan to detect overruns
	* - collect entropy 8 times and OR the result in an accumulator:
	* any byte should then be 0 with probably 2^(-64), so requiring
	* each of the 32 or 64 bytes to be non-zero has a false failure rate
	* of at most 2^(-58) which is acceptable.
	*/
	for( i = 0; i < 8; i++ )
	{
	if( ( ret = mbedtls_entropy_func( &ctx, buf, sizeof( buf ) ) ) != 0 )
	goto cleanup;

	for( j = 0; j < sizeof( buf ); j++ )
	acc[j] \|= buf[j];
	}

	for( j = 0; j < sizeof( buf ); j++ )
	{
	if( acc[j] == 0 )
	{
	ret = 1;
	goto cleanup;
	}
	}

	#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
	if( ( ret = mbedtls_entropy_source_self_test( 0 ) ) != 0 )
	goto cleanup;
	#endif

	cleanup:
	mbedtls_entropy_free( &ctx );
	#endif /* !MBEDTLS_TEST_NULL_ENTROPY */

	if( verbose != 0 )
	{
	if( ret != 0 )
	mbedtls_printf( "failed\n" );
	else
	mbedtls_printf( "passed\n" );

	mbedtls_printf( "\n" );
	}

	return( ret != 0 );
	}
	#endif /* MBEDTLS_SELF_TEST */

	#endif /* MBEDTLS_ENTROPY_C */