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

 /*
  *  Entropy accumulator implementation
  *
  *  Copyright (C) 2006-2014, ARM Limited, All Rights Reserved
  *
  *  This file is part of mbed TLS (https://www.polarssl.org)
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
  *  the Free Software Foundation; either version 2 of the License, or
  *  (at your option) any later version.
  *
  *  This program is distributed in the hope that it will be useful,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *  GNU General Public License for more details.
  *
  *  You should have received a copy of the GNU General Public License along
  *  with this program; if not, write to the Free Software Foundation, Inc.,
  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */

 #if !defined(POLARSSL_CONFIG_FILE)
 #include "polarssl/config.h"
 #else
 #include POLARSSL_CONFIG_FILE
 #endif

 #if defined(POLARSSL_ENTROPY_C)

 #include "polarssl/entropy.h"
 #include "polarssl/entropy_poll.h"

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

 #if defined(POLARSSL_HAVEGE_C)
 #include "polarssl/havege.h"
 #endif

 /* Implementation that should never be optimized out by the compiler */
 static void polarssl_zeroize( void *v, size_t n ) {
     volatile unsigned char *p = v; while( n-- ) *p++ = 0;
 }

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

 void entropy_init( entropy_context *ctx )
 {
     memset( ctx, 0, sizeof(entropy_context) );

 #if defined(POLARSSL_THREADING_C)
     polarssl_mutex_init( &ctx->mutex );
 #endif

 #if defined(POLARSSL_ENTROPY_SHA512_ACCUMULATOR)
     sha512_starts( &ctx->accumulator, 0 );
 #else
     sha256_starts( &ctx->accumulator, 0 );
 #endif
 #if defined(POLARSSL_HAVEGE_C)
     havege_init( &ctx->havege_data );
 #endif

 #if !defined(POLARSSL_NO_DEFAULT_ENTROPY_SOURCES)
 #if !defined(POLARSSL_NO_PLATFORM_ENTROPY)
     entropy_add_source( ctx, platform_entropy_poll, NULL,
                         ENTROPY_MIN_PLATFORM );
 #endif
 #if defined(POLARSSL_TIMING_C)
     entropy_add_source( ctx, hardclock_poll, NULL, ENTROPY_MIN_HARDCLOCK );
 #endif
 #if defined(POLARSSL_HAVEGE_C)
     entropy_add_source( ctx, havege_poll, &ctx->havege_data,
                         ENTROPY_MIN_HAVEGE );
 #endif
 #endif /* POLARSSL_NO_DEFAULT_ENTROPY_SOURCES */
 }

 void entropy_free( entropy_context *ctx )
 {
 #if defined(POLARSSL_HAVEGE_C)
     havege_free( &ctx->havege_data );
 #endif
     polarssl_zeroize( ctx, sizeof( entropy_context ) );
 #if defined(POLARSSL_THREADING_C)
     polarssl_mutex_free( &ctx->mutex );
 #endif
 }

 int entropy_add_source( entropy_context *ctx,
                         f_source_ptr f_source, void *p_source,
                         size_t threshold )
 {
     int index, ret = 0;

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

     index = ctx->source_count;
     if( index >= ENTROPY_MAX_SOURCES )
     {
         ret = POLARSSL_ERR_ENTROPY_MAX_SOURCES;
         goto exit;
     }

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

     ctx->source_count++;

 exit:
 #if defined(POLARSSL_THREADING_C)
     if( polarssl_mutex_unlock( &ctx->mutex ) != 0 )
         return( POLARSSL_ERR_THREADING_MUTEX_ERROR );
 #endif

     return( ret );
 }

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

     if( use_len > ENTROPY_BLOCK_SIZE )
     {
 #if defined(POLARSSL_ENTROPY_SHA512_ACCUMULATOR)
         sha512( data, len, tmp, 0 );
 #else
         sha256( data, len, tmp, 0 );
 #endif
         p = tmp;
         use_len = ENTROPY_BLOCK_SIZE;
     }

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

 #if defined(POLARSSL_ENTROPY_SHA512_ACCUMULATOR)
     sha512_update( &ctx->accumulator, header, 2 );
     sha512_update( &ctx->accumulator, p, use_len );
 #else
     sha256_update( &ctx->accumulator, header, 2 );
     sha256_update( &ctx->accumulator, p, use_len );
 #endif

     return( 0 );
 }

 int entropy_update_manual( entropy_context *ctx,
                            const unsigned char *data, size_t len )
 {
     int ret;

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

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

 #if defined(POLARSSL_THREADING_C)
     if( polarssl_mutex_unlock( &ctx->mutex ) != 0 )
         return( POLARSSL_ERR_THREADING_MUTEX_ERROR );
 #endif

     return( ret );
 }

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

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

     /*
      * Run through our entropy sources
      */
     for( i = 0; i < ctx->source_count; i++ )
     {
         olen = 0;
         if( ( ret = ctx->source[i].f_source( ctx->source[i].p_source,
                         buf, ENTROPY_MAX_GATHER, &olen ) ) != 0 )
         {
             return( ret );
         }

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

     return( 0 );
 }

 /*
  * Thread-safe wrapper for entropy_gather_internal()
  */
 int entropy_gather( entropy_context *ctx )
 {
     int ret;

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

     ret = entropy_gather_internal( ctx );

 #if defined(POLARSSL_THREADING_C)
     if( polarssl_mutex_unlock( &ctx->mutex ) != 0 )
         return( POLARSSL_ERR_THREADING_MUTEX_ERROR );
 #endif

     return( ret );
 }

 int entropy_func( void *data, unsigned char *output, size_t len )
 {
     int ret, count = 0, i, reached;
     entropy_context *ctx = (entropy_context *) data;
     unsigned char buf[ENTROPY_BLOCK_SIZE];

     if( len > ENTROPY_BLOCK_SIZE )
         return( POLARSSL_ERR_ENTROPY_SOURCE_FAILED );

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

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

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

         reached = 0;

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

     memset( buf, 0, ENTROPY_BLOCK_SIZE );

 #if defined(POLARSSL_ENTROPY_SHA512_ACCUMULATOR)
     sha512_finish( &ctx->accumulator, buf );

     /*
      * Reset accumulator and counters and recycle existing entropy
      */
     memset( &ctx->accumulator, 0, sizeof( sha512_context ) );
     sha512_starts( &ctx->accumulator, 0 );
     sha512_update( &ctx->accumulator, buf, ENTROPY_BLOCK_SIZE );

     /*
      * Perform second SHA-512 on entropy
      */
     sha512( buf, ENTROPY_BLOCK_SIZE, buf, 0 );
 #else /* POLARSSL_ENTROPY_SHA512_ACCUMULATOR */
     sha256_finish( &ctx->accumulator, buf );

     /*
      * Reset accumulator and counters and recycle existing entropy
      */
     memset( &ctx->accumulator, 0, sizeof( sha256_context ) );
     sha256_starts( &ctx->accumulator, 0 );
     sha256_update( &ctx->accumulator, buf, ENTROPY_BLOCK_SIZE );

     /*
      * Perform second SHA-256 on entropy
      */
     sha256( buf, ENTROPY_BLOCK_SIZE, buf, 0 );
 #endif /* POLARSSL_ENTROPY_SHA512_ACCUMULATOR */

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

     memcpy( output, buf, len );

     ret = 0;

 exit:
 #if defined(POLARSSL_THREADING_C)
     if( polarssl_mutex_unlock( &ctx->mutex ) != 0 )
         return( POLARSSL_ERR_THREADING_MUTEX_ERROR );
 #endif

     return( ret );
 }

 #if defined(POLARSSL_FS_IO)
 int entropy_write_seed_file( entropy_context *ctx, const char *path )
 {
     int ret = POLARSSL_ERR_ENTROPY_FILE_IO_ERROR;
     FILE *f;
     unsigned char buf[ENTROPY_BLOCK_SIZE];

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

     if( ( ret = entropy_func( ctx, buf, ENTROPY_BLOCK_SIZE ) ) != 0 )
         goto exit;

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

     ret = 0;

 exit:
     fclose( f );
     return( ret );
 }

 int entropy_update_seed_file( entropy_context *ctx, const char *path )
 {
     FILE *f;
     size_t n;
     unsigned char buf[ ENTROPY_MAX_SEED_SIZE ];

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

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

     if( n > ENTROPY_MAX_SEED_SIZE )
         n = ENTROPY_MAX_SEED_SIZE;

     if( fread( buf, 1, n, f ) != n )
     {
         fclose( f );
         return( POLARSSL_ERR_ENTROPY_FILE_IO_ERROR );
     }

     fclose( f );

     entropy_update_manual( ctx, buf, n );

     return( entropy_write_seed_file( ctx, path ) );
 }
 #endif /* POLARSSL_FS_IO */

 #if defined(POLARSSL_SELF_TEST)

 #if defined(POLARSSL_PLATFORM_C)
 #include "polarssl/platform.h"
 #else
 #include <stdio.h>
 #define polarssl_printf     printf
 #endif

 /*
  * 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 );
 }

 /*
  * 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 entropy_self_test( int verbose )
 {
     int ret = 0;
     entropy_context ctx;
     unsigned char buf[ENTROPY_BLOCK_SIZE] = { 0 };
     unsigned char acc[ENTROPY_BLOCK_SIZE] = { 0 };
     size_t i, j;

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

     entropy_init( &ctx );

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

     if( ( ret = entropy_gather( &ctx ) ) != 0 )
         goto cleanup;

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

     /*
      * To test that 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 = 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;
         }
     }

 cleanup:
     entropy_free( &ctx );

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

         polarssl_printf( "\n" );
     }

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

 #endif /* POLARSSL_ENTROPY_C */
	/*
	* Entropy accumulator implementation
	*
	* Copyright (C) 2006-2014, ARM Limited, All Rights Reserved
	*
	* This file is part of mbed TLS (https://www.polarssl.org)
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License along
	* with this program; if not, write to the Free Software Foundation, Inc.,
	* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
	*/

	#if !defined(POLARSSL_CONFIG_FILE)
	#include "polarssl/config.h"
	#else
	#include POLARSSL_CONFIG_FILE
	#endif

	#if defined(POLARSSL_ENTROPY_C)

	#include "polarssl/entropy.h"
	#include "polarssl/entropy_poll.h"

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

	#if defined(POLARSSL_HAVEGE_C)
	#include "polarssl/havege.h"
	#endif

	/* Implementation that should never be optimized out by the compiler */
	static void polarssl_zeroize( void *v, size_t n ) {
	volatile unsigned char p = v; while( n-- ) p++ = 0;
	}

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

	void entropy_init( entropy_context *ctx )
	{
	memset( ctx, 0, sizeof(entropy_context) );

	#if defined(POLARSSL_THREADING_C)
	polarssl_mutex_init( &ctx->mutex );
	#endif

	#if defined(POLARSSL_ENTROPY_SHA512_ACCUMULATOR)
	sha512_starts( &ctx->accumulator, 0 );
	#else
	sha256_starts( &ctx->accumulator, 0 );
	#endif
	#if defined(POLARSSL_HAVEGE_C)
	havege_init( &ctx->havege_data );
	#endif

	#if !defined(POLARSSL_NO_DEFAULT_ENTROPY_SOURCES)
	#if !defined(POLARSSL_NO_PLATFORM_ENTROPY)
	entropy_add_source( ctx, platform_entropy_poll, NULL,
	ENTROPY_MIN_PLATFORM );
	#endif
	#if defined(POLARSSL_TIMING_C)
	entropy_add_source( ctx, hardclock_poll, NULL, ENTROPY_MIN_HARDCLOCK );
	#endif
	#if defined(POLARSSL_HAVEGE_C)
	entropy_add_source( ctx, havege_poll, &ctx->havege_data,
	ENTROPY_MIN_HAVEGE );
	#endif
	#endif /* POLARSSL_NO_DEFAULT_ENTROPY_SOURCES */
	}

	void entropy_free( entropy_context *ctx )
	{
	#if defined(POLARSSL_HAVEGE_C)
	havege_free( &ctx->havege_data );
	#endif
	polarssl_zeroize( ctx, sizeof( entropy_context ) );
	#if defined(POLARSSL_THREADING_C)
	polarssl_mutex_free( &ctx->mutex );
	#endif
	}

	int entropy_add_source( entropy_context *ctx,
	f_source_ptr f_source, void *p_source,
	size_t threshold )
	{
	int index, ret = 0;

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

	index = ctx->source_count;
	if( index >= ENTROPY_MAX_SOURCES )
	{
	ret = POLARSSL_ERR_ENTROPY_MAX_SOURCES;
	goto exit;
	}

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

	ctx->source_count++;

	exit:
	#if defined(POLARSSL_THREADING_C)
	if( polarssl_mutex_unlock( &ctx->mutex ) != 0 )
	return( POLARSSL_ERR_THREADING_MUTEX_ERROR );
	#endif

	return( ret );
	}

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

	if( use_len > ENTROPY_BLOCK_SIZE )
	{
	#if defined(POLARSSL_ENTROPY_SHA512_ACCUMULATOR)
	sha512( data, len, tmp, 0 );
	#else
	sha256( data, len, tmp, 0 );
	#endif
	p = tmp;
	use_len = ENTROPY_BLOCK_SIZE;
	}

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

	#if defined(POLARSSL_ENTROPY_SHA512_ACCUMULATOR)
	sha512_update( &ctx->accumulator, header, 2 );
	sha512_update( &ctx->accumulator, p, use_len );
	#else
	sha256_update( &ctx->accumulator, header, 2 );
	sha256_update( &ctx->accumulator, p, use_len );
	#endif

	return( 0 );
	}

	int entropy_update_manual( entropy_context *ctx,
	const unsigned char *data, size_t len )
	{
	int ret;

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

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

	#if defined(POLARSSL_THREADING_C)
	if( polarssl_mutex_unlock( &ctx->mutex ) != 0 )
	return( POLARSSL_ERR_THREADING_MUTEX_ERROR );
	#endif

	return( ret );
	}

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

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

	/*
	* Run through our entropy sources
	*/
	for( i = 0; i < ctx->source_count; i++ )
	{
	olen = 0;
	if( ( ret = ctx->source[i].f_source( ctx->source[i].p_source,
	buf, ENTROPY_MAX_GATHER, &olen ) ) != 0 )
	{
	return( ret );
	}

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

	return( 0 );
	}

	/*
	* Thread-safe wrapper for entropy_gather_internal()
	*/
	int entropy_gather( entropy_context *ctx )
	{
	int ret;

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

	ret = entropy_gather_internal( ctx );

	#if defined(POLARSSL_THREADING_C)
	if( polarssl_mutex_unlock( &ctx->mutex ) != 0 )
	return( POLARSSL_ERR_THREADING_MUTEX_ERROR );
	#endif

	return( ret );
	}

	int entropy_func( void data, unsigned char output, size_t len )
	{
	int ret, count = 0, i, reached;
	entropy_context ctx = (entropy_context ) data;
	unsigned char buf[ENTROPY_BLOCK_SIZE];

	if( len > ENTROPY_BLOCK_SIZE )
	return( POLARSSL_ERR_ENTROPY_SOURCE_FAILED );

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

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

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

	reached = 0;

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

	memset( buf, 0, ENTROPY_BLOCK_SIZE );

	#if defined(POLARSSL_ENTROPY_SHA512_ACCUMULATOR)
	sha512_finish( &ctx->accumulator, buf );

	/*
	* Reset accumulator and counters and recycle existing entropy
	*/
	memset( &ctx->accumulator, 0, sizeof( sha512_context ) );
	sha512_starts( &ctx->accumulator, 0 );
	sha512_update( &ctx->accumulator, buf, ENTROPY_BLOCK_SIZE );

	/*
	* Perform second SHA-512 on entropy
	*/
	sha512( buf, ENTROPY_BLOCK_SIZE, buf, 0 );
	#else /* POLARSSL_ENTROPY_SHA512_ACCUMULATOR */
	sha256_finish( &ctx->accumulator, buf );

	/*
	* Reset accumulator and counters and recycle existing entropy
	*/
	memset( &ctx->accumulator, 0, sizeof( sha256_context ) );
	sha256_starts( &ctx->accumulator, 0 );
	sha256_update( &ctx->accumulator, buf, ENTROPY_BLOCK_SIZE );

	/*
	* Perform second SHA-256 on entropy
	*/
	sha256( buf, ENTROPY_BLOCK_SIZE, buf, 0 );
	#endif /* POLARSSL_ENTROPY_SHA512_ACCUMULATOR */

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

	memcpy( output, buf, len );

	ret = 0;

	exit:
	#if defined(POLARSSL_THREADING_C)
	if( polarssl_mutex_unlock( &ctx->mutex ) != 0 )
	return( POLARSSL_ERR_THREADING_MUTEX_ERROR );
	#endif

	return( ret );
	}

	#if defined(POLARSSL_FS_IO)
	int entropy_write_seed_file( entropy_context ctx, const char path )
	{
	int ret = POLARSSL_ERR_ENTROPY_FILE_IO_ERROR;
	FILE *f;
	unsigned char buf[ENTROPY_BLOCK_SIZE];

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

	if( ( ret = entropy_func( ctx, buf, ENTROPY_BLOCK_SIZE ) ) != 0 )
	goto exit;

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

	ret = 0;

	exit:
	fclose( f );
	return( ret );
	}

	int entropy_update_seed_file( entropy_context ctx, const char path )
	{
	FILE *f;
	size_t n;
	unsigned char buf[ ENTROPY_MAX_SEED_SIZE ];

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

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

	if( n > ENTROPY_MAX_SEED_SIZE )
	n = ENTROPY_MAX_SEED_SIZE;

	if( fread( buf, 1, n, f ) != n )
	{
	fclose( f );
	return( POLARSSL_ERR_ENTROPY_FILE_IO_ERROR );
	}

	fclose( f );

	entropy_update_manual( ctx, buf, n );

	return( entropy_write_seed_file( ctx, path ) );
	}
	#endif /* POLARSSL_FS_IO */

	#if defined(POLARSSL_SELF_TEST)

	#if defined(POLARSSL_PLATFORM_C)
	#include "polarssl/platform.h"
	#else
	#include <stdio.h>
	#define polarssl_printf printf
	#endif

	/*
	* 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 );
	}

	/*
	* 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 entropy_self_test( int verbose )
	{
	int ret = 0;
	entropy_context ctx;
	unsigned char buf[ENTROPY_BLOCK_SIZE] = { 0 };
	unsigned char acc[ENTROPY_BLOCK_SIZE] = { 0 };
	size_t i, j;

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

	entropy_init( &ctx );

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

	if( ( ret = entropy_gather( &ctx ) ) != 0 )
	goto cleanup;

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

	/*
	* To test that 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 = 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;
	}
	}

	cleanup:
	entropy_free( &ctx );

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

	polarssl_printf( "\n" );
	}

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

	#endif /* POLARSSL_ENTROPY_C */