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mbedtls/library/entropy.c
Simon Butcher 1ceab6e43a Adds a check and warning for the null entropy option 
If the option MBEDTLS_TEST_NULL_ENTROPY is enabled, the cmake generated
makefile will generate an error unless a UNSAFE_BUILD switch is also enabled.

Equally, a similar warning will always be generated if the Makefile is built,
and another warning is generated on every compilation of entropy.c.

This is to ensure the user is aware of what they're doing when they enable the
null entropy option.
2016-06-21 10:14:00 +01:00

543 lines
15 KiB
C
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/*
* 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 <string.h>
#if defined(MBEDTLS_FS_IO)
#include <stdio.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
/* Implementation that should never be optimized out by the compiler */
static void mbedtls_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 mbedtls_entropy_init( mbedtls_entropy_context *ctx )
{
memset( ctx, 0, sizeof(mbedtls_entropy_context) );
#if defined(MBEDTLS_THREADING_C)
mbedtls_mutex_init( &ctx->mutex );
#endif
#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
mbedtls_sha512_starts( &ctx->accumulator, 0 );
#else
mbedtls_sha256_starts( &ctx->accumulator, 0 );
#endif
#if defined(MBEDTLS_HAVEGE_C)
mbedtls_havege_init( &ctx->havege_data );
#endif
#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 );
#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
mbedtls_zeroize( ctx, sizeof( mbedtls_entropy_context ) );
}
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 index, ret = 0;
#if defined(MBEDTLS_THREADING_C)
if( ( ret = mbedtls_mutex_lock( &ctx->mutex ) ) != 0 )
return( ret );
#endif
index = ctx->source_count;
if( index >= MBEDTLS_ENTROPY_MAX_SOURCES )
{
ret = MBEDTLS_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[index].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;
if( use_len > MBEDTLS_ENTROPY_BLOCK_SIZE )
{
#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
mbedtls_sha512( data, len, tmp, 0 );
#else
mbedtls_sha256( data, len, tmp, 0 );
#endif
p = tmp;
use_len = MBEDTLS_ENTROPY_BLOCK_SIZE;
}
header[0] = source_id;
header[1] = use_len & 0xFF;
#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
mbedtls_sha512_update( &ctx->accumulator, header, 2 );
mbedtls_sha512_update( &ctx->accumulator, p, use_len );
#else
mbedtls_sha256_update( &ctx->accumulator, header, 2 );
mbedtls_sha256_update( &ctx->accumulator, p, use_len );
#endif
return( 0 );
}
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 )
{
return( ret );
}
/*
* Add if we actually gathered something
*/
if( olen > 0 )
{
entropy_update( ctx, (unsigned char) i, buf, olen );
ctx->source[i].size += olen;
}
}
if( have_one_strong == 0 )
return( MBEDTLS_ERR_ENTROPY_NO_STRONG_SOURCE );
return( 0 );
}
/*
* 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)
mbedtls_sha512_finish( &ctx->accumulator, buf );
/*
* Reset accumulator and counters and recycle existing entropy
*/
memset( &ctx->accumulator, 0, sizeof( mbedtls_sha512_context ) );
mbedtls_sha512_starts( &ctx->accumulator, 0 );
mbedtls_sha512_update( &ctx->accumulator, buf, MBEDTLS_ENTROPY_BLOCK_SIZE );
/*
* Perform second SHA-512 on entropy
*/
mbedtls_sha512( buf, MBEDTLS_ENTROPY_BLOCK_SIZE, buf, 0 );
#else /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */
mbedtls_sha256_finish( &ctx->accumulator, buf );
/*
* Reset accumulator and counters and recycle existing entropy
*/
memset( &ctx->accumulator, 0, sizeof( mbedtls_sha256_context ) );
mbedtls_sha256_starts( &ctx->accumulator, 0 );
mbedtls_sha256_update( &ctx->accumulator, buf, MBEDTLS_ENTROPY_BLOCK_SIZE );
/*
* Perform second SHA-256 on entropy
*/
mbedtls_sha256( buf, MBEDTLS_ENTROPY_BLOCK_SIZE, buf, 0 );
#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:
#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_MAX_SEED_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 );
mbedtls_entropy_update_manual( ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE );
return( 0 );
}
#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:
fclose( f );
return( ret );
}
int mbedtls_entropy_update_seed_file( mbedtls_entropy_context *ctx, const char *path )
{
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 )
{
fclose( f );
return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );
}
fclose( f );
mbedtls_entropy_update_manual( ctx, buf, n );
return( mbedtls_entropy_write_seed_file( ctx, path ) );
}
#endif /* MBEDTLS_FS_IO */
#if defined(MBEDTLS_SELF_TEST)
/*
* 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 mbedtls_entropy_self_test( int verbose )
{
int ret = 0;
mbedtls_entropy_context ctx;
unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
unsigned char acc[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
size_t i, j;
if( verbose != 0 )
mbedtls_printf( " ENTROPY test: " );
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;
}
}
cleanup:
mbedtls_entropy_free( &ctx );
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 */
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