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Merge pull request #3537 from piotr-now/platform_random

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Expanded the random number generator in the `platform_util.c` file
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Piotr Nowicki 2020-08-12 15:09:05 +02:00 committed by GitHub
parent fa635dfaa1 26c33692b0
commit 2bb1376560
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2 changed files with 89 additions and 60 deletions
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39
include/mbedtls/platform_util.h
View file

@ -167,11 +167,10 @@ void mbedtls_platform_zeroize( void *buf, size_t len );
/**
* \brief Secure memset
*
* This is a constant-time version of memset(). If
* MBEDTLS_ENTROPY_HARDWARE_ALT is defined, the buffer is
* initialised with random data and the order is also
* randomised using the hardware RNG in order to further harden
* against side-channel attacks.
* This is a constant-time version of memset(). The buffer is
* initialised with random data and the order is also randomised
* using the RNG in order to further harden against side-channel
* attacks.
*
* \param ptr Buffer to be set.
* \param value Value to be used when setting the buffer.
@ -184,11 +183,10 @@ void *mbedtls_platform_memset( void *ptr, int value, size_t num );
/**
* \brief Secure memcpy
*
* This is a constant-time version of memcpy(). If
* MBEDTLS_ENTROPY_HARDWARE_ALT is defined, the buffer is
* initialised with random data and the order is also
* randomised using the hardware RNG in order to further harden
* against side-channel attacks.
* This is a constant-time version of memcpy(). The buffer is
* initialised with random data and the order is also randomised
* using the RNG in order to further harden against side-channel
* attacks.
*
* \param dst Destination buffer where the data is being copied to.
* \param src Source buffer where the data is being copied from.
@ -218,9 +216,8 @@ int mbedtls_platform_memmove( void *dst, const void *src, size_t num );
* \brief Secure check if the buffers have the same data.
*
* This is a constant-time version of memcmp(), but without checking
* if the bytes are greater or lower. If MBEDTLS_ENTROPY_HARDWARE_ALT
* is defined, the order is also randomised using the hardware RNG in
* order to further harden against side-channel attacks.
* if the bytes are greater or lower. The order is also randomised
* using the RNG in order to further harden against side-channel attacks.
*
* \param buf1 First buffer to compare.
* \param buf2 Second buffer to compare against.
@ -234,11 +231,6 @@ int mbedtls_platform_memequal( const void *buf1, const void *buf2, size_t num );
/**
* \brief RNG-function for getting a random 32-bit integer.
*
*
* \note Currently the function is dependent of hardware providing an
* rng with MBEDTLS_ENTROPY_HARDWARE_ALT. By default, 0 is
* returned.
*
* \return The generated random number.
*/
uint32_t mbedtls_platform_random_uint32( void );
@ -253,10 +245,6 @@ uint32_t mbedtls_platform_random_uint32( void );
* cryptographically secure RNG, but provide an RNG for utility
* functions.
*
* \note Currently the function is dependent of hardware providing an
* rng with MBEDTLS_ENTROPY_HARDWARE_ALT. By default, 0 is
* returned.
*
* \note If the given range is [0, 0), 0 is returned.
*
* \param num Max-value for the generated random number, exclusive.
@ -264,7 +252,7 @@ uint32_t mbedtls_platform_random_uint32( void );
*
* \return The generated random number.
*/
uint32_t mbedtls_platform_random_in_range( size_t num );
uint32_t mbedtls_platform_random_in_range( uint32_t num );
/**
* \brief Random delay function.
@ -275,8 +263,9 @@ uint32_t mbedtls_platform_random_in_range( size_t num );
* Duration of the delay is random as number of variable increments
* is randomized.
*
* \note Currently the function is dependent of hardware providing an
* rng with MBEDTLS_ENTROPY_HARDWARE_ALT.
* \note This function works only if the MBEDTLS_FI_COUNTERMEASURES flag
* is defined in the configuration. Otherwise, the function does
* nothing.
*/
void mbedtls_platform_random_delay( void );

110
library/platform_util.c
View file

@ -51,9 +51,20 @@
#include <stddef.h>
#include <string.h>
/* Max number of loops for mbedtls_platform_random_delay */
/* Max number of loops for mbedtls_platform_random_delay. */
#define MAX_RAND_DELAY 100
/* Parameters for the linear congruential generator used as a non-cryptographic
* random number generator. The same parameters are used by e.g. ANSI C. */
#define RAND_MULTIPLIER 1103515245
#define RAND_INCREMENT 12345
#define RAND_MODULUS 0x80000000
/* The number of iterations after which the seed of the non-cryptographic
* random number generator will be changed. This is used only if the
* MBEDTLS_ENTROPY_HARDWARE_ALT option is enabled. */
#define RAND_SEED_LIFE 10000
#if !defined(MBEDTLS_PLATFORM_ZEROIZE_ALT)
/*
* This implementation should never be optimized out by the compiler
@ -96,7 +107,7 @@ void mbedtls_platform_zeroize( void *buf, size_t len )
void *mbedtls_platform_memset( void *ptr, int value, size_t num )
{
/* Randomize start offset. */
size_t start_offset = (size_t) mbedtls_platform_random_in_range( num );
size_t start_offset = (size_t) mbedtls_platform_random_in_range( (uint32_t) num );
/* Randomize data */
uint32_t data = mbedtls_platform_random_in_range( 256 );
@ -113,7 +124,7 @@ void *mbedtls_platform_memset( void *ptr, int value, size_t num )
void *mbedtls_platform_memcpy( void *dst, const void *src, size_t num )
{
/* Randomize start offset. */
size_t start_offset = (size_t) mbedtls_platform_random_in_range( num );
size_t start_offset = (size_t) mbedtls_platform_random_in_range( (uint32_t) num );
/* Randomize initial data to prevent leakage while copying */
uint32_t data = mbedtls_platform_random_in_range( 256 );
@ -152,7 +163,7 @@ int mbedtls_platform_memequal( const void *buf1, const void *buf2, size_t num )
/* Start from a random location and check the correct number of iterations */
size_t i, flow_counter = 0;
size_t start_offset = (size_t) mbedtls_platform_random_in_range( num );
size_t start_offset = (size_t) mbedtls_platform_random_in_range( (uint32_t) num );
for( i = start_offset; i < num; i++ )
{
@ -172,51 +183,80 @@ int mbedtls_platform_memequal( const void *buf1, const void *buf2, size_t num )
return( (int) diff | (int) ( flow_counter ^ num ) );
}
uint32_t mbedtls_platform_random_uint32( )
/* This function implements a non-cryptographic random number generator based
* on the linear congruential generator algorithm. Additionally, if the
* MBEDTLS_ENTROPY_HARDWARE_ALT flag is defined, the seed is set at the first
* call of this function with using a hardware random number generator and
* changed every RAND_SEED_LIFE number of iterations.
*
* The value of the returned number is in the range [0; 0xffff].
*
* Note: The range of values with a 16-bit precision is related to the modulo
* parameter of the generator and the fact that the function does not return the
* full value of the internal state of the generator.
*/
static uint32_t mbedtls_platform_random_uint16( void )
{
#if !defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
return 0;
#else
uint32_t result = 0;
size_t olen = 0;
/* Set random_state - the first random value should not be zero. */
static uint32_t random_state = RAND_INCREMENT;
mbedtls_hardware_poll( NULL, (unsigned char *) &result, sizeof( result ),
&olen );
return( result );
#endif
#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
static uint32_t random_seed_life = 0;
if( 0 < random_seed_life )
{
--random_seed_life;
}
else
{
size_t olen = 0;
uint32_t hw_random;
mbedtls_hardware_poll( NULL,
(unsigned char *) &hw_random, sizeof( hw_random ),
&olen );
if( olen == sizeof( hw_random ) )
{
random_state ^= hw_random;
random_seed_life = RAND_SEED_LIFE;
}
}
#endif /* MBEDTLS_ENTROPY_HARDWARE_ALT */
random_state = ( ( random_state * RAND_MULTIPLIER ) + RAND_INCREMENT ) % RAND_MODULUS;
/* Do not return the entire random_state to hide generator predictability for
* the next iteration */
return( ( random_state >> 15 ) & 0xffff );
}
uint32_t mbedtls_platform_random_in_range( size_t num )
uint32_t mbedtls_platform_random_uint32( void )
{
#if !defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
(void) num;
return 0;
#else
uint32_t result = 0;
size_t olen = 0;
return( ( mbedtls_platform_random_uint16() << 16 ) |
mbedtls_platform_random_uint16() );
}
mbedtls_hardware_poll( NULL, (unsigned char *) &result, sizeof( result ),
&olen );
uint32_t mbedtls_platform_random_in_range( uint32_t num )
{
uint32_t result;
if( num == 0 )
if( num <= 1 )
{
result = 0;
}
else
{
result %= num;
result = mbedtls_platform_random_uint32() % num;
}
return( result );
#endif
}
void mbedtls_platform_random_delay( void )
{
#if !defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
return;
#else
size_t rn_1, rn_2, rn_3;
#if defined(MBEDTLS_FI_COUNTERMEASURES)
uint32_t rn_1, rn_2, rn_3;
volatile size_t i = 0;
uint8_t shift;
@ -229,17 +269,17 @@ void mbedtls_platform_random_delay( void )
i++;
/* Dummy calculations to increase the time between iterations and
* make side channel attack more difficult by reducing predictability
* of its behaviour */
shift = rn_2 & 0x07;
* of its behaviour. */
shift = ( rn_2 & 0x07 ) + 1;
if ( i % 2 )
rn_2 = (uint32_t)( rn_2 >> shift | rn_2 << ( 32 - shift ) );
rn_2 = ( rn_2 >> shift ) | ( rn_2 << ( 32 - shift ) );
else
rn_3 = (uint32_t)( rn_3 << shift | rn_3 >> ( 32 - shift ) );
rn_3 = ( rn_3 << shift ) | ( rn_3 >> ( 32 - shift ) );
rn_2 ^= rn_3;
} while( i < rn_1 || rn_2 == 0 || rn_3 == 0 );
#endif /* MBEDTLS_FI_COUNTERMEASURES */
return;
#endif /* !MBEDTLS_ENTROPY_HARDWARE_ALT */
}
#if defined(MBEDTLS_HAVE_TIME_DATE) && !defined(MBEDTLS_PLATFORM_GMTIME_R_ALT)