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Use bitwise comparison in memcmp

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It is safer than == operator.
This commit is contained in:
Jarno Lamsa 2019-10-02 08:32:51 +03:00
parent 32db938463
commit 7cb902737b
1 changed files with 8 additions and 11 deletions
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19
library/platform_util.c
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@ -112,7 +112,9 @@ void mbedtls_platform_memcpy( void *dst, const void *src, size_t num )
int mbedtls_platform_memcmp( const void *buf1, const void *buf2, size_t num )
{
volatile unsigned int equal = 0;
volatile const unsigned char *A = (volatile const unsigned char *) buf1;
volatile const unsigned char *B = (volatile const unsigned char *) buf2;
volatile unsigned char diff = 0;
size_t i = num;
@ -120,22 +122,17 @@ int mbedtls_platform_memcmp( const void *buf1, const void *buf2, size_t num )
for( i = start_offset; i < num; i++ )
{
equal += ( ( (unsigned char *) buf1 )[i] ==
( (unsigned char *) buf2 )[i] );
unsigned char x = A[i], y = B[i];
diff |= x ^ y;
}
for( i = 0; i < start_offset; i++ )
{
equal += ( ( (unsigned char *) buf1 )[i] ==
( (unsigned char *) buf2 )[i] );
unsigned char x = A[i], y = B[i];
diff |= x ^ y;
}
if ( equal == num )
{
return 0;
}
return 1;
return( diff );
}
#if !defined(MBEDTLS_PLATFORM_GLOBAL_RNG)