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Move mbedtls_ct_uchar_mask_of_range function to the constant-time module

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Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
This commit is contained in:
Gabor Mezei
2021-11-15 16:13:01 +01:00
parent 7464f37e7b
commit 46f79c388d
4 changed files with 69 additions and 16 deletions
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23
library/constant_time.c
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@@ -40,6 +40,10 @@
#include "mbedtls/rsa.h"
#endif
#if defined(MBEDTLS_BASE64_C)
#include "constant_time_invasive.h"
#endif
#include <string.h>
int mbedtls_ct_memcmp( const void *a,
@@ -150,6 +154,25 @@ size_t mbedtls_ct_size_mask_ge( size_t x,
#endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
#if defined(MBEDTLS_BASE64_C)
/* Return 0xff if low <= c <= high, 0 otherwise.
*
* Constant flow with respect to c.
*/
unsigned char mbedtls_ct_uchar_mask_of_range( unsigned char low,
unsigned char high,
unsigned char c )
{
/* low_mask is: 0 if low <= c, 0x...ff if low > c */
unsigned low_mask = ( (unsigned) c - low ) >> 8;
/* high_mask is: 0 if c <= high, 0x...ff if c > high */
unsigned high_mask = ( (unsigned) high - c ) >> 8;
return( ~( low_mask | high_mask ) & 0xff );
}
#endif /* MBEDTLS_BASE64_C */
unsigned mbedtls_ct_size_bool_eq( size_t x,
size_t y )
{