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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 b8d78926eb
commit 28d611559e
4 changed files with 69 additions and 16 deletions
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16
library/base64.c
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@ -38,22 +38,6 @@
#define BASE64_SIZE_T_MAX ( (size_t) -1 ) /* SIZE_T_MAX is not standard */
/* Return 0xff if low <= c <= high, 0 otherwise.
*
* Constant flow with respect to c.
*/
MBEDTLS_STATIC_TESTABLE
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 );
}
/* Given a value in the range 0..63, return the corresponding Base64 digit.
* The implementation assumes that letters are consecutive (e.g. ASCII
* but not EBCDIC).