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Evolve mbedtls_ct_uchar_in_range_if interface

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Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
This commit is contained in:
Dave Rodgman 2023-05-09 10:39:03 +01:00
parent 0ee9683987
commit 8c94e219f9
2 changed files with 29 additions and 15 deletions
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24
library/constant_time_internal.h
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@ -333,13 +333,27 @@ int mbedtls_ct_rsaes_pkcs1_v15_unpadding(unsigned char *input,
#if defined(MBEDTLS_BASE64_C)
/* Return 0xff if low <= c <= high, 0 otherwise.
/** Constant-flow char selection
*
* Constant flow with respect to c.
* \param low Bottom of range
* \param high Top of range
* \param c Value to compare to range
* \param t Value to return, if in range
*
* \return \p t if \p low <= \p c <= \p high, 0 otherwise.
*/
unsigned char mbedtls_ct_uchar_mask_of_range(unsigned char low,
unsigned char high,
unsigned char c);
static inline unsigned char mbedtls_ct_uchar_in_range_if(unsigned char low,
unsigned char high,
unsigned char c,
unsigned char t)
{
/* 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 (unsigned char)
mbedtls_ct_uint_if(~mbedtls_ct_mpi_uint_mask(low_mask | high_mask), t, 0);
}
#endif /* MBEDTLS_BASE64_C */