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Move mbedtls_cf_memcpy_offset function to the constant-time module

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Signed-off-by: gabor-mezei-arm <gabor.mezei@arm.com>
This commit is contained in:
gabor-mezei-arm
2021-09-27 13:57:45 +02:00
parent dee0fd33f1
commit 0e7f71e1a9
3 changed files with 45 additions and 21 deletions
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21
library/constant_time.c
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@ -418,3 +418,24 @@ void mbedtls_cf_memcpy_if_eq( unsigned char *dst,
for( size_t i = 0; i < len; i++ )
dst[i] = ( src[i] & mask ) | ( dst[i] & ~mask );
}
/*
* Constant-flow memcpy from variable position in buffer.
* - functionally equivalent to memcpy(dst, src + offset_secret, len)
* - but with execution flow independent from the value of offset_secret.
*/
void mbedtls_cf_memcpy_offset(
unsigned char *dst,
const unsigned char *src_base,
size_t offset_secret,
size_t offset_min, size_t offset_max,
size_t len )
{
size_t offset;
for( offset = offset_min; offset <= offset_max; offset++ )
{
mbedtls_cf_memcpy_if_eq( dst, src_base + offset, len,
offset, offset_secret );
}
}