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[crypto] Calculate inverse of modulus on demand in bigint_montgomery()

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Reduce the number of parameters passed to bigint_montgomery() by
calculating the inverse of the modulus modulo the element size on
demand.  Cache the result, since Montgomery reduction will be used
repeatedly with the same modulus value.

In all currently supported algorithms, the modulus is a public value
(or a fixed value defined by specification) and so this non-constant
timing does not leak any private information.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2024-12-16 15:09:56 +00:00
parent 24db39fb29
commit 97079553b6
3 changed files with 23 additions and 36 deletions
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8
src/include/ipxe/bigint.h
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@@ -257,16 +257,15 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
* Perform Montgomery reduction (REDC) of a big integer product
*
* @v modulus Big integer modulus
* @v modinv Big integer inverse of the modulus modulo 2^k
* @v mont Big integer Montgomery product
* @v result Big integer to hold result
*
* Note that the Montgomery product will be overwritten.
*/
#define bigint_montgomery( modulus, modinv, mont, result ) do { \
#define bigint_montgomery( modulus, mont, result ) do { \
unsigned int size = bigint_size (modulus); \
bigint_montgomery_raw ( (modulus)->element, (modinv)->element, \
(mont)->element, (result)->element, \
bigint_montgomery_raw ( (modulus)->element, (mont)->element, \
(result)->element, \
size ); \
} while ( 0 )
@@ -377,7 +376,6 @@ void bigint_reduce_raw ( bigint_element_t *modulus0, bigint_element_t *value0,
void bigint_mod_invert_raw ( const bigint_element_t *invertend0,
bigint_element_t *inverse0, unsigned int size );
void bigint_montgomery_raw ( const bigint_element_t *modulus0,
const bigint_element_t *modinv0,
bigint_element_t *mont0,
bigint_element_t *result0, unsigned int size );
void bigint_mod_exp_raw ( const bigint_element_t *base0,