From 97079553b66ea9036348543e2b92cbe29bfd2c6b Mon Sep 17 00:00:00 2001 From: Michael Brown Date: Mon, 16 Dec 2024 15:09:56 +0000 Subject: [crypto] Calculate inverse of modulus on demand in bigint_montgomery() 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 --- src/include/ipxe/bigint.h | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) (limited to 'src/include') diff --git a/src/include/ipxe/bigint.h b/src/include/ipxe/bigint.h index 3058547a6..90e212b54 100644 --- a/src/include/ipxe/bigint.h +++ b/src/include/ipxe/bigint.h @@ -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, -- cgit v1.2.3-55-g7522