From d88eb0a1935942cdeccd3efee38f9765d2f1c235 Mon Sep 17 00:00:00 2001 From: Michael Brown Date: Fri, 10 Jan 2025 13:44:13 +0000 Subject: [crypto] Extract bigint_reduce_supremum() from bigint_mod_exp() Calculating the Montgomery constant (R^2 mod N) is done in our implementation by zeroing the double-width representation of N, subtracting N once to give (R^2 - N) in order to obtain a positive value, then reducing this value modulo N. Extract this logic from bigint_mod_exp() to a separate function bigint_reduce_supremum(), to allow for reuse by other code. Signed-off-by: Michael Brown --- src/include/ipxe/bigint.h | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) (limited to 'src/include') diff --git a/src/include/ipxe/bigint.h b/src/include/ipxe/bigint.h index db907f1cd..2dd99380d 100644 --- a/src/include/ipxe/bigint.h +++ b/src/include/ipxe/bigint.h @@ -236,9 +236,21 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL ); * @v value Big integer to be reduced */ #define bigint_reduce( modulus, value ) do { \ - unsigned int size = bigint_size (modulus); \ - bigint_reduce_raw ( (modulus)->element, \ - (value)->element, size ); \ + unsigned int size = bigint_size (modulus); \ + bigint_reduce_raw ( (modulus)->element, (value)->element, \ + size ); \ + } while ( 0 ) + +/** + * Reduce supremum of big integer representation + * + * @v modulus0 Big integer modulus + * @v result0 Big integer to hold result + */ +#define bigint_reduce_supremum( modulus, result ) do { \ + unsigned int size = bigint_size (modulus); \ + bigint_reduce_supremum_raw ( (modulus)->element, \ + (result)->element, size ); \ } while ( 0 ) /** @@ -385,6 +397,9 @@ void bigint_multiply_raw ( const bigint_element_t *multiplicand0, bigint_element_t *result0 ); void bigint_reduce_raw ( bigint_element_t *modulus0, bigint_element_t *value0, unsigned int size ); +void bigint_reduce_supremum_raw ( bigint_element_t *modulus0, + bigint_element_t *value0, + unsigned int size ); void bigint_mod_invert_raw ( const bigint_element_t *invertend0, bigint_element_t *inverse0, unsigned int size ); int bigint_montgomery_relaxed_raw ( const bigint_element_t *modulus0, -- cgit v1.2.3-55-g7522