diff options
Diffstat (limited to 'src/crypto/bigint.c')
| -rw-r--r-- | src/crypto/bigint.c | 30 |
1 files changed, 26 insertions, 4 deletions
diff --git a/src/crypto/bigint.c b/src/crypto/bigint.c index 92747982e..e5e6e2f12 100644 --- a/src/crypto/bigint.c +++ b/src/crypto/bigint.c @@ -278,6 +278,30 @@ void bigint_reduce_raw ( bigint_element_t *modulus0, bigint_element_t *value0, } /** + * Reduce supremum of big integer representation + * + * @v modulus0 Element 0 of big integer modulus + * @v result0 Element 0 of big integer to hold result + * @v size Number of elements in modulus and value + * + * Reduce the value 2^k (where k is the bit width of the big integer + * representation) modulo the specified modulus. + */ +void bigint_reduce_supremum_raw ( bigint_element_t *modulus0, + bigint_element_t *result0, + unsigned int size ) { + bigint_t ( size ) __attribute__ (( may_alias )) + *modulus = ( ( void * ) modulus0 ); + bigint_t ( size ) __attribute__ (( may_alias )) + *result = ( ( void * ) result0 ); + + /* Calculate (2^k) mod N via direct reduction of (2^k - N) mod N */ + memset ( result, 0, sizeof ( *result ) ); + bigint_subtract ( modulus, result ); + bigint_reduce ( modulus, result ); +} + +/** * Compute inverse of odd big integer modulo any power of two * * @v invertend0 Element 0 of odd big integer to be inverted @@ -629,10 +653,8 @@ void bigint_mod_exp_raw ( const bigint_element_t *base0, if ( ! submask ) submask = ~submask; - /* Calculate (R^2 mod N) via direct reduction of (R^2 - N) */ - memset ( &temp->product.full, 0, sizeof ( temp->product.full ) ); - bigint_subtract ( &temp->padded_modulus, &temp->product.full ); - bigint_reduce ( &temp->padded_modulus, &temp->product.full ); + /* Calculate (R^2 mod N) */ + bigint_reduce_supremum ( &temp->padded_modulus, &temp->product.full ); bigint_copy ( &temp->product.low, &temp->stash ); /* Initialise result = Montgomery(1, R^2 mod N) */ |