diff options
Diffstat (limited to 'mpi')
| -rw-r--r-- | mpi/mpi-internal.h | 3 | ||||
| -rw-r--r-- | mpi/mpih-const-time.c | 38 |
2 files changed, 41 insertions, 0 deletions
diff --git a/mpi/mpi-internal.h b/mpi/mpi-internal.h index fd44c0a8..4111d905 100644 --- a/mpi/mpi-internal.h +++ b/mpi/mpi-internal.h @@ -260,6 +260,7 @@ mpi_limb_t _gcry_mpih_rshift( mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, #define mpih_sub_n_cond(w,u,v,s,o) _gcry_mpih_sub_n_cond ((w),(u),(v),(s),(o)) #define mpih_swap_cond(u,v,s,o) _gcry_mpih_swap_cond ((u),(v),(s),(o)) #define mpih_abs_cond(w,u,s,o) _gcry_mpih_abs_cond ((w),(u),(s),(o)) +#define mpih_mod(v,vs,u,us) _gcry_mpih_mod ((v),(vs),(u),(us)) void _gcry_mpih_set_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned long op_enable); @@ -271,6 +272,8 @@ void _gcry_mpih_swap_cond (mpi_ptr_t up, mpi_ptr_t vp, mpi_size_t usize, unsigned long op_enable); void _gcry_mpih_abs_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned long op_enable); +mpi_ptr_t _gcry_mpih_mod (mpi_ptr_t vp, mpi_size_t vsize, + mpi_ptr_t up, mpi_size_t usize); /* Define stuff for longlong.h. */ diff --git a/mpi/mpih-const-time.c b/mpi/mpih-const-time.c index ea8d5292..d91bf1a9 100644 --- a/mpi/mpih-const-time.c +++ b/mpi/mpih-const-time.c @@ -23,6 +23,8 @@ #include "mpi-internal.h" #include "g10lib.h" +#define A_LIMB_1 ((mpi_limb_t)1) + /* * W = U when OP_ENABLED=1 * otherwise, W keeps old value @@ -142,3 +144,39 @@ _gcry_mpih_abs_cond (mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, wp[i] = up[i] ^ (mask & (x ^ up[i])); } } + + +/* + * Allocating memory for W, + * compute W = V % U, then return W + */ +mpi_ptr_t +_gcry_mpih_mod (mpi_ptr_t vp, mpi_size_t vsize, + mpi_ptr_t up, mpi_size_t usize) +{ + int secure; + mpi_ptr_t rp; + mpi_size_t i; + + secure = _gcry_is_secure (vp); + rp = mpi_alloc_limb_space (usize, secure); + MPN_ZERO (rp, usize); + + for (i = 0; i < vsize * BITS_PER_MPI_LIMB; i++) + { + unsigned int j = vsize * BITS_PER_MPI_LIMB - 1 - i; + unsigned int limbno = j / BITS_PER_MPI_LIMB; + unsigned int bitno = j % BITS_PER_MPI_LIMB; + mpi_limb_t limb = vp[limbno]; + unsigned int the_bit = ((limb & (A_LIMB_1 << bitno)) ? 1 : 0); + mpi_limb_t underflow; + + _gcry_mpih_lshift (rp, rp, usize, 1); + rp[0] |= the_bit; + + underflow = _gcry_mpih_sub_n (rp, rp, up, usize); + mpih_add_n_cond (rp, rp, up, usize, underflow); + } + + return rp; +} |