1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* mpi-pow.c  -  MPI functions
11  *	 to avoid revealing of sensitive data due to paging etc.
18 #include "mpi-internal.h"
39 	int rc = -ENOMEM;  in mpi_powm()
41 	esize = exp->nlimbs;  in mpi_powm()
42 	msize = mod->nlimbs;  in mpi_powm()
44 	msign = mod->sign;  in mpi_powm()
46 	rp = res->d;  in mpi_powm()
47 	ep = exp->d;  in mpi_powm()
50 		return -EINVAL;  in mpi_powm()
55 		res->nlimbs = (msize == 1 && mod->d[0] == 1) ? 0 : 1;  in mpi_powm()
56 		if (res->nlimbs) {  in mpi_powm()
59 			rp = res->d;  in mpi_powm()
62 		res->sign = 0;  in mpi_powm()
73 	mod_shift_cnt = count_leading_zeros(mod->d[msize - 1]);  in mpi_powm()
75 		mpihelp_lshift(mp, mod->d, msize, mod_shift_cnt);  in mpi_powm()
77 		MPN_COPY(mp, mod->d, msize);  in mpi_powm()
79 	bsize = base->nlimbs;  in mpi_powm()
80 	bsign = base->sign;  in mpi_powm()
83 		 * (The quotient is (bsize - msize + 1) limbs.)  */  in mpi_powm()
87 		MPN_COPY(bp, base->d, bsize);  in mpi_powm()
96 		bp = base->d;  in mpi_powm()
99 		res->nlimbs = 0;  in mpi_powm()
100 		res->sign = 0;  in mpi_powm()
104 	if (res->alloced < size) {  in mpi_powm()
116 			rp = res->d;  in mpi_powm()
159 		negative_result = (ep[0] & 1) && base->sign;  in mpi_powm()
161 		i = esize - 1;  in mpi_powm()
165 		c = BITS_PER_MPI_LIMB - 1 - c;  in mpi_powm()
173 		 * by RP (==RES->d), and with 50% probability in the area originally  in mpi_powm()
179 				mpi_ptr_t tp;  in mpi_powm()  local
210 				tp = rp;  in mpi_powm()
212 				xp = tp;  in mpi_powm()
238 					tp = rp;  in mpi_powm()
240 					xp = tp;  in mpi_powm()
244 				c--;  in mpi_powm()
248 			i--;  in mpi_powm()
256 		 * steps.  Adjust the result by reducing it with the original MOD.  in mpi_powm()
258 		 * Also make sure the result is put in RES->d (where it already  in mpi_powm()
263 			    mpihelp_lshift(res->d, rp, rsize, mod_shift_cnt);  in mpi_powm()
264 			rp = res->d;  in mpi_powm()
270 			MPN_COPY(res->d, rp, rsize);  in mpi_powm()
271 			rp = res->d;  in mpi_powm()
293 	res->nlimbs = rsize;  in mpi_powm()
294 	res->sign = rsign;  in mpi_powm()