1/* mpz_powm_sec(res,base,exp,mod) -- Set R to (U^E) mod M. 2 3 Contributed to the GNU project by Torbjorn Granlund. 4 5Copyright 1991, 1993, 1994, 1996, 1997, 2000-2002, 2005, 2008, 2009, 62012, 2015 Free Software Foundation, Inc. 7 8This file is part of the GNU MP Library. 9 10The GNU MP Library is free software; you can redistribute it and/or modify 11it under the terms of either: 12 13 * the GNU Lesser General Public License as published by the Free 14 Software Foundation; either version 3 of the License, or (at your 15 option) any later version. 16 17or 18 19 * the GNU General Public License as published by the Free Software 20 Foundation; either version 2 of the License, or (at your option) any 21 later version. 22 23or both in parallel, as here. 24 25The GNU MP Library is distributed in the hope that it will be useful, but 26WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 27or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 28for more details. 29 30You should have received copies of the GNU General Public License and the 31GNU Lesser General Public License along with the GNU MP Library. If not, 32see https://www.gnu.org/licenses/. */ 33 34 35#include "gmp-impl.h" 36 37 38void 39mpz_powm_sec (mpz_ptr r, mpz_srcptr b, mpz_srcptr e, mpz_srcptr m) 40{ 41 mp_size_t n; 42 mp_ptr rp, tp; 43 mp_srcptr bp, ep, mp; 44 mp_size_t rn, bn, es, en; 45 TMP_DECL; 46 47 n = ABSIZ(m); 48 49 mp = PTR(m); 50 51 if (UNLIKELY ((n == 0) || (mp[0] % 2 == 0))) 52 DIVIDE_BY_ZERO; 53 54 es = SIZ(e); 55 if (UNLIKELY (es <= 0)) 56 { 57 if (es == 0) 58 { 59 /* b^0 mod m, b is anything and m is non-zero. 60 Result is 1 mod m, i.e., 1 or 0 depending on if m = 1. */ 61 SIZ(r) = n != 1 || mp[0] != 1; 62 MPZ_NEWALLOC (r, 1)[0] = 1; 63 return; 64 } 65 DIVIDE_BY_ZERO; 66 } 67 en = es; 68 69 bn = ABSIZ(b); 70 71 if (UNLIKELY (bn == 0)) 72 { 73 SIZ(r) = 0; 74 return; 75 } 76 77 TMP_MARK; 78 TMP_ALLOC_LIMBS_2 (rp, n, 79 tp, mpn_sec_powm_itch (bn, en * GMP_NUMB_BITS, n)); 80 81 bp = PTR(b); 82 ep = PTR(e); 83 84 mpn_sec_powm (rp, bp, bn, ep, en * GMP_NUMB_BITS, mp, n, tp); 85 86 rn = n; 87 88 MPN_NORMALIZE (rp, rn); 89 90 if ((ep[0] & 1) && SIZ(b) < 0 && rn != 0) 91 { 92 mpn_sub (rp, PTR(m), n, rp, rn); 93 rn = n; 94 MPN_NORMALIZE (rp, rn); 95 } 96 97 MPZ_NEWALLOC (r, rn); 98 SIZ(r) = rn; 99 MPN_COPY (PTR(r), rp, rn); 100 101 TMP_FREE; 102} 103