|
282
|
1 #include <tommath.h> |
|
|
2 #ifdef BN_MP_INVMOD_SLOW_C |
|
|
3 /* LibTomMath, multiple-precision integer library -- Tom St Denis |
|
|
4 * |
|
|
5 * LibTomMath is a library that provides multiple-precision |
|
|
6 * integer arithmetic as well as number theoretic functionality. |
|
|
7 * |
|
|
8 * The library was designed directly after the MPI library by |
|
|
9 * Michael Fromberger but has been written from scratch with |
|
|
10 * additional optimizations in place. |
|
|
11 * |
|
|
12 * The library is free for all purposes without any express |
|
|
13 * guarantee it works. |
|
|
14 * |
|
386
|
15 * Tom St Denis, [email protected], http://math.libtomcrypt.com |
|
282
|
16 */ |
|
|
17 |
|
|
18 /* hac 14.61, pp608 */ |
|
|
19 int mp_invmod_slow (mp_int * a, mp_int * b, mp_int * c) |
|
|
20 { |
|
|
21 mp_int x, y, u, v, A, B, C, D; |
|
|
22 int res; |
|
|
23 |
|
|
24 /* b cannot be negative */ |
|
|
25 if (b->sign == MP_NEG || mp_iszero(b) == 1) { |
|
|
26 return MP_VAL; |
|
|
27 } |
|
|
28 |
|
|
29 /* init temps */ |
|
|
30 if ((res = mp_init_multi(&x, &y, &u, &v, |
|
|
31 &A, &B, &C, &D, NULL)) != MP_OKAY) { |
|
|
32 return res; |
|
|
33 } |
|
|
34 |
|
|
35 /* x = a, y = b */ |
|
|
36 if ((res = mp_mod(a, b, &x)) != MP_OKAY) { |
|
|
37 goto LBL_ERR; |
|
|
38 } |
|
|
39 if ((res = mp_copy (b, &y)) != MP_OKAY) { |
|
|
40 goto LBL_ERR; |
|
|
41 } |
|
|
42 |
|
|
43 /* 2. [modified] if x,y are both even then return an error! */ |
|
|
44 if (mp_iseven (&x) == 1 && mp_iseven (&y) == 1) { |
|
|
45 res = MP_VAL; |
|
|
46 goto LBL_ERR; |
|
|
47 } |
|
|
48 |
|
|
49 /* 3. u=x, v=y, A=1, B=0, C=0,D=1 */ |
|
|
50 if ((res = mp_copy (&x, &u)) != MP_OKAY) { |
|
|
51 goto LBL_ERR; |
|
|
52 } |
|
|
53 if ((res = mp_copy (&y, &v)) != MP_OKAY) { |
|
|
54 goto LBL_ERR; |
|
|
55 } |
|
|
56 mp_set (&A, 1); |
|
|
57 mp_set (&D, 1); |
|
|
58 |
|
|
59 top: |
|
|
60 /* 4. while u is even do */ |
|
|
61 while (mp_iseven (&u) == 1) { |
|
|
62 /* 4.1 u = u/2 */ |
|
|
63 if ((res = mp_div_2 (&u, &u)) != MP_OKAY) { |
|
|
64 goto LBL_ERR; |
|
|
65 } |
|
|
66 /* 4.2 if A or B is odd then */ |
|
|
67 if (mp_isodd (&A) == 1 || mp_isodd (&B) == 1) { |
|
|
68 /* A = (A+y)/2, B = (B-x)/2 */ |
|
|
69 if ((res = mp_add (&A, &y, &A)) != MP_OKAY) { |
|
|
70 goto LBL_ERR; |
|
|
71 } |
|
|
72 if ((res = mp_sub (&B, &x, &B)) != MP_OKAY) { |
|
|
73 goto LBL_ERR; |
|
|
74 } |
|
|
75 } |
|
|
76 /* A = A/2, B = B/2 */ |
|
|
77 if ((res = mp_div_2 (&A, &A)) != MP_OKAY) { |
|
|
78 goto LBL_ERR; |
|
|
79 } |
|
|
80 if ((res = mp_div_2 (&B, &B)) != MP_OKAY) { |
|
|
81 goto LBL_ERR; |
|
|
82 } |
|
|
83 } |
|
|
84 |
|
|
85 /* 5. while v is even do */ |
|
|
86 while (mp_iseven (&v) == 1) { |
|
|
87 /* 5.1 v = v/2 */ |
|
|
88 if ((res = mp_div_2 (&v, &v)) != MP_OKAY) { |
|
|
89 goto LBL_ERR; |
|
|
90 } |
|
|
91 /* 5.2 if C or D is odd then */ |
|
|
92 if (mp_isodd (&C) == 1 || mp_isodd (&D) == 1) { |
|
|
93 /* C = (C+y)/2, D = (D-x)/2 */ |
|
|
94 if ((res = mp_add (&C, &y, &C)) != MP_OKAY) { |
|
|
95 goto LBL_ERR; |
|
|
96 } |
|
|
97 if ((res = mp_sub (&D, &x, &D)) != MP_OKAY) { |
|
|
98 goto LBL_ERR; |
|
|
99 } |
|
|
100 } |
|
|
101 /* C = C/2, D = D/2 */ |
|
|
102 if ((res = mp_div_2 (&C, &C)) != MP_OKAY) { |
|
|
103 goto LBL_ERR; |
|
|
104 } |
|
|
105 if ((res = mp_div_2 (&D, &D)) != MP_OKAY) { |
|
|
106 goto LBL_ERR; |
|
|
107 } |
|
|
108 } |
|
|
109 |
|
|
110 /* 6. if u >= v then */ |
|
|
111 if (mp_cmp (&u, &v) != MP_LT) { |
|
|
112 /* u = u - v, A = A - C, B = B - D */ |
|
|
113 if ((res = mp_sub (&u, &v, &u)) != MP_OKAY) { |
|
|
114 goto LBL_ERR; |
|
|
115 } |
|
|
116 |
|
|
117 if ((res = mp_sub (&A, &C, &A)) != MP_OKAY) { |
|
|
118 goto LBL_ERR; |
|
|
119 } |
|
|
120 |
|
|
121 if ((res = mp_sub (&B, &D, &B)) != MP_OKAY) { |
|
|
122 goto LBL_ERR; |
|
|
123 } |
|
|
124 } else { |
|
|
125 /* v - v - u, C = C - A, D = D - B */ |
|
|
126 if ((res = mp_sub (&v, &u, &v)) != MP_OKAY) { |
|
|
127 goto LBL_ERR; |
|
|
128 } |
|
|
129 |
|
|
130 if ((res = mp_sub (&C, &A, &C)) != MP_OKAY) { |
|
|
131 goto LBL_ERR; |
|
|
132 } |
|
|
133 |
|
|
134 if ((res = mp_sub (&D, &B, &D)) != MP_OKAY) { |
|
|
135 goto LBL_ERR; |
|
|
136 } |
|
|
137 } |
|
|
138 |
|
|
139 /* if not zero goto step 4 */ |
|
|
140 if (mp_iszero (&u) == 0) |
|
|
141 goto top; |
|
|
142 |
|
|
143 /* now a = C, b = D, gcd == g*v */ |
|
|
144 |
|
|
145 /* if v != 1 then there is no inverse */ |
|
|
146 if (mp_cmp_d (&v, 1) != MP_EQ) { |
|
|
147 res = MP_VAL; |
|
|
148 goto LBL_ERR; |
|
|
149 } |
|
|
150 |
|
|
151 /* if its too low */ |
|
|
152 while (mp_cmp_d(&C, 0) == MP_LT) { |
|
|
153 if ((res = mp_add(&C, b, &C)) != MP_OKAY) { |
|
|
154 goto LBL_ERR; |
|
|
155 } |
|
|
156 } |
|
|
157 |
|
|
158 /* too big */ |
|
|
159 while (mp_cmp_mag(&C, b) != MP_LT) { |
|
|
160 if ((res = mp_sub(&C, b, &C)) != MP_OKAY) { |
|
|
161 goto LBL_ERR; |
|
|
162 } |
|
|
163 } |
|
|
164 |
|
|
165 /* C is now the inverse */ |
|
|
166 mp_exch (&C, c); |
|
|
167 res = MP_OKAY; |
|
|
168 LBL_ERR:mp_clear_multi (&x, &y, &u, &v, &A, &B, &C, &D, NULL); |
|
|
169 return res; |
|
|
170 } |
|
|
171 #endif |
|
386
|
172 |
|
|
173 /* $Source: /cvs/libtom/libtommath/bn_mp_invmod_slow.c,v $ */ |
|
|
174 /* $Revision: 1.3 $ */ |
|
|
175 /* $Date: 2006/03/31 14:18:44 $ */ |
