1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
|
package org.bouncycastle.math.ec.custom.djb;
import java.math.BigInteger;
import org.bouncycastle.math.ec.Nat;
import org.bouncycastle.math.ec.custom.sec.Nat256;
public class Curve25519Field
{
private static final long M = 0xFFFFFFFFL;
// 2^255 - 2^4 - 2^1 - 1
static final int[] P = new int[]{ 0xFFFFFFED, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF,
0xFFFFFFFF, 0x7FFFFFFF };
private static final int P7 = 0x7FFFFFFF;
private static final int[] PExt = new int[]{ 0x00000169, 0x00000000, 0x00000000, 0x00000000, 0x00000000,
0x00000000, 0x00000000, 0x00000000, 0xFFFFFFED, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF,
0xFFFFFFFF, 0x3FFFFFFF };
private static final int PInv = 0x13;
public static void add(int[] x, int[] y, int[] z)
{
Nat256.add(x, y, z);
if (Nat256.gte(z, P))
{
subPFrom(z);
}
}
public static void addExt(int[] xx, int[] yy, int[] zz)
{
Nat.add(16, xx, yy, zz);
if (Nat.gte(16, zz, PExt))
{
subPExtFrom(zz);
}
}
public static void addOne(int[] x, int[] z)
{
Nat.inc(8, x, z);
if (Nat256.gte(z, P))
{
subPFrom(z);
}
}
public static int[] fromBigInteger(BigInteger x)
{
int[] z = Nat256.fromBigInteger(x);
while (Nat256.gte(z, P))
{
Nat256.subFrom(P, z);
}
return z;
}
public static void half(int[] x, int[] z)
{
if ((x[0] & 1) == 0)
{
Nat.shiftDownBit(8, x, 0, z);
}
else
{
Nat256.add(x, P, z);
Nat.shiftDownBit(8, z, 0);
}
}
public static void multiply(int[] x, int[] y, int[] z)
{
int[] tt = Nat256.createExt();
Nat256.mul(x, y, tt);
reduce(tt, z);
}
public static void multiplyAddToExt(int[] x, int[] y, int[] zz)
{
Nat256.mulAddTo(x, y, zz);
if (Nat.gte(16, zz, PExt))
{
subPExtFrom(zz);
}
}
public static void negate(int[] x, int[] z)
{
if (Nat256.isZero(x))
{
Nat256.zero(z);
}
else
{
Nat256.sub(P, x, z);
}
}
public static void reduce(int[] xx, int[] z)
{
// assert xx[15] >>> 30 == 0;
int xx07 = xx[7];
Nat.shiftUpBit(8, xx, 8, xx07, z, 0);
int c = Nat256.mulByWordAddTo(PInv, xx, z) << 1;
int z7 = z[7];
c += (z7 >>> 31) - (xx07 >>> 31);
z7 &= P7;
z7 += Nat.addWordTo(7, c * PInv, z);
z[7] = z7;
if (Nat256.gte(z, P))
{
subPFrom(z);
}
}
public static void reduce27(int x, int[] z)
{
// assert x >>> 26 == 0;
int z7 = z[7];
int c = (x << 1 | z7 >>> 31);
z7 &= P7;
z7 += Nat.addWordTo(7, c * PInv, z);
z[7] = z7;
if (Nat256.gte(z, P))
{
subPFrom(z);
}
}
public static void square(int[] x, int[] z)
{
int[] tt = Nat256.createExt();
Nat256.square(x, tt);
reduce(tt, z);
}
public static void squareN(int[] x, int n, int[] z)
{
// assert n > 0;
int[] tt = Nat256.createExt();
Nat256.square(x, tt);
reduce(tt, z);
while (--n > 0)
{
Nat256.square(z, tt);
reduce(tt, z);
}
}
public static void subtract(int[] x, int[] y, int[] z)
{
int c = Nat256.sub(x, y, z);
if (c != 0)
{
addPTo(z);
}
}
public static void subtractExt(int[] xx, int[] yy, int[] zz)
{
int c = Nat.sub(16, xx, yy, zz);
if (c != 0)
{
addPExtTo(zz);
}
}
public static void twice(int[] x, int[] z)
{
Nat.shiftUpBit(8, x, 0, z);
if (Nat256.gte(z, P))
{
subPFrom(z);
}
}
private static int addPTo(int[] z)
{
long c = (z[0] & M) - PInv;
z[0] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.decAt(7, z, 1);
}
c += (z[7] & M) + ((P7 + 1) & M);
z[7] = (int)c;
c >>= 32;
return (int)c;
}
private static int addPExtTo(int[] zz)
{
long c = (zz[0] & M) + (PExt[0] & M);
zz[0] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.incAt(8, zz, 1);
}
c += (zz[8] & M) - PInv;
zz[8] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.decAt(15, zz, 9);
}
c += (zz[15] & M) + ((PExt[15] + 1) & M);
zz[15] = (int)c;
c >>= 32;
return (int)c;
}
private static int subPFrom(int[] z)
{
long c = (z[0] & M) + PInv;
z[0] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.incAt(7, z, 1);
}
c += (z[7] & M) - ((P7 + 1) & M);
z[7] = (int)c;
c >>= 32;
return (int)c;
}
private static int subPExtFrom(int[] zz)
{
long c = (zz[0] & M) - (PExt[0] & M);
zz[0] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.decAt(8, zz, 1);
}
c += (zz[8] & M) + PInv;
zz[8] = (int)c;
c >>= 32;
if (c != 0)
{
c = Nat.incAt(15, zz, 9);
}
c += (zz[15] & M) - ((PExt[15] + 1) & M);
zz[15] = (int)c;
c >>= 32;
return (int)c;
}
}
|
