Commit | Line | Data |
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0f3faccd | 1 | /* -*-c-*- |
2 | * | |
0f3faccd | 3 | * Raw formatting of elliptic curve points |
4 | * | |
5 | * (c) 2004 Straylight/Edgeware | |
6 | */ | |
7 | ||
45c0fd36 | 8 | /*----- Licensing notice --------------------------------------------------* |
0f3faccd | 9 | * |
10 | * This file is part of Catacomb. | |
11 | * | |
12 | * Catacomb is free software; you can redistribute it and/or modify | |
13 | * it under the terms of the GNU Library General Public License as | |
14 | * published by the Free Software Foundation; either version 2 of the | |
15 | * License, or (at your option) any later version. | |
45c0fd36 | 16 | * |
0f3faccd | 17 | * Catacomb is distributed in the hope that it will be useful, |
18 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
20 | * GNU Library General Public License for more details. | |
45c0fd36 | 21 | * |
0f3faccd | 22 | * You should have received a copy of the GNU Library General Public |
23 | * License along with Catacomb; if not, write to the Free | |
24 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, | |
25 | * MA 02111-1307, USA. | |
26 | */ | |
27 | ||
0f3faccd | 28 | /*----- Header files ------------------------------------------------------*/ |
29 | ||
30 | #include "ec.h" | |
31 | #include "ec-raw.h" | |
32 | ||
33 | /*----- Main code ---------------------------------------------------------*/ | |
34 | ||
6775a491 | 35 | /* --- @ec_ec2osp@ --- * |
0f3faccd | 36 | * |
37 | * Arguments: @ec_curve *c@ = elliptic curve | |
6775a491 | 38 | * @unsigned f@ = format flags for output |
0f3faccd | 39 | * @buf *b@ = pointer to a buffer |
40 | * @const ec *p@ = an elliptic curve point | |
41 | * | |
42 | * Returns: Zero on success, nonzero on failure. | |
43 | * | |
44 | * Use: Puts an elliptic curve point to the given buffer using the | |
6775a491 | 45 | * standard uncompressed format described in P1363 and SEC1. |
0f3faccd | 46 | * This requires at most @1 + 2 * c->f->noctets@ space in the |
6775a491 MW |
47 | * buffer. |
48 | * | |
49 | * Point compression features are determined by @f@ as follows. | |
50 | * If @EC_CMPR@ is set then point compression is performed and a | |
51 | * compressed form of the %$y$%-coordinate is contained in the | |
52 | * first output byte; if @EC_SORT@ is set then P1363a `SORT' | |
53 | * compression is used, otherwise LSB compression. If | |
54 | * @EC_EXPLY@ is set, then an explicit %$y$%-coordinate is | |
55 | * output in full. Otherwise the %$y$%-coordinate is | |
56 | * suppressed. | |
0f3faccd | 57 | */ |
58 | ||
6775a491 | 59 | int ec_ec2osp(ec_curve *c, unsigned f, buf *b, const ec *p) |
0f3faccd | 60 | { |
61 | octet *q; | |
62 | size_t n; | |
6775a491 MW |
63 | ec t = EC_INIT; |
64 | ||
65 | /* --- Point at infinity --- */ | |
0f3faccd | 66 | |
67 | if (EC_ATINF(p)) return (buf_putbyte(b, 0)); | |
6775a491 MW |
68 | |
69 | /* --- Fix up the format byte, compressing the %$y$%-coordinate --- */ | |
70 | ||
71 | if (!f) | |
72 | f = EC_XONLY; | |
73 | else if (f & EC_CMPR) { | |
74 | if (!(f & EC_SORT)) | |
75 | f |= EC_COMPR(c, p) ? EC_YBIT : 0; | |
76 | else { | |
77 | ec_neg(c, &t, p); | |
78 | f |= MP_CMP(p->y, >, t.y); | |
79 | EC_DESTROY(&t); | |
80 | } | |
81 | } | |
82 | ||
83 | /* --- Write the format byte --- */ | |
84 | ||
85 | if (buf_putbyte(b, f)) return (-1); | |
86 | ||
87 | /* --- Write the %$x$%-coordinate --- */ | |
88 | ||
0f3faccd | 89 | n = c->f->noctets; |
6775a491 | 90 | if ((q = buf_get(b, n)) == 0) return (-1); |
0f3faccd | 91 | mp_storeb(p->x, q, n); |
6775a491 MW |
92 | |
93 | /* --- Write the %$y$%-coordinate if we need one --- */ | |
94 | ||
95 | if (f & EC_EXPLY) { | |
96 | if ((q = buf_get(b, n)) == 0) return (-1); | |
97 | mp_storeb(p->y, q, n); | |
98 | } | |
99 | ||
100 | /* --- All done --- */ | |
101 | ||
0f3faccd | 102 | return (0); |
103 | } | |
104 | ||
6775a491 | 105 | /* --- @ec_os2ecp@ --- * |
0f3faccd | 106 | * |
6775a491 MW |
107 | * Arguments: @ec_curve *c = elliptic curve |
108 | * @unsigned f@ = format flags for input | |
0f3faccd | 109 | * @buf *b@ = pointer to a buffer |
110 | * @ec *d@ = an elliptic curve point | |
111 | * | |
112 | * Returns: Zero on success, nonzero on failure. | |
113 | * | |
114 | * Use: Reads an elliptic curve point from the given buffer using the | |
6775a491 MW |
115 | * standard uncompressed format described in P1363 and SEC1. |
116 | * | |
117 | * Point compression features are determined by @f@ as follows. | |
118 | * If @EC_LSB@ is set, then accept an LSB-compressed %$y$%- | |
119 | * coordinate; if @EC_SORT@ is set, then accept a SORT- | |
120 | * compressed %$y$%-coordinate; if @EC_EXPLY@ is set, then | |
121 | * accept an explicit %$y$%-coordinate; if @EC_XONLY@ is set | |
122 | * then accept a bare %$x$%-coordinate (a correct | |
123 | * %$y$%-coordinate is chosen arbitrarily). Hybrid forms are | |
124 | * acceptable, and the input is checked to verify that the | |
125 | * redundant representations are consistent. If no flags are | |
126 | * set in @f@, then no input (other than the point at infinity) | |
127 | * will be acceptable. | |
0f3faccd | 128 | */ |
129 | ||
6775a491 | 130 | int ec_os2ecp(ec_curve *c, unsigned f, buf *b, ec *d) |
0f3faccd | 131 | { |
132 | const octet *q; | |
133 | size_t n; | |
6775a491 MW |
134 | ec t = EC_INIT, tt = EC_INIT; |
135 | mp *x = MP_NEW, *y = MP_NEW; | |
136 | int g, gwant; | |
137 | int rc = -1; | |
138 | ||
139 | /* --- Read the format byte --- */ | |
140 | ||
141 | if ((g = buf_getbyte(b)) < 0) goto done; | |
142 | ||
143 | /* --- Point at infinity --- */ | |
144 | ||
145 | if (!g) { EC_SETINF(d); rc = 0; goto done; } | |
146 | ||
147 | /* --- Fetch the %$x$%-coordinate --- */ | |
0f3faccd | 148 | |
0f3faccd | 149 | n = c->f->noctets; |
6775a491 MW |
150 | if ((q = buf_get(b, n)) == 0) goto done; |
151 | x = mp_loadb(x, q, n); | |
152 | ||
153 | /* --- If we're compressing then figure out the right value --- * | |
154 | * | |
155 | * Also check that the format is acceptable to the caller. | |
156 | */ | |
157 | ||
158 | switch (g & ~EC_EXPLY) { | |
159 | case 0: | |
160 | t.x = x; x = MP_NEW; break; | |
161 | case EC_XONLY: | |
162 | gwant = EC_XONLY; goto decompr; | |
163 | case EC_CMPR: case EC_CMPR | EC_YBIT: | |
164 | gwant = EC_LSB; goto decompr; | |
165 | case EC_CMPR | EC_SORT: case EC_CMPR | EC_SORT | EC_YBIT: | |
166 | gwant = EC_SORT; goto decompr; | |
167 | default: goto done; | |
168 | decompr: | |
169 | if (!(f & gwant)) goto done; | |
170 | if (!ec_find(c, &t, x)) goto done; | |
171 | switch (gwant) { | |
172 | case EC_LSB: | |
173 | if (!EC_COMPR(c, &t) != !(g & EC_YBIT)) ec_neg(c, &t, &t); | |
174 | if (!EC_COMPR(c, &t) != !(g & EC_YBIT)) goto done; | |
175 | break; | |
176 | case EC_SORT: | |
177 | ec_neg(c, &tt, &t); | |
178 | if (!MP_CMP(t.y, >, tt.y) != !(g & EC_YBIT)) { | |
179 | if (MP_EQ(t.y, tt.y)) goto done; | |
180 | MP_DROP(t.y); t.y = MP_COPY(tt.y); | |
181 | } | |
182 | break; | |
183 | case EC_XONLY: | |
184 | break; | |
185 | default: | |
186 | abort(); | |
187 | } | |
188 | } | |
189 | ||
190 | /* --- If an explicit %$y$%-coordinate is specified, read it in --- */ | |
191 | ||
192 | if (g & EC_EXPLY) { | |
193 | if (!(f & EC_EXPLY)) goto done; | |
194 | if ((q = buf_get(b, n)) == 0) goto done; | |
195 | y = mp_loadb(y, q, n); | |
196 | if (!t.y) t.y = MP_COPY(y); | |
197 | else if (!MP_EQ(y, t.y)) goto done; | |
198 | } | |
199 | ||
200 | /* --- We're ready --- */ | |
201 | ||
202 | EC_COPY(d, &t); | |
203 | rc = 0; | |
204 | ||
205 | /* --- Clean up --- */ | |
206 | ||
207 | done: | |
208 | if (x) MP_DROP(x); | |
209 | if (y) MP_DROP(y); | |
210 | if (t.x) MP_DROP(t.x); if (t.y) MP_DROP(t.y); | |
211 | EC_DESTROY(&tt); | |
212 | return (rc); | |
0f3faccd | 213 | } |
214 | ||
6775a491 MW |
215 | /* --- @ec_putraw@ --- * |
216 | * | |
217 | * Arguments: @ec_curve *c@ = elliptic curve | |
218 | * @buf *b@ = pointer to a buffer | |
219 | * @const ec *p@ = an elliptic curve point | |
220 | * | |
221 | * Returns: Zero on success, nonzero on failure. | |
222 | * | |
223 | * Use: Puts an elliptic curve point to the given buffer using the | |
224 | * standard uncompressed format described in P1363 and SEC1. | |
225 | * This requires at most @1 + 2 * c->f->noctets@ space in the | |
226 | * buffer. We don't do point compression. | |
227 | */ | |
228 | ||
229 | int ec_putraw(ec_curve *c, buf *b, const ec *p) | |
230 | { return (ec_ec2osp(c, EC_EXPLY, b, p)); } | |
231 | ||
232 | /* --- @ec_getraw@ --- * | |
233 | * | |
234 | * Arguments: @ec_curve *c@ = elliptic curve | |
235 | * @buf *b@ = pointer to a buffer | |
236 | * @ec *d@ = an elliptic curve point | |
237 | * | |
238 | * Returns: Zero on success, nonzero on failure. | |
239 | * | |
240 | * Use: Reads an elliptic curve point from the given buffer using the | |
241 | * standard uncompressed format described in P1363 and SEC1. | |
242 | * We don't do point compression. | |
243 | */ | |
244 | ||
245 | int ec_getraw(ec_curve *c, buf *b, ec *d) | |
246 | { return (ec_os2ecp(c, EC_LSB | EC_SORT | EC_EXPLY, b, d)); } | |
247 | ||
0f3faccd | 248 | /*----- That's all, folks -------------------------------------------------*/ |