3 * Raw formatting of elliptic curve points
5 * (c) 2004 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of Catacomb.
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.
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.
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,
28 /*----- Header files ------------------------------------------------------*/
33 /*----- Main code ---------------------------------------------------------*/
35 /* --- @ec_ec2osp@ --- *
37 * Arguments: @ec_curve *c@ = elliptic curve
38 * @unsigned f@ = format flags for output
39 * @buf *b@ = pointer to a buffer
40 * @const ec *p@ = an elliptic curve point
42 * Returns: Zero on success, nonzero on failure.
44 * Use: Puts an elliptic curve point to the given buffer using the
45 * standard uncompressed format described in P1363 and SEC1.
46 * This requires at most @1 + 2 * c->f->noctets@ space in the
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
59 int ec_ec2osp(ec_curve *c, unsigned f, buf *b, const ec *p)
65 /* --- Point at infinity --- */
67 if (EC_ATINF(p)) return (buf_putbyte(b, 0));
69 /* --- Fix up the format byte, compressing the %$y$%-coordinate --- */
73 else if (f & EC_CMPR) {
75 f |= EC_COMPR(c, p) ? EC_YBIT : 0;
78 f |= MP_CMP(p->y, >, t.y);
83 /* --- Write the format byte --- */
85 if (buf_putbyte(b, f)) return (-1);
87 /* --- Write the %$x$%-coordinate --- */
90 if ((q = buf_get(b, n)) == 0) return (-1);
91 mp_storeb(p->x, q, n);
93 /* --- Write the %$y$%-coordinate if we need one --- */
96 if ((q = buf_get(b, n)) == 0) return (-1);
97 mp_storeb(p->y, q, n);
100 /* --- All done --- */
105 /* --- @ec_os2ecp@ --- *
107 * Arguments: @ec_curve *c = elliptic curve
108 * @unsigned f@ = format flags for input
109 * @buf *b@ = pointer to a buffer
110 * @ec *d@ = an elliptic curve point
112 * Returns: Zero on success, nonzero on failure.
114 * Use: Reads an elliptic curve point from the given buffer using the
115 * standard uncompressed format described in P1363 and SEC1.
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.
130 int ec_os2ecp(ec_curve *c, unsigned f, buf *b, ec *d)
134 ec t = EC_INIT, tt = EC_INIT;
135 mp *x = MP_NEW, *y = MP_NEW;
139 /* --- Read the format byte --- */
141 if ((g = buf_getbyte(b)) < 0) goto done;
143 /* --- Point at infinity --- */
145 if (!g) { EC_SETINF(d); rc = 0; goto done; }
147 /* --- Fetch the %$x$%-coordinate --- */
150 if ((q = buf_get(b, n)) == 0) goto done;
151 x = mp_loadb(x, q, n);
153 /* --- If we're compressing then figure out the right value --- *
155 * Also check that the format is acceptable to the caller.
158 switch (g & ~EC_EXPLY) {
160 t.x = x; x = MP_NEW; break;
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;
169 if (!(f & gwant)) goto done;
170 if (!ec_find(c, &t, x)) goto done;
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;
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);
190 /* --- If an explicit %$y$%-coordinate is specified, read it in --- */
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;
200 /* --- We're ready --- */
205 /* --- Clean up --- */
210 if (t.x) MP_DROP(t.x); if (t.y) MP_DROP(t.y);
215 /* --- @ec_putraw@ --- *
217 * Arguments: @ec_curve *c@ = elliptic curve
218 * @buf *b@ = pointer to a buffer
219 * @const ec *p@ = an elliptic curve point
221 * Returns: Zero on success, nonzero on failure.
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.
229 int ec_putraw(ec_curve *c, buf *b, const ec *p)
230 { return (ec_ec2osp(c, EC_EXPLY, b, p)); }
232 /* --- @ec_getraw@ --- *
234 * Arguments: @ec_curve *c@ = elliptic curve
235 * @buf *b@ = pointer to a buffer
236 * @ec *d@ = an elliptic curve point
238 * Returns: Zero on success, nonzero on failure.
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.
245 int ec_getraw(ec_curve *c, buf *b, ec *d)
246 { return (ec_os2ecp(c, EC_LSB | EC_SORT | EC_EXPLY, b, d)); }
248 /*----- That's all, folks -------------------------------------------------*/