| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * Raw formatting of elliptic curve points |
| 4 | * |
| 5 | * (c) 2004 Straylight/Edgeware |
| 6 | */ |
| 7 | |
| 8 | /*----- Licensing notice --------------------------------------------------* |
| 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. |
| 16 | * |
| 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. |
| 21 | * |
| 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 | |
| 28 | /*----- Header files ------------------------------------------------------*/ |
| 29 | |
| 30 | #include "ec.h" |
| 31 | #include "ec-raw.h" |
| 32 | |
| 33 | /*----- Main code ---------------------------------------------------------*/ |
| 34 | |
| 35 | /* --- @ec_ec2osp@ --- * |
| 36 | * |
| 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 |
| 41 | * |
| 42 | * Returns: Zero on success, nonzero on failure. |
| 43 | * |
| 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 |
| 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. |
| 57 | * |
| 58 | * Returns failure (@-1@) if the flags are invalid, or if there |
| 59 | * isn't enough space in the output buffer. |
| 60 | */ |
| 61 | |
| 62 | int ec_ec2osp(ec_curve *c, unsigned f, buf *b, const ec *p) |
| 63 | { |
| 64 | octet *q; |
| 65 | size_t n; |
| 66 | ec t = EC_INIT; |
| 67 | |
| 68 | /* --- Check the requested flags for sanity --- */ |
| 69 | |
| 70 | if (!f) f = EC_XONLY; |
| 71 | if (f & ~((f & EC_XONLY) ? EC_XONLY : |
| 72 | (f & EC_CMPR) ? (EC_CMPR | EC_EXPLY | EC_SORT) : |
| 73 | (f & EC_EXPLY) ? EC_EXPLY : |
| 74 | 0u)) |
| 75 | return (-1); |
| 76 | |
| 77 | /* --- Point at infinity --- */ |
| 78 | |
| 79 | if (EC_ATINF(p)) return (buf_putbyte(b, 0)); |
| 80 | |
| 81 | /* --- Fix up the format byte, compressing the %$y$%-coordinate --- */ |
| 82 | |
| 83 | if (f & EC_CMPR) { |
| 84 | if (!(f & EC_SORT)) |
| 85 | f |= EC_COMPR(c, p) ? EC_YBIT : 0; |
| 86 | else { |
| 87 | ec_neg(c, &t, p); |
| 88 | f |= MP_CMP(p->y, >, t.y); |
| 89 | EC_DESTROY(&t); |
| 90 | } |
| 91 | } |
| 92 | |
| 93 | /* --- Write the format byte --- */ |
| 94 | |
| 95 | if (buf_putbyte(b, f)) return (-1); |
| 96 | |
| 97 | /* --- Write the %$x$%-coordinate --- */ |
| 98 | |
| 99 | n = c->f->noctets; |
| 100 | if ((q = buf_get(b, n)) == 0) return (-1); |
| 101 | mp_storeb(p->x, q, n); |
| 102 | |
| 103 | /* --- Write the %$y$%-coordinate if we need one --- */ |
| 104 | |
| 105 | if (f & EC_EXPLY) { |
| 106 | if ((q = buf_get(b, n)) == 0) return (-1); |
| 107 | mp_storeb(p->y, q, n); |
| 108 | } |
| 109 | |
| 110 | /* --- All done --- */ |
| 111 | |
| 112 | return (0); |
| 113 | } |
| 114 | |
| 115 | /* --- @ec_os2ecp@ --- * |
| 116 | * |
| 117 | * Arguments: @ec_curve *c = elliptic curve |
| 118 | * @unsigned f@ = format flags for input |
| 119 | * @buf *b@ = pointer to a buffer |
| 120 | * @ec *d@ = an elliptic curve point |
| 121 | * |
| 122 | * Returns: Zero on success, nonzero on failure. |
| 123 | * |
| 124 | * Use: Reads an elliptic curve point from the given buffer using the |
| 125 | * standard uncompressed format described in P1363 and SEC1. |
| 126 | * |
| 127 | * Point compression features are determined by @f@ as follows. |
| 128 | * If @EC_LSB@ is set, then accept an LSB-compressed %$y$%- |
| 129 | * coordinate; if @EC_SORT@ is set, then accept a SORT- |
| 130 | * compressed %$y$%-coordinate; if @EC_EXPLY@ is set, then |
| 131 | * accept an explicit %$y$%-coordinate; if @EC_XONLY@ is set |
| 132 | * then accept a bare %$x$%-coordinate (a correct |
| 133 | * %$y$%-coordinate is chosen arbitrarily). Hybrid forms are |
| 134 | * acceptable, and the input is checked to verify that the |
| 135 | * redundant representations are consistent. If no flags are |
| 136 | * set in @f@, then no input (other than the point at infinity) |
| 137 | * will be acceptable. |
| 138 | */ |
| 139 | |
| 140 | int ec_os2ecp(ec_curve *c, unsigned f, buf *b, ec *d) |
| 141 | { |
| 142 | const octet *q; |
| 143 | size_t n; |
| 144 | ec t = EC_INIT, tt = EC_INIT; |
| 145 | mp *x = MP_NEW, *y = MP_NEW; |
| 146 | int g, gwant; |
| 147 | int rc = -1; |
| 148 | |
| 149 | /* --- Read the format byte --- */ |
| 150 | |
| 151 | if ((g = buf_getbyte(b)) < 0) goto done; |
| 152 | |
| 153 | /* --- Point at infinity --- */ |
| 154 | |
| 155 | if (!g) { EC_SETINF(d); rc = 0; goto done; } |
| 156 | |
| 157 | /* --- Fetch the %$x$%-coordinate --- */ |
| 158 | |
| 159 | n = c->f->noctets; |
| 160 | if ((q = buf_get(b, n)) == 0) goto done; |
| 161 | x = mp_loadb(x, q, n); |
| 162 | |
| 163 | /* --- If we're compressing then figure out the right value --- * |
| 164 | * |
| 165 | * Also check that the format is acceptable to the caller. |
| 166 | */ |
| 167 | |
| 168 | switch (g & ~EC_EXPLY) { |
| 169 | case 0: |
| 170 | t.x = x; x = MP_NEW; break; |
| 171 | case EC_XONLY: |
| 172 | gwant = EC_XONLY; goto decompr; |
| 173 | case EC_CMPR: case EC_CMPR | EC_YBIT: |
| 174 | gwant = EC_LSB; goto decompr; |
| 175 | case EC_CMPR | EC_SORT: case EC_CMPR | EC_SORT | EC_YBIT: |
| 176 | gwant = EC_SORT; goto decompr; |
| 177 | default: goto done; |
| 178 | decompr: |
| 179 | if (!(f & gwant)) goto done; |
| 180 | if (!ec_find(c, &t, x)) goto done; |
| 181 | switch (gwant) { |
| 182 | case EC_LSB: |
| 183 | if (!EC_COMPR(c, &t) != !(g & EC_YBIT)) ec_neg(c, &t, &t); |
| 184 | if (!EC_COMPR(c, &t) != !(g & EC_YBIT)) goto done; |
| 185 | break; |
| 186 | case EC_SORT: |
| 187 | ec_neg(c, &tt, &t); |
| 188 | if (!MP_CMP(t.y, >, tt.y) != !(g & EC_YBIT)) { |
| 189 | if (MP_EQ(t.y, tt.y)) goto done; |
| 190 | MP_DROP(t.y); t.y = MP_COPY(tt.y); |
| 191 | } |
| 192 | break; |
| 193 | case EC_XONLY: |
| 194 | break; |
| 195 | default: |
| 196 | abort(); |
| 197 | } |
| 198 | } |
| 199 | |
| 200 | /* --- If an explicit %$y$%-coordinate is specified, read it in --- */ |
| 201 | |
| 202 | if (g & EC_EXPLY) { |
| 203 | if (!(f & EC_EXPLY)) goto done; |
| 204 | if ((q = buf_get(b, n)) == 0) goto done; |
| 205 | y = mp_loadb(y, q, n); |
| 206 | if (!t.y) t.y = MP_COPY(y); |
| 207 | else if (!MP_EQ(y, t.y)) goto done; |
| 208 | } |
| 209 | |
| 210 | /* --- We're ready --- */ |
| 211 | |
| 212 | EC_COPY(d, &t); |
| 213 | rc = 0; |
| 214 | |
| 215 | /* --- Clean up --- */ |
| 216 | |
| 217 | done: |
| 218 | if (x) MP_DROP(x); |
| 219 | if (y) MP_DROP(y); |
| 220 | if (t.x) MP_DROP(t.x); if (t.y) MP_DROP(t.y); |
| 221 | EC_DESTROY(&tt); |
| 222 | return (rc); |
| 223 | } |
| 224 | |
| 225 | /* --- @ec_putraw@ --- * |
| 226 | * |
| 227 | * Arguments: @ec_curve *c@ = elliptic curve |
| 228 | * @buf *b@ = pointer to a buffer |
| 229 | * @const ec *p@ = an elliptic curve point |
| 230 | * |
| 231 | * Returns: Zero on success, nonzero on failure. |
| 232 | * |
| 233 | * Use: Puts an elliptic curve point to the given buffer using the |
| 234 | * standard uncompressed format described in P1363 and SEC1. |
| 235 | * This requires at most @1 + 2 * c->f->noctets@ space in the |
| 236 | * buffer. We don't do point compression. |
| 237 | */ |
| 238 | |
| 239 | int ec_putraw(ec_curve *c, buf *b, const ec *p) |
| 240 | { return (ec_ec2osp(c, EC_EXPLY, b, p)); } |
| 241 | |
| 242 | /* --- @ec_getraw@ --- * |
| 243 | * |
| 244 | * Arguments: @ec_curve *c@ = elliptic curve |
| 245 | * @buf *b@ = pointer to a buffer |
| 246 | * @ec *d@ = an elliptic curve point |
| 247 | * |
| 248 | * Returns: Zero on success, nonzero on failure. |
| 249 | * |
| 250 | * Use: Reads an elliptic curve point from the given buffer using the |
| 251 | * standard uncompressed format described in P1363 and SEC1. |
| 252 | * We don't do point compression. |
| 253 | */ |
| 254 | |
| 255 | int ec_getraw(ec_curve *c, buf *b, ec *d) |
| 256 | { return (ec_os2ecp(c, EC_LSB | EC_SORT | EC_EXPLY, b, d)); } |
| 257 | |
| 258 | /*----- That's all, folks -------------------------------------------------*/ |