| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * $Id: oaep.c,v 1.6 2004/04/08 01:36:15 mdw Exp $ |
| 4 | * |
| 5 | * Optimal asymmetric encryption packing |
| 6 | * |
| 7 | * (c) 2000 Straylight/Edgeware |
| 8 | */ |
| 9 | |
| 10 | /*----- Licensing notice --------------------------------------------------* |
| 11 | * |
| 12 | * This file is part of Catacomb. |
| 13 | * |
| 14 | * Catacomb is free software; you can redistribute it and/or modify |
| 15 | * it under the terms of the GNU Library General Public License as |
| 16 | * published by the Free Software Foundation; either version 2 of the |
| 17 | * License, or (at your option) any later version. |
| 18 | * |
| 19 | * Catacomb is distributed in the hope that it will be useful, |
| 20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 22 | * GNU Library General Public License for more details. |
| 23 | * |
| 24 | * You should have received a copy of the GNU Library General Public |
| 25 | * License along with Catacomb; if not, write to the Free |
| 26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
| 27 | * MA 02111-1307, USA. |
| 28 | */ |
| 29 | |
| 30 | /*----- Header files ------------------------------------------------------*/ |
| 31 | |
| 32 | #include <string.h> |
| 33 | |
| 34 | #include <mLib/alloc.h> |
| 35 | #include <mLib/bits.h> |
| 36 | #include <mLib/dstr.h> |
| 37 | |
| 38 | #include "gcipher.h" |
| 39 | #include "ghash.h" |
| 40 | #include "grand.h" |
| 41 | #include "rsa.h" |
| 42 | |
| 43 | /*----- Main code ---------------------------------------------------------*/ |
| 44 | |
| 45 | /* --- @oaep_encode@ --- * |
| 46 | * |
| 47 | * Arguments: @mp *d@ = where to put the answer |
| 48 | * @const void *m@ = pointer to message data |
| 49 | * @size_t msz@ = size of message data |
| 50 | * @octet *b@ = spare buffer |
| 51 | * @size_t sz@ = size of the buffer (big enough) |
| 52 | * @unsigned long nbits@ = length of bits of @n@ |
| 53 | * @void *p@ = pointer to OAEP parameter block |
| 54 | * |
| 55 | * Returns: The encoded plaintext, or null on failure. |
| 56 | * |
| 57 | * Use: Implements the operation @EME-OAEP-ENCODE@, as defined in |
| 58 | * PKCS#1 v. 2.0 (RFC2437). |
| 59 | */ |
| 60 | |
| 61 | mp *oaep_encode(mp *d, const void *m, size_t msz, octet *b, size_t sz, |
| 62 | unsigned long nbits, void *p) |
| 63 | { |
| 64 | oaep *o = p; |
| 65 | size_t hsz = o->ch->hashsz; |
| 66 | ghash *h; |
| 67 | octet *q, *mq, *qq; |
| 68 | octet *pp; |
| 69 | gcipher *c; |
| 70 | size_t n; |
| 71 | |
| 72 | /* --- Ensure that everything is sensibly sized --- */ |
| 73 | |
| 74 | if (2 * hsz + 2 + msz > sz) |
| 75 | return (0); |
| 76 | |
| 77 | /* --- Make the `seed' value --- */ |
| 78 | |
| 79 | q = b; |
| 80 | *q++ = 0; sz--; |
| 81 | mq = q + hsz; |
| 82 | qq = q + sz; |
| 83 | GR_FILL(o->r, q, hsz); |
| 84 | |
| 85 | /* --- Fill in the rest of the buffer --- */ |
| 86 | |
| 87 | h = GH_INIT(o->ch); |
| 88 | GH_HASH(h, o->ep, o->epsz); |
| 89 | GH_DONE(h, mq); |
| 90 | GH_DESTROY(h); |
| 91 | pp = mq + hsz; |
| 92 | n = sz - 2 * hsz - msz - 1; |
| 93 | memset(pp, 0, n); |
| 94 | pp += n; |
| 95 | *pp++ = 1; |
| 96 | memcpy(pp, m, msz); |
| 97 | |
| 98 | /* --- Do the packing --- */ |
| 99 | |
| 100 | n = sz - hsz; |
| 101 | c = GC_INIT(o->cc, q, hsz); |
| 102 | GC_ENCRYPT(c, mq, mq, n); |
| 103 | GC_DESTROY(c); |
| 104 | |
| 105 | c = GC_INIT(o->cc, mq, n); |
| 106 | GC_ENCRYPT(c, q, q, hsz); |
| 107 | GC_DESTROY(c); |
| 108 | |
| 109 | /* --- Done --- */ |
| 110 | |
| 111 | return (mp_loadb(d, b, sz + 1)); |
| 112 | } |
| 113 | |
| 114 | /* --- @oaep_decode@ --- * |
| 115 | * |
| 116 | * Arguments: @mp *m@ = the decrypted message |
| 117 | * @octet *b@ = pointer to a buffer to work in |
| 118 | * @size_t sz@ = the size of the buffer (big enough) |
| 119 | * @unsigned long nbits@ = the number of bits in @n@ |
| 120 | * @void *p@ = pointer to OAEP parameter block |
| 121 | * |
| 122 | * Returns: The length of the output string if successful, negative on |
| 123 | * failure. |
| 124 | * |
| 125 | * Use: Implements the operation @EME-OAEP-DECODE@, as defined in |
| 126 | * PKCS#1 v. 2.0 (RFC2437). |
| 127 | */ |
| 128 | |
| 129 | static int memeq(const void *xx, const void *yy, size_t sz) |
| 130 | { |
| 131 | int eq = 1; |
| 132 | const octet *x = xx, *y = yy; |
| 133 | while (sz) { /* Always check every byte */ |
| 134 | if (*x++ != *y++) eq = 0; |
| 135 | sz--; |
| 136 | } |
| 137 | return (eq); |
| 138 | } |
| 139 | |
| 140 | int oaep_decode(mp *m, octet *b, size_t sz, unsigned long nbits, void *p) |
| 141 | { |
| 142 | oaep *o = p; |
| 143 | gcipher *c; |
| 144 | ghash *h; |
| 145 | octet *q, *mq, *qq; |
| 146 | octet *pp; |
| 147 | unsigned bad = 0; |
| 148 | size_t n; |
| 149 | size_t hsz = o->ch->hashsz; |
| 150 | |
| 151 | /* --- Ensure that the block is large enough --- */ |
| 152 | |
| 153 | if (sz < 2 * hsz) /* Doesn't depend on ciphertext */ |
| 154 | return (-1); |
| 155 | |
| 156 | /* --- Decrypt the message --- */ |
| 157 | |
| 158 | mp_storeb(m, b, sz); |
| 159 | q = b; |
| 160 | bad = *q; |
| 161 | q++; sz--; |
| 162 | mq = q + hsz; |
| 163 | qq = q + sz; |
| 164 | n = sz - hsz; |
| 165 | c = GC_INIT(o->cc, mq, n); |
| 166 | GC_DECRYPT(c, q, q, hsz); |
| 167 | GC_DESTROY(c); |
| 168 | |
| 169 | c = GC_INIT(o->cc, q, hsz); |
| 170 | GC_DECRYPT(c, mq, mq, n); |
| 171 | GC_DESTROY(c); |
| 172 | q--; |
| 173 | |
| 174 | /* --- Check the hash on the encoding parameters --- */ |
| 175 | |
| 176 | h = GH_INIT(o->ch); |
| 177 | GH_HASH(h, o->ep, o->epsz); |
| 178 | GH_DONE(h, q); |
| 179 | GH_DESTROY(h); |
| 180 | bad |= !memeq(q, mq, hsz); |
| 181 | |
| 182 | /* --- Now find the start of the actual message --- */ |
| 183 | |
| 184 | pp = mq + hsz; |
| 185 | while (*pp == 0 && pp < qq) |
| 186 | pp++; |
| 187 | bad |= (pp >= qq) | (*pp++ != 1); |
| 188 | n = qq - pp; |
| 189 | memmove(q, pp, n); |
| 190 | return (bad ? -1 : n); |
| 191 | } |
| 192 | |
| 193 | /*----- That's all, folks -------------------------------------------------*/ |