3 * $Id: oaep.c,v 1.6 2004/04/08 01:36:15 mdw Exp $
5 * Optimal asymmetric encryption packing
7 * (c) 2000 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of Catacomb.
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.
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.
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,
30 /*----- Header files ------------------------------------------------------*/
34 #include <mLib/alloc.h>
35 #include <mLib/bits.h>
36 #include <mLib/dstr.h>
43 /*----- Main code ---------------------------------------------------------*/
45 /* --- @oaep_encode@ --- *
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
55 * Returns: The encoded plaintext, or null on failure.
57 * Use: Implements the operation @EME-OAEP-ENCODE@, as defined in
58 * PKCS#1 v. 2.0 (RFC2437).
61 mp *oaep_encode(mp *d, const void *m, size_t msz, octet *b, size_t sz,
62 unsigned long nbits, void *p)
65 size_t hsz = o->ch->hashsz;
72 /* --- Ensure that everything is sensibly sized --- */
74 if (2 * hsz + 2 + msz > sz)
77 /* --- Make the `seed' value --- */
83 GR_FILL(o->r, q, hsz);
85 /* --- Fill in the rest of the buffer --- */
88 GH_HASH(h, o->ep, o->epsz);
92 n = sz - 2 * hsz - msz - 1;
98 /* --- Do the packing --- */
101 c = GC_INIT(o->cc, q, hsz);
102 GC_ENCRYPT(c, mq, mq, n);
105 c = GC_INIT(o->cc, mq, n);
106 GC_ENCRYPT(c, q, q, hsz);
111 return (mp_loadb(d, b, sz + 1));
114 /* --- @oaep_decode@ --- *
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
122 * Returns: The length of the output string if successful, negative on
125 * Use: Implements the operation @EME-OAEP-DECODE@, as defined in
126 * PKCS#1 v. 2.0 (RFC2437).
129 static int memeq(const void *xx, const void *yy, size_t sz)
132 const octet *x = xx, *y = yy;
133 while (sz) { /* Always check every byte */
134 if (*x++ != *y++) eq = 0;
140 int oaep_decode(mp *m, octet *b, size_t sz, unsigned long nbits, void *p)
149 size_t hsz = o->ch->hashsz;
151 /* --- Ensure that the block is large enough --- */
153 if (sz < 2 * hsz) /* Doesn't depend on ciphertext */
156 /* --- Decrypt the message --- */
165 c = GC_INIT(o->cc, mq, n);
166 GC_DECRYPT(c, q, q, hsz);
169 c = GC_INIT(o->cc, q, hsz);
170 GC_DECRYPT(c, mq, mq, n);
174 /* --- Check the hash on the encoding parameters --- */
177 GH_HASH(h, o->ep, o->epsz);
180 bad |= !memeq(q, mq, hsz);
182 /* --- Now find the start of the actual message --- */
185 while (*pp == 0 && pp < qq)
187 bad |= (pp >= qq) | (*pp++ != 1);
190 return (bad ? -1 : n);
193 /*----- That's all, folks -------------------------------------------------*/