1/* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 *
9 * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
10 */
11#include "tomcrypt.h"
12
13/**
14  @file pkcs_1_oaep_encode.c
15  OAEP Padding for PKCS #1, Tom St Denis
16*/
17
18#ifdef PKCS_1
19
20/**
21  PKCS #1 v2.00 OAEP encode
22  @param msg             The data to encode
23  @param msglen          The length of the data to encode (octets)
24  @param lparam          A session or system parameter (can be NULL)
25  @param lparamlen       The length of the lparam data
26  @param modulus_bitlen  The bit length of the RSA modulus
27  @param prng            An active PRNG state
28  @param prng_idx        The index of the PRNG desired
29  @param hash_idx        The index of the hash desired
30  @param out             [out] The destination for the encoded data
31  @param outlen          [in/out] The max size and resulting size of the encoded data
32  @return CRYPT_OK if successful
33*/
34int pkcs_1_oaep_encode(const unsigned char *msg,    unsigned long msglen,
35                       const unsigned char *lparam, unsigned long lparamlen,
36                             unsigned long modulus_bitlen, prng_state *prng,
37                             int           prng_idx,         int  hash_idx,
38                             unsigned char *out,    unsigned long *outlen)
39{
40   unsigned char *DB, *seed, *mask;
41   unsigned long hLen, x, y, modulus_len;
42   int           err;
43
44   LTC_ARGCHK(msg    != NULL);
45   LTC_ARGCHK(out    != NULL);
46   LTC_ARGCHK(outlen != NULL);
47
48   /* test valid hash */
49   if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
50      return err;
51   }
52
53   /* valid prng */
54   if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {
55      return err;
56   }
57
58   hLen        = hash_descriptor[hash_idx].hashsize;
59   modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
60
61   /* test message size */
62   if ((2*hLen >= (modulus_len - 2)) || (msglen > (modulus_len - 2*hLen - 2))) {
63      return CRYPT_PK_INVALID_SIZE;
64   }
65
66   /* allocate ram for DB/mask/salt of size modulus_len */
67   DB   = XMALLOC(modulus_len);
68   mask = XMALLOC(modulus_len);
69   seed = XMALLOC(hLen);
70   if (DB == NULL || mask == NULL || seed == NULL) {
71      if (DB != NULL) {
72         XFREE(DB);
73      }
74      if (mask != NULL) {
75         XFREE(mask);
76      }
77      if (seed != NULL) {
78         XFREE(seed);
79      }
80      return CRYPT_MEM;
81   }
82
83   /* get lhash */
84   /* DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */
85   x = modulus_len;
86   if (lparam != NULL) {
87      if ((err = hash_memory(hash_idx, lparam, lparamlen, DB, &x)) != CRYPT_OK) {
88         goto LBL_ERR;
89      }
90   } else {
91      /* can't pass hash_memory a NULL so use DB with zero length */
92      if ((err = hash_memory(hash_idx, DB, 0, DB, &x)) != CRYPT_OK) {
93         goto LBL_ERR;
94      }
95   }
96
97   /* append PS then 0x01 (to lhash)  */
98   x = hLen;
99   y = modulus_len - msglen - 2*hLen - 2;
100   XMEMSET(DB+x, 0, y);
101   x += y;
102
103   /* 0x01 byte */
104   DB[x++] = 0x01;
105
106   /* message (length = msglen) */
107   XMEMCPY(DB+x, msg, msglen);
108   x += msglen;
109
110   /* now choose a random seed */
111   if (prng_descriptor[prng_idx].read(seed, hLen, prng) != hLen) {
112      err = CRYPT_ERROR_READPRNG;
113      goto LBL_ERR;
114   }
115
116   /* compute MGF1 of seed (k - hlen - 1) */
117   if ((err = pkcs_1_mgf1(hash_idx, seed, hLen, mask, modulus_len - hLen - 1)) != CRYPT_OK) {
118      goto LBL_ERR;
119   }
120
121   /* xor against DB */
122   for (y = 0; y < (modulus_len - hLen - 1); y++) {
123       DB[y] ^= mask[y];
124   }
125
126   /* compute MGF1 of maskedDB (hLen) */
127   if ((err = pkcs_1_mgf1(hash_idx, DB, modulus_len - hLen - 1, mask, hLen)) != CRYPT_OK) {
128      goto LBL_ERR;
129   }
130
131   /* XOR against seed */
132   for (y = 0; y < hLen; y++) {
133      seed[y] ^= mask[y];
134   }
135
136   /* create string of length modulus_len */
137   if (*outlen < modulus_len) {
138      *outlen = modulus_len;
139      err = CRYPT_BUFFER_OVERFLOW;
140      goto LBL_ERR;
141   }
142
143   /* start output which is 0x00 || maskedSeed || maskedDB */
144   x = 0;
145   out[x++] = 0x00;
146   XMEMCPY(out+x, seed, hLen);
147   x += hLen;
148   XMEMCPY(out+x, DB, modulus_len - hLen - 1);
149   x += modulus_len - hLen - 1;
150
151   *outlen = x;
152
153   err = CRYPT_OK;
154LBL_ERR:
155#ifdef LTC_CLEAN_STACK
156   zeromem(DB,   modulus_len);
157   zeromem(seed, hLen);
158   zeromem(mask, modulus_len);
159#endif
160
161   XFREE(seed);
162   XFREE(mask);
163   XFREE(DB);
164
165   return err;
166}
167
168#endif /* PKCS_1 */
169
170
171/* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_oaep_encode.c,v $ */
172/* $Revision: 1.7 $ */
173/* $Date: 2006/06/16 21:53:41 $ */
174