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 dsa_decrypt_key.c
15  DSA Crypto, Tom St Denis
16*/
17
18#ifdef MDSA
19
20/**
21  Decrypt an DSA encrypted key
22  @param in       The ciphertext
23  @param inlen    The length of the ciphertext (octets)
24  @param out      [out] The plaintext
25  @param outlen   [in/out] The max size and resulting size of the plaintext
26  @param key      The corresponding private DSA key
27  @return CRYPT_OK if successful
28*/
29int dsa_decrypt_key(const unsigned char *in,  unsigned long  inlen,
30                          unsigned char *out, unsigned long *outlen,
31                          dsa_key *key)
32{
33   unsigned char  *skey, *expt;
34   void           *g_pub;
35   unsigned long  x, y, hashOID[32];
36   int            hash, err;
37   ltc_asn1_list  decode[3];
38
39   LTC_ARGCHK(in     != NULL);
40   LTC_ARGCHK(out    != NULL);
41   LTC_ARGCHK(outlen != NULL);
42   LTC_ARGCHK(key    != NULL);
43
44   /* right key type? */
45   if (key->type != PK_PRIVATE) {
46      return CRYPT_PK_NOT_PRIVATE;
47   }
48
49   /* decode to find out hash */
50   LTC_SET_ASN1(decode, 0, LTC_ASN1_OBJECT_IDENTIFIER, hashOID, sizeof(hashOID)/sizeof(hashOID[0]));
51
52   if ((err = der_decode_sequence(in, inlen, decode, 1)) != CRYPT_OK) {
53      return err;
54   }
55
56   hash = find_hash_oid(hashOID, decode[0].size);
57   if (hash_is_valid(hash) != CRYPT_OK) {
58      return CRYPT_INVALID_PACKET;
59   }
60
61   /* we now have the hash! */
62
63   if ((err = mp_init(&g_pub)) != CRYPT_OK) {
64      return err;
65   }
66
67   /* allocate memory */
68   expt   = XMALLOC(mp_unsigned_bin_size(key->p) + 1);
69   skey   = XMALLOC(MAXBLOCKSIZE);
70   if (expt == NULL || skey == NULL) {
71      if (expt != NULL) {
72         XFREE(expt);
73      }
74      if (skey != NULL) {
75         XFREE(skey);
76      }
77      mp_clear(g_pub);
78      return CRYPT_MEM;
79   }
80
81   LTC_SET_ASN1(decode, 1, LTC_ASN1_INTEGER,          g_pub,      1UL);
82   LTC_SET_ASN1(decode, 2, LTC_ASN1_OCTET_STRING,      skey,      MAXBLOCKSIZE);
83
84   /* read the structure in now */
85   if ((err = der_decode_sequence(in, inlen, decode, 3)) != CRYPT_OK) {
86      goto LBL_ERR;
87   }
88
89   /* make shared key */
90   x = mp_unsigned_bin_size(key->p) + 1;
91   if ((err = dsa_shared_secret(key->x, g_pub, key, expt, &x)) != CRYPT_OK) {
92      goto LBL_ERR;
93   }
94
95   y = MIN(mp_unsigned_bin_size(key->p) + 1, MAXBLOCKSIZE);
96   if ((err = hash_memory(hash, expt, x, expt, &y)) != CRYPT_OK) {
97      goto LBL_ERR;
98   }
99
100   /* ensure the hash of the shared secret is at least as big as the encrypt itself */
101   if (decode[2].size > y) {
102      err = CRYPT_INVALID_PACKET;
103      goto LBL_ERR;
104   }
105
106   /* avoid buffer overflow */
107   if (*outlen < decode[2].size) {
108      *outlen = decode[2].size;
109      err = CRYPT_BUFFER_OVERFLOW;
110      goto LBL_ERR;
111   }
112
113   /* Decrypt the key */
114   for (x = 0; x < decode[2].size; x++) {
115     out[x] = expt[x] ^ skey[x];
116   }
117   *outlen = x;
118
119   err = CRYPT_OK;
120LBL_ERR:
121#ifdef LTC_CLEAN_STACK
122   zeromem(expt,   mp_unsigned_bin_size(key->p) + 1);
123   zeromem(skey,   MAXBLOCKSIZE);
124#endif
125
126   XFREE(expt);
127   XFREE(skey);
128
129   mp_clear(g_pub);
130
131   return err;
132}
133
134#endif
135
136/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_decrypt_key.c,v $ */
137/* $Revision: 1.9 $ */
138/* $Date: 2006/12/04 03:18:43 $ */
139
140