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comparison libtomcrypt/src/pk/dsa/dsa_decrypt_key.c @ 382:0cbe8f6dbf9e

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propagate from branch 'au.asn.ucc.matt.ltc.dropbear' (head 2af22fb4e878750b88f80f90d439b316d229796f) to branch 'au.asn.ucc.matt.dropbear' (head 02c413252c90e9de8e03d91e9939dde3029f5c0a)
author Matt Johnston <matt@ucc.asn.au>
date Thu, 11 Jan 2007 02:41:05 +0000
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children f849a5ca2efc
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379:b66a00272a90 382:0cbe8f6dbf9e
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, [email protected], 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 */
29 int 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;
120 LBL_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