1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis */
2 /* SPDX-License-Identifier: Unlicense */
3 #include "tomcrypt_private.h"
4
5 /**
6 @file dsa_decrypt_key.c
7 DSA Crypto, Tom St Denis
8 */
9
10 #ifdef LTC_MDSA
11
12 /**
13 Decrypt an DSA encrypted key
14 @param in The ciphertext
15 @param inlen The length of the ciphertext (octets)
16 @param out [out] The plaintext
17 @param outlen [in/out] The max size and resulting size of the plaintext
18 @param key The corresponding private DSA key
19 @return CRYPT_OK if successful
20 */
dsa_decrypt_key(const unsigned char * in,unsigned long inlen,unsigned char * out,unsigned long * outlen,const dsa_key * key)21 int dsa_decrypt_key(const unsigned char *in, unsigned long inlen,
22 unsigned char *out, unsigned long *outlen,
23 const dsa_key *key)
24 {
25 unsigned char *skey, *expt;
26 void *g_pub;
27 unsigned long x, y;
28 unsigned long hashOID[32] = { 0 };
29 int hash, err;
30 ltc_asn1_list decode[3];
31
32 LTC_ARGCHK(in != NULL);
33 LTC_ARGCHK(out != NULL);
34 LTC_ARGCHK(outlen != NULL);
35 LTC_ARGCHK(key != NULL);
36
37 /* right key type? */
38 if (key->type != PK_PRIVATE) {
39 return CRYPT_PK_NOT_PRIVATE;
40 }
41
42 /* decode to find out hash */
43 LTC_SET_ASN1(decode, 0, LTC_ASN1_OBJECT_IDENTIFIER, hashOID, sizeof(hashOID)/sizeof(hashOID[0]));
44 err = der_decode_sequence(in, inlen, decode, 1);
45 if (err != CRYPT_OK && err != CRYPT_INPUT_TOO_LONG) {
46 return err;
47 }
48
49 hash = find_hash_oid(hashOID, decode[0].size);
50 if (hash_is_valid(hash) != CRYPT_OK) {
51 return CRYPT_INVALID_PACKET;
52 }
53
54 /* we now have the hash! */
55
56 if ((err = mp_init(&g_pub)) != CRYPT_OK) {
57 return err;
58 }
59
60 /* allocate memory */
61 expt = XMALLOC(mp_unsigned_bin_size(key->p) + 1);
62 skey = XMALLOC(MAXBLOCKSIZE);
63 if (expt == NULL || skey == NULL) {
64 if (expt != NULL) {
65 XFREE(expt);
66 }
67 if (skey != NULL) {
68 XFREE(skey);
69 }
70 mp_clear(g_pub);
71 return CRYPT_MEM;
72 }
73
74 LTC_SET_ASN1(decode, 1, LTC_ASN1_INTEGER, g_pub, 1UL);
75 LTC_SET_ASN1(decode, 2, LTC_ASN1_OCTET_STRING, skey, MAXBLOCKSIZE);
76
77 /* read the structure in now */
78 if ((err = der_decode_sequence(in, inlen, decode, 3)) != CRYPT_OK) {
79 goto LBL_ERR;
80 }
81
82 /* make shared key */
83 x = mp_unsigned_bin_size(key->p) + 1;
84 if ((err = dsa_shared_secret(key->x, g_pub, key, expt, &x)) != CRYPT_OK) {
85 goto LBL_ERR;
86 }
87
88 y = mp_unsigned_bin_size(key->p) + 1;
89 y = MIN(y, MAXBLOCKSIZE);
90 if ((err = hash_memory(hash, expt, x, expt, &y)) != CRYPT_OK) {
91 goto LBL_ERR;
92 }
93
94 /* ensure the hash of the shared secret is at least as big as the encrypt itself */
95 if (decode[2].size > y) {
96 err = CRYPT_INVALID_PACKET;
97 goto LBL_ERR;
98 }
99
100 /* avoid buffer overflow */
101 if (*outlen < decode[2].size) {
102 *outlen = decode[2].size;
103 err = CRYPT_BUFFER_OVERFLOW;
104 goto LBL_ERR;
105 }
106
107 /* Decrypt the key */
108 for (x = 0; x < decode[2].size; x++) {
109 out[x] = expt[x] ^ skey[x];
110 }
111 *outlen = x;
112
113 err = CRYPT_OK;
114 LBL_ERR:
115 #ifdef LTC_CLEAN_STACK
116 zeromem(expt, mp_unsigned_bin_size(key->p) + 1);
117 zeromem(skey, MAXBLOCKSIZE);
118 #endif
119
120 XFREE(expt);
121 XFREE(skey);
122
123 mp_clear(g_pub);
124
125 return err;
126 }
127
128 #endif
129
130