1 // SPDX-License-Identifier: BSD-2-Clause
2 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
3 *
4 * LibTomCrypt is a library that provides various cryptographic
5 * algorithms in a highly modular and flexible manner.
6 *
7 * The library is free for all purposes without any express
8 * guarantee it works.
9 */
10 #include "tomcrypt_private.h"
11
12 /**
13 @file pkcs_1_oaep_encode.c
14 OAEP Padding for PKCS #1, Tom St Denis
15 */
16
17 #ifdef LTC_PKCS_1
18
19 /**
20 PKCS #1 v2.00 OAEP encode
21 @param msg The data to encode
22 @param msglen The length of the data to encode (octets)
23 @param lparam A session or system parameter (can be NULL)
24 @param lparamlen The length of the lparam data
25 @param modulus_bitlen The bit length of the RSA modulus
26 @param prng An active PRNG state
27 @param prng_idx The index of the PRNG desired
28 @param hash_idx The index of the hash desired
29 @param out [out] The destination for the encoded data
30 @param outlen [in/out] The max size and resulting size of the encoded data
31 @return CRYPT_OK if successful
32 */
pkcs_1_oaep_encode(const unsigned char * msg,unsigned long msglen,const unsigned char * lparam,unsigned long lparamlen,unsigned long modulus_bitlen,prng_state * prng,int prng_idx,int hash_idx,unsigned char * out,unsigned long * outlen)33 int pkcs_1_oaep_encode(const unsigned char *msg, unsigned long msglen,
34 const unsigned char *lparam, unsigned long lparamlen,
35 unsigned long modulus_bitlen, prng_state *prng,
36 int prng_idx, int hash_idx,
37 unsigned char *out, unsigned long *outlen)
38 {
39 unsigned char *DB, *seed, *mask;
40 unsigned long hLen, x, y, modulus_len;
41 int err;
42
43 LTC_ARGCHK(msg != NULL);
44 LTC_ARGCHK(out != NULL);
45 LTC_ARGCHK(outlen != NULL);
46
47 /* test valid hash */
48 if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
49 return err;
50 }
51
52 /* valid prng */
53 if ((err = prng_is_valid(prng_idx)) != CRYPT_OK) {
54 return err;
55 }
56
57 hLen = hash_descriptor[hash_idx]->hashsize;
58 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
59
60 /* test message size */
61 if ((2*hLen >= (modulus_len - 2)) || (msglen > (modulus_len - 2*hLen - 2))) {
62 return CRYPT_PK_INVALID_SIZE;
63 }
64
65 /* allocate ram for DB/mask/salt of size modulus_len */
66 DB = XMALLOC(modulus_len);
67 mask = XMALLOC(modulus_len);
68 seed = XMALLOC(hLen);
69 if (DB == NULL || mask == NULL || seed == NULL) {
70 if (DB != NULL) {
71 XFREE(DB);
72 }
73 if (mask != NULL) {
74 XFREE(mask);
75 }
76 if (seed != NULL) {
77 XFREE(seed);
78 }
79 return CRYPT_MEM;
80 }
81
82 /* get lhash */
83 /* DB == lhash || PS || 0x01 || M, PS == k - mlen - 2hlen - 2 zeroes */
84 x = modulus_len;
85 if (lparam != NULL) {
86 if ((err = hash_memory(hash_idx, lparam, lparamlen, DB, &x)) != CRYPT_OK) {
87 goto LBL_ERR;
88 }
89 } else {
90 /* can't pass hash_memory a NULL so use DB with zero length */
91 if ((err = hash_memory(hash_idx, DB, 0, DB, &x)) != CRYPT_OK) {
92 goto LBL_ERR;
93 }
94 }
95
96 /* append PS then 0x01 (to lhash) */
97 x = hLen;
98 y = modulus_len - msglen - 2*hLen - 2;
99 XMEMSET(DB+x, 0, y);
100 x += y;
101
102 /* 0x01 byte */
103 DB[x++] = 0x01;
104
105 /* message (length = msglen) */
106 XMEMCPY(DB+x, msg, msglen);
107 x += msglen;
108
109 /* now choose a random seed */
110 if (prng_descriptor[prng_idx]->read(seed, hLen, prng) != hLen) {
111 err = CRYPT_ERROR_READPRNG;
112 goto LBL_ERR;
113 }
114
115 /* compute MGF1 of seed (k - hlen - 1) */
116 if ((err = pkcs_1_mgf1(hash_idx, seed, hLen, mask, modulus_len - hLen - 1)) != CRYPT_OK) {
117 goto LBL_ERR;
118 }
119
120 /* xor against DB */
121 for (y = 0; y < (modulus_len - hLen - 1); y++) {
122 DB[y] ^= mask[y];
123 }
124
125 /* compute MGF1 of maskedDB (hLen) */
126 if ((err = pkcs_1_mgf1(hash_idx, DB, modulus_len - hLen - 1, mask, hLen)) != CRYPT_OK) {
127 goto LBL_ERR;
128 }
129
130 /* XOR against seed */
131 for (y = 0; y < hLen; y++) {
132 seed[y] ^= mask[y];
133 }
134
135 /* create string of length modulus_len */
136 if (*outlen < modulus_len) {
137 *outlen = modulus_len;
138 err = CRYPT_BUFFER_OVERFLOW;
139 goto LBL_ERR;
140 }
141
142 /* start output which is 0x00 || maskedSeed || maskedDB */
143 x = 0;
144 out[x++] = 0x00;
145 XMEMCPY(out+x, seed, hLen);
146 x += hLen;
147 XMEMCPY(out+x, DB, modulus_len - hLen - 1);
148 x += modulus_len - hLen - 1;
149
150 *outlen = x;
151
152 err = CRYPT_OK;
153 LBL_ERR:
154 #ifdef LTC_CLEAN_STACK
155 zeromem(DB, modulus_len);
156 zeromem(seed, hLen);
157 zeromem(mask, modulus_len);
158 #endif
159
160 XFREE(seed);
161 XFREE(mask);
162 XFREE(DB);
163
164 return err;
165 }
166
167 #endif /* LTC_PKCS_1 */
168
169
170 /* ref: $Format:%D$ */
171 /* git commit: $Format:%H$ */
172 /* commit time: $Format:%ai$ */
173