1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
6 * The library is free for all purposes without any express
9 * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
13 /*! \file pkcs_1_v1_5_encode.c
15 * PKCS #1 v1.5 Padding (Andreas Lange)
20 /*! \brief PKCS #1 v1.5 encode.
22 * \param msg The data to encode
23 * \param msglen The length of the data to encode (octets)
24 * \param block_type Block type to use in padding (\sa ltc_pkcs_1_v1_5_blocks)
25 * \param modulus_bitlen The bit length of the RSA modulus
26 * \param prng An active PRNG state (only for LTC_PKCS_1_EME)
27 * \param prng_idx The index of the PRNG desired (only for LTC_PKCS_1_EME)
28 * \param out [out] The destination for the encoded data
29 * \param outlen [in/out] The max size and resulting size of the encoded data
31 * \return CRYPT_OK if successful
33 int pkcs_1_v1_5_encode(const unsigned char *msg,
36 unsigned long modulus_bitlen,
40 unsigned long *outlen)
42 unsigned long modulus_len, ps_len, i;
46 /* valid block_type? */
47 if ((block_type != LTC_PKCS_1_EMSA) &&
48 (block_type != LTC_PKCS_1_EME)) {
49 return CRYPT_PK_INVALID_PADDING;
52 if (block_type == LTC_PKCS_1_EME) { /* encryption padding, we need a valid PRNG */
53 if ((result = prng_is_valid(prng_idx)) != CRYPT_OK) {
58 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
60 /* test message size */
61 if ((msglen + 11) > modulus_len) {
62 return CRYPT_PK_INVALID_SIZE;
65 if (*outlen < modulus_len) {
66 *outlen = modulus_len;
67 result = CRYPT_BUFFER_OVERFLOW;
71 /* generate an octets string PS */
73 ps_len = modulus_len - msglen - 3;
75 if (block_type == LTC_PKCS_1_EME) {
76 /* now choose a random ps */
77 if (prng_descriptor[prng_idx].read(ps, ps_len, prng) != ps_len) {
78 result = CRYPT_ERROR_READPRNG;
82 /* transform zero bytes (if any) to non-zero random bytes */
83 for (i = 0; i < ps_len; i++) {
85 if (prng_descriptor[prng_idx].read(&ps[i], 1, prng) != 1) {
86 result = CRYPT_ERROR_READPRNG;
92 XMEMSET(ps, 0xFF, ps_len);
95 /* create string of length modulus_len */
97 out[1] = (unsigned char)block_type; /* block_type 1 or 2 */
98 out[2 + ps_len] = 0x00;
99 XMEMCPY(&out[2 + ps_len + 1], msg, msglen);
100 *outlen = modulus_len;
105 } /* pkcs_1_v1_5_encode */
107 #endif /* #ifdef PKCS_1 */
109 /* $Source: /cvs/libtom/libtomcrypt/src/pk/pkcs1/pkcs_1_v1_5_encode.c,v $ */
110 /* $Revision: 1.2 $ */
111 /* $Date: 2006/11/01 09:12:06 $ */