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
11 /*! \file pkcs_1_v1_5_encode.c
13 * PKCS #1 v1.5 Padding (Andreas Lange)
18 /*! \brief PKCS #1 v1.5 encode.
20 * \param msg The data to encode
21 * \param msglen The length of the data to encode (octets)
22 * \param block_type Block type to use in padding (\sa ltc_pkcs_1_v1_5_blocks)
23 * \param modulus_bitlen The bit length of the RSA modulus
24 * \param prng An active PRNG state (only for LTC_PKCS_1_EME)
25 * \param prng_idx The index of the PRNG desired (only for LTC_PKCS_1_EME)
26 * \param out [out] The destination for the encoded data
27 * \param outlen [in/out] The max size and resulting size of the encoded data
29 * \return CRYPT_OK if successful
31 int pkcs_1_v1_5_encode(const unsigned char *msg,
34 unsigned long modulus_bitlen,
38 unsigned long *outlen)
40 unsigned long modulus_len, ps_len, i;
44 /* valid block_type? */
45 if ((block_type != LTC_PKCS_1_EMSA) &&
46 (block_type != LTC_PKCS_1_EME)) {
47 return CRYPT_PK_INVALID_PADDING;
50 if (block_type == LTC_PKCS_1_EME) { /* encryption padding, we need a valid PRNG */
51 if ((result = prng_is_valid(prng_idx)) != CRYPT_OK) {
56 modulus_len = (modulus_bitlen >> 3) + (modulus_bitlen & 7 ? 1 : 0);
58 /* test message size */
59 if ((msglen + 11) > modulus_len) {
60 return CRYPT_PK_INVALID_SIZE;
63 if (*outlen < modulus_len) {
64 *outlen = modulus_len;
65 result = CRYPT_BUFFER_OVERFLOW;
69 /* generate an octets string PS */
71 ps_len = modulus_len - msglen - 3;
73 if (block_type == LTC_PKCS_1_EME) {
74 /* now choose a random ps */
75 if (prng_descriptor[prng_idx].read(ps, ps_len, prng) != ps_len) {
76 result = CRYPT_ERROR_READPRNG;
80 /* transform zero bytes (if any) to non-zero random bytes */
81 for (i = 0; i < ps_len; i++) {
83 if (prng_descriptor[prng_idx].read(&ps[i], 1, prng) != 1) {
84 result = CRYPT_ERROR_READPRNG;
90 XMEMSET(ps, 0xFF, ps_len);
93 /* create string of length modulus_len */
95 out[1] = (unsigned char)block_type; /* block_type 1 or 2 */
96 out[2 + ps_len] = 0x00;
97 XMEMCPY(&out[2 + ps_len + 1], msg, msglen);
98 *outlen = modulus_len;
103 } /* pkcs_1_v1_5_encode */
105 #endif /* #ifdef LTC_PKCS_1 */
107 /* ref: $Format:%D$ */
108 /* git commit: $Format:%H$ */
109 /* commit time: $Format:%ai$ */