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, tomstdenis@gmail.com, http://libtomcrypt.com
10 */
11
12 /* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
13 *
14 * All curves taken from NIST recommendation paper of July 1999
15 * Available at http://csrc.nist.gov/cryptval/dss.htm
16 */
17 #include "tomcrypt.h"
18
19 /**
20 @file ecc_sign_hash.c
21 ECC Crypto, Tom St Denis
22 */
23
24 #ifdef MECC
25
26 /**
27 Sign a message digest
28 @param in The message digest to sign
29 @param inlen The length of the digest
30 @param out [out] The destination for the signature
31 @param outlen [in/out] The max size and resulting size of the signature
32 @param prng An active PRNG state
33 @param wprng The index of the PRNG you wish to use
34 @param key A private ECC key
35 @return CRYPT_OK if successful
36 */
ecc_sign_hash(const unsigned char * in,unsigned long inlen,unsigned char * out,unsigned long * outlen,prng_state * prng,int wprng,ecc_key * key)37 int ecc_sign_hash(const unsigned char *in, unsigned long inlen,
38 unsigned char *out, unsigned long *outlen,
39 prng_state *prng, int wprng, ecc_key *key)
40 {
41 ecc_key pubkey;
42 void *r, *s, *e, *p;
43 int err;
44
45 LTC_ARGCHK(in != NULL);
46 LTC_ARGCHK(out != NULL);
47 LTC_ARGCHK(outlen != NULL);
48 LTC_ARGCHK(key != NULL);
49
50 /* is this a private key? */
51 if (key->type != PK_PRIVATE) {
52 return CRYPT_PK_NOT_PRIVATE;
53 }
54
55 /* is the IDX valid ? */
56 if (ltc_ecc_is_valid_idx(key->idx) != 1) {
57 return CRYPT_PK_INVALID_TYPE;
58 }
59
60 if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
61 return err;
62 }
63
64 /* get the hash and load it as a bignum into 'e' */
65 /* init the bignums */
66 if ((err = mp_init_multi(&r, &s, &p, &e, NULL)) != CRYPT_OK) {
67 return err;
68 }
69 if ((err = mp_read_radix(p, (char *)key->dp->order, 16)) != CRYPT_OK) { goto errnokey; }
70 if ((err = mp_read_unsigned_bin(e, (unsigned char *)in, (int)inlen)) != CRYPT_OK) { goto errnokey; }
71
72 /* make up a key and export the public copy */
73 for (;;) {
74 if ((err = ecc_make_key_ex(prng, wprng, &pubkey, key->dp)) != CRYPT_OK) {
75 goto errnokey;
76 }
77
78 /* find r = x1 mod n */
79 if ((err = mp_mod(pubkey.pubkey.x, p, r)) != CRYPT_OK) { goto error; }
80
81 if (mp_iszero(r) == LTC_MP_YES) {
82 ecc_free(&pubkey);
83 } else {
84 /* find s = (e + xr)/k */
85 if ((err = mp_invmod(pubkey.k, p, pubkey.k)) != CRYPT_OK) { goto error; } /* k = 1/k */
86 if ((err = mp_mulmod(key->k, r, p, s)) != CRYPT_OK) { goto error; } /* s = xr */
87 if ((err = mp_add(e, s, s)) != CRYPT_OK) { goto error; } /* s = e + xr */
88 if ((err = mp_mod(s, p, s)) != CRYPT_OK) { goto error; } /* s = e + xr */
89 if ((err = mp_mulmod(s, pubkey.k, p, s)) != CRYPT_OK) { goto error; } /* s = (e + xr)/k */
90 ecc_free(&pubkey);
91 if (mp_iszero(s) == LTC_MP_NO) {
92 break;
93 }
94 }
95 }
96
97 /* store as SEQUENCE { r, s -- integer } */
98 err = der_encode_sequence_multi(out, outlen,
99 LTC_ASN1_INTEGER, 1UL, r,
100 LTC_ASN1_INTEGER, 1UL, s,
101 LTC_ASN1_EOL, 0UL, NULL);
102 goto errnokey;
103 error:
104 ecc_free(&pubkey);
105 errnokey:
106 mp_clear_multi(r, s, p, e, NULL);
107 return err;
108 }
109
110 #endif
111 /* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_sign_hash.c,v $ */
112 /* $Revision: 1.9 $ */
113 /* $Date: 2006/12/04 02:50:11 $ */
114
115