diff options
Diffstat (limited to 'libtomcrypt/src/pk/ecc/ecc_verify_hash.c')
| -rw-r--r-- | libtomcrypt/src/pk/ecc/ecc_verify_hash.c | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/libtomcrypt/src/pk/ecc/ecc_verify_hash.c b/libtomcrypt/src/pk/ecc/ecc_verify_hash.c new file mode 100644 index 0000000..bd8a840 --- /dev/null +++ b/libtomcrypt/src/pk/ecc/ecc_verify_hash.c @@ -0,0 +1,165 @@ +/* LibTomCrypt, modular cryptographic library -- Tom St Denis + * + * LibTomCrypt is a library that provides various cryptographic + * algorithms in a highly modular and flexible manner. + * + * The library is free for all purposes without any express + * guarantee it works. + * + * Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com + */ + +/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b + * + * All curves taken from NIST recommendation paper of July 1999 + * Available at http://csrc.nist.gov/cryptval/dss.htm + */ +#include "tomcrypt.h" + +/** + @file ecc_verify_hash.c + ECC Crypto, Tom St Denis +*/ + +#ifdef MECC + +/* verify + * + * w = s^-1 mod n + * u1 = xw + * u2 = rw + * X = u1*G + u2*Q + * v = X_x1 mod n + * accept if v == r + */ + +/** + Verify an ECC signature + @param sig The signature to verify + @param siglen The length of the signature (octets) + @param hash The hash (message digest) that was signed + @param hashlen The length of the hash (octets) + @param stat Result of signature, 1==valid, 0==invalid + @param key The corresponding public ECC key + @return CRYPT_OK if successful (even if the signature is not valid) +*/ +int ecc_verify_hash(const unsigned char *sig, unsigned long siglen, + const unsigned char *hash, unsigned long hashlen, + int *stat, ecc_key *key) +{ + ecc_point *mG, *mQ; + void *r, *s, *v, *w, *u1, *u2, *e, *p, *m; + void *mp; + int err; + + LTC_ARGCHK(sig != NULL); + LTC_ARGCHK(hash != NULL); + LTC_ARGCHK(stat != NULL); + LTC_ARGCHK(key != NULL); + + /* default to invalid signature */ + *stat = 0; + mp = NULL; + + /* is the IDX valid ? */ + if (ltc_ecc_is_valid_idx(key->idx) != 1) { + return CRYPT_PK_INVALID_TYPE; + } + + /* allocate ints */ + if ((err = mp_init_multi(&r, &s, &v, &w, &u1, &u2, &p, &e, &m, NULL)) != CRYPT_OK) { + return CRYPT_MEM; + } + + /* allocate points */ + mG = ltc_ecc_new_point(); + mQ = ltc_ecc_new_point(); + if (mQ == NULL || mG == NULL) { + err = CRYPT_MEM; + goto error; + } + + /* parse header */ + if ((err = der_decode_sequence_multi(sig, siglen, + LTC_ASN1_INTEGER, 1UL, r, + LTC_ASN1_INTEGER, 1UL, s, + LTC_ASN1_EOL, 0UL, NULL)) != CRYPT_OK) { + goto error; + } + + /* get the order */ + if ((err = mp_read_radix(p, (char *)key->dp->order, 16)) != CRYPT_OK) { goto error; } + + /* get the modulus */ + if ((err = mp_read_radix(m, (char *)key->dp->prime, 16)) != CRYPT_OK) { goto error; } + + /* check for zero */ + if (mp_iszero(r) || mp_iszero(s) || mp_cmp(r, p) != LTC_MP_LT || mp_cmp(s, p) != LTC_MP_LT) { + err = CRYPT_INVALID_PACKET; + goto error; + } + + /* read hash */ + if ((err = mp_read_unsigned_bin(e, (unsigned char *)hash, (int)hashlen)) != CRYPT_OK) { goto error; } + + /* w = s^-1 mod n */ + if ((err = mp_invmod(s, p, w)) != CRYPT_OK) { goto error; } + + /* u1 = ew */ + if ((err = mp_mulmod(e, w, p, u1)) != CRYPT_OK) { goto error; } + + /* u2 = rw */ + if ((err = mp_mulmod(r, w, p, u2)) != CRYPT_OK) { goto error; } + + /* find mG and mQ */ + if ((err = mp_read_radix(mG->x, (char *)key->dp->Gx, 16)) != CRYPT_OK) { goto error; } + if ((err = mp_read_radix(mG->y, (char *)key->dp->Gy, 16)) != CRYPT_OK) { goto error; } + if ((err = mp_set(mG->z, 1)) != CRYPT_OK) { goto error; } + + if ((err = mp_copy(key->pubkey.x, mQ->x)) != CRYPT_OK) { goto error; } + if ((err = mp_copy(key->pubkey.y, mQ->y)) != CRYPT_OK) { goto error; } + if ((err = mp_copy(key->pubkey.z, mQ->z)) != CRYPT_OK) { goto error; } + + /* compute u1*mG + u2*mQ = mG */ + if (ltc_mp.ecc_mul2add == NULL) { + if ((err = ltc_mp.ecc_ptmul(u1, mG, mG, m, 0)) != CRYPT_OK) { goto error; } + if ((err = ltc_mp.ecc_ptmul(u2, mQ, mQ, m, 0)) != CRYPT_OK) { goto error; } + + /* find the montgomery mp */ + if ((err = mp_montgomery_setup(m, &mp)) != CRYPT_OK) { goto error; } + + /* add them */ + if ((err = ltc_mp.ecc_ptadd(mQ, mG, mG, m, mp)) != CRYPT_OK) { goto error; } + + /* reduce */ + if ((err = ltc_mp.ecc_map(mG, m, mp)) != CRYPT_OK) { goto error; } + } else { + /* use Shamir's trick to compute u1*mG + u2*mQ using half of the doubles */ + if ((err = ltc_mp.ecc_mul2add(mG, u1, mQ, u2, mG, m)) != CRYPT_OK) { goto error; } + } + + /* v = X_x1 mod n */ + if ((err = mp_mod(mG->x, p, v)) != CRYPT_OK) { goto error; } + + /* does v == r */ + if (mp_cmp(v, r) == LTC_MP_EQ) { + *stat = 1; + } + + /* clear up and return */ + err = CRYPT_OK; +error: + ltc_ecc_del_point(mG); + ltc_ecc_del_point(mQ); + mp_clear_multi(r, s, v, w, u1, u2, p, e, m, NULL); + if (mp != NULL) { + mp_montgomery_free(mp); + } + return err; +} + +#endif +/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_verify_hash.c,v $ */ +/* $Revision: 1.12 $ */ +/* $Date: 2006/12/04 05:07:59 $ */ + |