Mercurial > dropbear
view libtomcrypt/src/pk/dsa/dsa_verify_key.c @ 285:1b9e69c058d2
propagate from branch 'au.asn.ucc.matt.ltc.dropbear' (head 20dccfc09627970a312d77fb41dc2970b62689c3)
to branch 'au.asn.ucc.matt.dropbear' (head fdf4a7a3b97ae5046139915de7e40399cceb2c01)
author | Matt Johnston <matt@ucc.asn.au> |
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date | Wed, 08 Mar 2006 13:23:58 +0000 |
parents | |
children | 0cbe8f6dbf9e |
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/* 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, [email protected], http://libtomcrypt.org */ #include "tomcrypt.h" /** @file dsa_verify_key.c DSA implementation, verify a key, Tom St Denis */ #ifdef MDSA /** Verify a DSA key for validity @param key The key to verify @param stat [out] Result of test, 1==valid, 0==invalid @return CRYPT_OK if successful */ int dsa_verify_key(dsa_key *key, int *stat) { mp_int tmp, tmp2; int res, err; LTC_ARGCHK(key != NULL); LTC_ARGCHK(stat != NULL); /* default to an invalid key */ *stat = 0; /* first make sure key->q and key->p are prime */ if ((err = is_prime(&key->q, &res)) != CRYPT_OK) { return err; } if (res == 0) { return CRYPT_OK; } if ((err = is_prime(&key->p, &res)) != CRYPT_OK) { return err; } if (res == 0) { return CRYPT_OK; } /* now make sure that g is not -1, 0 or 1 and <p */ if (mp_cmp_d(&key->g, 0) == MP_EQ || mp_cmp_d(&key->g, 1) == MP_EQ) { return CRYPT_OK; } if ((err = mp_init_multi(&tmp, &tmp2, NULL)) != MP_OKAY) { goto error; } if ((err = mp_sub_d(&key->p, 1, &tmp)) != MP_OKAY) { goto error; } if (mp_cmp(&tmp, &key->g) == MP_EQ || mp_cmp(&key->g, &key->p) != MP_LT) { err = CRYPT_OK; goto done; } /* 1 < y < p-1 */ if (!(mp_cmp_d(&key->y, 1) == MP_GT && mp_cmp(&key->y, &tmp) == MP_LT)) { err = CRYPT_OK; goto done; } /* now we have to make sure that g^q = 1, and that p-1/q gives 0 remainder */ if ((err = mp_div(&tmp, &key->q, &tmp, &tmp2)) != MP_OKAY) { goto error; } if (mp_iszero(&tmp2) != MP_YES) { err = CRYPT_OK; goto done; } if ((err = mp_exptmod(&key->g, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; } if (mp_cmp_d(&tmp, 1) != MP_EQ) { err = CRYPT_OK; goto done; } /* now we have to make sure that y^q = 1, this makes sure y \in g^x mod p */ if ((err = mp_exptmod(&key->y, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; } if (mp_cmp_d(&tmp, 1) != MP_EQ) { err = CRYPT_OK; goto done; } /* at this point we are out of tests ;-( */ err = CRYPT_OK; *stat = 1; goto done; error: err = mpi_to_ltc_error(err); done : mp_clear_multi(&tmp, &tmp2, NULL); return err; } #endif /* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_verify_key.c,v $ */ /* $Revision: 1.3 $ */ /* $Date: 2005/05/05 14:35:59 $ */