Mercurial > dropbear
view libtomcrypt/src/pk/dsa/dsa_make_key.c @ 708:b207d5183bb7
document a few more changes
author | Matt Johnston <matt@ucc.asn.au> |
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date | Wed, 20 Mar 2013 00:05:19 +0800 |
parents | 0cbe8f6dbf9e |
children | f849a5ca2efc |
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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.com */ #include "tomcrypt.h" /** @file dsa_make_key.c DSA implementation, generate a DSA key, Tom St Denis */ #ifdef MDSA /** Create a DSA key @param prng An active PRNG state @param wprng The index of the PRNG desired @param group_size Size of the multiplicative group (octets) @param modulus_size Size of the modulus (octets) @param key [out] Where to store the created key @return CRYPT_OK if successful, upon error this function will free all allocated memory */ int dsa_make_key(prng_state *prng, int wprng, int group_size, int modulus_size, dsa_key *key) { void *tmp, *tmp2; int err, res; unsigned char *buf; LTC_ARGCHK(key != NULL); LTC_ARGCHK(ltc_mp.name != NULL); /* check prng */ if ((err = prng_is_valid(wprng)) != CRYPT_OK) { return err; } /* check size */ if (group_size >= MDSA_MAX_GROUP || group_size <= 15 || group_size >= modulus_size || (modulus_size - group_size) >= MDSA_DELTA) { return CRYPT_INVALID_ARG; } /* allocate ram */ buf = XMALLOC(MDSA_DELTA); if (buf == NULL) { return CRYPT_MEM; } /* init mp_ints */ if ((err = mp_init_multi(&tmp, &tmp2, &key->g, &key->q, &key->p, &key->x, &key->y, NULL)) != CRYPT_OK) { XFREE(buf); return err; } /* make our prime q */ if ((err = rand_prime(key->q, group_size, prng, wprng)) != CRYPT_OK) { goto error; } /* double q */ if ((err = mp_add(key->q, key->q, tmp)) != CRYPT_OK) { goto error; } /* now make a random string and multply it against q */ if (prng_descriptor[wprng].read(buf+1, modulus_size - group_size, prng) != (unsigned long)(modulus_size - group_size)) { err = CRYPT_ERROR_READPRNG; goto error; } /* force magnitude */ buf[0] |= 0xC0; /* force even */ buf[modulus_size - group_size - 1] &= ~1; if ((err = mp_read_unsigned_bin(tmp2, buf, modulus_size - group_size)) != CRYPT_OK) { goto error; } if ((err = mp_mul(key->q, tmp2, key->p)) != CRYPT_OK) { goto error; } if ((err = mp_add_d(key->p, 1, key->p)) != CRYPT_OK) { goto error; } /* now loop until p is prime */ for (;;) { if ((err = mp_prime_is_prime(key->p, 8, &res)) != CRYPT_OK) { goto error; } if (res == LTC_MP_YES) break; /* add 2q to p and 2 to tmp2 */ if ((err = mp_add(tmp, key->p, key->p)) != CRYPT_OK) { goto error; } if ((err = mp_add_d(tmp2, 2, tmp2)) != CRYPT_OK) { goto error; } } /* now p = (q * tmp2) + 1 is prime, find a value g for which g^tmp2 != 1 */ mp_set(key->g, 1); do { if ((err = mp_add_d(key->g, 1, key->g)) != CRYPT_OK) { goto error; } if ((err = mp_exptmod(key->g, tmp2, key->p, tmp)) != CRYPT_OK) { goto error; } } while (mp_cmp_d(tmp, 1) == LTC_MP_EQ); /* at this point tmp generates a group of order q mod p */ mp_exch(tmp, key->g); /* so now we have our DH structure, generator g, order q, modulus p Now we need a random exponent [mod q] and it's power g^x mod p */ do { if (prng_descriptor[wprng].read(buf, group_size, prng) != (unsigned long)group_size) { err = CRYPT_ERROR_READPRNG; goto error; } if ((err = mp_read_unsigned_bin(key->x, buf, group_size)) != CRYPT_OK) { goto error; } } while (mp_cmp_d(key->x, 1) != LTC_MP_GT); if ((err = mp_exptmod(key->g, key->x, key->p, key->y)) != CRYPT_OK) { goto error; } key->type = PK_PRIVATE; key->qord = group_size; #ifdef LTC_CLEAN_STACK zeromem(buf, MDSA_DELTA); #endif err = CRYPT_OK; goto done; error: mp_clear_multi(key->g, key->q, key->p, key->x, key->y, NULL); done: mp_clear_multi(tmp, tmp2, NULL); XFREE(buf); return err; } #endif /* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_make_key.c,v $ */ /* $Revision: 1.10 $ */ /* $Date: 2006/12/04 03:18:43 $ */