diff options
Diffstat (limited to 'libtomcrypt/src/pk/dsa/dsa_make_key.c')
| -rw-r--r-- | libtomcrypt/src/pk/dsa/dsa_make_key.c | 146 |
1 files changed, 146 insertions, 0 deletions
diff --git a/libtomcrypt/src/pk/dsa/dsa_make_key.c b/libtomcrypt/src/pk/dsa/dsa_make_key.c new file mode 100644 index 0000000..02f69e0 --- /dev/null +++ b/libtomcrypt/src/pk/dsa/dsa_make_key.c @@ -0,0 +1,146 @@ +/* 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.org + */ +#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) +{ + mp_int tmp, tmp2; + int err, res; + unsigned char *buf; + + LTC_ARGCHK(key != 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)) != MP_OKAY) { + err = mpi_to_ltc_error(err); + goto LBL_ERR; + } + + /* make our prime q */ + if ((err = rand_prime(&key->q, group_size*8, prng, wprng)) != CRYPT_OK) { goto LBL_ERR; } + + /* double q */ + if ((err = mp_mul_2(&key->q, &tmp)) != MP_OKAY) { 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 LBL_ERR; + } + + /* 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)) != MP_OKAY) { goto error; } + if ((err = mp_mul(&key->q, &tmp2, &key->p)) != MP_OKAY) { goto error; } + if ((err = mp_add_d(&key->p, 1, &key->p)) != MP_OKAY) { goto error; } + + /* now loop until p is prime */ + for (;;) { + if ((err = is_prime(&key->p, &res)) != CRYPT_OK) { goto LBL_ERR; } + if (res == MP_YES) break; + + /* add 2q to p and 2 to tmp2 */ + if ((err = mp_add(&tmp, &key->p, &key->p)) != MP_OKAY) { goto error; } + if ((err = mp_add_d(&tmp2, 2, &tmp2)) != MP_OKAY) { 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)) != MP_OKAY) { goto error; } + if ((err = mp_exptmod(&key->g, &tmp2, &key->p, &tmp)) != MP_OKAY) { goto error; } + } while (mp_cmp_d(&tmp, 1) == 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 LBL_ERR; + } + if ((err = mp_read_unsigned_bin(&key->x, buf, group_size)) != MP_OKAY) { goto error; } + } while (mp_cmp_d(&key->x, 1) != MP_GT); + if ((err = mp_exptmod(&key->g, &key->x, &key->p, &key->y)) != MP_OKAY) { goto error; } + + key->type = PK_PRIVATE; + key->qord = group_size; + + /* shrink the ram required */ + if ((err = mp_shrink(&key->g)) != MP_OKAY) { goto error; } + if ((err = mp_shrink(&key->p)) != MP_OKAY) { goto error; } + if ((err = mp_shrink(&key->q)) != MP_OKAY) { goto error; } + if ((err = mp_shrink(&key->x)) != MP_OKAY) { goto error; } + if ((err = mp_shrink(&key->y)) != MP_OKAY) { goto error; } + +#ifdef LTC_CLEAN_STACK + zeromem(buf, MDSA_DELTA); +#endif + + err = CRYPT_OK; + goto done; +error: + err = mpi_to_ltc_error(err); +LBL_ERR: + 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: 1.4 $ */ +/* $Date: 2005/06/11 05:45:35 $ */ |