/* 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://libtom.org
 */
#include "tomcrypt.h"

/**
   @file rsa_make_key.c
   RSA key generation, Tom St Denis
 */

#ifdef LTC_MRSA

/**
   Create an RSA key
   @param prng     An active PRNG state
   @param wprng    The index of the PRNG desired
   @param size     The size of the modulus (key size) desired (octets)
   @param e        The "e" value (public key).  e==65537 is a good choice
   @param key      [out] Destination of a newly created private key pair
   @return CRYPT_OK if successful, upon error all allocated ram is freed
 */
int rsa_make_key(prng_state *prng, int wprng, int size, long e, rsa_key *key) {
    void *p, *q, *tmp1, *tmp2, *tmp3;
    int  err;

    LTC_ARGCHK(ltc_mp.name != NULL);
    LTC_ARGCHK(key != NULL);

    if ((size < (MIN_RSA_SIZE / 8)) || (size > (MAX_RSA_SIZE / 8))) {
        return CRYPT_INVALID_KEYSIZE;
    }

    if ((e < 3) || ((e & 1) == 0)) {
        return CRYPT_INVALID_ARG;
    }

    if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
        return err;
    }

    if ((err = mp_init_multi(&p, &q, &tmp1, &tmp2, &tmp3, NULL)) != CRYPT_OK) {
        return err;
    }

    /* make primes p and q (optimization provided by Wayne Scott) */
    if ((err = mp_set_int(tmp3, e)) != CRYPT_OK) {
        goto errkey;
    }                                                                                  /* tmp3 = e */

    /* make prime "p" */
    do {
        if ((err = rand_prime(p, size / 2, prng, wprng)) != CRYPT_OK) {
            goto errkey;
        }
        if ((err = mp_sub_d(p, 1, tmp1)) != CRYPT_OK) {
            goto errkey;
        }                                                                              /* tmp1 = p-1 */
        if ((err = mp_gcd(tmp1, tmp3, tmp2)) != CRYPT_OK) {
            goto errkey;
        }                                                                              /* tmp2 = gcd(p-1, e) */
    } while (mp_cmp_d(tmp2, 1) != 0);                                                  /* while e divides p-1 */

    /* make prime "q" */
    do {
        if ((err = rand_prime(q, size / 2, prng, wprng)) != CRYPT_OK) {
            goto errkey;
        }
        if ((err = mp_sub_d(q, 1, tmp1)) != CRYPT_OK) {
            goto errkey;
        }                                                                             /* tmp1 = q-1 */
        if ((err = mp_gcd(tmp1, tmp3, tmp2)) != CRYPT_OK) {
            goto errkey;
        }                                                                             /* tmp2 = gcd(q-1, e) */
    } while (mp_cmp_d(tmp2, 1) != 0);                                                 /* while e divides q-1 */

    /* tmp1 = lcm(p-1, q-1) */
    if ((err = mp_sub_d(p, 1, tmp2)) != CRYPT_OK) {
        goto errkey;
    }                                                                                 /* tmp2 = p-1 */
                                                                                      /* tmp1 = q-1 (previous do/while loop) */
    if ((err = mp_lcm(tmp1, tmp2, tmp1)) != CRYPT_OK) {
        goto errkey;
    }                                                                                 /* tmp1 = lcm(p-1, q-1) */

    /* make key */
    if ((err = mp_init_multi(&key->e, &key->d, &key->N, &key->dQ, &key->dP, &key->qP, &key->p, &key->q, NULL)) != CRYPT_OK) {
        goto errkey;
    }

    if ((err = mp_set_int(key->e, e)) != CRYPT_OK) {
        goto errkey;
    }                                                                                   /* key->e =  e */
    if ((err = mp_invmod(key->e, tmp1, key->d)) != CRYPT_OK) {
        goto errkey;
    }                                                                                   /* key->d = 1/e mod lcm(p-1,q-1) */
    if ((err = mp_mul(p, q, key->N)) != CRYPT_OK) {
        goto errkey;
    }                                                                                   /* key->N = pq */

    /* optimize for CRT now */
    /* find d mod q-1 and d mod p-1 */
    if ((err = mp_sub_d(p, 1, tmp1)) != CRYPT_OK) {
        goto errkey;
    }                                                                                   /* tmp1 = q-1 */
    if ((err = mp_sub_d(q, 1, tmp2)) != CRYPT_OK) {
        goto errkey;
    }                                                                                   /* tmp2 = p-1 */
    if ((err = mp_mod(key->d, tmp1, key->dP)) != CRYPT_OK) {
        goto errkey;
    }                                                                                   /* dP = d mod p-1 */
    if ((err = mp_mod(key->d, tmp2, key->dQ)) != CRYPT_OK) {
        goto errkey;
    }                                                                                   /* dQ = d mod q-1 */
    if ((err = mp_invmod(q, p, key->qP)) != CRYPT_OK) {
        goto errkey;
    }                                                                                   /* qP = 1/q mod p */

    if ((err = mp_copy(p, key->p)) != CRYPT_OK) {
        goto errkey;
    }
    if ((err = mp_copy(q, key->q)) != CRYPT_OK) {
        goto errkey;
    }

    /* set key type (in this case it's CRT optimized) */
    key->type = PK_PRIVATE;

    /* return ok and free temps */
    err = CRYPT_OK;
    goto cleanup;
errkey:
    mp_clear_multi(key->d, key->e, key->N, key->dQ, key->dP, key->qP, key->p, key->q, NULL);
cleanup:
    mp_clear_multi(tmp3, tmp2, tmp1, p, q, NULL);
    return err;
}
#endif

/* $Source: /cvs/libtom/libtomcrypt/src/pk/rsa/rsa_make_key.c,v $ */
/* $Revision: 1.16 $ */
/* $Date: 2007/05/12 14:32:35 $ */
