/* mostly taken from libtomcrypt's rsa key generation routine */
dropbear_rsa_key * gen_rsa_priv_key(unsigned int size) {
dropbear_rsa_key * key;
DEF_MP_INT(pminus);
DEF_MP_INT(qminus);
DEF_MP_INT(lcm);
if (size < 512 || size > 4096 || (size % 8 != 0)) {
dropbear_exit("Bits must satisfy 512 <= bits <= 4096, and be a"
" multiple of 8");
}
key = m_malloc(sizeof(*key));
m_mp_alloc_init_multi(&key->e, &key->n, &key->d, &key->p, &key->q, NULL);
m_mp_init_multi(&pminus, &lcm, &qminus, NULL);
if (mp_set_int(key->e, RSA_E) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
while (1) {
getrsaprime(key->p, &pminus, key->e, size/16);
getrsaprime(key->q, &qminus, key->e, size/16);
if (mp_mul(key->p, key->q, key->n) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
if ((unsigned int)mp_count_bits(key->n) == size) {
break;
}
}
/* lcm(p-1, q-1) */
if (mp_lcm(&pminus, &qminus, &lcm) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
/* de = 1 mod lcm(p-1,q-1) */
/* therefore d = (e^-1) mod lcm(p-1,q-1) */
if (mp_invmod(key->e, &lcm, key->d) != MP_OKAY) {
fprintf(stderr, "RSA generation failed\n");
exit(1);
}
mp_clear_multi(&pminus, &qminus, &lcm, NULL);
return key;
}
dropbear_dss_key * gen_dss_priv_key(unsigned int size) {
dropbear_dss_key *key;
if (size != 1024) {
dropbear_exit("DSS keys have a fixed size of 1024 bits");
}
key = m_malloc(sizeof(*key));
m_mp_alloc_init_multi(&key->p, &key->q, &key->g, &key->y, &key->x, NULL);
getq(key);
getp(key, size/8);
getg(key);
getx(key);
gety(key);
return key;
}
