/**
* DSA verify.
*
* @param string $message Message.
* @param string $hash_alg Hash algorithm.
* @param \phpseclib\Math\BigInteger $r r.
* @param \phpseclib\Math\BigInteger $s s.
*
* @return bool True if verified.
*/
public function verify($message, $hash_alg, $r, $s)
{
$hash = new Crypt\Hash($hash_alg);
$hash_m = new BigInteger($hash->hash($message), 256);
$g = new BigInteger($this->_key->key['g'], 256);
$p = new BigInteger($this->_key->key['p'], 256);
$q = new BigInteger($this->_key->key['q'], 256);
$y = new BigInteger($this->_key->key['y'], 256);
$w = $s->modInverse($q);
$hash_m_mul = $hash_m->multiply($w);
$u1_base = $hash_m_mul->divide($q);
$u1 = $u1_base[1];
$r_mul = $r->multiply($w);
$u2_base = $r_mul->divide($q);
$u2 = $u2_base[1];
$g_pow = $g->modPow($u1, $p);
$y_pow = $y->modPow($u2, $p);
$g_pow_mul = $g_pow->multiply($y_pow);
$g_pow_mul_mod_base = $g_pow_mul->divide($p);
$g_pow_mul_mod = $g_pow_mul_mod_base[1];
$v_base = $g_pow_mul_mod->divide($q);
$v = $v_base[1];
return $v->compare($r) == 0;
}
