form.php

<?php

use Phalcon\Forms\Element\Password,
  Phalcon\Validation\Validator\PresenceOf,
	Phalcon\Validation\Validator\StringLength,
	Phalcon\Validation\Validator\Confirmation;

class MyForm extends Phalcon\Forms\Form
{
	public function initialize()
	{

		$password = new Password('password', array(
			'required' => true,
			'class' => 'span12'
		));

		$password->addValidators(array(
			new PresenceOf(array(
				'message' => 'password required',
			)),
			new StringLength(array(
				'min' => 8,
				'messageMinimum' => 'Password is too short. Minimum 8 characters'
			)),
			new Confirmation(array(
				'message' => 'Password doesn\'t match confirmation',
				'with' => 'repassword'
			))
		));

		$this->add($password);
	}
}

$myForm = new MyForm();

if (!$myForm->isValid(array())) {
	foreach ($myForm->getMessages() as $message) {
		echo $message->getType(), ': ', $message->getMessage(), '<br>';
	}
}