Symfony2 Validation comapring string with its Hash

MessageType.php

use Acme\DemoBundle\Validator\Constraints\StringMatchItsHash;


class SmokeType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
        	->add('smoke', 'hidden', array(
        			'data' => 'smoke'
        		)
        	)
        	->add('smoke_hash', 'hidden', array(
        			'data' => sha1('MYSUPERSECURESALT'.'smoke'),
        			'property_path' => false,
        			'constraints' => array(
        					new StringMatchItsHash('smoke'),
        				)

        		)
        	)
    }
}

StringMatchItsHash.php

namespace Acme\DemoBundle\Validator\Constraints;

use Symfony\Component\Validator\Constraint;

/**
 * @Annotation
 */
class StringMatchItsHash extends Constraint
{
	public $message = 'Are you craking me?';

	public $field;

	/**
	 * {@inheritDoc}
	 */
	public function getDefaultOption()
	{
		return 'field';
	}

	/**
	 * {@inheritDoc}
	 */
	public function getRequiredOptions()
	{
		return array('field');
	}

}

StringMatchItsHashValidator.php

namespace Acme\DemoBundle\Validator\Constraints;

use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;

class StringMatchItsHashValidator extends ConstraintValidator
{
	public function validate($value, Constraint $constraint)
	{
                $user = sha1('MYSUPERSECURESALT'.$this->context->getRoot()->get($constraint->field)->getData());
		if ($value !== $user) {
			$this->context->addViolation($constraint->message);
		}
	}
}