electronic signature

I would like to have a single line of input to act as a digital signature. For this, I would like the rule to be that the name in this box needs to match {First Name + " " + Last Name} boxes entered in earlier in the form.

Is there a way to do this?

I'm not sure I understand this code .. Where is the conditional statement testing whether or not the field value is valid?

And thank you for your replies as always!

<?php
add_filter('gform_validation', 'custom_validation');
function custom_validation($validation_result){

// set the form validation to false
$validation_result["is_valid"] = false;
$form = $validation_result["form"];

// specify the first field to be invalid and provide custom validation message
$form["fields"][0]["failed_validation"] = true;
$form["fields"][0]["validation_message"] = "This field is invalid!";

// update the form in the validation result with the form object you modified
$validation_result["form"] = $form;

return $validation_result;

}
?>