Angular Form Validation using Ng Model - angularjs

Question

Question: How can I show the validation error using only the ng-model if I cannot name the form and its elements.
I have a html form to collect credit card details. To prevent the credit card data from touching my server, I cannot name the form elements. So my form looks like:
<form ng-submit="vm.processForm()">
<div class="form-row">
<label>
<span>Card Number</span>
<input type="text" size="20" data-stripe="number" ng-model="vm.number" required>
</label>
</div>
<div class="form-row">
<label>
<span>Expiration (MM/YY)</span>
<input type="text" size="2" data-stripe="exp_month" ng-model="vm.exp_month" required>
</label>
<span> / </span>
<input type="text" size="2" data-stripe="exp_year" ng-model="vm.exp_year" required>
</div>
<div class="form-row">
<label>
<span>CVC</span>
<input type="text" size="4" data-stripe="cvc" ng-model="vm.cvc" required>
</label>
</div>
<input type="submit" class="submit" value="Submit Payment">
</form>
Usually in Angular, I used to check validation using the form elements name, for example like this:
<p ng-show="userForm.creditcard.$error.required">Your credit card number is required.</p>
But since I cannot name the form and its elements, how can I show the validation error using only the ng-model? Because, the following doesn't work:
<p ng-show="vm.number.$error.required">Your credit card number is required.</p>
I am using Angular v1.4.8.

Answer 1

I created a directive to export de the model controller. I don't think that is the best way but it works.
.directive('exportModel', function () {
return {
restrict: 'A',
require: 'ngModel',
link: function (scope, element, attr, ngModel) {
attr.$observe('exportModel', function (value) {
scope[value] = ngModel;
})
}
}
})
http://jsfiddle.net/Lvc0u55v/11352/