Entering confidential information in a form

I want to develop an application for students to complete. A requirement is for their teacher to review and sign the form electronically with a code that I would provide. I want to keep the code secret so students can't "sign" the form with their teacher's name. Is there a way for someone to input data that, to them, is hidden (like ******) but is visible to me, the form creator?

Currently, there is no option in JotForm that will allow you to hide input data on your form (like ******).  It is not possible to set your form as a login form so this field is not available in JotForm. You can only use a regular textbox field for the access code of your form.