"United States v. Rosen" was also a pioneering use of the silent witness rule in a courtroom. The rule allows for sensitive (classified, or otherwise) evidence to be hidden from the public, but available to the jury & counsel, by the use of "substitution" of code-words using a "key card," to which witnesses and the jury would refer during the trial, but which the public would not have access to. Most previous attempts by the government to use the rule had been banned by various judges or the case had been settled before trial. Ellis was the first to allow it, although he limited it to 4 minutes of use at trial, and devised a "fairness test" as to whether the rule should be allowed, and to how much it would make the trial "closed." Critics worried about the Fifth Amendment due process and Sixth amendment Confrontation Clause implications of the use of this rule. In particular, Ellis describes it as a "partial closing" of the trial, while the Sixth Amendment guarantees a public trial.