Encryption, the Fifth Amendment, and Aaron Burr:
Following my posts last week on encryption and the Fifth Amendment, a few readers asked about how courts have dealt with such issues before. As far as I know, there is only one other judicial decision specifically addressing the Fifth Amendment implications of decrypting ciphertext. Remarkably, it arose 200 years ago, in the treason trial of former Vice-President Aaron Burr.

  The prosecution had charged Burr with treason for leading a failed rebellion against the United States in the western territories. The evidence included an encrypted communication Burr had sent to his alleged co-conspirators. To decrypt the communication, the prosecutor subpoenaed Burr's private secretary, Willie, (who knew the key to Burr's cryptography) and forced him to testify as to the communication's plaintext meaning. Willie objected on Fifth Amendment grounds.

  In United States v. Burr, 25 F. Cas. 38 (C.C. Va. 1807), Chief Justice Marshall ruled that Willie could be compelled to answer because revealing his knowledge of the cipher would not incriminate him. Here was Marshall's analysis:
To know and conceal the treason of another is misprision of treason, and is punishable by law. No witness, therefore, is compellable by law to disclose a fact which would form a necessary and essential part of this crime. If the letter in question contain evidence of treason, which is a fact not dependent on the testimony of the witness before the court, and, therefore, may be proved without the aid of his testimony; and if the witness were acquainted with that treason when the letter was written, he may probably be guilty of misprision of treason, and, therefore, the court ought not to compel him to answer any question, the answer to which might disclose his former knowledge of the contents of that letter.

But if the letter should relate to misdemeanor and not to the treason, the court is not apprized that a knowledge and concealment of the misdemeanor would expose the witness to any prosecution whatever. On this account the court was, at first, disposed to inquire whether the letter could be deciphered, in order to determine from its contents how far the witness could be examined respecting it. The court was inclined to this course from considering the question as one which might require a disclosure of the knowledge which the witness might have had of the contents of this letter when it was put in cipher, or when it was copied by himself; if, indeed, such were the fact. But, on hearing the question more particularly and precisely stated, and finding that it refers only to the present knowledge of the cipher, it appears to the court that the question may be answered without implicating the witness, because his present knowledge would not, it is believed, in a criminal prosecution, justify the inference that his knowledge was acquired previous to this trial, or afford the means of proving that fact.

The court is, therefore, of opinion that the witness may answer the question now propounded.
John (mail):
But the question is, could Burr have been asked for the encryption scheme?

I don't have access to the case to know if he was asked, or if the prosecutor thought the notion so contrary to good Fifth Amendment practice that he wouldn't ask Burr to reveal it, but it would be interesting to know...
12.26.2007 7:43pm
Moreover, even using the analysis from Marshall, doesn't it support the decision of the magistrate. The question in the Burr case was whether knowledge of decryption now implicated knowledge of the treason at a prior time. Note that two assumptions have to be made in order to determine that knowledge of decryption implicates knowledge of the treason. First, that knowing how to decrypt now means you knew how to decrypt then. Second, that he had decrypted the piece in question, or otherwise knew of the treason. It seems to me the first assumption is pretty warranted, but the second one is not (ie., he could know how to decrypt, but never have decrypted the document).
Now look at the PGP encryption case. The officers didn't actually see him enter the code to decrypt, but apparently he had access when they couldn't get it. For him to enter the code now, would implicate that he knew how to enter the code at the time. And, that is enough for conviction I believe. He merely has to have access and control over the kiddie porn drive.
12.26.2007 7:59pm
Anderson (mail):
John's and Hattio's were my thoughts as well. I defer to Prof. Kerr on this area of the law that he knows well and I know not at all; but I would look forward to his distinguishing Burr's case from the present-day one.
12.26.2007 8:36pm
George Weiss (mail):
also the burr decision says nothing of the inevitability doctrine used by the magistrate in the recent decision.
12.26.2007 10:59pm

I think of the Burr case as being akin to Hiibel v. Sixth Judicial District Court; in the circumstances of the case, there was no clear reason to think complying with the subpoena would be incriminating. I don't see it as really relevant to the reasoning in the Boucher case, which I have addressed at significant length in the other two posts; I just thought it was cool that the other case was 200 years old and was such a high-profile matter. I also am just interested in Aaron Burr; a fascinating historical figure.
12.26.2007 11:54pm
Two hundred years ago, did courts grant immunity from prosecution in order to secure testimony? Seems to my nonlegal mind that Burr's secretary might have suspected, but not known, that the letter contained something to incriminate him (the secretary), leading him to refuse to give up the cipher. If so, a grant of immunity should have removed his objection to testifying.
12.27.2007 9:46am
BruceM (mail) (www):
The way I read this, there has never been a crime if misprision of misdemeanor, only misprision of felony (treason, of course, being a felony). That's the way the statute reads today, too. The crime is called "misprision of felony." I'm not sure what misdemeanor Marshall is referring to, but I think his point was that until the letter is decyphered in camera, there is no way to know that it relates to the felony of treason (rather than to a misdemeanor). In other words, just because the letter would incriminate you of misprision of a crime is not enough to assert the 5th, it has to be misprision of a felony.
12.27.2007 12:30pm
I'm troubled by Marshall's implication that an alternative (and innocent) explanation for the knowledge to be testified to -- "the present knowledge of the cipher" -- is grounds for finding the privilege inapplicable. The possibility of an innocent explanation is, by itself, hardly enough to vitiate the incriminatory risk; otherwise, prosecutors would always be free to demand an answer to such questions as "Do you know what the scope and objectives of [insert relevant conspiracy] were?" on the theory that the witness could theoretically have come to know that information after the fact without participating in the crime.
12.27.2007 2:24pm
I have legally irrelevant question, which answer might underscore another historical irony in this case.

Was Burr's letter encrypted with Jefferson's wheel cipher?
12.28.2007 8:17am