Personal opinions: People should not be able to be forced by a subpoena duces tecum to provide incriminating documents. The fifth amendment protection against self- incrimination normally extends to personal papers. There are cases which show that corporate officers cannot avoid turning over corporate papers even if they incriminate themselves, but personal papers are provided much wider protection. People can be forced to produce handwriting samples, where the content of what is written is not significant but the physical writing will be analyzed; they can be forced to produce breath, blood or urine samples; they can be forced to stand in a police lineup, and to repeat words which a witness may have heard a criminal make (but the words do not carry significance); they may be forced to submit to psychiatric evaluation. But none of these involve giving testimony against themselves. Producing a personal diary or notes which provide incriminating testimony should be protected by the fifth amendment. By this reasoning, someone may be able to be forced to reveal an encryption key, since that is not testimony. But if the resulting documents, when decrypted, are personal and contain damaging, incriminating statements, they would not be usable in court. To introduce them in court against the wishes of the defendant would be a clear violation of his fifth amendment rights. By the same token, people are not obligated to keep records specifically to facilitate government investigation of any crime they may have committed. (They are required to keep normal records, such as those relating to the income tax.) It is perfectly permissible for people to destroy their personal records, notebooks, mail, in any way they wish, whether those records would be of use to law enforcement or not. (This is not true, of course, after receipt of a subpoena calling for those records.) "Digital flash paper" should be perfectly legal for all record keeping, whether or not those records would have contained evidence of a crime.