Edward Felten, who earlier took the Honorable Richard A. Posner to task for embracing a technological "non-starter" for stopping copyright infringment on P2P networks (tagging content + filtering), enters the fray once more -- countering Judge Posner's suggestion that encryption stops copying: "Why do copyright owners keep building encryption-based systems? The answer is not technical but legal and economic. Encryption does not prevent infringement, but it does provide a basis for legal strategems. ...If you make the decryption key a trade secret, you can control entry to the market for players, by giving the key only to acceptable parties who will agree to your licensing terms. This ought to raise antitrust concerns in some cases, but the antitrust authorities have not shown much interest in scrutinizing such arrangements."