First, the third paragraph of the introductory page, which reads:
Public Law 106-197 amended 18 U.S.C. 2519(2)(b) to require that reporting should reflect the number of wiretap applications granted for which encryption was encountered and whether such encryption prevented law enforcement officials from obtaining the plain text of communications intercepted pursuant to the court orders. In 2006, no instances were reported of encryption encountered during any federal or state wiretap.
Second, on page 11 of the PDF (under the section “Summary and Analysis of Reports by Prosecuting Officials”), we learn that the federal government doesn’t encounter computers all that often:
The electronic wiretap, which includes devices such as digital display pagers, voice pagers, fax machines, and transmissions via computer such as electronic mail accounted for less than 1 percent (13 cases) of intercepts installed in 2006; 6 of these involved electronic pagers, and 7 involved computers.
For comparative purposes, the report notes that 1,839 wiretaps concluded in 2006.
Most voice communications are not encrypted. The exception is mobile telephones, which are encrypted only on the radio link. (Mobile phone wiretaps, however, generally take place at the switching office, where the voice traffic is not encrypted.) This certainly includes most VoIP calls today, and is a reason that is often cited for the lack of use of SIP-based services on corporate networks. Most VoIP data is transmitted using the Real-Time Protocol (RTP), which does not encrypt payload data. The Secure Real-Time Transport (SRTP) offers a potential solution, and implementations are now available.
After that very long introduction, I’d like to point out that the Interop Labs next week will have an interoperability demonstration featuring SRTP. It’s open to the public, so if you happen to be on the show floor, stop on by!