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According to the US 2011 Wiretap Report, encryption — on the off chance that it is encountered — has been no hurdle to retrieving the content of a conversation.

Public Law 106-197 amended 18 U.S.C. § 2519(2)(b) in 2001 to require that reporting should reflect the number of wiretap applications granted in which encryption was encountered and whether such encryption prevented law enforcement officials from obtaining the plain text of the communications intercepted pursuant to the court orders. In 2011, encryption was reported during 12 state wiretaps, but did not prevent officials from obtaining the plain text of the communications.

— US 2011 Wiretap Report, page 8–9 (emphasis added)

Why was this encryption not successful?

Unfortunately the report includes very little detail about what kind of transmission and encryption was involved in any of the 12 cases.

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up vote 5 down vote accepted

Many reasons, including:

  • federal law requiring companies (e.g. telephone) to surrender encryption keys
  • interception before encryption (it's pretty easy to eavesdrop on keyboard input purely via electromagnetic radiation even several meters away)
  • MITM on an insecure channel (quite effective)
  • outright broken encryption algorithms
  • social engineering to recover key
  • Van Eck phreaking
  • weak keys
  • if all else fails, save the ciphertext for until you can subpoena the suspect and retrieve the key (but I guess this doesn't count)

etc... when you are being heavily monitored, purely cryptographic measures become too intangible and no longer suffice. You need to employ physical means to remain in a secure position.

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First two seem most likely to me. – CodesInChaos Jun 30 '12 at 9:49
You can add "email stored on the servers of the email providers such a gmail". So while the communication with gmail is encrypted using SSL, the stored mails are not. – Hendrik Brummermann Jun 30 '12 at 12:40

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