I understand data is encrypted before it ever leaves your machine, but I certainly wouldn't want encrypted data at-rest being exposed. Which gives me concern about Tarnap's terms: "I may provide information concerning your account and your use of the service to 3rd parties, at my sole discretion, if ... It is requested by law enforcement authorities ..." note - no requirement for a court order or subpoena.
https://www.tarsnap.com/legal-why.html#PRIVACYLAW