Open Whisper Systems, the developer of encrypted messaging app Signal, received a subpoena earlier this year requesting user information but was only able to supply the duration of a user's membership, according to court documents unsealed last week.
An assistant attorney in the U.S. state of Virginia requested email addresses, history logs, browser cookie data, and other information associated with two phone numbers as part of a grand jury probe, the redacted documents showed. The request was made in the first half of this year, the documents showed.
Citing its encryption technology, which is also used in other messaging services such as Facebook's (fb) Whatsapp, Open Whisper Systems said it was only able to supply the registration date and the last date one of the numbers was used. The company had no information about the other number, according to the documents.
"We've designed Signal so it minimizes the amount of data we retain on users, and we don't really have anything to respond with in situations like this," Open Whisper Systems security expert Moxie Marlinspike told Reuters.
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The subpoena was the first the company has received, he said.
More than two billion people use a form of Signal's code, though companies licensed to use the code keep related information about users, Marlinspike said.