This message will self-destruct

By G.F. | SEATTLE

ASK Nico Sell who makes use of her and Robert Statica's Wickr secure-communication app and she can honestly say, "We don't know who our users are." The free iPhone and iPad app uses well-tested strong-encryption techniques to prevent anyone snooping on text messages, images and video, or voicemail exchanged between its users. Accounts are created on the device and checked with a central registry to prevent duplicate names, but no passwords or other identifying information passes to Wickr's servers. Only Wickr users may send messages to other Wickr users, and the software can be set to allow communications only from a preset white list.

Ms Sell says that adopters are particularly fond of Wickr's self-destruct timer, which irretrievably scrambles the transmission after a period, from seconds to days, set by the sender, and which cannot be overridden once transmitted. A sender may delete a message at any time after sending, too, removing it from the recipient's account.

Wickr is part of a growing backlash against the culture of constant sharing and permanent archiving that Facebook, Twitter and other social networks encourage—and often expand without consulting with users. Another app, called Path, limits one's social circle to no more than 150 people, matching "Dunbar's number", as evolutionary anthropologists call the limit to the how many people one can maintain stable social relationships with (which may explain why the Path's original limit of 50 did not stand the test of time).

The Pair app is aimed at love birds and does not automatically self-destruct when a relationship breaks up, though its creators will destroy the exchanged messages and pictures on request. The Snapchat app sends pictures, which are automatically deleted no later than ten seconds after receipt, as set by the sender. Snapchat, however, is still vulnerable to a screen capture by the recipient (he need only hold down the "home" button and press and release the "standby" button on an iOS device). With Wickr, if the device's built-in accelerometer detects it is in motion while viewing a photo or video, the screen goes black. Ms Sell says that her firm designed the app to make it easy to use, even for her septuagenarian mother with whom she exchanges texts via the app. The hardest part of using Wickr is picking and remembering a password.

Ms Sell, for many years the person in charge of press relations at the annual Defcon hacking conference, confesses she does not use Facebook and advises her family to keep information off social networks and other sites, whose privacy and information-retention policies might allow uploaded images or personal details to be retained forever. This is one reason Wickr sports a data scrubber that can wipe remnants of old files that remain in an iOS device's seemingly empty storage areas. The founders have also enlisted leading security experts to probe and test their system, and plan to offer a bug bounty, paying for discovered flaws.

A trial version of an encrypted-voice-call feature is in the offing. Wickr plans eventually to spread to Macintosh and Windows platforms, although there's no timetable as of yet. That would make it a direct competitor to Skype. Skype calls, too, are encrypted, but security is wholly controlled by the company. By contrast, Wickr relies on independent third parties to ensure its security protocols are robust.

Wickr does not scour any social networks or other systems to discover existing relationships, and exposes nothing to the outside world. It collects no information about users and will not include ads. (Future versions will generate revenues for the firm by offering premium upgrades that will appeal to some of the more paranoid punters.) The most detail that Wickr can obtain its customers is a breakdown of app's downloads by country, provided by Apple. Ms Sell notes that in many places where Wickr is popular, like Pakistan or South Africa, its use is considered a crime because of its high-grade encryption or because it lacks a "back-door" for law enforcement.

In America the situation is somewhat schizophrenic. The state department has backed efforts to help citizens in repressive states with anonymous and secure communications (and Wickr has received its export license, says Mr Statica), while the justice department and security agencies would rather they not be used domestically, fearful that such tools might be useful to criminals or terrorists. But then, says Ms Sell, "Good tools are always going to be used by good people and bad people."