![]() ![]() Unfortunately the numbers don’t appear to work here. The former involves computing an iterated SHA-256 with N iterations to compute a Wickr ID from sensitive information. These attacks are similar to password cracking, suggesting Wickr could potentially mitigate this problem through the use of two defensive techniques: hash strengthening and salting. Similarly, one could precompute the hashes of email addresses from a list obtained through a variety of sources (legitimate or otherwise) and conduct a dictionary attack. Precomputing and indexing the hashes for all possible phone numbers ahead of time allows the search to complete almost instantaneously (using up to 320 GB of storage, though this could be significantly compressed via a “ time-memory trade off”). Since there are less than 10^10 possible phone numbers in North America, a consumer-grade desktop with a decently powered GPU can compute the hash for all of them in a matter of seconds. With this in mind, let’s consider how difficult it is for Wickr to uncover who its users are (or how difficult it is for somebody else who has obtained the list of Wickr IDs by a court order or compromising Wickr’s servers). ![]() A great explanation on the use of cryptographic hash functions in attempts to anonymize data can be found here. Unfortunately, this is a recurring theme in a variety of applications as a result of misunderstanding cryptography - specifically, the fact that hash functions are not one-way if the input space is small. If the number of possible inputs is small, we can simply try all of them. The problem here is that while it’s not always possible to determine the input to a hash function given the output, we can leverage the fact that the same input always yields the same output. This process simplifies the discovery of other users, supposedly without Wickr having the ability to identify the users of the anonymous service. Wickr looks this up in its database to determine if you’ve registered with the service to facilitate message exchange. When your friends want to find you, they enter your phone number or email address, which is then put through the same hash function, resulting in the same output (Wickr ID). Wickr IDs are then stored server-side and used for discovery. The app utilizes a cryptographic hash function (SHA-256 in this case) to obtain “anonymous” Wickr IDs from the non-Wickr IDs. During registration, users enter their email address and/or phone number (non-Wickr IDs). Wickr claims that it cannot identify who has registered with the service or which of its users are communicating with each other. This startup offers a simple app featuring “military grade encryption” of text, photo, video, and voice messages as well as anonymous registration for its users. However, maintaining anonymity is difficult while simultaneously offering a straightforward way for users to find each other.Įnter Wickr. When coupled with anonymity, end-to-end encryption can prevent a central service provider from obtaining any information about its users or their communications. Following the revelations of wide-scale surveillance by US intelligence agencies and their allies, a myriad of services offering end-to-end encrypted communications have cropped up to take advantage of the increasing demand for privacy from surveillance.
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