Highly appreciated by users of Apple devices, the AirDrop functionality makes it easy to share files. For security reasons, it is limited by default to contacts that are in the address book. However, security researchers have found a flaw in this communication protocol allowing a malicious person to collect, under certain conditions, the phone number of any user, even their e-mail address.
Indeed, AirDrop uses a pre-authentication procedure where the sender and the receiver exchange the cryptographic fingerprints (SHA-256) of their telephone numbers and / or their e-mail addresses, in order to verify that the two are indeed contacts of each other. However, according to the researchers, it is not very complicated to find the original values from these fingerprints. Since the telephone number space is relatively small, it is possible to partially pre-calculate the telephone number fingerprints. In the end, a few fractions of a second would be enough to find the initial number. Revealing the email is more complicated, but not impossible based on databases of past leaks, the researchers say.
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Alerted by researchers, Apple has so far not moved a finger. It must be said that attack scenarios are only possible under certain conditions. First of all, you have to be close to the victim. Then, to retrieve the fingerprints of a transmitter, the hacker must wait for the latter to discover the surrounding terminals by going to the AirDrop sharing menu. So you have to be there at the right time. This time constraint does not exist if the hacker plays the role of sender, because it is he who decides when to initiate authentication. But to receive a recipient’s fingerprints, he must be in his address book, which is unlikely.
Regardless, the researchers offered an open source version of the AirDrop protocol that was improved. Called PrivateDrop, it ensures that these data leaks are impossible in any condition.