Sim cards hacked: A single text that unlocks millions of mobiles

New vulnerability identified by mobile security experts blamed on 1970s encryption standards

Millions of mobile phones could be at risk from hackers according to new research identifying vulnerabilities in the encryption used by Sim cards. Just by sending a specially designed text, security analysts were able to remotely download malware onto handsets.

Although often thought of as just providing a mobile phone’s number, Sim cards (it stands for subscriber identity module) often store users personal data and are the mark by which carriers authenticate individual users.

“With over seven billion cards in active use, Sims may well be the most widely used security token in the world,” says German security expert Karsten Nohl, the individual responsible for uncovering the flaw.

“The cards protect the mobile identity of subscribers, associate devices with phone numbers, and increasingly store payment credentials, for example in NFC-enabled phones with mobile wallets.”

Nohl’s research covered the different systems of encryption used to secure Sim cards, with one particular standard named DES (Data Encryption Standard) identified as particularly insecure.

Dating back to the 1970s DES has long been considered insecure, with Nohl’s method allowing the encryption to be cracked “within two minutes on a standard computer”.

By sending a text containing a specially designed binary code Nohl was able to trick phones into authenticating him as their network provider.

Once this protocol had been established Nohl could then remotely download software onto the phone allowing him to send texts, access voicemail and even receive reports on the phone’s physical location.

“These capabilities alone provide plenty of potential for abuse,” said Nohl. “This allows for remote cloning of possibly millions of SIM cards including their mobile identity (IMSI, Ki) as well as payment credentials stored on the card.”

Speaking to the BBC Nohl suggested that about one in eight of all Sim cards are vulnerable to the hack, and that Africa-based users were particularly at risk. He did, however, say that network operators would be quick to secure their software.

Nohl will give full details of his method at a Black Hat security conference on July 31st but has already provided industry body GSMA with all of his research.

"Karsten's early disclosure to the GSMA has given us an opportunity for preliminary analysis,” said a GSMA spokeswoman. "It would appear that a minority of Sims produced against older standards could be vulnerable."

"There is no evidence to suggest that today's more secure Sims, which are used to support a range of advanced services, will be affected".