Vulnerability on SIM cards compromises security for millions of phones

A vulnerability on SIM cards, and in particular on the DES algorithm for the encryption, could compromise the security of mobile phones.

A serious vulnerability on SIM cards used in some mobile phones has been found, exploiting the flaw an attacker could eavesdrop on phone conversations, could install malicious applications on the device or it could impersonalize handset’s owner. The discovery is very concerning, the vulnerability could compromise the security for 750 million mobile phones.

Karsten Nohl, founder of Security Research Labs in Berlin, revealed to The New York Times that he has identified a vulnerability in encryption technology used for SIM that could allow an attacker to obtain the 56-digit SIM card’s digital key necessary for the card modification.

Nohl revealed that it is possible to exploit the vulnerability in less than two minutes using a common PC.

“We can remotely install software on a handset that operates completely independently from your phone,” “We can spy on you. We know your encryption keys for calls. We can read your SMSs. More than just spying, we can steal data from the SIM card, your mobile identity, and charge to your account.” Nohl said explaining the effect of the exploitation of the vulnerability.

The vulnerability on SIM cards was related to the DES (Digital Encryption Standard)  algorithm for the encryption of electronic data developed by IBM in the 1970s  and that is used by numerous cell phones today.

Nohl demonstrated that 1,000 cards in Europe and North America are affected by the vulnerability, the researcher will provide more details on its discovery during the next Black Hat security conference in Las Vegas.

The New York Times in his post described the vulnerability on SIM cards with the following statements:

“Mr. Nohl was able to derive the SIM card’s digital key by sending an SMS disguised as having been sent from the mobile operator. Carriers routinely send specially coded messages to handsets to validate customers’ identities for billing and mobile transactions.

For each message, the network and the phone verify their identities by comparing digital signatures. The message sent by Mr. Nohl deliberately used a false signature for the network. In three-quarters of messages sent to mobile phones using D.E.S. encryption, the handset recognized the false signature and ended communication.

But in a quarter of cases, the phone broke off the communication and sent an error message back to Mr. Nohl that included its own encrypted digital signature. The communication provided Mr. Nohl with enough information to derive the SIM card’s digital key.”

The expert also confirmed to have shared the results of his researches with the GSM Association, an association of mobile operators and related companies founded to support the standardizing, deployment and promotion of the GSM mobile telephone system.

In a statement, a GSM Association spokeswoman, Claire Cranton said:

“We have been able to consider the implications and provide guidance to those network operators and SIM vendors that may be impacted,” Ms. Cranton said. She added that it was likely only a minority of phones using the older standard “could be vulnerable.”

Ms. Cranton hasn’t commented the estimation that 750 million cell phones might be open to attack. Principal maker of SIM cards such as the Dutch company Gemalto and the German company Giesecke & Devrient are aware of Nohl study and are analyzing the possible attack scenario.

Pierluigi Paganini

(Security Affairs – Mobile, Vulnerability on SIM cards)