New Attack Lets Hackers Decrypt VoLTE Encryption to Spy on Phone Calls

A team of tutorial researchers—who earlier made the headlines earlier this year for uncovering critical safety issues in the 4G LTE and 5G networks—today presented a new attack termed ‘ReVoLTE,’ that could let remote attackers crack the encryption used by VoLTE voice phone calls and spy on specific cellular phone calls.

The attack would not exploit any flaw in the Voice about LTE (VoLTE) protocol alternatively, it leverages weak implementation of the LTE cell community by most telecommunication providers in apply, allowing an attacker to eavesdrop on the encrypted phone calls produced by qualified victims.

VoLTE or Voice around Extended Time period Evolution protocol is a standard high-pace wireless communication for cellular phones and information terminals, which include World-wide-web of items (IoT) units and wearables, deploying 4G LTE radio accessibility engineering.


The crux of the trouble is that most cellular operators usually use the similar keystream for two subsequent calls inside a single radio connection to encrypt the voice facts amongst the cellphone and the exact foundation station, i.e., mobile cellular phone tower.

Thus, the new ReVoLTE attack exploits the reuse of the same keystream by vulnerable foundation stations, permitting attackers to decrypt the contents of VoLTE driven voice calls in the subsequent state of affairs.

However, reuse of a predictable keystream is not new and was first pointed out by Raza & Lu, but the ReVoLTE attack turns it into a functional assault.

How Does the ReVoLTE Assault Operate?

To initiate this attack, the attacker must be linked to the identical base station as the sufferer and position a downlink sniffer to monitor and document a ‘targeted call’ produced by the victim to anyone else that demands to be decrypted afterwards, as section of the to start with phase of ReVoLTE attack.

After the target hangs up the ‘targeted phone,’ the attacker is demanded to simply call the target, usually in just 10 seconds quickly, which would pressure the vulnerable network into initiating a new contact involving target and attacker on the very same radio connection as applied by prior qualified simply call.

“The keystream reuse happens when the target and keystream connect with use the identical person-airplane encryption crucial. As this essential is current for every single new radio connection, the attacker should make sure that the first packet of the keystream connect with comes within the lively phase immediately after the goal get in touch with,” the researchers said.

The moment related, as component of the 2nd section, the attacker requirements to engage the target into a discussion and document it in plaintext, which would assistance the attacker later reverse compute the keystream used by the subsequent get in touch with.

In accordance to researchers, XOR-ing the keystreams with the corresponding encrypted frame of the targeted get in touch with captured in the initial stage decrypts its material, letting attackers to pay attention to what conversation its sufferer had in the preceding telephone get in touch with.

“As this benefits in the same keystream, all RTP data is encrypted in the similar way as the voice knowledge of the target call. As before long as a enough volume of keystream data was produced, the adversary cancels the simply call,” the paper reads.

However, the duration of the next contact should be bigger than or equivalent to the initial contact in get to decrypt each body otherwise, it can only decrypt a section of the conversation.

“It is critical to be aware that the attacker has to interact the victim in a lengthier discussion. The longer he/she talked to the sufferer, the a lot more content of the preceding interaction he/she can decrypt,” the paper reads.

“Every single body is linked with a rely and encrypted with an particular person keystream that we extract for the duration of the keystream computation. As the same count generates the very same keystream, the count synchronizes the keystreams with encrypted frames of the focus on connect with. XOR-ing the keystreams with the corresponding encrypted frame decrypts the focus on connect with.”

“As we aim to decrypt the finish connect with, the keystream call need to be as long as the goal phone to supply a ample variety of packets, as or else we can only decrypt a element of the dialogue.”

Detecting ReVoLTE Assault and Demonstration

To show the useful feasibility of the ReVoLTE attack, the workforce of teachers from Ruhr University Bochum applied an close-to-finish variation of the assault in just a professional, vulnerable network and business phones.

The team utilised the downlink analyzer Airscope by Computer software Radio Program to sniff the encrypted website traffic and a few Android-based phones to get hold of the regarded-plaintext at the attacker’s cellphone. It then compared the two recorded conversations, determined the encryption essential, and eventually decrypted a part of the earlier phone.

You can see the demo online video of the ReVoLTE assault, which, according to the researchers, could charge significantly less than $7000 to attackers for setting up the assault and, finally, decrypting downlink targeted traffic.

The group tested a variety of randomly picked radio cells throughout Germany to determine the scope of the challenge and identified that it affects 12 out of 15 foundation stations in Germany, but researchers reported the safety gap also affects other nations.

Scientists notified the afflicted German base station operators about the ReVoLTE attack by means of the GSMA Coordinated Vulnerability Disclosure Programme process in early December 2019, and the operators managed to deploy the patches by the time of publication.

Since the difficulty also affects a significant quantity of companies throughout the world, researchers produced an open up source Android app, named ‘Mobile Sentinel,’ that you can use to detect no matter if their 4G community and base stations are vulnerable to the ReVoLTE assault or not.

Researchers—David Rupprecht, Katharina Kohls and Thorsten Holz of RUB University Bochum and Christina Pöpper of NYU Abu Dhabi—have also introduced a committed site and investigate paper PDF, titled “Connect with Me It’s possible: Eavesdropping Encrypted LTE Phone calls With REVOLTE,” detailing the ReVoLTE assault, where by you can discover much more aspects.

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