Securing the NHS C19 Contact Tracing App

The combined NHS Digital Taskforce, NHSX, recently beta tested the new UK Covid-19 contact tracing app on the Isle of Wight, and have released code to the cyber security community to review.

The app logs interactions with other bluetooth-enabled smartphones each day, and allows the NHS to notify users who have been in contact with self-reporting Covid-19 cases that they should re-enter isolation as a precaution.

A recent blog post by the UK National Cyber Security Centre identified a number of areas for improvement, with the contact tracing app itself expected to be officially released in June 2020.

 

The Pairing Problem

NHS servers ping the app every 8 seconds to confirm active connections, and the app itself records received signal strength indicators (RSSI) via Bluetooth to gauge where users have been in contact with each other. Users then upload their records if they experience symptoms.

Any attacker with access to this upload traffic, (which does not include the user ID but is unencrypted) could begin comparing submissions via start/end times and signal strength readings, and would theoretically be able to pair these users together.

This problem of uniquely identifiable pairs potentially compromises the identity of the individuals using the app, as well as their location history relative to each other.

The NCSC have confirmed that in the release version, even ‘anonymised’ RSSI data will itself be encrypted, to stop any third-parties attempting to ‘re-identify’ either or both of the users.

 

Intercepting the Public Key

In beta testing, the Authority’s Public Key was not transferred to the user’s phone via TLS encryption (like a secured web-page) raising the possibility that although the app could be downloaded successfully, this important piece of information used for submitting data could be compromised.

This would be akin to a kind of ‘man-in-the-middle’ attack, where a user’s encrypted uploads could be (even if not unencrypted) sabotaged or withheld during transmission back to NHS systems.

Security researchers have suggested that since this key is not secret, it should be wrapped into the installation of the app itself.

The NCSC have since confirmed that intermediate certificate pinning has been used to reduce the risk of this happening, and that this limitation will be fixed once the Isle of Wight trial ends.

 

Bluetooth Broadcast Values

The app operates via broadcast values with change every 24 hours to prevent a device being tracked by Bluetooth over longer periods of time. This is significantly longer than the industry standard 15 minutes.

However, more controversially, a predictable ‘KeepAlive’ counter is used to connect old and new broadcast values, raising the potential for an attacker to re-identify the user beyond the 24-hour limit.

The NCSC defends the longer-term tracing as necessary to establish social interactions more accurately, but has resolved to randomise the counter to stop broadcast values being easily matched or the user re-identified endlessly.

 

Whistleblowing

Under beta testing, the app’s original policy documentation contained the line: “You may not publicly disclose any details of the vulnerability [that you’re reporting] without consent from NHSX.”

This would have run counter to the NCSC’s own vulnerability disclosure policy, which suggests that members of the technology community should be encouraged to highlight system weaknesses (particularly during public consultation beta-tests) for correction.

This line is to be removed from the public release version.

 

For cybersecurity support & IT expertise, please contact our team today.


WhatsApp Encryption Launches

 

Popular messaging app WhatsApp have launched end-to-end WhatsApp encryption for over one billion users.

The new security capabilities introduced by the Facebook owned company ensures that every message remains encrypted during transmission, preventing even WhatsApp from reading user data.

With encryption and technological privacy issues regularly appearing in recent news headlines, the WhatsApp encryption upgrade comes at just the right moment for the security concerned, after more than two years of delays in development across multiple platforms.

Much like during Apple’s recent legal dispute with the FBI, the move would also prevent the release of confidential user data following a court order. According to reports from the New York Times, the technology provider have been reported to already be in a longstanding dispute with the US Department of Justice over user data.

WhatsApp are making it clear they support absolute user privacy, with “not even WhatsApp” able to read the encrypted data, and users able to verify their connections are secure via a 60 digit or QR code swap.

From today, the WhatsApp conversation screen will now display an official notification to all users – confirming that their messages are encrypted successfully.

 

For hardware and software security advice – contact Lineal today.


Google and Apple unite over user privacy

 

Google and Apple’s respective CEOs have joined forces over the issue of customer privacy, with Apple CEO Tim Cook publicly refusing the Federal Bureau of Investigation (FBI) ‘backdoor’ access to iPhone software.

Google CEO Sundar Pichai backed Apple’s decision on Twitter, arguing that assisting the FBI to gain such access to a private individual’s smartphone would be a ’troubling precedent.’

The mobile phone privacy dispute with the FBI over encryption comes 2 months after Farook and Tashfeen Malik killed 14 people in a mass shooting in San Bernadino, California, with investigators demanding that Apple now assist the authorities in accessing Farook Malik’s iPhone 5C.

Both Apple and Google argue that ‘backdoor’ decryption would put the privacy of millions of ordinary smartphone users at risk from Government intrusion, with Tim Cook famously arguing that ‘You can’t have a back door that’s only for the good guys’. In theory, each iPhone’s encryption method is unique, and Apple argue that there should be no possible method for accessing a given user’s data.

On Tuesday however a Federal Judge ordered Apple to disable Farook Malik’s suspected phone setting which enforces usage delays or wipes the iPhone in the event of multiple incorrect password attempts, giving the FBI the opportunity to automatically test millions of possible passwords without penalty.

Both companies’ actions are being driven by the issue of reputation: giving law enforcement authorities the ability to access an individual’s data would utterly undermine smartphone manufacturers’ advertisement of user security.

With neither side willing to back down, expect the dispute to go to the courts, with the key issue being whether Apple can control permitted access to this iPhone, and this iPhone only.

 

For specialist IT Support, contact Lineal today: 01271 375999 or email: [email protected]