Feeds

WhatsApp crypto snafu drops trou on users' privates

'Very basic error' leaves messaging app open to snoopers

Choosing a cloud hosting partner with confidence

Mobile messaging service WhatsApp came for criticism over the robustness of its cryptography last week after a fix for a January security snafu was slammed for not being robust enough.

Back at the beginning of the year WhatsApp was investigated in Canada and the Netherlands for indefinitely retaining users' email address book data that it snaffled when they joined the service.

It was also criticised for generating cryptographic keys from data such as a mobile phone's IMEI (International Mobile Equipment Identity) number or their network MAC (Media Access Code) addresses.

The IMEI number is programmed into a mobile phone during the manufacturing process. Under certain circumstances it can be broadcast in clear text messages from a phone. They are a terrible choice for passwords because every network packet has the MAC address within it.

WhatsApp revised its encryption in the wake of these criticisms. However, a review of the fix by Dutch mathematics and computer science student Thijs Alkemade has revealed that WhatsApp's approach, while improved, remains deeply flawed.

WhatsApp generates a session key that it uses to initialise a stream cipher. But the same cipher stream is used for both outgoing and incoming messages.

This is a cryptographic mistake akin to using a one-time pad more than once, which creates serious security shortcomings in the system, as Sophos security researcher Paul Ducklin explains:

"A stream cipher works as a pseudorandom number generator, emitting an unpredictable string of bytes that you XOR with the plaintext to encrypt," Ducklin writes on Sophos' Naked Security blog. "In other words, you mustn't use the same string of bytes to encrypt anything else, because that would make it predictable, and that is a cryptographic disaster."

"A stream cipher works like a pseudo one time pad. A crypto-system that relies on a string of hardware random numbers to create an unbreakable cipher if – and only if – the pad is used just once," he added.

In addition, WhatsApp uses the cryptographically flawed RC4 cipher instead of more robust alternatives.

The upshot is that, as things stand at the time of writing, anyone capable of eavesdropping on your WhatsApp connection would also be able to decrypt messages with minimal difficulty.

Ducklin advises WhatsApp users only to use the service for messages they are happy to be considered public until a more robust encryption scheme is introduced.

Alkemade, the Dutch researcher who created a buzz in the security community by publicising the flaws last week, suggests that WhatsApp should use Transaction Layer Security, or TLS – the same end-to-end encryption used by secure websites.

Michael Sutton, director of security research at Zscaler, criticised WhatsApp for basic cryptographic mistakes.

"WhatsApp made a very basic error when implementing their message encryption by leveraging the same encryption key for both incoming and outgoing messages," Sutton said. "While compromise of the flaw is not simple, it is quite possible and as such, WhatsApp communication cannot be considered secure until this issue is addressed. It is not yet clear if the implementation flaw is uniform across all WhatsApp implementations but for now, all implementations should be considered insecure."

The Register forwarded these criticisms to WhatsApp last week, inviting it to comment. We are yet to hear back. So it's unclear whether or not WhatsApp acknowledges that there's a problem, much less how and when it might deliver a fix.

A successful social engineering attack last week against domain name firm Network Solutions, used by WhatsApp, meant that the messaging app was one of a number of firms to suffer a DNS hijack attack in turn. Surfers attempting to visit its site were redirected to a pro-Palestinian propaganda website instead.

While that particular problem was resolved within hours on Tuesday, the crypto problem may take a far greater effort to resolve. ®

Beginner's guide to SSL certificates

More from The Register

next story
Russian hackers exploit 'Sandworm' bug 'to spy on NATO, EU PCs'
Fix imminent from Microsoft for Vista, Server 2008, other stuff
FYI: OS X Yosemite's Spotlight tells Apple EVERYTHING you're looking for
It's on by default – didn't you read the small print?
Microsoft pulls another dodgy patch
Redmond makes a hash of hashing add-on
'LulzSec leader Aush0k' found to be naughty boy not worthy of jail
15 months home detention leaves egg on feds' faces as they grab for more power
Forget passwords, let's use SELFIES, says Obama's cyber tsar
Michael Daniel wants to kill passwords dead
Kill off SSL 3.0 NOW: HTTPS savaged by vicious POODLE
Pull it out ASAP, it is SWISS CHEESE
Facebook slurps 'paste sites' for STOLEN passwords, sprinkles on hash and salt
Zuck's ad empire DOESN'T see details in plain text. Phew!
prev story

Whitepapers

Forging a new future with identity relationship management
Learn about ForgeRock's next generation IRM platform and how it is designed to empower CEOS's and enterprises to engage with consumers.
Cloud and hybrid-cloud data protection for VMware
Learn how quick and easy it is to configure backups and perform restores for VMware environments.
Three 1TB solid state scorchers up for grabs
Big SSDs can be expensive but think big and think free because you could be the lucky winner of one of three 1TB Samsung SSD 840 EVO drives that we’re giving away worth over £300 apiece.
Reg Reader Research: SaaS based Email and Office Productivity Tools
Read this Reg reader report which provides advice and guidance for SMBs towards the use of SaaS based email and Office productivity tools.
Security for virtualized datacentres
Legacy security solutions are inefficient due to the architectural differences between physical and virtual environments.