UK student develops antidote for first Android file-encrypting ransomware

A hardcoded encryption key allows recovering files held hostage by the Simplocker Android malware

Victims of Simplocker, the first file-encrypting ransomware threat for Android devices, can recover files without paying cybercriminals because the malicious program uses a hardcoded encryption key.

Simon Bell, a computer science student in his final year at the University of Sussex in the U.K., recently analyzed the threat in detail and was the first to reveal the existence of the key.

Simplocker was identified by security researchers from antivirus vendor ESET at the beginning of June and is the first ransomware application for Android to use encryption as an extortion method.

The malware scans the SD memory cards of infected devices for files with the jpeg, jpg, png, bmp, gif, pdf, doc, docx, txt, avi, mkv, 3gp and mp4 extensions and encrypts them using the AES (Advanced Encryption Standard) algorithm. Another interesting aspect of the threat is that it communicates with a command-and-control server hosted on the Tor anonymity network.

The ESET researchers said that Simplocker is most likely a proof-of-concept or a work in progress, an idea further enforced by Bell's discovery that the malware uses a master encryption key included in its code instead of separate unique keys for each infected device obtained from the C&C server.

A Java class called AesCrypt that's used by Simplocker "contains a method called encrypt() which uses AES encryption and cipher password 'jndlasf074hr'," Bell said Monday in a blog post.

He used that information and the malware's own decrypt() method to create a separate Java program that can recover files encrypted by the threat.

"The antidote for this ransomware was incredibly easy to create because the ransomware came with both the decryption method and the decryption password," Bell said in a separate blog post Tuesday. "Therefore producing an antidote was more of a copy-and-paste job than anything."

Future versions of Simplocker will probably better protect the decryption keys and will likely obtain them from the C&C server, he said.

"Since the Simplelocker ransomware is a proof-of-concept, the antidote provided here is simply a solution to this proof-of-concept," Bell said. "Future versions of advanced smartphone ransomware will likely prove significantly harder to reverse engineer."

Antivirus vendor Avast also released a free Simplocker removal tool Tuesday that's capable of decrypting the files affected by the malware. The tool is called AVAST Ransomware Removal and is easier to use than Bell's antidote because it's packaged as an app that can be downloaded from Google Play.

Encrypting files proved a profitable technique for ransomware programs on Windows, so security researchers expect Android ransomware to take a similar approach. Users are advised to install apps only from trusted sources such as Google Play in order to limit the chances of becoming victims of such threats.

Join the newsletter!

Or

Sign up to gain exclusive access to email subscriptions, event invitations, competitions, giveaways, and much more.

Membership is free, and your security and privacy remain protected. View our privacy policy before signing up.

Error: Please check your email address.

Tags fraudmalwaremobile securityscamsonline safetyesetAvastSimon Bell

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.
Lucian Constantin

Lucian Constantin

IDG News Service
Show Comments

Cool Tech

Bang and Olufsen Beosound Stage - Dolby Atmos Soundbar

Learn more >

Toys for Boys

ASUS ROG, ACRONYM partner for Special Edition Zephyrus G14

Learn more >

Sony WF-1000XM3 Wireless Noise Cancelling Headphones

Learn more >

Nakamichi Delta 100 3-Way Hi Fi Speaker System

Learn more >

Family Friendly

Mario Kart Live: Home Circuit for Nintendo Switch

Learn more >

Philips Sonicare Diamond Clean 9000 Toothbrush

Learn more >

Stocking Stuffer

SunnyBunny Snowflakes 20 LED Solar Powered Fairy String

Learn more >

Teac 7 inch Swivel Screen Portable DVD Player

Learn more >

Christmas Gift Guide

Click for more ›

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Tom Pope

Dynabook Portégé X30L-G

Ultimately this laptop has achieved everything I would hope for in a laptop for work, while fitting that into a form factor and weight that is remarkable.

Tom Sellers

MSI P65

This smart laptop was enjoyable to use and great to work on – creating content was super simple.

Lolita Wang

MSI GT76

It really doesn’t get more “gaming laptop” than this.

Jack Jeffries

MSI GS75

As the Maserati or BMW of laptops, it would fit perfectly in the hands of a professional needing firepower under the hood, sophistication and class on the surface, and gaming prowess (sports mode if you will) in between.

Taylor Carr

MSI PS63

The MSI PS63 is an amazing laptop and I would definitely consider buying one in the future.

Christopher Low

Brother RJ-4230B

This small mobile printer is exactly what I need for invoicing and other jobs such as sending fellow tradesman details or step-by-step instructions that I can easily print off from my phone or the Web.

Featured Content

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?