Skype 2.5's new stealth mode 'cracked'

Stealth techniques introduced to make the latest version of Skype harder to detect and block, have been cracked only days after them being in the open.

Last week, P2P security specialist iPoque reported that the recently-announced beta of Skype 2.5 had changed its call setup in order to bypass the growing band of packet filtering systems aiming to stop the software running on company networks.

The company has now been able to reverse-engineer the work of Skype's designers, but only by radically overhauling its detection procedure.

According to CEO Klaus Mochalski, Skype 2.5's call setup no longer conformed to a small number of predictable patterns, which could be identified and filtered at packet level. The company's PRX Traffic Manager now used a heuristic model as the basis of its filtering.

The re-engineering of Skype is not merely a refresh, as the program has been randomized to make established pattern-matching techniques useless.

From running the Skype client and watching it attempt to set up connections many thousands of times, it had been possible to find a tell-tale pattern of packet lengths, timings, and small-scale packet consistencies that betrayed its presence.

"The hand-shaking at packet level has changed quite a bit," he confirmed.

Once the call connection is established, of course, Skype's encryption makes it impossible to block from other packet traffic, hence the need to stop it before this point.

"They (Skype) talk about new features but never about new stealth features."

Mochalski suggested that Skype could one day become impossible to detect if the program integrated more advanced encryption into its make-up. Skype then would have to manage and distribute encryption keys. That probably is some way off.

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

John E. Dunn

Techworld.com
Show Comments

Cool Tech

Bang and Olufsen Beosound Stage - Dolby Atmos Soundbar

Learn more >

Toys for Boys

Sony WF-1000XM3 Wireless Noise Cancelling Headphones

Learn more >

Nakamichi Delta 100 3-Way Hi Fi Speaker System

Learn more >

ASUS ROG, ACRONYM partner for Special Edition Zephyrus G14

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

Product Launch Showcase

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?