Password store for iPhone protects you by letting attackers in every time

The iMobileSitter app generates plausible fake passwords in place of the real ones, making it hard for hackers to know they've been tricked

A password store that lets attackers in every time may not sound very useful, but researchers at Germany's Fraunhofer Institute for Secure Information Technology beg to disagree.

Traditional password stores, even those with the strongest encryption, have a weakness, according to Ruben Wolf: They help attackers trying to guess the master password by telling them when their guess is wrong.

Wolf, an expert in cloud computing, identity and privacy at the Institute, thinks it's better to let attackers in every time, but replace the real passwords and PINs in the password store with fake ones when the master password is entered incorrectly.

That's the approach taken with iMobileSitter, an app for the iPhone and iPad developed by researchers at the institute and now available through the iTunes Store. An Android version is in the works and, when that's complete, a PC version will follow. The encrypted password store can be exported in an email to share between devices, all using the same master password, or as a backup.

The app uses the master password to generate a long sequence of bits using a cryptographic algorithm. To save a password in the store, it takes each character of the password in turn, finds an occurrence of the character in the generated sequence of bits, and then notes the position.

To retrieve a password from the store, the app generates characters corresponding to the patterns of bits at each of the positions noted. If the master password entered is the correct one, the long sequence of bits will be the same as when the password was stored, and the retrieved password too will be the same. If the master password is incorrect, the sequence of bits will differ, and so too will the retrieved password.

The app is able to generate fake passwords using only the set of characters valid for the original password, so if you store your bank PIN, the fake will still be a four-digit code and not, say, XLYT, which would be a dead giveaway to an attacker that something was wrong.

It's possible -- with a chance of one in 10,000 -- that a fake PIN could be the same as the real PIN, Wolf said. That's necessary because otherwise an attacker could enter millions of fake passwords looking for the one PIN that never came up.

While iMobileSitter gives attackers no useful feedback about their password guesses, it does offer the user a little clue if they mistype the master password (a distinct possibility on a virtual keyboard): a small symbol derived from the password is displayed in one of four slots at the top of the login screen. A given password will always correspond to the same symbol, color combination and position -- a black circle on a pink background in the second slot, say, or a red-on-yellow mushroom in the third. If you don't see your usual symbol, you mistyped. But an attacker can't work back from the symbol to the correct password, as there are only around 8,000 or so symbol-color-position combinations, and billions upon billions of possible passwords: It's a sort of visual hash, said Wolf.

The truly paranoid (with good memories) can even deliberately use multiple master passwords to separate passwords stored in the same file into different domains: If one master password is compromised, at least the passwords stored using other master passwords are still safe.

There is one downside to iMobileSitter's hidden-in-plain-sight approach. Only the passwords are hidden: The websites and usernames are not. That means anyone with access to your iPhone will not only see that you're a secret Twitter addict, they'll also know your handle -- they just won't be able to log in as you.

The app is in the iTunes Store now and costs €4.99.

Peter Sayer covers open source software, European intellectual property legislation and general technology breaking news for IDG News Service. Send comments and news tips to Peter at peter_sayer@idg.com.

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.
Peter Sayer

Peter Sayer

IDG News Service
Show Comments

Essentials

Brother MFC-L3745CDW Colour Laser Multifunction

Learn more >

Mobile

Exec

Budget

Back To Business Guide

Click for more ›

Brand Post

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?