In ““Secure Password Managers” and “Military-Grade Encryption” on Smartphones: Oh, Really?” Andrey Belenko and Dmitry Sklyarov write quite a bit about a lot of password management tools. This is admirable work, and I’m glad BlackHat provided a forum for it. However, as a user of 1Password, I was concerned to read the following about that program:
However, because PKCS7 padding is used when encrypting database encryption key, it is possible to verify password just by computing KEK (using MD5 hash function), decrypting last block of encrypted database key, and checking if it equals to 16 bytes with value 0x10 (this will be the PKCS7-compliant padding when encrypting data whose length is exactly N blocks of underlying cipher). Thus, very fast password recovery attack is possible, requiring one MD5 computation and one AES trial decryption per password.
As a result of this design issue, password guessing against passwords [stored by 1Password for iPhone] is estimated (by Belenko and Sklyarov) as 15 Million per second. This is the 3rd worst performance out of a group of 11, and 3,000-fold worse than the best performer in the table (Strip Lite Password Manager, at 5,000 per second).
The folks at Agile Bits, makers of 1Password took the time to blog about the paper, and accept the implications of the work in “Strong Security Requires Strong Passwords.”
However, I think they misunderstand the paper and the issue when they write:
The main reason the password can be determined so quickly is because 6 characters provide relatively few possible password combinations.
I believe the main reason for the issue is because of the way in which 1Password has chosen to store passwords. They alude to this further down in the post when they write:
With that said, as Dmitry and Andrey point out, 1Password could do more to slow the password discovery process, thereby making it take even longer. For example, on the desktop (both Windows and Mac), 1Password uses PBKDF2 to significantly slow down attackers. Currently this is not available on iOS as we needed to support older devices. The next major release of 1Password will only support iOS 5 and at that time we will be incorporating these additional defences.
I still don’t think that’s an adequate response. Several of their competitors on iOS use their own implementation of PBKDF2. Now that’s a risky thing to do, and I’m aware that it might be expensive to implement and test, and the impact of a bug in such code might reasonably be pretty high. So it’s not a slam dunk to do so, in the general case. But in this case, it appears that Apple ships an open source version of PBKDF2: http://opensource.apple.com/source/CommonCrypto/CommonCrypto-55010/Source/API/CommonKeyDerivation.c. So the risk is far lower than creating a new implementation. Therefore, I think Agile Bits should change the way it validates passwords, and incorporate PBKDF2 into all versions of 1Password soon.
They also state:
1Password for iPhone will no longer allow items to be protected by just the PIN code. The PIN code was meant for less sensitive items and we always expected the Master Password protection to be enabled on important items. To simplify things, all items will be protected with the Master Password, just like on iPad, Mac, and Windows.
I understand the choice to do this, and move to stronger protection for all items. At the same time, I like the PIN-only protection for my low-value password. Entering passwords on a phone is a pain. It’s not an easy trade-off, and a 4-digit PIN is always going to be easy to brute force with modern CPUs, however much salting and stretching is applied. I’m capable of making a risk management decisions, but I also understand that many people may feel that Agile Bits wouldn’t offer the choice if it wasn’t secure. I respect the choice that Agile Bits is making to force stronger protection on all their customers.
In summary, 1Password is not storing passwords as securely as they could, and if your phone is stolen, or your phone backups are accessed, those choices leave your passwords at more risk than competing products. I don’t think the fixes to this require iOS5. I think the right thing for Agile Bits to do is to ship an update with better protection against brute force attacks for all their customers, and to do so soon.
[Update 3 (April 10) Agile Bits has released an update which implements 10K PBKDF2 iterations.]
[Update 2: 1Password has now stated that they will do this, adding PBKDF2 to all versions for iOS, which had been the only platform impacted by these issues. They have a hard balance of speed versus security to make, and I encourage them to think it through and test appropriately, rather than rushing a bad fix. ]
[Updated to clarify that this applies only to the iPhone version of 1Password.]