Pierluigi Paganini September 24, 2016

Experts from Elcomsoft discovered a new vector of attack to access password-protected local backups produced by iOS 10 devices.

According to security experts from the computer forensics company Elcomsoft, Apple has weakened the backup security protection of its recently-issued iOS 10 skipping certain security checks. This means that hackers could easily crack password protection used to protect the backups of iOS devices that are stored on Macs and PCs.

“We discovered a major security flaw in the iOS 10 backup protection mechanism. This security flaw allowed us developing a new attack that is able to bypass certain security checks when enumerating passwords protecting local (iTunes) backups made by iOS 10 devices.” reads a blog post published by Elcomsoft.

The researchers reported the presence of a security hole that opens the door for a new type of iOS brute-force password attack.

“We looked into it, and found out that the new mechanism (in iOS 10) skips certain security checks, allowing us to try passwords approximately 2,500 times faster compared to the old mechanism used in iOS 9 and older,” continues the post.

Apple has downgraded the hashing algorithm for iOS 10 from “PBKDF2 SHA-1 with 10,000 iterations” to“plain SHA256 with a single iteration.” With this premise, an attacker can brute-force the password via a standard desktop computer processor faster.

PBKDF2 (Password-Based Key Derivation Function) leverages on a SHA-1 hash with thousands of password iterations, making it hard the password cracking.

In iOS 9 and prior versions back to iOS 4, Apple was using the PBKDF2 function to generate the final crypto key using a pseudorandom function (PRF) 10,000 times (password iterations).

In a real attack scenario, hackers need to have a local or remote access to the machine where the Apple backup is stored, then crack it by running a brute-force attack.

The experts explained that the new security checks implemented by Apple allow 2,500 times faster brute force attacks compared to the old one that was used in iOS 9 backups.

Below data related to brute-force attacks reported by Elcomsoft:

• iOS 9 (CPU): 2,400 passwords per second (Intel i5)
• iOS 9 (GPU): 150,000 passwords per second (NVIDIA GTX 1080)
• iOS 10 (CPU): 6,000,000 passwords per second (Intel i5)

Elcomsoft confirmed that the password hole could be exploited to gain access to Apple Keychain. iOS 10 backups allow a hacker to extract and decrypt Keychain data.

“Keychain contains information such as saved passwords or authentication tokens to applications requesting secure storage for authentication credentials, Safari logins and passwords, credit card information, Wi-Fi network information, and any data that third-party app developer consider worthy of extra protection.” states the post about the Keychain.

Users can download the Elcomsoft Phone Breaker 6.10 that comes with 6 million passwords per second (CPU only) for iOS 10 backups.

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Pierluigi Paganini

(Security Affairs – iOS 10 Backup Encryption, mobile)