Why Secure Containers Are Needed
iOS has solid encryption, there is no backdoor, hence, your firm’s data is safe under lock and key, correct? Not necessarily. Enlightening new research by cryptographers at Johns Hopkins University (1) has surfaced weaknesses in the iOS and Android encryption schemes. Ironically, in the case of iOS, part of the weakness is related to a security hierarchy which is often unused.
“Apple provides interfaces to enable encryption in both first-party and third-party software, using the iOS Data Protection API. Within this package, Apple specifies several encryption “protection classes” that application developers can select when creating new data files and objects. These classes allow developers to specify the security properties of each piece of encrypted data, including whether the keys corresponding to that data will be evicted from memory after the phone is locked (“Complete Protection” or CP) or shut down (“After First Unlock” or AFU) …
… the selection of protection class makes an enormous practical difference in the security afforded by Apple’s file encryption. Since in practice, users reboot their phones only rarely, many phones are routinely carried in a locked-but-authenticated state (AFU). This means that for protection classes other than CP, decryption keys remain available in the device’s memory. Analysis of forensic tools shows that to an attacker who obtains a phone in this state, encryption provides only a modest additional protection over the software security and authentication measures described above.” (JHU – bold is our addition)
The reality is that most of our iPhones are commonly in “After First Unlock” state because we rarely reboot our phones. To achieve maximum security, we would have to power down our iPhones and authenticate after each use. That is, scores or hundreds of times per day. Otherwise, all data in the AFU state is vulnerable to law enforcement agencies or criminals with the right forensic tools. As the Hopkins researchers noted, “Law enforcement agencies, including local departments, can unlock devices with Advanced Services for as cheap as $2,000 USD per phone, and even less in bulk, and commonly do so.”
“There’s great crypto available, but it’s not necessarily in use all the time,” says Maximilian Zinkus, Johns Hopkins University. The Hopkins researchers also extended their analysis to include the vulnerability of iCloud services and device backups:
In an interview, Apple stressed that its goal is to balance security and convenience. The result: law firms and other enterprises who rely on iOS’ first-party apps (e.g., iOS Mail) may be unknowingly using an encryption scheme which does not meet their requirements.
Device owners may take actions to ensure greater security. Apple Insider cites a few user actions including: Use SOS mode; use the setting which locks iOS devices after 10 failed login attempts; and don’t use iCloud back-ups. But these user-optional mitigations are not adequate for enterprise security, and they don’t address the forensic techniques used to steal data in the AFU state. Enterprises need systematic approaches across all firm-managed devices.
Why Secure Containers Are Needed
Sophisticated attackers and government agencies have a variety of available tools at their disposable to extract sensitive data from a seized or stolen device. The preponderance of evidence shows that law enforcement is largely successful in cracking open a device and extracting sensitive information as needed. Evidence further suggests that these techniques are ported to even the latest iOS versions and devices (take a close look at https://www.grayshift.com/ – they offer the state-of-the-art in device forensics). What can you do to truly protect sensitive data? The built-in capabilities of the operating system are not sufficient.
Secure containers provide an additional layer of encryption by implementing an entirely independent encryption mechanism to protect data. To examine the protection offered by secure contain apps, we will refer to our LINK app in this discussion. LINK not only uses its own, independent encryption scheme, Link also uses its own built-in encryption technology. In other words, the LINK encryption software stands entirely independent from the operating system, regardless of whether that operating system is intact or compromised. As long as encryption keys are protected well, then secure containers can provide the kind of locked-down encryption that law firms want to protect email and documents, which encapsulate a large majority of a firm’s most sensitive data.
LINK’s data protection exceeds iOS in a few significant ways:
- LINK is an app, and iOS apps are routinely removed from memory. Hence, while LINK does necessarily keep encryption keys in memory when the app is active, once the app is removed from memory its encryption keys are too. This stands in contrast to iOS’ “AFU” encryption.
- LINK allows IT to identify data that is only accessible when the device is online. This makes it awfully difficult to get the encryption keys for that data, especially once the device has been identified as lost or stolen and flagged for a remote wipe.
- LINK’s online encryption keys are really hard to guess. Offline keys are hard to guess too, as long as your organization uses complex A-D passwords. Online keys are not derived from a user’s passcode or even a user’s A-D password. LINK’s encryption keys are derived from randomized 32-character strings that are generated on the LINK servers using entropy available on the server. Brute-forcing the key derivation is unlikely to work, which means an attacker would have to compromise the LINK Controller that sits safely inside our customers’ networks, then break the encryption scheme protecting sensitive data stored in our Controller database. Getting LINK data is a lot more complicated than stealing or seizing a mobile device.
- LINK aggressively limits the amount of data available on the device, online or offline. We do so by simply expiring away data that sits unused on the device. This is a really simple way to limit exposure without much practical impact on a user. Users can always go back to their email (via search) or to the document management system to find what they were working on. There is no practical reason to store lots of old, unused data on a device that is easy to steal and, as it turns out, compromise once stolen.
- LINK’s data is useless when obtained from an iCloud backup or a local backup to a Mac device. LINK’s encryption keys are never backed up. An attacker’s best hope is to brute force both the iOS device passcode and the user’s A-D password before IT notices that the device is lost or stolen. This is incredibly difficult to accomplish given Apple’s built-in protections against brute-forcing passcode and given a reasonably complex, hard-to-guess A-D password.
The JHU research simply reminds us that Apple’s interests diverge widely from those of an individual law firm. Apple has to balance the needs of law enforcement and users to make data accessible while still providing a reasonable degree of protection. Law firms’ best interests lie in maximally protecting data against unauthorized access. In order to achieve this latter goal, Apple’s built-in technology simply won’t suffice.
Seth Hallem is the CEO, Chief Architect, and Co-Founder of Mobile Helix, makers of the LINK App. With LINK professionals can review, annotate, compare, and email files, as well as use the firm intranet, using a single secure container app. www.mobilehelix.com
- “Data Security on Mobile Devices,” Maximilian Zinkus, Tushar M. Jois, and Matthew Green, Johns Hopkins University.
- “How Law Enforcement Gets Around Your Smartphone’s Encryption,” Lily Hay Newman, Wired.
- “Many iOS Encryption Measures ‘Unused,” Say Cryptogographers,” Hartley Charlton, MacRumors.
- “Apple encryption is a balance between user convenience and total security, new study shows,” Wesley Hilliard, AppleInsider.