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NB: While you are free to answer this question, there is a more specific discussion here

Excerpt from Apple's Whitepaper "iOS Security" on Effaceable Storage:

A dedicated area of NAND storage, used to store cryptographic keys, that can be addressed directly and wiped securely. While it doesn’t provide protection if an attacker has physical possession of a device, keys held in Effaceable Storage can be used as part of a key hierarchy to facilitate fast wipe and forward security

Does this mean that the system encryption is useless against forensics? Or is it only vulnerable when it's locked and not turned off?

The question relates to iOS 8+ non-jailbroken Iphone 4s+.

EDIT:
this blog on forensic possiblities on locked devices running iOS 8.3 has interesting points:

  • Turned on and with lockdown certificate
    You can create a local backup The same problem as the previous case applies if the user has previously set a backup password Be sure that the device keep charging during the backup process
  • Turned off device and with lockdown certificate
    Use AFC protocol and recover the most information that you can, as explained in this article
  • Turned on/off device without a lockdown certificate
    Only device information (name, UDID, etc.)

If I have correctly understood what a lockdown cert is it requires access to the computer used for Itunes communications with the IPhone. For this scenario, that PC is impenetrable.
SO, can someone confirm that a locked Iphone 4s iOS 8.3 cannot be cracked in the case of no access to lockdown certificate?
Furthermore, what if the same phone is powered off?

EDIT 2:
This site says

If they don't have your computer, Zdziarski claimed they can try and generate a pairing record by tricking you into connecting to a compromised accessory, like a dock (juice jacking), and/or by using mobile device management (MDM) tools intended for the enterprise to get around safeguards like Apple's Trusted Device requestor.”

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  • 1
    The iPhone 4 can't run iOS 8, only iOS 7. Is this rhetorical or do you mean the iPhone 4S? Let me change this around -- let's assume iPhone 5S, which contains the Secure Enclave. In this case, some data (non-iOS-dpapi) is recoverable except when the phone is off --or-- if the phone has just booted and no PIN/passphrase has yet been entered. An MDM certificate on the phone could also be used for full data recovery. More info here -- darthnull.org/2014/10/06/ios-encryption
    – atdre
    Jun 13, 2015 at 20:00
  • related question
    – alx9r
    Jun 16, 2015 at 1:47

2 Answers 2

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The purpose of Effaceable Storage is really to be able to quickly erase everything on the device, not to provide any confidentiality for your data. It works like this: Effaceable Storage stores a key (which is itself is encrypted with device-specific key) that is used to encrypt device's filesystem. When device needs to wipe itself (e.g. due to remote wipe command) it simply erases that key from Effaceable Storage. Data on the filesystem remains untouched, but because it's encrypted using the key that was stored in Effaceable Storage (but not anymore), that filesystem data effectively became cryptographically inaccessible.

Does this mean that the system encryption is useless against forensics? Or is it only vulnerable when it's locked and not turned off?

Yes and no. Yes in the sense that protection provided by Effaceable Storage is useless against forensics (unless we're considering the possibility that remote wipe command can reach device while it's already in custody). No in the sense that there are additional layers of protection/encryption above that filesystem encryption, and those can be (and are) a considerable obstacle for forensics.

SO, can someone confirm that a locked Iphone 4s iOS 8.3 cannot be cracked in the case of no access to lockdown certificate?

If that iPhone 4s is not jailbroken then there is no public tools that can get into it. Nobody can confirm that device cannot be "cracked" because, if nothing else, Apple can create a signed ramdisk that will obtain at least some of the data (that isn't protected by layers of encryption above Effaceable Storage, so to speak).

MDM scenario is only relevant if that device is enrolled with some MDM. Basically, in this case MDM has a "lockdown certificate" that can be used to access and decrypt data on the device, change passcode, etc.

Hope this helps.

UPDATE:

Powered down device is at least as secure as a powered up one. What really matters for iOS devices though is if the passcode has been entered at least once since device boot.

If it has been then number of encryption keys will remain in device memory but without a pairing record (aka 'lockdown certificate') or a jailbreak there's no way to exploit this AFAIK.

As for sources, this slides and this project are an excellent source of information on the subject.

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  • Can you also elaborate on the scenario with a powered down iPhone? Info source is also essential in general. Thanks.
    – Manumit
    Jun 19, 2015 at 17:31
  • I can't find any information for anything *above iOS 5 in your site
    – Manumit
    Jun 20, 2015 at 1:39
  • That's simply because there weren't much updates to iOS Data Protection since iOS 5: there's a "Trust this device" confirmation prompt to prevent accidental pairings since iOS 7 and stricter default protection class for files (NSFileProtectionCompleteUntilFirstAuthentication) since iOS 8. There are considerably more important changes related to Secure Enclave but those do not apply to iPhone 4s.
    – Andrey
    Jun 20, 2015 at 9:19
  • You might be right. I found some more info in my "answer", but I can't discern if the security is implied exclusively for secure enclave devices or not.
    – Manumit
    Jun 20, 2015 at 11:29
  • 1
    With publicly available tools you can do this for up to iPhone 4 and 1st-gen iPad. This relies on a boot-ROM exploit that was fixed in subsequent devices (4s and newer aren't vulnerable). Apple can do this for any device because they have keys to sign the payload and do not need to rely on exploits. But even if they do so, they can only read NSFileProtectionNone files without bruteforcing the passcode first. Pairing record won't help because on-device part of pairing record is ...UntilFirstUserAuthentication itself (since iOS 5), so need passcode to decrypt it too.
    – Andrey
    Jun 22, 2015 at 8:18
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this answer is to show what (incomplete) data I have found so far to spark up some discussion, furthermore, my interpretation of the following technical details might be plain wrong.

Legal Process Guidelines: U.S. Law Enforcement by Apple
Page 9

I. Extracting Data from Passcode Locked iOS Devices
For all devices running iOS 8.0 and later versions, Apple will not perform iOS data extractions as data extraction tools are no longer effective. The files to be extracted are protected by an encryption key that is tied to the user’s passcode, which Apple does not possess. For iOS devices running iOS versions earlier than iOS 8.0, upon receipt of a valid search warrant issued upon a showing of probable cause, Apple can extract certain categories of active data from passcode locked iOS devices. Specifically, the user generated active files on an iOS device that are contained in Apple’s native apps and for which the data is not encrypted using the passcode (“user generated active files”), can be extracted and provided to law enforcement on external media. Apple can perform this data extraction process on iOS devices running iOS 4 through iOS 7.

What they don't mention is the pairing record attack which requires unencrypted access to iTunes synced computer.

iPhone Encryption, Apple, and The Feds - NoVA Hackers:

  • iOS 4 - 6 is “no protection”
  • iOS 7 - 8: Complete until First Authentication
  • Most system apps through iOS 7 still used None

enter image description here

When rebooting/power off

  • File Protection Complete key lost
  • Complete until First Authentication key also lost
  • Only “File Protection: None” files are readable (And then only by the OS on the device. Because FDE...) [NoVA Hackers are claiming here that a powered down iOS 8+ on a 4s or later has NO information for recovery. Please contribute if you find conflicting data]

When locked

  • Anything with “FileProtectionNone” is readable

What uses “None”?

  • Any apps not updated for iOS 7+
  • Most system apps (up to iOS 7)
  • Preferences, etc

[Does this mean that after first user authenticathion on iOS 8 there are several system apps, like photos, that are no longer protected by lock?]

On a side note: Bruteforcing delay of 80 ms, 5 seconds for iPhone's with A7/A8 chips.

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