Cracking and Analyzing Apple iCloud

1.

Cracking and Analyzing Apple iCloud
backups, Find My iPhone, Document
Storage
CanSecWest 2013
Vladimir Katalov, ElcomSoft Co. Ltd.

2.

The need for iOS forensics
• More than 5 years on the market
• 7 iPhones, 5 iPods, 5 iPads
• 320+ million iPhones, 280+ million iPods,
120+ million iPads sold worldwide
• “Smart devices” – they do carry a lot of
sensitive data
• Corporate deployments are increasing

3.

iOS
data
• Device
passcode
protection
• Protect unauthorized access to the
device
• Bypassing is not enough (used in
encryption)
• Disk encryption
• Keychain
• System-wide storage for sensitive data
(keys, passwords etc)

4.

iOS forensics
• Logical acquisition (iTunes backups)
• Physical acquisition
• iCloud backups and storage

5.

iOS forensics
- logical acquisition
• “Ask” device to produce backup
• Device must be unlocked (by passcode or
iTunes)
• Device may produce encrypted backup
• Limited amount of information

6.

iOS forensics
- physical acquisition
•Boot-time exploit to run unsigned code
or
•Jailbreak
•Device lock state isn’t relevant, can bruteforce
passcode
•Can get all information from the device

7.

iOS Data Protection
Every iOS device contains secure AES engine
with two embedded keys:
•GID – shared by all devices of same “family”
•UID – unique per device
•Newer devices have additional UID+ key
There is no known way to extract GID or UID

8.

iOS data protection (contd)
• Content grouped by accessibility requirements:
• Available only when device is unlocked
• Available after first device unlock (and until power off)
• Always available
• Each protection class has a master key
• Master keys are protected by device key and passcode
• Protected master keys form system keybag
• New keys created during device restore

9.

iOS 4+ passcode
• Passcode is used to compute passcode key
• Computation is tied to hardware key (UID/UID+)
• Same passcode will yield different passcode keys on different
devices!
• Passcode key is required to unlock most keys from the system keybag
• Most files are protected with NSProtectionNone and don’t require a
passcode
• Most keychain items are protected with ...WhenUnlocked or
...AfterFirstUnlock and require a passcode

10.

iOS 4+ passcode (cont-d)
• Passcode-to-Key transformation is slow
• Offline brute-force currently is not possible
• Requires extracting UID/UID+ key
• On-device bruteforce is slow
• 2 p/s on iPhone 3G, 7 p/s on iPad
• System keybag contains hint on password complexity

11.

iOS 4+ passcode (cont-d)

12.

iOS 5 Keychain
• SQLite3 DB, all columns are encrypted Available protection
classes
• kSecAttrAccessibleWhenUnlocked (+ ...ThisDeviceOnly)
• kSecAttrAccessibleAfterFirstUnlock (+ ...ThisDeviceOnly)
• kSecAttrAccessibleAlways (+ ...ThisDeviceOnly)
• Random key for each item (AES)
• Item key is protected with corresponding protection class
master key

13.

iOS 5 Storage
• Only User partition is encrypted
• Available protection classes:
• NSProtectionNone
• NSProtectionComplete
• NSFileProtectionCompleteUntilFirstUserAuthentication
• NSFileProtectionCompleteUnlessOpen
• Per-file random encryption key
• File key protected with master key is stored in extended attributes (pretty much like
Microsoft EFS)
• No protection class - partition key is used
• File system metadata and unprotected files
• Transparent encryption and decryption (same as pre-iOS 4)

14.

iCloud
• Introduced in Oct 2011
• Introduced with iOS 5
• Successor to MobileMe, .Mac, iTools
• 5 GB free storage
• Up to 50 GB paid storage
• Over 125 million users in April 2012

15.

iCloud services

16.

iCloud Control Panel

17.

iPhone backup - why?

18.

Mission: impossible :)

19.

iCloud backup - what
• Messages (including iMessages)
• Application data
• Device settings
• Camera roll (photos and videos)
• Visual voicemails
• Purchases (music, movies, TV, apps, books)
• Home screen arrangement
• Ringtones

20.

iCloud backup - when
• Backup runs daily when device is:
• Connected to the Internet over Wi-Fi
• Connected to a power source
• Locked
• Can force backup
• [Settings] | [iCloud] | [Storage & Backup] | [Back Up Now]

21.

iCloud backup - how

22.

iCloud CP: backups

23.

iCloud backup protocol
flow
• Dynamic: endpoints depend on Apple ID
• Built on Google Protocol Buffers (mostly)
• Files are split into chunks
• Apple provides file-to-chunks mapping, chunk encryption
keys, and full request info to 3rd-party storage provider
(Amazon/Microsoft)
• Encryption key depends on chunk data (deduplication?)

24.

iCloud backup protocol
flow (cont-d)
• /mbs/<personId>
• List of backups
• /mbs/<personId>/<backupUDID>/getKeys
• OTA backup keybag
• /mbs/<personId>/<backupUDID>/<snapshotId>/listFiles
• File manifest
• /mbs/<personId>/<backupUDID>/<snapshotId>/getFiles
• File auth tokens
• /mbs/<personId>/authorizeGet
• Info about containers of chunks for "les (FileGroups)
• Request containers of chunks (FileGroups)
• Containers of chunks

25.

iCloud encryption
• Data stored at 3rd-party storage providers is encrypted
• Apple has encryption keys to that data
• Few files are further encrypted using keys from OTA
backup keybag
• Keychain items are encrypted using keys from OTA
backup keybag
• Need key 0x835 (securityd) to decrypt most keys from
OTA backup keybag

26.

iCloud backups - summary
• There is no user-con"gurable encryption for iCloud backups
• iCloud backups are stored in Microsoft and Amazon clouds in
encrypted form
• Apple holds encryption keys and thus have access to data in
iCloud backups
• If Apple stores 0x835 keys then it can also have access to
Keychain data (i.e. passwords)
• Apple may have legal obligations to do this (e.g. LE)

27.

Find My Phone

28.

FindMyPhone protocol

29.

FindMyPhone - demo
output

30.

iCloud documents

31.

iCloud CP: documents

32.

Get files from iCloud
To get list of files
•Authentication request (with given AppleID & password). Client gets mmeAuthToken in
return; which, in order, is used to create authentication token (together with dsid). dsid
(Destination Signaling IDentifier) is an unique ID assigned to the user when registering
at iCloud.com.
•Request to get AccountSettings. Client gets an URL (ubiquityUrl) with an address to get
UUID (unique user identifier), file list, info on file tokens and for authorization.
•Request to get file list (POST). Output (for every file):
• file name
• file id
• parent folder id
• last change time
• checksum
• access rights
To download given file
•Request to get file token (using file id, checksum and aliasMap).
•Authorization request. Returns information on file chunks and containers. Output:
container list (with URLs) and chunk information.

33.

Files in iCloud

34.

35.

iCloud docs: demo output

36.

Possible usage
• Backups in iCloud
• near-realtime acquisition (SMS, iMessage, mail, call logs)
• browse backup data without actual device
• download only data of specific type (need further work)
• Find My Phone
• keep track
• using Google Maps (or whatever)
• enter/leave some are
• 2+ devices
• Documents in iCloud
• open from 3rd party apps
• track changes
• download unsupported document data
• Forensics!

37.

Conclusion
• Balance between security, privacy and
convenience
• iCloud security risks
• Use additional encryption
• Need further work (contacts, calendar, mode
documents, converting documents, partial
backup download, decrypting keychain, photo
stream, 3rd party apps data: 1Password etc)

38.

Cracking and Analyzing Apple iCloud
backups, Find My iPhone, Document
Storage
CanSecWest 2013
Vladimir Katalov, ElcomSoft Co. Ltd.
http://www.elcomsoft.com
http://blog.crackpassword.com
Facebook: ElcomSoft
Twitter: @elcomsoft