patches no longer use the BSDIFF40 format they use a modified version dubbed BXDIFF41.Strings that begin with '=' are symlink targets and following strings that begin with '+' are places where symlinks should be created.
In particular, the filesystem contents are now stored in a large, proprietary archive. There are quite a number of changes to note between format 2.0 and 3.0. is used to check payload.bom which contains CRC32 of all files inside AssetData folder. patch for /sbin/launchctl will be found at AssetData/payload/patches/sbin/launchctl). patches folder file hierarchy is similar to devices root file system (ex. They can be easily applied manually with bsdiff utility. patches folder is used to store BSDIFF40 patches that are applied to files during update process. It contains only two folders: added folder with unencrypted files which are to be added during update process and patches folder.
libupdate_brain.dylib - stage 2 update process library (encrypted).Īll updates with 2.0 package version have payload folder inside AssetData instead of file from 1.0 updates. - asymmetric signature of ist validated against /System/Library/Lockdown/iPhoneSoftwareUpdate.pem. Contains a list of BSDIFF40 patches and baseband firmware updates, if available, with the associated flashing tools (bbupdater/imeisv). - the actual cpio patch archive (encrypted). These updates do not contain payload.bom file and are deprecated. ist file from AssetData folder contains PackageVersion field which can be 1.0, 2.0 or 3.0. It also contains boot folder where bootchain-related files are stored (iBoot, kernelcache, etc.), payloadv2 or payload (depends on PackageVersion value of AssetData/ist file) and ist file which describes the update. pre.bom states filesystem before update, post.bom - after and payload.bom describes the patches to be applied during update process. META-INF has only one file which describes bundle contents.ĪssetData contains three Bill-Of-Materials files (they can be viewed with lsbom and created with mkbom). OTA update bundles contain an ist file and two folders: META-INF and AssetData. There are three known versions of OTA updates. The updates are delivered in plain unencrypted ZIP files. The device checks an XML-based PLIST file on or sends a POST JSON request to (codenamed Pallas) for updates. This allows a user of a device to go into Settings > General > Software Update and download and install the latest iOS software on-device, without the need for iTunes. 
OTA Updates ( Over-the-Air Updates, also known as wireless updates) were introduced with iOS 5.
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