XPost: misc.phone.mobile.iphone   
   From: marianjones@helpfulpeople.com   
      
   badgolferman wrote:   
   > Marian wrote:   
   >   
   >>Because of these mechanisms, an iOS IPA is not a portable software   
   >>artifact. It is a cryptographically-constrained container that can   
   >>only be installed when Apple authorizes the transaction for a   
   >>specific Apple ID on a specific device class.   
   >   
   > When I used iTunes to back up my device to the computer, you had the   
   > ability to save IPAs and reinstall older versions to your new device.   
   > When a newer version of iTunes came out that removed that capability I   
   > complained about it here and nospam directed me to a version of iTunes   
   > which still did that.  I still have the installation program he   
   > recommended but haven't installed it on my Windows 11 laptop.  These   
   > days I back up my phone to iCloud.  I know you don't approve of that   
   > but I'm fine with it.   
      
   Hi badgolferman,   
      
   Happy New Year!   
      
   These technical threads are asked so that ALL of us have a better chance of   
   understanding how iOS works, since it works like no other OS on earth.   
      
   I have used the "old" iTunes in the past myself, and, as a short anecdote,   
   it was actually my *first* experience ever with an Apple mobile device!   
      
   I had purchased iPods from Costco decades ago, and I simply wanted to   
   populate them with the thousands of MP3s I had on my Panasonic player.   
      
   What I "thought" I would do is slide the files from the PC to the iPod.   
       
      
   That's what I ended up doing - and what I still do - but that's too easy to   
   be what Apple wants me to do - yet again proving Apple does things the   
   hardest way possible - for no other reason than to lock in their profits.   
      
   The official method, of course, was to use "iTunes", so I installed it, and   
   instantly realized it was an abomination in every possible way imaginable.   
      
   Luckily I'm intelligent, so I promptly ditched iTunes for the free SharePod   
   software, which allowed me to copy both ways any MP3 that I wanted to.   
      
   That's where I learned that almost everything you do with iOS is more   
   difficult than doing that same task on any other OS (including macOS).   
      
   It was a rude awakening, especially as SharePod was eventually bought by   
   Apple and destroyed - but the old copies on my old iPods still work fine!   
      
   That 1st lesson that Apple handcuffs interoperability was learned the hard   
   way, just as the lesson IPAs are locked to an AppleID/device was learned.   
      
   We both have experience with the older iTunes versions on Windows.   
   What you describe is absolutely correct from the user side, which is that   
   older iTunes did let you download and store IPA files locally, and   
   it appeared to the user that we were backing up the actual app.   
      
   A lot of people remember it the same way, so your recollection is not   
   unusual. Jolly Roger, for example, still, to this day, insists that a   
   portable IPA is being backed up, but he doesn't understand how it works.   
      
   The part that is easy to miss is what was actually inside those IPAs and   
   how iOS handled them during restore. Even though the old iTunes showed a   
   local IPA file, that file was not a portable installer in the same sense   
   as an APK, EXE, DEB, or RPM. It was a container that held an encrypted   
   binary plus a receipt proving you were entitled to download that version.   
      
   The executable inside the IPA was encrypted with FairPlay, and the keys   
   needed to decrypt it were never stored in the IPA itself. Those keys were   
   delivered separately by Apple to a specific device at install time. That   
   is why an IPA copied from iTunes was not portable. It would not install on   
   another device unless Apple authorized that other device for your Apple ID.   
      
   To be clear, you are right that the older iTunes let you keep older IPA   
   versions around, and you are right that you could sometimes reinstall them   
   on your own devices.   
      
   So it "appeared" to people like Jolly Roger, who don't understand how it   
   actually works, that the IPA was being installed on the 2nd device.   
      
   However...   
      
   The most interesting part that was happening behind the scenes is that the   
   new device was not actually using the IPA file as the installer!   
      
   During a restore, the new device simply contacted Apple, and the new device   
   presented the receipt from the IPA, and then Apple issued a fresh,   
   device-specific encrypted build of that IPA to that new device.   
      
   The IPA on disk looked like an installer, but in reality it only served as   
   proof of entitlement. Not as the executable that would run on the device.   
      
   I agree this is tricky.   
   I agree this is not intuitive.   
      
   With Apple, almost everything you do is not what Apple claims it is.   
   You have to keep Descartes in mind when trying to understand Apple's claims   
   "we should doubt what can be doubted in order to understand what it is".   
      
   The fact that the IPA was just a ruse, in that the IPA the old iTunes saved   
   was merely an entitlement record, is also why restoring an older version of   
   the app only worked when Apple still allowed that version to be reissued.   
      
   A fact lost on Jolly Roger was that when Apple stopped signing that older   
   version, the IPA on disk could no longer be used to install it.   
      
   So the IPA file the old iTunes saved to (and taking up space on) your   
   Windows disk was merely an entitlement. A proof of ownership file.   
      
   The IPA the old iTunes saved was never a usable installer executable.   
      
   You brought up the concept of iCloud backup, but it works the same way.   
   The cloud is simply another computer that isn't your own desktop PC.   
      
   Whether you use iTunes, iCloud, or device-to-device transfer, the IPA app   
   binaries themselves are never copied between devices. Only the app data is   
   transferred. The app installers are always re-downloaded from Apple's App   
   Store and then re-encrypted for the specific device that requested them.   
      
   Your personal information is embedded directly into the new app also.   
      
   Think about that.   
   Nobody but Apple embeds your unique personal information into every app.   
      
   Just Apple.   
   And just for iOS.   
      
   Why?   
      
   In summary, thank you for bringing up how the old iTunes worked, as iTunes   
   holds a very dear place in my heart as my first horrid experience with how   
   Apple designed "interoperability" (which, for me, was with the iPods).   
      
   I didn't realize Apple could make something so simple as sliding an MP3   
   file back and forth from the PC to the iPod, so horribly difficult!   
      
   That's where I began to learn that everything is more difficult with Apple   
      
   [continued in next message]   
      
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