The code signature version is no longer supported
code-signing, ios, xcode
Solution
Notice
This answer is mostly for people using older versions of Xcode. My build farm was for a time stuck at Xcode 12.4 because some Mac minis couldn't be upgraded past Catalina. If you are using a recent Xcode 13+ this is not your issue. Probably cruft of some kind in your project.
If you're still using an Xcode 12 release it is time to let go. The only reason to use 12.4 would be because you're stuck on Catalina and new problems are cropping up that will not be worked around so easily.
codesign --generate-entitlement-der
Apple has changed the codesign signature to include DER encoded entitlements in addition to the plist encoded entitlements. This additional DER encoded entitlements section is required in iOS 15 and becomes the default behavior of codesign in the latest Xcode. To use codesign on an older machines with an older version of Xcode add the `--generate-entitlement-der` flag to your call to codesign.
If signing through Xcode, you can add this flag to the `OTHER_CODE_SIGN_FLAGS` setting in the Build Settings tab.
If codesigning at the command-line:
CODESIGN_ALLOCATE=$( xcrun --find codesign_allocate ); export CODESIGN_ALLOCATE
xcrun codesign --generate-entitlement-der ...
The source of this information was the Apple Forum thread and the answer from Matt Eaton in DTS at Apple.
In the Xcode 12.5 Release Notes there is also a reference to the new signature format. However, it seems the information is not entirely correct.
General advice
If you have a non-trivial setup like CocoaPods, you should probably de-integrate and re-integrate and of course do a project clean. These sorts of 'me too' answers really just add noise to the signal and anyone doing this sort of development should have already tried this.
Problem
An app signed with a codesign version provided on an older macOS, like Catalina (10.15) will not run on iOS 15 because the lastest version you can install is Xcode 12.4. Xcode 12.5 seems to change the behavior of codesigning. When installing you get the error message: The code signature version is no longer supported Is there a workaround?