FairPlay is an algorithm created by Apple for digital rights management (DRM) to secure iOS applications during installation on Apple devices. It uses encryption and decryption methods to protect the content of IPAs (application archives) from unauthorized access and sharing. Apple encrypts the IPA file with a public key and decrypts it using a private key on the device. The FairPlay technology employs dynamic keys that depend on the installation device and user account, making it difficult for attackers to decrypt the content. The FairPlay system utilizes obfuscation techniques to hide the decryption process and protect against reverse engineering. These techniques involve complex arithmetic and boolean expressions to obfuscate the code.
https://nicolo.dev/en/blog/fairplay-apple-obfuscation/