The following copyright from Landon J. Fuller applies to the isAppEncrypted function.

Copyright (c) 2017 Landon J. Fuller <landon@landonf.org>
All rights reserved.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software
and associated documentation files (the "Software"), to deal in the Software without
restriction, including without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or
substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Comment from <a href="http://iphonedevwiki.net/index.php/Crack_prevention">iPhone Dev Wiki
Crack Prevention</a>:
App Store binaries are signed by both their developer and Apple. This encrypts the binary so
that decryption keys are needed in order to make the binary readable. When iOS executes the
binary, the decryption keys are used to decrypt the binary into a readable state where it is
then loaded into memory and executed. iOS can tell the encryption status of a binary via the
cryptid structure member of LC_ENCRYPTION_INFO MachO load command. If cryptid is a non-zero
value then the binary is encrypted.

'Cracking' works by letting the kernel decrypt the binary then siphoning the decrypted data into
a new binary file, resigning, and repackaging. This will only work on jailbroken devices as
codesignature validation has been removed. Resigning takes place because while the codesignature
doesn't have to be valid thanks to the jailbreak, it does have to be in place unless you have
AppSync or similar to disable codesignature checks.

More information at <a href="http://landonf.org/2009/02/index.html">Landon Fuller's blog</a>
