sadly, xcode has been long broken. there are a couple (that i've seen) source code implementations on the internet. there are also companies that have some xcode decoding service, if you can prove the source code is yours.
http://pdecode.webpark.sk/
although if the files were encrypted using some random key, that you don't have, it maybe practically impossible to break.
it'd be interesting to start a discussion on how we could still use xcode. one option i thought of, but i'm not really sure about
1. encrypting the files using a pseudo random generated key that maybe be substantially difficult enough or practically impossible to break
2. use an executable (machine executable, like, .exe) written in c or other, that holds the key hidden/obfuscated, or receives input like serial code and uses its own encryption algorithm to generate a key.
3. the executable uses os command or another way to pass the key and have a 4gl procedure to compile the files.