|Without seeing your code neither I nor any other here can help.
If you just need working code, use an existing implementation.
Otherwise show your code and what you have tried / where it fails. To do this, edit your question and add the relevant code formatting it using the 'code' option above the edit window (should be not too much code).
Another tip is using an existing implementation with the same arguments and comparing the results. So you can detect if encryption, decryption or both are failing.