Java Substitution Cipher with files

1. Randomly generate an encryption and decryption key and store each in a separate file (1 file for encrypt key, 1 file for decrypt key) (Key is to be used for cipher, be sure key can map to any ASCII character) 2. Read in a file that contains the words "Hello Friend" (Input.txt) 3. Read in the file that contains encryption key (encryptKey.txt) 4. Perform a substitution cipher on Input.txt using encryptKey.txt and save the encrypted text to a file (Output.txt) 5. Read in file Output.txt containing encrypted text 6. Read in file containing decryption key and decrypt the text in Output.txt 7. Output decrypted text to a new file called DecryptedOutput.txt

At the end, Input.txt and DecrypteOutput.txt should have matching text!

I am having issue randomly generating the keys and saving them in a file. I am also having issues with the decryption part. When I read in the file containing "Hello Friend" (Input.txt) it gets encrypted but when I try to decrypt using a randomly generated key it doesn't return back the original text "Hello Friend"

Help please!