unpack "C", "f" or unpack "c", "f" or unpack "U", "f" or ord "f" all give the character code of "f", which is 102. unpack "H", "A" gives "4", and you can replace the "A" with any other letter between "@" and "O". Thus, unpack "HC", "Af" returns ("4", 102). If you concatenate and reverse that list, you get "2014". From there, I just had to modify the strings until it gave something meaningful instead of random letters.