Another excellent free checksum calculator for Windows is IgorWare Hasher, and it's completely portable so you don't have to install anything. If you're not comfortable with command-line tools, this program is probably a better choice. It supports MD5 and SHA-1, as well as CRC32. Calculate enormous mathematical equations from within your browser.

If you want to crack a message encrypted with the substitution cipher, then here is an interactive tool. Cut and paste your enciphered message in the box marked cipher text, or click on random ciphertext if you do not have a message to hand.