Random monoalphabet cipher. The Caesar cipher, which shifts all letters by a fixed amount, is far too easy to crack. Here is a better idea. For the key, don’t use numbers but words. Suppose the keyword is FEATHER. Then first remove duplicate let ters, yielding FEATHR, and append the other letters of the alphabet in reverse order. Now encrypt the letters as follows:

Write a program that encrypts or decrypts a file using this cipher. The keyword is specified with the -k command line option. The -d command line option specifies decryption. For example,

decrypts a file using the keyword FEATHER. It is an error not to supply a keyword.

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z FEATHRZY X W V USO PO N M L K J I G D C B