Substitution Ciphers With Keys

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Much easier to remember than random substitution ciphers, and therefore more practical for spies, these ciphers start with a keyword, say TUESDAY, then continue  alphabetically, omitting all repeated letters, until every letter has been used.

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

To use this code, a spy would simply have to remember the key TUESDAY and know the rules for constructing substitution ciphers.

Why not compose your own substitution cipher, using your own key? (Remember to omit any repeated letters in the key).