Simple Caesar Cipher

The Caesar (or shift substitution) cipher is a widely known encryption method in which each character in the message is simply shifted a set number of places in the alphabet (e.g., with an offset of two, A is encoded as C, B as D, etc.). Decryption is achieved either by simply reversing the shift with its inverse or adding a further shift such that .
On the encoding panel, a message with spaces (chosen from a list or entered directly) is converted to a single plaintext string by replacing all the spaces with the letter X, then encrypted with an offset controlled by the slider. On the decoding panel, the encrypted string can be intercepted (using the "intercept an encrypted message" button) or a ciphertext string entered directly, then decrypted with an offset controlled by a second slider. String matching code highlights the message once an appropriate decoding offset has been applied (English words only).


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See "Caesar Cipher" on Wikipedia.
String matching code is derived from the Mathematica tutorial Working with String Patterns, especially the sections General String Patterns & Some Examples  Highlight Patterns. In coding the PaneSelector statements, the author was greatly helped by inspecting the Demonstration "Volumes of Solids of Revolution: Shell Method" by Helen Papadopoulos.
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