Vigenère

Based somewhat on the Caesarian shift cipher, this changes the shift amount with each letter in the message and those shifts are based on a passphrase. A pretty strong cipher for beginners. Functionally similar to "Variant Beaufort" and this also supports autokey.

A 16th century French diplomat, Blaise de Vigenère, created a very simple cipher that is moderately difficult for any unintended parties to decipher. It is somewhat like a variable Caesar cipher, but the N changed with every letter. You would "encode" your message with a passphrase, and the letters of your passphrase would determine how each letter in the message would be encrypted.

This is the exact opposite of a "Variant Beaufort." To do the variant, just "decode" your plain text to get the cipher text and "encode" the cipher text to get the plain text again.

A judge created his own Smithy code, which is the same as a Vigenère cipher. It had a couple mistakes in the original, but don't let that stop you from trying to decode his message.

This also supports the "autokey" method, where letters from the plaintext are used to extend the key. This eliminates a weakness in the cipher, but now the security depends on everything being spelled correctly and the strength can be compromised by picking bad combinations of words in your plaintext.