How It Works

The key is stripped of any redundant letters, then the English alphabet is stripped of all key letters and appended to the key.

This is the keyed alphabet.

Each password letter is replaced with its position in the English alphabet (A is replaced with 1). This resulting sequence of numbers is written repeatedly beneath the plaintext.

Perform the following operation for each letter of the plaintext:

Take the number below the plaintext letter and add it to the letter's position in the keyed alphabet. In version 2, also add it to the English alphabet position of whatever letter happens to be first in the keyed alphabet.

If this number is greater than 26, repeatedly subtract 26 until it isn't.

The letter at that position in the keyed alphabet becomes the newest ciphertext letter.

In order to further scramble the keyed alphabet, locate the plaintext letter and new ciphertext letter, and swap their places within it.

Decryption is the same, except the addition steps are replaced with subtraction, and if one ends up with a negative number, 26 is to be repeatedly added to it until it's positive.