Trithemius Cipher

The encryption uses successive shifts (positive and ascending - ie. to the right) in the alphabet from 0 to N where N is the length of the text.

Example: To code DCODE shift D from 0 an get D, shift C by 1 and get D, shift O by 2 and get Q, shift D by 3 and get G, and shift E by 4 and get I. The coded message is DDQGI.

With a classical alphabet ABCDEFGHIJKLMNOPQRSTUVWXYZ, Trithemius cipher is equivalent to a Vigenere cipher with ABCDEFGHIJKLMNOPQRSTUVWXYZ or equivalent to a Caesar cipher with a shift that increases by 1 by each letter starting at 0.

Decryption requires successively shifting in the other direction in the alphabet. To shift negatively to the right is equivalent to shift positively to the left.

Example: To decode TSKWLJSPCB shift T by 0 and get T, shift S by -1 and get R, shift K by -2 and get I, etc. The plain message is TRITHEMIUS.

- The shift may be ascending/increasing or descending/decreasing.

- By default, the shift starts at 0, but it is conceivable to start it at 1 or any other number.

- The alphabet used can be a deranged alphabet or a completely personalized alphabet.

- Other types of shift sequences may be imagined (see shift ciphers).

The ciphered message has a low index of coincidence (0.04-0.05).

During Renaissance, near 1480.