Tool to decrypt/encrypt Alberti. The Alberti cipher is a polyalphabetic cipher system that uses two mobile concentric disks which can rotate.
Alberti Cipher - dCode
Tag(s) : Poly-Alphabetic Cipher
dCode is free and its tools are a valuable help in games, maths, geocaching, puzzles and problems to solve every day!
A suggestion ? a feedback ? a bug ? an idea ? Write to dCode!
Alberti Cipher
Alberti's Disk Decoder
Alberti's Disk Encoder
Answers to Questions (FAQ)
How to encrypt using Alberti cipher?
Encryption uses a disk with two alphabets, one fixed (stabilis) one moving (mobilis). By rotating a disk, it shifts an alphabet to the next letter.
To encrypt, the disk is set in one position, the initial shift (which can be zero) corresponds to the number of letters shifted at the beginning.
Example: The disk is composed of ABCDEFGHIJKLMNOPQRSTUVWXYZ for the large outer ring, and abcdefghijklmnopqrstuvwxyz for the small inner ring. A is in line with a, B is inline with b, etc. Rotating a disk by 2, then A is in line with c, and the initial shift becomes 2.
Each letter of the plain text found on the outer ring, is replaced by the corresponding one (the one aligned) in the inner ring.
By default, every 4 characters (4 = period), the disk is rotated clockwise of 1 letter (1 = periodic increment), this changes the substituting alphabet.
Example: Encrypt DCODE with the parameters: initial shift: 1, periodic increment: 2, period: 3.
Alphabets are such as ABCDEFGHIJKLMNOPQRSTUVWXYZ is aligned with bcdefghijklmnopqrstuvwxyza.
The period begins, D is coded by e, C by d, O by p, the period (length 3) ends, the disk is rotated by 2 letters.
Alphabets are now aligned like this : ABCDEFGHIJKLMNOPQRSTUVWXYZ with defghijklmnopqrstuvwxyzabc, the new period begins, etc.
The encrypted message is edpgh
How to decrypt Alberti cipher
Le decryption needs the disk (or the 2 alphabets) and the parameters: initial position, period and shift.
To cipher a message, the disk is set with the corresponding initial shift. Each letter is identified on the inner disk, and is coded by the letter aligned in the outer disk.
By default, every 4 characters (4 = period), the disk is rotated counter-clockwise of 1 letter (1 = periodic increment).
Example: The parameters are: initial shift: 1, periodic increment: 2, period: 3, and the cipher message edpgh.
Alphabets are such as ABCDEFGHIJKLMNOPQRSTUVWXYZ is aligned with bcdefghijklmnopqrstuvwxyza
The period begins, e is decoded by D, d by C, p by O, the period (length 3) ends, the disk is rotated by 2 letters.
Alphabets are now aligned like this: ABCDEFGHIJKLMNOPQRSTUVWXYZ with defghijklmnopqrstuvwxyzabc, the new period begins, etc.
The original plain text is DCODE
How to recognize an Alberti ciphertext?
The ciphered message has a polyalphabetic index of coincidence.
In its original version, the message has only these letters: ABCDEFGHIKLMNOPQRSTVXYZ and &, no J, U or W
The mention of De Cifris refers to the treaty published by Alberti presenting his cipher.
How to decipher Alberti without period or shift?
One can crack Alberti but brute-forcing the period first, then initial shift and periodic increment. Use the 'Bruteforce attack' button.
When this Alberti cipher have been invented?
Leon Battista Alberti would have invented this wheel around 1460.
Source code
dCode retains ownership of the online "Alberti Cipher" tool source code. Except explicit open source licence (indicated CC / Creative Commons / free), any "Alberti Cipher" algorithm, applet or snippet (converter, solver, encryption / decryption, encoding / decoding, ciphering / deciphering, translator), or any "Alberti Cipher" function (calculate, convert, solve, decrypt / encrypt, decipher / cipher, decode / encode, translate) written in any informatic language (Python, Java, PHP, C#, Javascript, Matlab, etc.) and no data download, script, copy-paste, or API access for "Alberti Cipher" will be for free, same for offline use on PC, tablet, iPhone or Android ! dCode is free and online.
Need Help ?
Please, check our dCode Discord community for help requests!
NB: for encrypted messages, test our automatic cipher identifier!
Questions / Comments
Thanks to your feedback and relevant comments, dCode has developed the best 'Alberti Cipher' tool, so feel free to write! Thank you!