Created: 16 Dec 2025 Updated: 24 Dec 2025
A pure GO application to generate two images which, when put together, are used to implement a Caesar cipher encoding/decoding disk. Simply overlap the inner disk over the outer disk and pin it through the middle hole.
Unlike most prefabricated Caesar disks out there in the wild, with
my application you can use your own selection of letters. It is
thus not English centric. With the provided XIROD font, you can
use it for many languages, including those supported by my
goCaesarX suite: English, Spanish, Italian, Portuguese, German
and Czech. If you plan to generate your disk for Cyrillic or
Greek characters, you will need to supply a TrueType (*.ttf) font
that supports those characters or use any of BreamCatcher or Toxicogenesis.
The XIROD font is a free font, also free for commercial use and developed by 1001 Fonts.
The Ubuntu fonts are free fonts, also free for commercial use and developed by Dalton Maag and funded by Canonical.
The BreamCatcher & Toxicogenesis fonts are free fonts, also free
for commercial use and developed by RaymondLarabie.
For German (-DE flag) I recommend BreamCatcher which supports all
German characters.
Whether you plan to use the library, or install the application and use it, we got you covered. Just follow the simple instructions.
To get the library for development purposes while keeping in mind the License:
go get github.com/lordofscripts/caesardisk
But if you are only interested in using the application to generate your own disk sets for yourself, family or friends:
go get github.com/lordofscripts/caesardisk/cmd/disk
And the graphical front-end application:
go get github.com/lordofscripts/caesardisk/cmd/gui
For the Graphical Front-end simply type:
caesar-gui
To generate the English disks using the default fonts:
caesardisk
To generate discs containing the Spanish alphabet with the default built-in fonts:
caesardisk -title "Spanish" -ES caesardisk -title "Spanish" -ES -dual
If you wish to override the default Alphabet letters font and use the same for the indexes printed on the outer disk:
caesardisk -title "Spanish" -ES -text-font xirod.regular.ttf
If you want to override both alphabet and indices fonts:
caesardisk -title "Spanish" -ES -text-font xirod.regular.ttf -digit-font
Each run of the application generates two PNG image files, one for the outer disk (background) and one for the inner disk (foreground) which are printed and pinned through the middle hole.
In case you didn't notice, in v1.2 I added the possibility of genearing
Dual Wheels. Basically, the same two disks but each containing two
rows of characters, the outer row contains letters (a language alphabet),
and the inner row of the disk containing symbols. Instead of assembling
2 disks you only need one! But this only works when your symbol alphabet
has the same length as the letter/language alphabet. At present, it
is supported by the default English & Spanish (-ES):
caesardisk -title "Spanish" -dual -ES caesardisk -title "English" -dual
which results in two disk images that, when assembled together with a pin
yields this with the inner disk rotated to Key=03 (or "D" in this alphabet):
For the dual Spanish disk the standard -ES alphabet is stripped of the
accented vowels, they are usually not part of passwords anyway:
Spanish (-ES):
Size: 27 characters
Letter alphabet: ABCDEFGHIJKLMNÑOPQRSTUVWXYZ
Symbol alphabet: !"#$%&()*+,-./ 0123456789=?
English:
Size: 26 characters
Letter alphabet: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Symbol alphabet: !"#$%&()*+,-./ 0123456789?
The basis of the Caesar cipher is the single-letter key, say A..Z in the English alphabet. To each of these letters there is a shift-value or index-value that goes from zero (0) to the amount of letters in the alphabet minus one. English has 26 letters (A..Z) so the key would be between 0..25. Key 'A' corresponds to a shift of zero which basically results in no encryption/decryption (try it!).
First of all you have to generate your Caesar disk as shown in the instructions above. Make sure the alphabet contains the characters used in your language. Most people simplify using the ASCII A..Z, but let's face it, the world is not US-centric, there are many languages in the world. I write code with globality in mind.
The thing is, the Caesar cipher is certainly not secure by modern standards. It was invented in an era where most people were analphabets. But it is still fun to use these days it. And, most people don't actually know what is a Caesar cipher unless they read something about cryptography. Therefore, by analogy, you could say most people these days are cryptographically analphabets and thus, the cipher is not totally useless to hide stuff from the casual overlooker.
In any case, for those who know, if you only encode letters then your cipher message is suceptible to attacks and could be easy to guess some letters and thus derive the single letter encryption key.
How could you improve that? By also encoding digits (0..9), some symbols and punctuation that would make it more difficult to guess. That technique even throws your attacker off-the-path to a good guess. Additionally, if you also add the SPACE character to the list of encoded characters, it will be even more difficult!
Most people would then add those digits, symbols and spaces to the letter set. That is fine but it makes for a very long table or big disk! Additionally, you won't be able to preserve upper/lowercase because you are mixing letters and non-letters in the same alphabet.
The recommended method is to use two disks:
- The primary disk for the alphabet letters (A..Z and whatever other special characters are used in your language like ß, Á, Ü, Ñ, etc.)
- A secondary disk for the space character, the digits and a bunch of useful symbols and punctuation.
Therefore, for encrypting or decrypting a Caesar-encoded message where your set includes characters, digits, symbols, etc. as described, you would need two disk sets:
- A disk set (inner & outer) for the Letters, your primary.
- A disk set (inner & outer) for the non-letters, your secondary.
Then you would use them to process the message character by character, but using the appropriate disk set to encrypt/decrypt. There are two methods I devised:
Due to language/letter alphabet limitations, or simply because you choose to use less symbols or punctuation (I advise to at least keep digits and space), it is possible that your non-letter disk may be shorter.
In that situation, for any encryption key from the Primary alphabet,
you would need to use a derived key for your Secondary alphabet.
That is what I do in my goCaesarX application suite. For that you
use the modulo operation:
If your main/primary key is M which corresponds to a shift value
of 12 in the English alphabet (or in the Spanish shown in the next
alternative). You will do this:
Alphabet (English): ABCDEFGHIJKLMNOPQRSTUVWXYZ
Size of Primary : 26
Secondary Alphabet: #$%*+,-./ 0123456789
Size of Secondary : 20
In the primary you use the main key but you can't in the secondary
because it is shorter. To make it work in this situation you apply
a modulo N operation denoted mathematically as % N. Look it up
because it is beyond the scope of this tutorial!
Primary Key : M
Primary Shift : 12 (count starting from zero for the 1st letter)
Secondary Shift: 12 % 20 = 12
Plain : AKZ$12
Encoded : MWL3*+
As long as the main shift is less than the length of the secondary you are okay. But if you choose a main key/shift that has a shift value beyond the size of the Secondary alphabet, you will have to apply the modulo operation to get the secondary/derived key. For example:
Primary Key : W
Primary Shift : 23
Secondary Shift: 23 % 20 = 3
Plain : AKZ$12
Encoded : DNC+45
The chosen shift value corresponding to the main key corresponds to a shift greater than the size of the secondary/auxillary alphabet. But by applying the modulo operation using as modulo the size of the Secondary/Auxillary alphabet
First of all, this is more practical, though the other is slightly
harder to break. For this use the -dual CLI option with either
the default English (ASCII) or Spanish alphabets.
This would be optimal because then you can use the same key (shift value) in both disks. Consider this case:
0 1 2 3
01234567890123456789012345678901
-------------------------------
ABCDEFGHIJKLMNÑOPQRSTUVWXYZÁÉÍÓÚ
!"#$%&'()*+,-./ 0123456789:;<=>?
The header has the shift value. Then below you find a row
with the Primary alphabet (letters only) and a row with the
non-letters, the second disk set or Secondary alphabet. Do
notice I included the SPACE between the / and 0.
Because the amount of characters is the same in both, you can use the same shift value/key in both disk sets.
I did the work for the Spanish alphabet. If you have a different alphabet, you will have to adjust the selection of non-letters (secondary disk) so that you achive the same lengths.
Main Key : M
Main Shift : 12
Main Size : 32
Secondary Size : 32
Secondary Shift: 12
Plain : AKZ$12
Encoded : MWL
Try to decipher this with -ES -dual:
Pmv-Imoa-mc-qeb-Qmb-Ofkdp
