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6x6 Polybius Square with Letters and Numbers

A 6x6 Polybius square has room for all 26 letters and ten digits. This workflow opens a digit-preserving example, JAM2026, using A to Z followed by 0 to 9 and one-based coordinates. J remains distinct from I. An optional keyword fills the square first; Decode requires the same square and numbering base. Case and punctuation do not survive this numerical representation.

Cipher textPolybius 6 x 6, A to Z then 0 to 9
24 11 31 55 53 55 63

encode row then column, numbered 1 to 6; letters become two-digit pairs and / marks a space between words; case is not kept; punctuation and letters outside A to Z are dropped

123456
1ABCDEF
2GHIJKL
3MNOPQR
4STUVWX
5YZ0123
6456789
  1. Jrow 2, column 4, 24
  2. Arow 1, column 1, 11
  3. Mrow 3, column 1, 31
  4. 2row 5, column 5, 55
  5. 0row 5, column 3, 53
  6. 2row 5, column 5, 55
  7. 6row 6, column 3, 63

decode read each pair back as row then column

Square
Numbered from
Square keyword
Method
Polybius 6 x 6, A to Z then 0 to 9
Characters to pairs
7
Dropped, no cell
0
Decode
read each pair back as row then column

Each letter becomes its row and column in a square: 5 x 5 with I and J sharing a cell, or 6 x 6 with the digits 0 to 9 added.

Textbook checks, one per method

Each row is worked by the same code as the stage above. Load puts it in the workbench with its keys.

  • Caesar, shift 3ABCXYZ
    DEFABC
  • Keyword KRYPTOSKNOWLEDGE IS POWER
    DGHVETPST BM IHVTL
  • Polybius 5 x 5, I and J share cell 24JAM
    24 11 32, which decodes as IAM
  • A1Z26, numbers separated by spaces1 26
    AZ
  • Nihilist, square ZEBRAS, key RUSSIANDYNAMITE WINTER PALACE
    37 106 62 36 67 47 86 26 / 104 53 62 77 27 55 / 57 66 55 36 54 27
  • Book cipher, a 40-word reference text3 17 52
    error: word 52 is outside the 40-word reference, and nothing is guessed
  • One-time pad, key XMCKLHELLO
    EQNVZ
Puzzles and teaching, not secrets. These are historical and puzzle ciphers. Caesar has only 25 shifts on A to Z, so the ranked list that Decode shows reads most messages without the key, and keyword, Polybius and A1Z26 text gives way to letter counting. The one-time pad mode shows the arithmetic of a key you type and nothing more: this tool does not make keys and makes no claim that a message stays secret.
Accuracy. Each method follows the convention shown beside it: Caesar shifts count from 0 at the first letter of the alphabet and wrap after the last, the 5 x 5 Polybius and Nihilist squares give I and J one cell, A1Z26 reads 1 26 as AZ, and a book number outside your reference is an error, never a guess. The ranked list of Caesar shifts is an estimate from English letter frequency. These are historical and puzzle ciphers, not modern secure encryption, and the one-time pad mode only shows the arithmetic of the key you type, with no claim that it keeps a message secret.

Common questions

How is 6x6 different from the classical square?
The 5x5 square holds 25 cells and merges I/J. The 6x6 square holds 36 cells: A to Z plus 0 to 9, so digits and J can be represented separately.
Can I use zero-based coordinates?
Yes. Choose Numbered from 0 to use rows and columns 0 to 5. The decoder must use the sender's same base and keyword.

Each method follows the convention shown beside it: Caesar shifts count from 0 at the first letter of the alphabet and wrap after the last, the 5 x 5 Polybius and Nihilist squares give I and J one cell, A1Z26 reads 1 26 as AZ, and a book number outside your reference is an error, never a guess. The ranked list of Caesar shifts is an estimate from English letter frequency. These are historical and puzzle ciphers, not modern secure encryption, and the one-time pad mode only shows the arithmetic of the key you type, with no claim that it keeps a message secret.