Playfair Cipher
Build a 5×5 Playfair square and transform letters locally. I and J share a cell; filler X separates repeated pairs and completes odd length.
Only A–Z letters are used; J becomes I. X separates repeated pairs and fills an odd final letter.
A QUICK WALKTHROUGH
How to use this tool
- Enter a key and letters.
- Choose encrypt or decrypt.
- Review the digraph result and the documented filler rules.
Defined classroom rules
The key is normalized to A–Z, duplicates removed, and J merged into I. The remaining alphabet fills the square row by row.
Pair processing
Encryption shifts same-row letters right and same-column letters down; rectangle pairs take the other corners. Decryption reverses those shifts. X is inserted between equal pair letters and appended when needed.
Scope and limits
Only A–Z letters are transformed; other characters are ignored in the cipher stream. This is a historical teaching cipher, not secure encryption.
GOOD TO KNOW
Common questions
What happens to J?
J is normalized to I, so the square has 25 cells.
How is padding removed?
Decryption returns the transformed stream; it cannot know which X characters were original, so inspect or remove filler X manually.
Is this secure?
No. Playfair is for education and demonstrations, not protecting secrets.