Cipher Academy
Every code in Doomsday Protocol lives here as a working tool. Play with them, and the modules get easy. All encoding happens in your browser — nothing is sent anywhere.
Caesar shift
Slide the alphabet a fixed number of places. Shifting back by the same number decodes it.
Atbash & ROT13
Atbash mirrors the alphabet (A↔Z, B↔Y). ROT13 shifts by 13, so the same operation encodes and decodes.
Morse code
Dot = short, dash = long. Letters are separated by a space; words by a slash. Use the chart to read a transmission.
Binary & ASCII
Each character is a number. In ASCII, 'A' is 65, so 01000001 is A. Read a byte with the place values 128 64 32 16 8 4 2 1.
Vigenère
A keyword shifts each letter differently, so simple letter-counting fails. The message and key below are a classic historical example.
How to read a cipher under pressure
1 · Identify the rule
The clue tells you the family: shifted, mirrored, reversed, signals, bits or arithmetic. Each family has one obvious first move.
2 · Work one letter
Decode the first letter by hand. If it lands on a plausible word start, the rule is right — repeat.
3 · Check the pattern
Repeated ciphertext letters mean repeated plaintext letters in a simple substitution. Real messages also have repeated endings.
Want the history behind these codes? The Field Manual covers Caesar, Enigma, one-time pads and more.