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Ready CipherOne-time pad encrypt & decrypt

Turn a message into five-figure groups that only someone holding the same pad can read, and turn received groups back into plain language. Works offline in your browser. Nothing you type is saved or sent anywhere.

Encrypt

Shorter messages: common words go as a single five-digit code.

Worksheet and groups to send

Type a message and paste your pad.

Decrypt

Message

Paste the received groups and your pad.

The conversion checkerboard

Before a message is encrypted, each letter becomes a number. The six most used letters get one digit, everything else gets two. This is the same checkerboard Ready Ledger uses, so a message made here can be read there, and the other way round.

  • Numbers go between two 90s (figures), with each digit written three times: 19 becomes 90 111 999 90. Writing each digit three times stops a 9 followed by a 0 from closing figures early, and catches a miscopied digit.
  • Space is 99 and ? is 98. Leave out spaces you don't need to keep the message short.
  • The last group is filled with 9s to make five digits. A trailing 9 is read as filler.
  • Characters not on the board (like ! or @) are skipped, and Ready Cipher tells you which ones.
⚠ FOR TRAINING ONLY. NOT FOR OPERATIONAL USE. ⚠

Ready Cipher training sheet

Make a practice sheet to learn the method with a partner. Digits come from your browser's cryptographic random source. A practice sheet is not a real pad: it was made on a computer that may be watched, and it lives in your browser's memory. Real pads are made, held and destroyed under your own control.

Nothing is saved: the sheet is gone when you close or reload this page. Print it if you want to keep it for the exercise, then destroy it.

AmRRON “TREE” series practice pads

Twelve published practice pads of 25 five-figure groups (Cherry appears twice). They are public, so anyone can read traffic made with them. Use them to practise with other groups who know the series.

⚠ FOR TRAINING ONLY. NOT FOR OPERATIONAL USE. ⚠

Send a message

  1. Agree pads in advance. You and the receiver each hold an identical pad sheet. Every pad starts with a five-digit key indicator group that names it.
  2. Write the message on the Encrypt page. Keep it short and plain.
  3. Paste the pad digits (key indicator first). Ready Cipher converts the message with the checkerboard, then subtracts the pad digit by digit with no borrowing: 3 − 7 = 6 (13 − 7).
  4. Send the groups in the green box, five to a line. The first group is the key indicator, sent in the clear so the receiver finds the matching sheet.
  5. Destroy the pad once it has been used. Never use a pad twice, and never stretch a short pad.

Read a message

  1. Find the sheet whose key indicator matches the first group you received.
  2. Paste the groups and the pad on the Decrypt page. Ready Cipher adds the pad digit by digit with no carrying: 6 + 7 = 3 (13, keep the 3).
  3. Read the message. A ▉ mark means a digit was miscopied; ask for that group again.
  4. Destroy the pad.

Good habits

  • One pad, one message. Reusing a pad is the classic way one-time pad traffic gets broken.
  • Pads must be truly random. Dice (ten-sided), a lottery-ball method or a trusted hardware source. A pattern you made up is not random.
  • Pad security is everything. Anyone who gets a copy of the pad can read the traffic. Keep sheets locked up and burn used ones.
  • Check by hand while you learn. The worksheet on the Encrypt page shows the PLAIN, PAD and SEND rows exactly as you would write them on paper.
  • Learn more: the free comms guides at Fortune Favors the Prepared.

Want shorter messages and a full comms plan?

Ready Ledger has this one-time pad tool built in, plus a brevity codebook that sends common words as one five-digit code, training sheets with a destroy-by date, DRYAD authentication sheets, codewords, a channel code matrix and an incident message log. All offline, all in one file.

See Ready Ledger →