Home › Make › The DIANA cryptosystem

The DIANA cryptosystem

Print a DIANA table and a practice pad and use a one-time pad for real, with no arithmetic at all.

about 20 minutes no cutting, but do it carefully makes a working machine

What you need

The printed table and pad, two copies of each
A pencil
A friend who has the matching copy
Somewhere to burn or shred the used pages

How to build it

Print two copies of both sheetsOne set for you, one for your friend. The pad must be identical or nothing works.
Pick a starting group and say where it isSend the first five letters of the pad in the clear. That tells your friend where to start and nothing else.
Write the key letters under your messageOne key letter under each message letter, straight off the pad, in order.
Find each letter in the tableMessage letter across the top, key letter down the side. The letter where they meet is your cipher letter.
Send only the cipher lettersNever the pad, never the starting position twice.
Cross the used groups outThen destroy the page. A pad used twice is worse than no cipher at all.
This pad is printed in a book, so it is not secret. Anybody with this page can read anything you send with it. It is here to practise on. A real pad has to be random, made by you, and it has to exist in exactly two copies.

The template

Print this at 100 per cent, not fit to page, or the sizes will be wrong. The ruler line below tells you whether it printed correctly.

message letter across the top, key letter down the sidekeyABCDEFGHIJKLMNOPQRSTUVWXYZAZYXWVUTSRQPONMLKJIHGFEDCBABYXWVUTSRQPONMLKJIHGFEDCBAZCXWVUTSRQPONMLKJIHGFEDCBAZYDWVUTSRQPONMLKJIHGFEDCBAZYXEVUTSRQPONMLKJIHGFEDCBAZYXWFUTSRQPONMLKJIHGFEDCBAZYXWVGTSRQPONMLKJIHGFEDCBAZYXWVUHSRQPONMLKJIHGFEDCBAZYXWVUTIRQPONMLKJIHGFEDCBAZYXWVUTSJQPONMLKJIHGFEDCBAZYXWVUTSRKPONMLKJIHGFEDCBAZYXWVUTSRQLONMLKJIHGFEDCBAZYXWVUTSRQPMNMLKJIHGFEDCBAZYXWVUTSRQPONMLKJIHGFEDCBAZYXWVUTSRQPONOLKJIHGFEDCBAZYXWVUTSRQPONMPKJIHGFEDCBAZYXWVUTSRQPONMLQJIHGFEDCBAZYXWVUTSRQPONMLKRIHGFEDCBAZYXWVUTSRQPONMLKJSHGFEDCBAZYXWVUTSRQPONMLKJITGFEDCBAZYXWVUTSRQPONMLKJIHUFEDCBAZYXWVUTSRQPONMLKJIHGVEDCBAZYXWVUTSRQPONMLKJIHGFWDCBAZYXWVUTSRQPONMLKJIHGFEXCBAZYXWVUTSRQPONMLKJIHGFEDYBAZYXWVUTSRQPONMLKJIHGFEDCZAZYXWVUTSRQPONMLKJIHGFEDCBthe three letters always add up to Z. that is why it works both ways.
PAD 001 · cross out every group as you use itJYAWZ BAVNU FGQGN RHLCJ MCYCU ZWXEMCFQUF OLFRT CXEIQ QLLJZ BNGXQ TVCQPSEUBQ WPUJP MNDSA SXBGR JCIFM XYPHCITWRH XADMQ VIWGE LOCOJ KFNAH TSSDJZPVPJ PKBVW JFGPS CRLQQ XXCBO HQQCAJHZYO MHTQO WDAEL BOYOB DFQGA IOADPUVWOX JEOUA ORNMQ MDWHI LGEVD RWNHHAHIUC JFGOI BVNVI IIUIA RJTGW YSIYA
The bar above should measure exactly 10 centimetres. If it does not, your printer has shrunk the page.

Now send something

Send MEET ME AT NOON. Then decode your friend’s reply using exactly the same steps, because the table works both ways round.

Where it comes from

Vietnam, and anywhere with a radio
A cipher you can use in the dark

The one-time pad cannot be broken, and it is also awkward: adding numbers to letters, in a hurry, without mistakes. DIANA solved that with a printed table where the answer is simply where two letters meet, and the same table both encodes and decodes. American special forces carried pads of them on paper you could destroy in seconds.

Why it works

The table is reciprocal: the three letters always add up to Z. That is why the same table encodes and decodes, with no arithmetic and no second chart to carry. Under pressure, in the dark, that is the whole point.

When it goes wrong

It usually does, the first time. Almost always one of these.

The answer decodes to nonsenseYou have drifted a line on the pad. Start again from the group you agreed, and count carefully.
You are not sure it workedEncode a short word, then run the answer back through the same table. If it does not return the word, one of the two of you slipped a letter.

Where to go next

Why it cannot be brokenBack to Make

Read more elsewhere

Longer, harder and written for grown-ups. Worth a look when this page runs out.

One-time pad