One-time Pad - Making One-time Pads By Hand

Making One-time Pads By Hand

One-time pads were originally made without the use of a computer and this is still possible today. The process can be tedious, but if done correctly and the pad used only once, the result is unbreakable.

There are two components needed to make a one-time pad: a way to generate letters at random and a way to record two copies of the result. The traditional way to do the latter was to use a typewriter and carbon paper. The carbon paper and typewriter ribbon would then be destroyed since it is often possible to recover the pad data from them. As typewriters have become scarce, it is also acceptable to hand write the letters neatly in groups of five on two part carbonless copy paper sheets, which can be purchased at office supply stores. Each sheet can given a serial number or some other unique marking.

The simplest way to generate random letters in the Roman alphabet is to obtain 26 identical objects with a different letter of the alphabet marked on each object. Tiles from the game Scrabble can be used, as long as only one of each letter is selected. Kits for making name charm bracelets are another possibility. One can also write the letters on 26 otherwise identical coins with a marking pen. The objects are placed in a box or cup and shaken vigorously, then one object is withdrawn and its letter is recorded. The object is returned to the box and the process is repeated.

Another way to make one time pads is to use dice. One can generate random number groups by rolling several ten-sided dice at a time and recording the numbers for each roll. This method will generate random code groups much faster than using Scrabble tiles. The plaintext message is converted into numeric values with A =1, B =2 and so on. The resulting numeric values are encrypted by adding digits from the one time pads using non-carrying addition. You can then either transmit the numeric groups as is, or use the straddling checkerboard to convert the numbers back into letters and transmit that result.

Regular six-sided dice can be used in pairs to generate random digits with a table:

If the row die comes up six, one simply re-rolls. It is important that the target set values are all occurring with the same frequency. That's why the table has the size 5×6: So that every x ∈ {0..9} is occurring 5×6/30=10 times. One could also use base-6 to interpret the number without a lookup table.