[Cryptography] Brainstorming for encrypted text messaging ideas...with a twist

[Arnold Reinhold]

Here is my take on a non-electronic system for securing text messages.

As described in the Boak lectures,  http://www.governmentattic.org/18docs/Hist_US_COMSEC_Boak_NSA_1973u.pdf, the NSA developed several formats to simplify the use of one time pads. One of these, code named ORION, https://commons.wikimedia.org/wiki/File:NSA_ORION_one_time_pad.tiff , consists of a sheet printed on both sides. The front side had 100 sets of complete mono-spaced, ordered alphabets (ABCDEFGHIJKLMNOPQRSTUVWXYZ). The back had 100 randomly permuted alphabets, one behind each ordered alphabet on the front, and aligned so that the the letter positions on both sides matched to a fraction of a letter’s dimensions. To encode with such a sheet, one placed it on a sheet of carbon paper with the carbon side up. The user circles  one letter of plain text in each alphabet. After the letters in the message (up to 100 characters) were circled, one flipped the page over and read off the ciphertext from the randomized alphabets. To decode, the procedure was reversed.

A naive way to use the ORION system would be to follow the encoding procedure above and then take a picture of the reverse side and send it to recipient (who is assumed to have a matching pad). She could print it out the image, place it over the matching pad sheet and follow the decode procedure above. One could include fiducial marks on the OTP sheets that the computer could use to correct for any distortions, insuring the printed-out image would be in proper registration.

The problem, of course, it that the position of the circled letter in each line of the ciphertext side reveals the plaintext letter.  I propose to overcome this as follows. Instead of ordered alphabets on the  front side, have randomly scrambled alphabets. In other words, the front side of my OTP would look like the back of an ORION sheet. The reverse side would be blank except for the calibration marks and an identifying number or bar code for the OTP sheet. Encoding would be slower, since the user would have to hunt for the right letter in each scrambled alphabet, but our eyes are pretty good at that. After encoding, the reverse with its carbon paper circles and fiducial marks, would be photographed, and the image sent to the recipient. There would be no need for alphabets on the reverse, The position of the marks in the image would encode the ciphertext. As above, the recipient could print it out the image, place it over the matching pad sheet and follow the decode procedure above.

On variation would be to have the calibration marks printed on the front as open bubbles and require the user to fill them in when encoding, or have a combination of pre-prided marks on the back plus a few user supplied ones to correct registration. This would eliminate the need to print the OTP sheets in exact registration, the difficulty of which is the reason Boak gave for NSA is no longer using ORION.

Arnold Reinhold