The Spy Among Us (2015) | Hacker News Reader

The Spy Among Us (2015)

magazine.utoronto.ca

27 pointscollapse3 comments

The only way it could have been unbreakable would be if it relied on one-time pads.

Leo Marks, in England, championed a one-time pad system for field agents in occupied areas.

There was a one-time pad audio telephone system relying on phonograph record copies at bot ends, physically broken after use. Churchill and Roosevelt used it.

It did use one time pads:

Two paper tape readers are mounted in front of the 700 Unit at the top. One is a 5-level tape reader, which is used to read the plaintext (when used offline). The other one is a 6-level reader which is used to read the keystream tape. The signals of both readers are 'mixed' in the 804 unit by means of modulo-2 addition (XOR).

…

For proper security it is important that the keystream tape contains a sequence of evenly spread truely random characters. Producing such a random keystream was a major challenge during WWII.

When the need for keystream tapes increased during the course of war, the manual production was replaced by electromechanical methods. The machine that was used for the production of Rockex key tapes was codenamed DONALD DUCK, possibly because it speaks gibberish [3]. It wasn't before the application of a noise source however, that truely random key streams were produced. In the UK, a noise generator with five flip-flops was developed at GCHQ just after WWII by former GPO-engineer Don Horwood, who had also worked on Colossus at Bletchley Park.

…

Furthermore, he allowed only two identical tapes and instructed them to be both destroyed immediately after use. This way the machine became a real One-Time Pad system.

From https://www.cryptomuseum.com/crypto/uk/rockex/index.htm

It is amazing how much difficulty people made for themselves in creating random numbers. But people still do. I know somebody who, all in earnest, rolls physical dice to get entropy.

Back then, it would have sufficed to drive a counter from a megahertz oscillator, and take a sample of the low bits each time somebody pushed a button. They could even have collected samples while somebody typed unrelated text.

Nowadays, of course, everything has a camera on board, and you can just hash the collection of least-significant bits from any image snapped from the camera, regardless what it is pointing at. Or, the low bits off an audio sample, even with nothing plugged in.

Reply on news.ycombinator.com