I know theres AES and PGP, but all electronics stuff still has backdoors. You can’t backdoor a piece of paper and a writing utensil.
You can do RC4 on pen and paper, more precisely 256 pieces of paper. There’s also a variant of this cipher that uses deck of cards instead, RC4-52. There’s also another stream cipher that uses deck of cards to store state and it’s called Pontifex/Solitaire. Both have some weaknesses
VIC has way too short key for modern uses, but maybe there’s a way to strenghten it
On related note, i guess that it would be possible to implement modern stream cipher with NLFSR in electromechanical machine, no silicon needed. WW2 era cryptography like this (enigma, M209 etc) were in a way stream ciphers and these require some of least hardware. Key storage and scheduling becomes bigger problem
Book cypher. 2 copies of the exact same book. The cypher is an agreed upon system of indicating letters or words.
Make your own language
The Navajo did pretty well in WWII
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Learn Navajo and ancient Babylonian. Write everything in a custom pidgin of Mandarin, Navajo, and ancient Babylonian.
It’s a good algorithm but if you need to decode any message, you must get drunk and listen to creepy radio stations at 1AM in the forest or something.
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In-band periodic key-exchange. Pre-arrange that keys expire every X messages, and that the last (Xth) message is dedicated to sending the new key encrypted by the previous one.
I’m certainly not an expert.
But could you generate pads from mutually accessible data sources?
Like use hit_me_baby_one_more_time_not_a_virus.mp3 appended with a password, as a seed in a pseudo random number generating algorithm, then do the same thing with another data source, repeat however many times, then XOR the generated numbers together, and use the result as a pad?
That’s no longer a one time pad. That’s closer to a homebrew stream cipher with the weakness of having a key that you just hope no one notices.
Steganography may be interesting in that vein. Hiding data within larger images / sound files etc.
This is how all modern cryptography works. A deterministic cipher is functionally no different from pig Latin when it comes to actual security. An electronic solution like public key cryptography is infinitely more secure. If you’re especially paranoid you can generate the cryptotext locally and send it by email; that would be much safer than anything you could achieve by hand.
That’s why you make a stack of them. Generate hundreds up-front and you don’t need to generate new every time.
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I recommend the solitaire cipher.
No, not possible.
The closet we’ve seen are the zodiac killer’s scribbles and they lasted as long as they did because he made a mistake (and frankly because no security researcher was really trying).
Modern cryptography works because it shuffles data around so much that it appears random. There’s simply no way to do those sorts of operations with just pen and paper.
The code could associate skipped or unskipped symbols with the location of stars in the sky at a distant point in time unknown to those trying to break the code
The chair is against the wall and John has a long moustache.
