https://en.wikipedia.org/wiki/Caesar_cipher

But if I have to explain the joke, it means I didn't tell it right ;_;

I wasn't aware of it being Caesar's cipher (although I know the cipher in general was used for ages), I only recall ROT13 because it's sorta infamous.

Learn something new every day.


Even more complex I'm aware that a far more complex cipher was used using a pair of letters or whole words (rather than single character replacement). King Louis XIV's accounts or something similar? The cipher was known/used only by a man and his son, and only them (making the cipher unbreakable til recently). Rather than the man in the iron mask being the son/prince/twin, he was a military general. I think I learned this while reading and learning about the Enigma machine and ciphers in general some 10 years ago.

That pun was so bad, I'm afraid we're going to have to make a Caesar of your computer to erase all pun files on it. We can't have dangerous men like you Roman around on the streets.

There's also ROT26 or 2ROT13, which is equivalent to not encrypting the data at all; I could call the "don't encrypt" algorithm NOP encryption (NOP is short for no-op).

I believe it is possible to get ssh to not encrypt, but you have to go out of your way to do so (so it doesn't happen by accident), and situations where you would need to do so are rare. One thing to note: It is possible (though extremely unlikely) for the routine that checks to see if a number is prime to let a composite number pass.through. If this happens, the encryption will, I believe, be easily breakable (either that or the encryption will become lossy making decryption not work).

You sunk my battleship!

More complex how?

I recall my first encryption attempt was revolved around a single assembly language instruction, which was XLAT (7b?). This instruction was effectively a fast simple translation table using BX as a pointer, and you fed it a number and it would translate it. Since it was limited to the lower 8bit types (ah, al, bh, bl, etc) that meant the table had a max of 256 entries. Good for quick translation.

The code originally went something like this:
[code]
loop_entry:
mov ah, [si]
cmp ah, 0
jez finished
mov cx, [loopBy]
loop_encode:
xlat ah
mov [di], ah
loopnz loop_encode
inc si
inc di
inc [loopBy]
jmp loop_entry

finished:
[/code]

This code would be encoded in about 20 bytes... fairly simple encryption once you have the tables set up...

I meant in terms of things like rotating letters. Needless busywork compared to sorting out binary or HEX.

Depends on the technology the complexity, and how secure you need your data. I've heard before to send secure messages they'd shave a messenger's head, then tattoo the message on his head. When his hair grew back they'd give him a fake scroll message and send him on his way...

While we're spoiled by having computers do all the complex stuff for us, this is still relatively new. For thousands of years crypto of other kinds were in popular use.

Well, sometimes just pure plain obfuscation...

01001001 00100000 01110000 01110010 01100101 01100110 01100101 01110010 00100000 01110011 01101001 01101101 01110000 01101100 01100101 00100000 01101111 01100010 01100110 01110101 01110011 01100011 01100001 01110100 01101001 01101111 01101110 00101110

If you say so. Although it's not necessarily so simple...

Any other interesting ciphers to talk about? Have you done your own crypto and used it to pass notes to your girlfriend? Do you program or use your own cipher for computer/college classes? Come on, I want to know these things :)

One simple crypto you could use in theory is simply converting characters to numbers. This is really really easy. Let's say I wanted to encode the word 'CRYPT' right?

C - 3
R - 18
Y - 25
P - 16
T - 20

Well for simplicity start with our last number, then multiply by 27 and add the new character. Most importantly we encode it BACKWARDS. We do that so when you decode it, you get it forwards.

0 + 20 = 20
(20 * 27) + 16 = 556
(556 * 27) + 25 = 15,037
(15,037 * 27) + 18 = 406,017
(406,017 * 27) + 3 = 10,962,462 (A7461E)

So CRYPT = A7461E

Decryption is the exact opposite, get the modulus of 27 and convert that to a letter, then divide the number by 27 to remove the letter you just decoded...

An advantage is this actually compresses the data a bit, unfortunately it doesn't preserve spaces, symbols, or any other data (although 0 is unused and could be spaces). Of course you can extend the character set above 26, or for certain letters reduce the set down like W is technically double-u, so encoding U twice would give you W.

edit: for 10-14 characters 26 vs 27 makes no difference in size for 64bits, so changed to 27.

Coming to CBS this Fall!

Ciphers & Crypto

They're cops.


Thursdays this Fall, right after MacGyver!

Found a saved lecture on Cryptography and Ciphers.

https://www.youtube.com/channel/UC1usFRN4LCMcfIV7UjHNuQg/videos

Although to note, it looks like the person controlling the camera is doing a crappy job and giving me a headache a bit... If I find another list or good lecture I'll post it here.

edit: Seems it's part of the cropping they did, while the actual web-page has flv files you can download that aren't cropped weirdly. Fun...

http://www.crypto-textbook.com/

So... anyone have any original ideas for a cipher?