Cryptanalysis of Vigenere cipher: not just how, but why it works

[@rabeebibrat1805]

Awesome video. Good job! Note: At 9:48, if anyone is wondering if there is a cos θ in higher dimensions, the Cauchy Schwarz inequality handles just that.

[@ninmarwarda5154]

What a brilliant video, you have literally explained it 100 times better than my lecturer! Thanks for the clarification.

[@Khan-vy1sj]

i don’t know why youtube suggested me this video but this is what i’ve been looking for without knowing that i’ve been looking for it..

[@user-jg6kg1hn1k]

Best Informational Video I ever watched,

[@iliasp4275]

Excelent video! you just saved a students life

[@WeAreAllHumanBeings2]

Awesome. Been looking for a good vid about this. Glad found this.

[@electra_]

the matching up of various shifts reminds me of the Fourier transform

[@zucc4764]

that's a good intuition!

[@shubhamsharma3559]

Very well explained. Thanks!

[@shihminglin229]

Amazing video about decrypting vigenere cipher

[@gwynnalagao5066]

Easiest to understand so far... Thanks

[@user-qz5is9dc2n]

Awesome video.

[@attirahmunir5298]

Awesome video! First time learning about this and it makes so much sense! Thank you!!!!!

[@averageevil801]

Thank you so much, this is so much easier now

[@lm1890owpke]

Really fun video, much appreciated

[@kayleighlehrman9566]

Could you hypothetically use the plaintext to be encoded as the key to encode itself?

[@ProofofConceptMath]

Interesting. If I understand you correctly, I think you'd end up essentially doubling every letter, so A=0 goes to A=0, B=1 goes to C=2, C=2 goes to E=4 etc. This would be an example of what's called an affine cipher (in this case, multiplication by 2). One problem is that the alphabet has an even number of letters, so you'd have no way to get odd numbers out. You'd have repeats like A=0 and N=13 both going to A=0. This would make decoding a little bit of a guessing game.

[@marcgutgesell794]

This is basically a polyphonic substitution cipher.

[@luciddoggo5094]

Very helpful video

[@Varaldar]

My text is ciphered from the entire text of the lord of the rings which is ciphered from the text of "a pickle for the knowing ones" which is ciphered from the wheel of time series, which is ciphred from the eye of argon. (It's a grocery list)

[@marcgutgesell794]

Great video. I'm currently working on a solver for the Keyed Vigenere Cipher (Quagmire III), which is a bit more challenging. Do you have any recommendations for that?

[@gokulsreekumar4371]

Super Helpful

[@creeperthecat9120]

Really useful tutorial. Is the probability that two squares are the same; the same as the Index Of Coincidence? What would you do if there was no clear peak between the number of coincidences, or if a low shift such as 3 peaks, shift 6 doesn't peak and 9 peaks again? If you couldn't tell, this is what I seem to be facing at the moment.

[@gusrallim]

great vid

[@harshjoshi6257]

eargasm

[@MarcelLehmann-m6o]

Cool

[@amjadtrablsi4051]

Amazing

[@MrAzira]

Great!

[@vinaykumardaivajna5260]

That is a great explanation i could have saved 4-5 hours .

[@fjonisch]

It sounds easy when the key is shorter than the plain text and repeats. What if when the key has the same length as the plain text. I generate the key with a pseudo random generator where the seed is the master key. And then the usual mod26 for coding and decoding. I tested it with free42, a HP42 reimplementation available for all platforms.

[@electra_]

When the key has the same length as the plain text this is called a "one time pad" and is unbreakable. this is because for every message, there is a key that could take it to any other message. So without knowledge of the key, any ciphertext could have feasibly come from any message you could think of. The trick is making sure your random number generator is secure. Since it is not "true" randomness, you could theoretically find patterns in the randomness and exploit them. Also, keeping track of the current state of the random number generator between different messages is fairly impractical, so often instead you'll use a pseudo random function where both the key and some other seed value such as the current time or a previous message is used.

[@averageevil801]

So does anybody know what it means if there are 2 big numbers in a row? I’m doing a kinda small ciphertext but last time it happened with a much larger one. Is it just a …coincidence?

[@Fmn-u9k]

its' 13 of lentgh

[@tamekkaknuth9612]

Total is 7

[@shifu117]

I rather look at small repeated words, THE, AND...

[@I3uzzzzzz]

omg ur voice i blundered kreygasm

[@charlier.2752]

nope

[@prurpru7821]

i lost

[@Fmn-u9k]

swallow😂

[@tamekkaknuth9612]

I'm divorced and single