Это видео недоступно.
Сожалеем об этом.
The Caesar cipher | Journey into cryptography | Computer Science | Khan Academy
HTML-код
- Опубликовано: 26 мар 2012
- Courses on Khan Academy are always 100% free. Start practicing-and saving your progress-now: www.khanacadem...
Brit explains the Caesar cipher, the first popular substitution cipher, and shows how it was broken with "frequency analysis"
Watch the next lesson: www.khanacadem...
Missed the previous lesson? www.khanacadem...
Computer Science on Khan Academy: Learn select topics from computer science - algorithms (how we solve common problems in computer science and measure the efficiency of our solutions), cryptography (how we protect secret information), and information theory (how we encode and compress information).
About Khan Academy: Khan Academy is a nonprofit with a mission to provide a free, world-class education for anyone, anywhere. We believe learners of all ages should have unlimited access to free educational content they can master at their own pace. We use intelligent software, deep data analytics and intuitive user interfaces to help students and teachers around the world. Our resources cover preschool through early college education, including math, biology, chemistry, physics, economics, finance, history, grammar and more. We offer free personalized SAT test prep in partnership with the test developer, the College Board. Khan Academy has been translated into dozens of languages, and 100 million people use our platform worldwide every year. For more information, visit www.khanacademy.org, join us on Facebook or follow us on Twitter at @khanacademy. And remember, you can learn anything.
For free. For everyone. Forever. #YouCanLearnAnything
Subscribe to Khan Academy’s Computer Science channel: / channel
Subscribe to Khan Academy: www.youtube.co...
these videos are really high quality in terms of production and presentation, it seems like something that should be on the discovery channel. I really hope to see more coming!
cryptology! it's extremely interesting, I love solving puzzles, they take you on a fun journey.
Start doing crypto ctfs
You'll love it
Make more. I did my graduate pre-thesis work on the KA expanding into new territory, and I'm excited to see this stuff actually happening. I look forward to further videos from you.
just learned this in discrete math a week ago! good stuff!
Probably because they precomputed the ciphertext to a handwritten copy and were transcribing it in filming so it would be faster, and probably to be more accurate. But Murphy sneaked in and made them misread the "W" as an "N during filming. Then the problem wasn't noticed when they transcribed back to plaintext or the message would have decrypted as "Meek me at Elephant Lake". :)
I am a cryptography-cryptoanalysis-combinatorics 1st degree student and I have to correct something...
Frequency analysis (for example in this video: English language letters frequency) was NOT used to decrypt simple permutation-based ciphers (which can be easily brute-forced, only 26 such combinations), but rather more complex crypto-functions such as Vigenere or Auto-key (which used more complex key-spaces).
@silentassassin9 Good point, although I can't see how counting every letter in the message would be much of a "breakthrough" that crippled the effectiveness of the encryption. The decipherer would still need to know ot was encrypted this way.
A "shift" in the usual order of the alphabet is only one way changing the mapping of the substitute symbols for the original ones. The mapping could be anything, so the Caesar cypher is really a method of making & communicating the substitution arrangement conveniently.
I got hooked into this topic... Did it all in 1 day :P
Congrats on a successful nerd snipe; I couldn't help myself but to spend the last half hour writing a Python program to figure out what you said. I could have asked Professor Google to find a Caesar Cipher decoder for me...but then I wouldn't be a proper nerd.
Dude that's awesome! Never realized it like that before.
MIND = BLOWN
agreed
Where were you when I was taking a cryptography course as an undergraduate?? These vids are so nice for refreshers. :-)
I think the only reason this wasn't broken sooner is that no thought of counting the letters in Latin or Greek to see how frequently each one was used. It didn't help that there were very few people who had access to books and that very few people could read. Maybe the other problem is that statistics wasn't invented yet.
We need more cryptography videos!!
I'm really excited for this unit. Thanks!
Wow, just, wow!
Way to go Al-Kindi :) !
Correct & good point. This is definitely not the first use. Just a "well known" use.
Amazing!
Wow. Interesting to know!
Sal, can you make a series on linear and non linear regression techniques and use climate science journal papers for examples?
Ciphering was used prior to caesar. The ancients used it in their mystery schools from Egypt to India south America to china.
You are correct, however it was the realization that the frequency distribution was invariant across different messages.
Amazing
Wow Khan Academy's videos are getting better and better :D
Great video thanks
@teargardens They don't always need the reference to solve it. Although one of the hardest, it's no different than choosing arbitrary letters and numbers.
i discovered an error "MEET" is encryptet in "PHHW"
hahahaa
HAHAHHA
So what's wrong in this?
Thank you.
Thank you
that was a more basic frame work to make it non decryptable, you could simply also add random words that stood for specific things, add non sense words, have a number word system, in addition to symbols, have it in a poem or haiku from etc. simple yet complex.
Wow that is so cool.
Thanks for that
interesting, thanks!
thanks mate!
Awesome
This doesn't apply if the message is short right? You would need a long cipher to apply the frequency stability of a language?
That was great
The whole E thing is brilliant, but can be quickly fixed by simply removing any E's in your message.
For example: "My name is John Smith, nice to meet you"
Now remove the E's: "My nam is John Smith, nic to mt you"
Now all you do is encrypt it.
(I'm too lazy to do it.)
Once unencrypted you can easily work out what my message was by adding E's.
That cipher is actually, at least when dealing with computer programming, called ROT-3.
That is really awesome!
What software would someone use for frequency analysis?
This is originally from Art of the Problem's series about Cryptography. You should give credit where it's due.
Cool
awesome. why can't schools teach this? it would be interesting
That's cool!
I'll die to know ,who are the 6 jerks who put dislike O_o , thank you khan
i will have a big shoutout to my assignment :)
nowadays, you could just make a computer program that scans the message and tries every possible combination while checking to see if the results form real words.
@brewster99 Indeed you'd think so... Pick one word, try up to 26 different shifts until a meaningful word pops out. I don't really understand how this was secure at all.
I agree
at that time, evn this did not cross their mind
plus their wasnt enough time for them to pursue every possible combination
or
some of them actually knew this n broke it, but kept is a secret for obvious reasons
cool
there is a crypto course in Coursera. The guys from Stanford are teaching it. But I have to tell you, its not an easy one
the music is creepy
Pitou #i agree
U csn check from my lecture
not creep its horrifying
you can say that again.
Who had to watch this for school
Uff excelente
wow
Anyone know what this music is? I'd like to know. It sounds nice
+Jokerhaha01 Cameron Murray, I have a link to whole album
Need more cryptography videos
I can't tell what order these go in at least in the youtube app. This one is way down in the list and more complex things ae at the top
this was an interesting video*8
Wrote a code in C for a caesar cipher last year. That was fun :|
PLEASE tell me we're going to get an entire series on encryption. My greatest regret from my college days was not taking Cryptography
11yrs later but khan aca has somthing on cryptography for free 👍 its how I got here
May I know why everyone uses Alice and Bob as example? Are they any famous people or did anything to inventions?
Palakondarayudu Uppu
It’s most likely a coincidence. As well as that, people often choose names going up the alphabet which is why the initials of Alice and Bob are A and B. A third person is often called Charlie or Carol for the same reason.
Tag kulera ning maistra tapolan mag klasi!.
1:04 which movie is that?
Caeser
My guess is Ceasar 13
i cant seem to find it anywhere on yt any suggestions where to search?
No way... I actually understood that!!!
could i pls use this video in an assingment?
You are close. The trailer awaits you. Below is the encrypted video ID. Not much else to say really.
5JFZ834EqmS
thx
interesting
PagMan
Wow. Interesting bro.
that comment was written before my younger cousin was born in 2014 (3 years after I was born so there's 3 years between us)and I would be only 1 when it was written xD
and u got a reply 8 years later lol
do i decrypt this or something?
(Hieu Do already pointed this out.)
The coded message in the vid 1:00 correctly decypers to "Meek me at Elephant lake". Not "meet". www.adfg.alaska.gov/SF_Lakes/Content/Documents/05102012-110000_%28bath_main%29_Elephant.gif
What does this mean?
huh neat
surely they could just test out the cypher using different shifts, eventually one would make sense, and that'd be the right message?
the only reason why i learn this bc i need to solve a detective game ( dont ask why i comment this cuz even i myself dont know )
hi
I want to know how to unlock locks now....
Yes it was
WELL MADE. VERY WITTY
anyone knows the name of the song in the background?
With a key.
*THREE LETTERS BACK*
actually as per cipher T is W but you have written N why?
Well ... it's not like brute forcing all 26 possible shifts is hard or anything. The frequency analysis gets more important for arbitrary substitutions.
This is just the most primitive version though. Rotating cipher (Vigenere cipher) makes brute-forcing by hand less practical if you only have a limited time.
what is the letter for y and z
so like y is b and z is c
And I thought Khan Academy was for math
Meh I'm still using that cypher in my journal
what is the name of the song?
The laymans uncrackable chiper is to find a book out of print & base your letter off of random pages & lines from within the book. Uncrackable.
there were no bob's and alice's in those times....
i need help... i dont know what cipher this is set in... it says Proxy code
14 20 6 19 0 6 0 4 12 16 15 10 15 0 8 10 20 0 2 20 1 0 9 0 2 15 5
Vamos papus
lol anyone else notice that in the first message the letter T is represented by both N and W?
Shiizaaaaaa
the enemy didnt always know how it was encrypted
@john smith have you thought of how many combinations a sentence with a length of 35 letters such as "the quick brown fox jumps over the lazy dog" could have? 26 letters in the alphabet to the power of 35 is 3.34 followed by 49 zeros. No computer we have now can figure that out by trying every combination
That's... not how cyphers work. Using a Caesar cypher, there's only 25 possible cyphers total as it shifts all the letters equally. You can brute force crack it in maybe half an hour on paper. And there are even easier ways. Any computer would take less than a second. You're correct if you don't know what cypher it is at all, but every cypher has its clues and giveaways. They have to. If a cypher were as perfect as you're saying (every letter can be any other letter), then it's by definition meaningless information and useless as a code.
22 ceaser shift
In the message from the video at 1:00, how is "N" = "T" when it's suppose to be "W" = "T" because it's a shift of 3. -__-