What is cryptography? | Journey into cryptography | Computer Science | Khan Academy


Imagine two people who share an important secret have to split up. This requires them to communicate private information from a distance. However, an eavesdropper named Eve also wants this information, and has the ability to intercept their messages. So, Alice decides to communicate using letters written in some kind of secret code. The following analogy is helpful. First, Alice locks her message in a box, using a lock that only she and Bob know the combination to. This is known as ‘encryption.’ Then, the locked message is sent to Bob. When Bob receives the box, he opens it using the code they shared in advance. This is called ‘decryption.’ Cryptography begins when we abandon physical locks and use ‘ciphers’ instead. Think of [ciphers] as virtual locks. Ciphers allow Alice and Bob to scramble and descramble their messages so that they would appear meaningless if Eve intercepted them. Cryptography has been around for thousands of years. It has decided wars, and is at the heart of the worldwide communication network today. The fascinating story of cryptography requires us to understand two very old ideas related to number theory and probability theory.

94 thoughts on “What is cryptography? | Journey into cryptography | Computer Science | Khan Academy”

  1. Can't wait for the videos! I am always fascinated by cryptography. I suggest reading The Code Book by Simon Singh because it's what got me into this stuff!

  2. What ever happened to the good old days? Get box – put lock on box – send – have other person put lock on box – send – take lock off box – send – take lock off box – open?

  3. For those that don't know Alan Turing, he was a scholar that worked in the UK during WW2 and decripted the Nazi messages at Bletchley Park etc. Look up his name on Wikipedia and its got everything on him.

    Im looking forward to the rest of the series on codes.

  4. For anyone interested, I can only recommend you the software "Cryptool". It's pretty awesome and you can learn a lot from it (Free & Open Source afaik). Maybe khan should show it in his videos to teach things?

  5. Cool. Will you be covering the basics of how once can crack codes in future? I'm intrigued about how mathematicians cracked codes, say, during WWII.

  6. This is correct but the whole preshared cipher/key is rare when this is applied modernly. I like the box example but with TWO locks, one for Alice and one for Bob. A inserts msg and locks with her lock. Sends box to Bob where he cant open A's lock but attaches his own lock. Sends it back to A where she unlocks her lock and keeps B lock on. Send back to Bob and he unlocks and reads the msg. Anyone in the middle would always have a locked box they couldn't open and read the msg.

  7. Pls also post some more videos on crytography as i find it very interesting. Pls come up with advanced as well as beginner topics

  8. Well, another idiot here. Selenography is a branch of astronomy that deals with the charting of the moon's surface. How in the hell is that related to the invisible ink?

    Stop talking non-sense people.

  9. Average Cryptographer's Password of Choice: &!*sgv=afk"S'8L/;!!>.#^fB;_HY
    Average Person's Password of Choice: password123

  10. One way is frequency analysis, if the poeple hid the secret just by shifting the letters it still doesn't change their patterns for example what are letters that commonly occur in pairs when we write words? Examples include o and e get it? After you break part of the secret message then you can try figuring out the rest.

  11. Eve 2.0 is a hacker. She pulls out a saw and cuts the box in half, circumventing the encryption entirely. Eve is now root 😀

  12. Actually the truth is somewhere in between, as while your example of a good password is (probably) impossible to crack it is also impossible to remember. A better choice would be a nonsense sentence, easily remembered, vanishingly unlikely to be cracked by machine. e.g. alicef0ll0wedthera88it

  13. I'm so sad to have discovered that this series are actually a copy of another channel.
    watch?v=M23z5Ch8NSk
    Just look at the upload dates… Can't believe this…

  14. http://youtu.be/fLaTJYY30wM here is a tutorfriendnow video,a new company that homeschools kids with 5th grade math and science.and its ALL FREE.

  15. Hello Khan team,

    I enjoy your channel very much and I hope I will do so for a long time. But as a former carpenter I have to say that the finger joint on the box is awful terrible. 😉

    Best regards.

  16. :37 "that only her and Bob know" should be "that only she and Bob know." You would not say, "her knows", you would say "she knows" the secret code.

  17. Vídeos de criptografía y seguridad informática en español en YouTube en el proyecto de píldoras formativas Thoth. Saludos Dr. J. Ramió.

  18. KEY 10 STD 26+1

    64312 595 386146 94763 5837304 959725 8645 78 49286 9659 1622 287 843 782929 8645 78 49286 9659 1622 287 843 782929 83 5381 492 7836 86853 689248 264 6949 2414 681764 84562 99676 583 4849 65893 159382 59887 285 856294 357 553 118993 54489 771 884548 2225 49 77664 5833 988 5856 289855 77 69 868 4899 1217 77797 88 2386 719564 681 445897 83 333897 461 865 7896 488692 754 8698 69157 48648 657 438 91837 23228956 3859 4897 68 717 59176 7985 556597 844 28993 798 77 7778 466894 591864 883 6646 895 89992 66 78 488368 9993 9982 92 798 28991 97 96 51958 8893 78 68 477784 739 21957 88885 7779 882 8956 663 429 4556674 86946 357 483 8355 7787 4633894 966 2238 744 4886 86995 94 799 788 788 49684 5964 883 184 47 76791 586 7864 996 49682 487873 83838 4849 484849 461 697 366 9982 286482 1138134592 48945 882 4897 3372 474 439696

  19. Video transcript

    Imagine two people who share an important secret have to split up This requires them to communicate private information from a distance. However, an eavesdropper named Eve also wants this information, and has the ability to intercept their messages. So, Alice decides to communicate using letters written in some kind of secret code. The following analogy is helpful. First, Alice locks her message in a box, using a lock that only she and Bob know the combination to. This is known as 'encryption.' Then, the locked message is sent to Bob. When Bob receives the box, he opens it using the code they shared in advance. This is called 'decryption.' Cryptography begins when we abandon physical locks and use 'ciphers' instead. Think of [ciphers] as virtual locks. Ciphers allow Alice and Bob to scramble and descramble their messages so that they would appear meaningless if Eve intercepted them. Cryptography has been around for thousands of years. It has decided wars, and is at the heart of the worldwide communication network today. The fascinating story of cryptography requires us to understand two very old ideas related to number theory and probability theory.

  20. I was searching for any Cryptography Community to join but I could'd find one. So I've created a Telegram Group all about "Cryptography" , if you are a Cryptography enthusiast , You can join community here : https://t.me/joinchat/E6oALUYaubzaKIMvAmnR9Q
    We love ♥️ Cryptography

Leave a Reply

Your email address will not be published. Required fields are marked *