[Script Info]
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[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:02.94,0:00:08.50,Default,,0000,0000,0000,,The Internet: Encryption and Public Keys
Dialogue: 0,0:00:08.99,0:00:14.15,Default,,0000,0000,0000,,Hi my name is Mia Gil-Epner, I'm majoring\Nin Computer Science at UC Berkeley and I work
Dialogue: 0,0:00:14.15,0:00:19.46,Default,,0000,0000,0000,,for the Department of Defense, where I try\Nto keep information safe. The Internet is
Dialogue: 0,0:00:19.46,0:00:25.51,Default,,0000,0000,0000,,an open and public system. We all send and\Nreceive information over shared wires and
Dialogue: 0,0:00:25.51,0:00:30.04,Default,,0000,0000,0000,,connections. But even though it's an open\Nsystem we still exchange a lot of private
Dialogue: 0,0:00:30.04,0:00:35.89,Default,,0000,0000,0000,,data. Things like credit card numbers,\Nbank information, passwords, and emails. So
Dialogue: 0,0:00:35.89,0:00:40.69,Default,,0000,0000,0000,,how is all this private stuff kept secret?\NData of any kind can be kept secret through
Dialogue: 0,0:00:40.69,0:00:45.30,Default,,0000,0000,0000,,a process known as encryption, the scrambling\Nor changing of the message to hide the original
Dialogue: 0,0:00:45.31,0:00:51.90,Default,,0000,0000,0000,,text. Now decryption is the process of un-scrambling\Nthat message to make it readable. This is
Dialogue: 0,0:00:51.90,0:00:56.97,Default,,0000,0000,0000,,a simple idea, and people have been doing\Nit for centuries. One of the first well known
Dialogue: 0,0:00:56.97,0:01:02.38,Default,,0000,0000,0000,,methods of encryption was Caesar's Cipher.\NNamed after Julius Caesar, a Roman general
Dialogue: 0,0:01:02.38,0:01:07.22,Default,,0000,0000,0000,,who encrypted his military commands to make\Nsure that if a message was intercepted by
Dialogue: 0,0:01:07.22,0:01:12.54,Default,,0000,0000,0000,,enemies, they wouldn't be able to read it.\NCaesar Cipher is an Algorithm that substitutes
Dialogue: 0,0:01:12.54,0:01:16.76,Default,,0000,0000,0000,,each letter in the original message with a\Nletter a certain number of steps down the
Dialogue: 0,0:01:16.76,0:01:21.26,Default,,0000,0000,0000,,alphabet. If the number is something only\Nthe sender and receiver know, then it's called
Dialogue: 0,0:01:21.26,0:01:28.64,Default,,0000,0000,0000,,the key. It allows the reader to unlock the\Nsecret message. For example, if your original
Dialogue: 0,0:01:28.64,0:01:35.87,Default,,0000,0000,0000,,message is 'HELLO' then using the Caesar Cipher\Nalgorithm with a key of 5 the encrypted message
Dialogue: 0,0:01:35.87,0:01:43.26,Default,,0000,0000,0000,,would be this... To decrypt the message, the\Nrecipient would simple use the key to reverse
Dialogue: 0,0:01:43.26,0:01:50.18,Default,,0000,0000,0000,,the processes. But there is a big problem\Nwith Caesar Cipher, anybody can easily break
Dialogue: 0,0:01:50.18,0:01:55.57,Default,,0000,0000,0000,,or crack the encrypted message, by trying\Nevery possible key, and in the english alphabet
Dialogue: 0,0:01:55.57,0:02:00.39,Default,,0000,0000,0000,,there are only 26 letters, which means you\Nwould only need to try at most 26 keys to
Dialogue: 0,0:02:00.39,0:02:06.81,Default,,0000,0000,0000,,decrypt the message. Now trying 26 possible\Nkeys isn't very hard, it would take at most
Dialogue: 0,0:02:06.81,0:02:13.05,Default,,0000,0000,0000,,an hour or two. So lets make it harder. Instead\Nof shifting every letter by the same amount,
Dialogue: 0,0:02:13.05,0:02:18.92,Default,,0000,0000,0000,,let's shift each letter by a different amount.\NIn this example a ten digit key shows how many
Dialogue: 0,0:02:18.92,0:02:26.56,Default,,0000,0000,0000,,positions each successive letter will be changed\Nto encrypt a longer message. Guessing this
Dialogue: 0,0:02:26.56,0:02:34.16,Default,,0000,0000,0000,,key would be really hard. Using 10 digit encryption\Nthere could be 10 billion possible key solutions.
Dialogue: 0,0:02:34.16,0:02:39.86,Default,,0000,0000,0000,,Obviously that's more then any human could\Never solve, it would take many centuries.
Dialogue: 0,0:02:39.86,0:02:46.03,Default,,0000,0000,0000,,But an average computer today, would take\Njust a few seconds to try all 10 billion possibilities.
Dialogue: 0,0:02:46.03,0:02:51.24,Default,,0000,0000,0000,,So in a modern world were the bad guys are\Narmed with computers instead of pencils how
Dialogue: 0,0:02:51.24,0:02:57.89,Default,,0000,0000,0000,,can you encrypt messages so securely that\Nthey're too hard to crack? Now too hard means
Dialogue: 0,0:02:57.89,0:03:03.76,Default,,0000,0000,0000,,that there are too many possibilities to compute\Nin a reasonable amount of time. Today's secure
Dialogue: 0,0:03:03.76,0:03:10.20,Default,,0000,0000,0000,,communications are encrypted using 256 bit\Nkeys. That means a bad guy's computer that
Dialogue: 0,0:03:10.20,0:03:16.29,Default,,0000,0000,0000,,intercepts your message would need to try\Nthis many possible options... until they discover
Dialogue: 0,0:03:16.29,0:03:24.04,Default,,0000,0000,0000,,the key and crack the message. Even if you\Nhad a 100,000 super computers and each of
Dialogue: 0,0:03:24.04,0:03:30.68,Default,,0000,0000,0000,,them was able to try a million billion keys\Nevery second it would take trillions of trillions
Dialogue: 0,0:03:30.68,0:03:37.69,Default,,0000,0000,0000,,of years to try every option, just to crack\Na single message protected with 256 bit encryption.
Dialogue: 0,0:03:37.69,0:03:43.32,Default,,0000,0000,0000,,Of course computer chips get twice as fast\Nand half the size every year or so. If that
Dialogue: 0,0:03:43.32,0:03:48.40,Default,,0000,0000,0000,,pace of exponential progress continues, today's\Nimpossible problems will be solvable just
Dialogue: 0,0:03:48.40,0:03:54.68,Default,,0000,0000,0000,,a few hundred years in the future and 256\Nbits won't be enough to be safe. In fact
Dialogue: 0,0:03:54.68,0:04:01.07,Default,,0000,0000,0000,,we've already had to increase the standard key\Nlength to keep up with the speed of computers.
Dialogue: 0,0:04:01.07,0:04:05.54,Default,,0000,0000,0000,,The good news is using a longer key doesn't\Nmake encrypting messages much harder but it
Dialogue: 0,0:04:05.54,0:04:11.66,Default,,0000,0000,0000,,exponentially increases the number of guesses\Nthat it would take to crack a cipher. When
Dialogue: 0,0:04:11.66,0:04:16.78,Default,,0000,0000,0000,,the sender and receiver share the same key\Nto scramble and unscramble a message its called
Dialogue: 0,0:04:16.78,0:04:24.20,Default,,0000,0000,0000,,Symmetric Encryption. With Symmetric Encryption,\Nlike Caesar Cipher, the secret key has to be
Dialogue: 0,0:04:24.20,0:04:29.71,Default,,0000,0000,0000,,agreed on ahead of time by two people in private.\NSo that's great for people, but the internet
Dialogue: 0,0:04:29.71,0:04:35.84,Default,,0000,0000,0000,,is open and public so it's impossible for\Ntwo computers to "meet" in private to agree
Dialogue: 0,0:04:35.84,0:04:41.60,Default,,0000,0000,0000,,on a secret key. Instead computers use Asymmetric\NEncryption keys, a public key that can be
Dialogue: 0,0:04:41.60,0:04:49.02,Default,,0000,0000,0000,,exchanged with anybody and a private key that is\Nnot shared. The Public Key is used to encrypt
Dialogue: 0,0:04:49.02,0:04:55.80,Default,,0000,0000,0000,,data and anybody can use it to create a secret\Nmessage, but the secret can only be decrypted
Dialogue: 0,0:04:55.80,0:05:01.27,Default,,0000,0000,0000,,by a computer with access to the private key.\NHow this works is with some math that we won't
Dialogue: 0,0:05:01.27,0:05:06.13,Default,,0000,0000,0000,,get into right now. Think of it this way,\Nimagine that you have a personal mailbox,
Dialogue: 0,0:05:06.13,0:05:11.43,Default,,0000,0000,0000,,where anybody can deposit mail but they need\Na key to do it. Now you can make many copies
Dialogue: 0,0:05:11.43,0:05:16.51,Default,,0000,0000,0000,,of the deposit key and send one to your friend\Nor even just make it publicly available. Your
Dialogue: 0,0:05:16.51,0:05:21.40,Default,,0000,0000,0000,,friend or even a stranger can use the public\Nkey to access your deposit slot and drop a
Dialogue: 0,0:05:21.40,0:05:27.40,Default,,0000,0000,0000,,message in, But only you can open the mailbox\Nwith your private key, to access all of the
Dialogue: 0,0:05:27.40,0:05:31.54,Default,,0000,0000,0000,,secret messages you've received. And you can\Nsend a secure message back to your friend
Dialogue: 0,0:05:31.54,0:05:37.62,Default,,0000,0000,0000,,by using the public deposit key to their mailbox.\NThis way people can exchange secure messages
Dialogue: 0,0:05:37.62,0:05:43.70,Default,,0000,0000,0000,,without ever needing to agree on a private\Nkey. Public Key cryptography is the foundation
Dialogue: 0,0:05:43.70,0:05:49.34,Default,,0000,0000,0000,,of all secure messaging on the open internet.\NIncluding the Security Protocols known as
Dialogue: 0,0:05:49.34,0:05:55.90,Default,,0000,0000,0000,,SSL and TLS, which protect us when we are\Nbrowsing the web. Your computer uses this
Dialogue: 0,0:05:55.90,0:06:01.40,Default,,0000,0000,0000,,today, anytime you see the little lock or\Nthe letters https in your browser's address
Dialogue: 0,0:06:01.40,0:06:07.41,Default,,0000,0000,0000,,bar. This means your computer is using public\Nkey encryption to exchange data securely with
Dialogue: 0,0:06:07.41,0:06:13.40,Default,,0000,0000,0000,,the website you're on. As more and more people\Nget on the internet more and more private
Dialogue: 0,0:06:13.40,0:06:19.08,Default,,0000,0000,0000,,data will be transmitted, and the need to\Nsecure that data will be even more important.
Dialogue: 0,0:06:19.08,0:06:24.06,Default,,0000,0000,0000,,And as computers become faster and faster\Nwe will have to develop new ways to make encryption
Dialogue: 0,0:06:24.06,0:06:29.26,Default,,0000,0000,0000,,too hard for computers to break. This is what\NI do with my work and it's always changing.