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The Internet: Encryption and Public Keys

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Hi my name is Mia Gil-Epner, I'm majoring[br]in Computer Science at UC Berkeley and I work

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for the Department of Defense, where I try[br]to keep information safe. The Internet is

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an open and public system. We all send and[br]receive information over shared wires and

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connections. But even though it's an open[br]system we still exchange a lot of private

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data. Things like credit card numbers,[br]bank information, passwords, and emails. So

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how is all this private stuff kept secret?[br]Data of any kind can be kept secret through

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a process known as encryption, the scrambling[br]or changing of the message to hide the original

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text. Now decryption is the process of un-scrambling[br]that message to make it readable. This is

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a simple idea, and people have been doing[br]it for centuries. One of the first well known

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methods of encryption was Caesar's Cipher.[br]Named after Julius Caesar, a Roman general

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who encrypted his military commands to make[br]sure that if a message was intercepted by

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enemies, they wouldn't be able to read it.[br]Caesar Cipher is an Algorithm that substitutes

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each letter in the original message with a[br]letter a certain number of steps down the

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alphabet. If the number is something only[br]the sender and receiver know, then it's called

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the key. It allows the reader to unlock the[br]secret message. For example, if your original

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message is 'HELLO' then using the Caesar Cipher[br]algorithm with a key of 5 the encrypted message

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would be this... To decrypt the message, the[br]recipient would simple use the key to reverse

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the processes. But there is a big problem[br]with Caesar Cipher, anybody can easily break

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or crack the encrypted message, by trying[br]every possible key, and in the english alphabet

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there are only 26 letters, which means you[br]would only need to try at most 26 keys to

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decrypt the message. Now trying 26 possible[br]keys isn't very hard, it would take at most

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an hour or two. So lets make it harder. Instead[br]of shifting every letter by the same amount,

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let's shift each letter by a different amount.[br]In this example a ten digit key shows how many

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positions each successive letter will be changed[br]to encrypt a longer message. Guessing this

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key would be really hard. Using 10 digit encryption[br]there could be 10 billion possible key solutions.

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Obviously that's more then any human could[br]ever solve, it would take many centuries.

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But an average computer today, would take[br]just a few seconds to try all 10 billion possibilities.

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So in a modern world were the bad guys are[br]armed with computers instead of pencils how

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can you encrypt messages so securely that[br]they're too hard to crack? Now too hard means

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that there are too many possibilities to compute[br]in a reasonable amount of time. Today's secure

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communications are encrypted using 256 bit[br]keys. That means a bad guy's computer that

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intercepts your message would need to try[br]this many possible options... until they discover

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the key and crack the message. Even if you[br]had a 100,000 super computers and each of

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them was able to try a million billion keys[br]every second it would take trillions of trillions

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of years to try every option, just to crack[br]a single message protected with 256 bit encryption.

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Of course computer chips get twice as fast[br]and half the size every year or so. If that

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pace of exponential progress continues, today's[br]impossible problems will be solvable just

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a few hundred years in the future and 256[br]bits won't be enough to be safe. In fact

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we've already had to increase the standard key[br]length to keep up with the speed of computers.

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The good news is using a longer key doesn't[br]make encrypting messages much harder but it

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exponentially increases the number of guesses[br]that it would take to crack a cipher. When

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the sender and receiver share the same key[br]to scramble and unscramble a message its called

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Symmetric Encryption. With Symmetric Encryption,[br]like Caesar Cipher, the secret key has to be

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agreed on ahead of time by two people in private.[br]So that's great for people, but the internet

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is open and public so it's impossible for[br]two computers to "meet" in private to agree

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on a secret key. Instead computers use Asymmetric[br]Encryption keys, a public key that can be

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exchanged with anybody and a private key that is[br]not shared. The Public Key is used to encrypt

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data and anybody can use it to create a secret[br]message, but the secret can only be decrypted

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by a computer with access to the private key.[br]How this works is with some math that we won't

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get into right now. Think of it this way,[br]imagine that you have a personal mailbox,

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where anybody can deposit mail but they need[br]a key to do it. Now you can make many copies

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of the deposit key and send one to your friend[br]or even just make it publicly available. Your

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friend or even a stranger can use the public[br]key to access your deposit slot and drop a

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message in, But only you can open the mailbox[br]with your private key, to access all of the

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secret messages you've received. And you can[br]send a secure message back to your friend

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by using the public deposit key to their mailbox.[br]This way people can exchange secure messages

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without ever needing to agree on a private[br]key. Public Key cryptography is the foundation

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of all secure messaging on the open internet.[br]Including the Security Protocols known as

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SSL and TLS, which protect us when we are[br]browsing the web. Your computer uses this

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today, anytime you see the little lock or[br]the letters https in your browser's address

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bar. This means your computer is using public[br]key encryption to exchange data securely with

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the website you're on. As more and more people[br]get on the internet more and more private

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data will be transmitted, and the need to[br]secure that data will be even more important.

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And as computers become faster and faster[br]we will have to develop new ways to make encryption

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too hard for computers to break. This is what[br]I do with my work and it's always changing.