The Internet: Encryption and Public Keys Hi my name is Mia Gil-Epner, I'm majoring
in Computer Science at UC Berkeley and I work for the Department of Defense, where I try
to keep information safe. The Internet is an open and public system. We all send and
receive information over shared wires and connections. But even though it's an open
system we still exchange a lot of private data. Things like credit card numbers,
bank information, passwords, and emails. So how is all this private stuff kept secret?
Data of any kind can be kept secret through a process known as encryption, the scrambling
or changing of the message to hide the original text. Now decryption is the process of un-scrambling
that message to make it readable. This is a simple idea, and people have been doing
it for centuries. One of the first well known methods of encryption was Caesar's Cipher.
Named after Julius Caesar, a Roman general who encrypted his military commands to make
sure that if a message was intercepted by enemies, they wouldn't be able to read it.
Caesar Cipher is an Algorithm that substitutes each letter in the original message with a
letter a certain number of steps down the alphabet. If the number is something only
the sender and receiver know, then it's called the key. It allows the reader to unlock the
secret message. For example, if your original message is 'HELLO' then using the Caesar Cipher
algorithm with a key of 5 the encrypted message would be this... To decrypt the message, the
recipient would simple use the key to reverse the processes. But there is a big problem
with Caesar Cipher, anybody can easily break or crack the encrypted message, by trying
every possible key, and in the english alphabet there are only 26 letters, which means you
would only need to try at most 26 keys to decrypt the message. Now trying 26 possible
keys isn't very hard, it would take at most an hour or two. So lets make it harder. Instead
of shifting every letter by the same amount, let's shift each letter by a different amount.
In this example a ten digit key shows how many positions each successive letter will be changed
to encrypt a longer message. Guessing this key would be really hard. Using 10 digit encryption
there could be 10 billion possible key solutions. Obviously that's more then any human could
ever solve, it would take many centuries. But an average computer today, would take
just a few seconds to try all 10 billion possibilities. So in a modern world were the bad guys are
armed with computers instead of pencils how can you encrypt messages so securely that
they're too hard to crack? Now too hard means that there are too many possibilities to compute
in a reasonable amount of time. Today's secure communications are encrypted using 256 bit
keys. That means a bad guy's computer that intercepts your message would need to try
this many possible options... until they discover the key and crack the message. Even if you
had a 100,000 super computers and each of them was able to try a million billion keys
every second it would take trillions of trillions of years to try every option, just to crack
a single message protected with 256 bit encryption. Of course computer chips get twice as fast
and half the size every year or so. If that pace of exponential progress continues, today's
impossible problems will be solvable just a few hundred years in the future and 256
bits won't be enough to be safe. In fact we've already had to increase the standard key
length to keep up with the speed of computers. The good news is using a longer key doesn't
make encrypting messages much harder but it exponentially increases the number of guesses
that it would take to crack a cipher. When the sender and receiver share the same key
to scramble and unscramble a message its called Symmetric Encryption. With Symmetric Encryption,
like Caesar Cipher, the secret key has to be agreed on ahead of time by two people in private.
So that's great for people, but the internet is open and public so it's impossible for
two computers to "meet" in private to agree on a secret key. Instead computers use Asymmetric
Encryption keys, a public key that can be exchanged with anybody and a private key that is
not shared. The Public Key is used to encrypt data and anybody can use it to create a secret
message, but the secret can only be decrypted by a computer with access to the private key.
How this works is with some math that we won't get into right now. Think of it this way,
imagine that you have a personal mailbox, where anybody can deposit mail but they need
a key to do it. Now you can make many copies of the deposit key and send one to your friend
or even just make it publicly available. Your friend or even a stranger can use the public
key to access your deposit slot and drop a message in, But only you can open the mailbox
with your private key, to access all of the secret messages you've received. And you can
send a secure message back to your friend by using the public deposit key to their mailbox.
This way people can exchange secure messages without ever needing to agree on a private
key. Public Key cryptography is the foundation of all secure messaging on the open internet.
Including the Security Protocols known as SSL and TLS, which protect us when we are
browsing the web. Your computer uses this today, anytime you see the little lock or
the letters https in your browser's address bar. This means your computer is using public
key encryption to exchange data securely with the website you're on. As more and more people
get on the internet more and more private data will be transmitted, and the need to
secure that data will be even more important. And as computers become faster and faster
we will have to develop new ways to make encryption too hard for computers to break. This is what
I do with my work and it's always changing.
of course I think not enough covered here, but at least for newbie its not so frustrating & even fun to watch
It's a good basic tutorial. Minor nitpick -- the stats given on the example are not entirely accurate. I think a human actually probably could crack the 10 digit key by hand because the spaces in the text leak information about the contents. In reality for any modern cryptographic method, spaces would also be encrypted so you wouldn't know where the spaces are.