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## Internet safety

### Course: Internet safety>Unit 1

Lesson 10: Data encryption techniques

# Public key cryptography: What is it?

After WWII, the US and Soviet Union raced to become global superpowers, leading to the creation of NORAD and computer networking. As the internet grew, encryption became essential for secure communication. Diffie & Hellman devised a trick using one-way functions to share secret keys without eavesdroppers intercepting them. Created by Brit Cruise.

## Want to join the conversation?

• I don't understand. Eve has the public color (yellow), as well as each of the colors created by Alice and Bob. Couldn't Eve simply use logic and the color wheel to determine the private colors by both Alice and Bob? Example: Bob's color was green. Eve could just "subtract" yellow from the color green to get blue, therefore getting Bob's "secret color", therefore getting the mixture, or key. Right?
• Certainly Eve can try to guess what their original colors were, but only come close to the exact colors. On the other hand neither Alice nor Bob need to struggle to know their joint combination color.
• I dont understand how they end up with the same color. I mean. if you mix Your public color with bobs red, how is it that is it guarenteed that they will end up with the same color!?
• They both mix the same colours, but in a different order. Because order does not matter, they end up with the same colour.
• how come Eve can not make her own private number?
• bacause bob and alices private colour is never revealed. Eve only gets to see half-constructed keys. But no way to find out how the yellow was converted to these half constructed keys. Except to try every possible combination, and it is arranged to be a lot of guesses.
• couldn't eve just not mix all the colours she has? that way she would(probably) get the common colour
(1 vote)
• This wouldn't work and wouldn't be practical in the numerical procedure.
• why does eve have a yellow colour if she is not using it.?
• Because yellow was agreed on publicly (like on the internet)
Hope this helps
• You know how Brit Cruise said it would be hard to decode a mixed color? Then how do Alice and Bob both decode the colors do find each others private colors. Or is the mixed-mixed color the secret shared private color?
(1 vote)
• The mixed-mixed color is the private color, yes.
• At , eve, with the green could fairly easily go into the color wheel and decode the secret colors. I don't get how that is hard
• It's harder than mixing two colors. However, It's not really hard in case of colors but it is insanely hard if you used the method in the next videos.
This analogy were made just to make it easy to understand the general concept.
• I am confused. If I use encryption software and I have a key that I need to give another person (and them vice versa) I don't know understand how careful I need to be with the string of letters it gives me. By posting the key on a social network, for example, is it analogous to the video where the private color and the yellow can be seen, but their private color is kept secret to mix later? I don't know if I'm making sense. I think that I can post my key that someone has to enter for connection, but I am afraid that when everyone else sees the key they can decode communications. Thanks.
(1 vote)
• If you are using a symmetric cipher, like the Caesar cipher or AES, then the key must be kept secret and no one except the sender and receiver should be allowed to see it.

If you are using public key cryptography then you will have two keys: a public key and a private key. Everyone in the world should be allowed to see your public key, but you must keep the private key secret (or everyone will be able to read your messages).

If you encrypt a message with a good cipher then you shouldn't care who sees the cipher text, because they shouldn't be able to figure out what the original message was (unless they have the secret key).
• Why was the most vulnerable part of the US the North Pole
(1 vote)
• It's the shortest distance from Russia. This means that the time for the US to detect and respond to a missile launched over the North Pole is smaller than a missile taking a different path. The North Pole also has the problem of being an area where it is very tough to set up and maintain equipment for detection, or interception, due to its hostile environment (Non-ownership of the area by the US would also complicate setting up military equipment there. .
(1 vote)
• is public key cryptography same as symmetric encryption ??
(1 vote)
• No.
Public key cryptography uses two keys:
1) a public key used by the sender to encrypt messages
2) a private key used by the receiver to decrypt messages

Symmetric key cryptography uses 1 key, that can be used to both encrypt and decrypt messages.
(1 vote)