Diffie–Hellman

For us who know network security, the IPsec VPN is very familiar, and the Diffie–Hellman key exchange to establish a secure connection. In short the VPN is a way to communicate privately and securely over a public network, basically the internet. companies uses it between its branches and employees use it to connect to there company's network from outside the company premises

Now the problem that the key to encrypt the connection shouldn't be sent for the security reasons of compromising the connection. And here is what Diffie–Hellman key exchange algorithm comes in handy, it is an asymmetric algorithm that generated a secret key. Asymmetric meaning different keys are used to encrypt and decrypt, while secret means the same key used in both operations.

So how is that? the famous Alice and Bob, the both agreed on a base number let's say 5, then each chose a number and add's it, let's say Alice chose 2 and Bob choose 3. Each of them will add this secret number to the common number, so Alice will have 7 and Bob has 8. they then send those numbers to each other, so Alice now has 8 and Bob 7, they will then add to those numbers to there secret number they choose, and viola, they both have the same number which is 10 and this is the key they will use in the rest of the connection. 

Ofcouse it is more complicated algorithm in real life, you can check it here: Diffie–Hellman key exchange - Wikipedia, the free encyclopedia

Till another day, happy calculations...