DH key exchanges

DANMOH009

I ve been re-reading my security notes and im starting to get confused. Is it safe to say that this short youtube video explains diffe helman? or is this explaining some other kind of key exchange?

Private and Public Key Encryption - YouTube


Reason im asking is because when im reading about DH im going into a lot of detail about mixing a combination of keys etc... im wondering if the above just explains it but in a lot simpler way.

EdTheLad

DH id the process by which the keys are exchanged. That video describes the concept of key exchange but not the DH process.
On a Cisco router you configure a DH group, what that is doing is effectively configuring a Generator and Prime number pair between the two peers.
This is used in DH calculations R=G^x mod p, where x is the private key. Both sides will choose a different value for x, i.e. the secret integer.

Both sides will perform this calculation and exchange the result R. R is the public key.
To put this in perspective, if you are using DH group 5, the generator G =2;
The prime is: 2^1536 - 2^1472 - 1 + 2^64 * { [2^1406 pi] + 741804 }

Both sides receive different values for R and use it to calculate S the secret key which will work out to be the same due to a symmetrical computatin done on both sides.