CALCULATE DIFFIE HELLMAN KEY EXCHANGE ALGORITHM

Agree two shared related values
MOD = "p"
BASE= "g"
"p" must be prime number and "g" a primitive root modulo of P
Choose random secret numbers
client= "a"
server- "b"
secret numbers do NOT need to be prime
Generate shareable value (A) from secrets
A = g^a MOD p
B = g^b MOD p
client sends A to server and server sends B to client
at this point p g A B are known globally - only a and b kept secret
Calculate shared key
client: B^a MOD p
server: A^b MOD p
Both these calculations will produce the same number - the shared key
shared key now used by AES for bulk symmetric encryption


SIMPLE EXAMPLE
Variables
"p" = 23
"g" = 5
"a" = 4
"b" = 3
Formulas
Create shareable values
A = g^a Mod P --> 5^4 MOD 23 =4
B = g^b Mod P --> 5^3 MOD 23 =10
Create shared secret
B^a MOD p --> 10^4 MOD 23 = 18
A^b MOD p --> 4^3 MOD 23 = 18
Both values are 18 which is the shared secret


EPHEMERAL DIFFIE HELLMAN
Secret keys ("a" and "b") are changed with each session
This provides PERFECT FORWARD SECRECY
past communication is still secure if breached as same key not used