RSA is a block cipher, the block size must be less than or equal \(\log_{2}(n)+1\), if block size =i bits \(2^{i}<n<2^{i}+1\)
The encryption and decryption are on the following form \(C = M^{e} mod(n)\)
\(M = C^{d} mod(n) = (M^{e})^d mod(n) = M^{ed} mod(n)\)
The relationship between e and d are multiplicative inverse modulo Q(n) as in Euler Totient Function ed mod(Q(n))=1 which d is relatively prime to Q(n) and e also.

Diffie-Hellman is a key exchange algorithm based on public key cryptography written by Diffie and Hellman
Diffie-Hellman Algorithm First we have to know the concept “Primitive root of a prime number” ,a primitive root x of a prime number p means : \(x \ mod(p), x^{2} mod(p), x^{3} mod(p),…, x^{p-1}mod(p)\) generates numbers from 1 to p-1.
In Diffie-Hellman algorithm there are two numbers
1- Prime number \(q\).
2- Primitive root of \(q = a\).