Perform encryption and decryption operation using RSA algorithm for a specific case.
Subject Computer and Network Security
NU Year Set: 2.(c) Marks: 6 Year: 2017

RSA algorithm is a typical public-key cryptosystem.

It is a basic technique of many security protocols. It

can be described briefly as follows:

1. Choose two large strong primes, p and q. Let n =

pq.

2. Compute Euler value of n: )(n) = (p - 1)(q - 1).

3. Find a random number e satisfying 1 < e < )(n) and

gcd(e,)(n)) = 1.

4. Compute a number d such that d = e-1 mod )(n).

5. Encryption: Given a message m satisfying m < n,

then the cipher text c = me mod n.

6. Decryption: m = cd mod n.

The security of RSA is based on the hard of

factoring n. To enhance the hardness of factoring n,

Ogiwara [6] suggests the following constraints on p and

q:

1. Both (p - 1) and (q - 1) should contain a large prime

factor such that r1|(p – 1) and t1|(q – 1), where r1

and t1 are two large primes.

2. Both (p + 1) and (q + 1) should contain a large prime

factor such that s1|(p + 1) and u1|(q + 1), where s1

and u1 are two large primes

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