Secure Communication in a Public Key System

Rivest Shamir-Adleman (RSA) Method

RSA Method and Example

1. Choose two large (100 digit) prime numbers, p and q, and set
           n = p x q

2. Choose any large integer, d, so that:
           GCD( d, ((p-1)x(q-1)) = 1

3. Find e so that:
           e x d = 1 (modulo (p-1)x(q-1))


Example:

1.  p = 5, q = 11 and n = 55.
    (p-1)x(q-1) = 4 x 10 = 40

2.  A valid d is 23 since GCD(40, 23) = 1

3.  Then e = 7 since:
    23 x 7 = 161 modula 40 = 1

Go Back to the Operating Systems page.