Not sure if this is the correct place to ask a cryptography question, but here goes.
I am trying to work out "d" in RSA, I have worked out p, q, e, n and øn;
p = 79, q = 113, e = 2621 n = pq øn = (p-1)(q-1) n = 79 x 113 = 8927 øn = 78 x 112 = 8736 e = 2621 d =
I cant seem to find d, I know that d is meant to be a value that.. ed mod ø(n) = 1. Any help will be appreciated
edit: an example would be e = 17, d = 2753, øn = 3120
17 * 2753 mod 3120 = 1
You are looking for the modular inverse of e (mod n), which can be computed using the extended Euclidean algorithm:
function inverse(x, m) a, b, u := 0, m, 1 while x > 0 q := b // x # integer division x, a, b, u := b % x, u, x, a - q * u if b == 1 return a % m error "must be coprime"
Thus, in your examples,
inverse(17, 3120) = 2753 and
inverse(2621, 8736) = 4373. If you don't want to implement the algorithm, you can ask Wolfram|Alpha for the answer.