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.