# How does RSA decryption works? [closed]

I have this exercise:

we have the following RSA public key $n = 275398901700898900724918474136345950999$
$e = 5$
Alice encrypts the message $M$ with the native RSA. She computes $C = M^e \pmod n$ and sends to Bob $C = 170841202002112185870598344402287193795$ Recover the original message $M$.

I'm playing some ctf online. I'm new in crypto and just want to know if I can decrypt the message using a tool.

## closed as off-topic by fkraiem, otus, Maarten Bodewes♦, e-sushiAug 4 '16 at 16:55

This question appears to be off-topic. The users who voted to close gave this specific reason:

If this question can be reworded to fit the rules in the help center, please edit the question.

• – Biv Aug 3 '16 at 9:38
• and mode – Biv Aug 3 '16 at 9:39
• did you actually search ? – Biv Aug 3 '16 at 9:39
• I'm voting to close this question as off-topic because it is a dump of a homework question. – fkraiem Aug 3 '16 at 9:42

## 1 Answer

This is an homework question so my answer won't be an answer but the very basic steps to find your answer. I let voluntarily enough informations hidden so you still have some work to do.

1. Factorise $n$

2. find $d$ the private key using $\varphi(n)$ and the extended euclidean algorithm.

3. compute $C^d \pmod n$ this should be your initial $M$.