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.

  • $\begingroup$ Some more readings. $\endgroup$
    – Biv
    Aug 3, 2016 at 9:38
  • $\begingroup$ and mode $\endgroup$
    – Biv
    Aug 3, 2016 at 9:39
  • $\begingroup$ did you actually search ? $\endgroup$
    – Biv
    Aug 3, 2016 at 9:39
  • 1
    $\begingroup$ I'm voting to close this question as off-topic because it is a dump of a homework question. $\endgroup$
    – fkraiem
    Aug 3, 2016 at 9:42

1 Answer 1


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 $M$.


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