From the contents of the file it is clear that we are given the public modulus, n the encryption exponent e and a cipher text. In order to be able to decrypt the cipher text, we should be able to exploit some inherent mathematical vulnerability in the prime factors used to compute the public modulus n.

we can easily see that are public modulus is not large enough and should be easily factorable. As factordb lookup is one of the attacks implemented within the RsaCtfTool we directly go ahead and run it.

Original writeup (https://c12yptonic.github.io/ctf-writeups/ctfs/deconstructf21#rsa-1).