No Padding No Problem

Attacking RSA for fun and CTF points – part 1

The provided netcat connection gives the public modulus n and public exponent e as well as the ciphertext. This is also a Oracle because we can provide come ciphertext and the program will decrypt it for us.
Reading Bitsdeep's article on RSA Oracle, we could multiply the ciphertext my another cipher text c2 which me know the plain text of and recover the decrypted c1 ciphertext. Heres how the math works: C = c*c_2 = M^e*2^e = 2M^e. So we just need to divide the returned plaintext by 2 to get the deciphered flag.

Script

Using pwntools we could easily store and manipulate given data as well as enter data to the nc connection.