Rating:
# CTFNAME
#### RSA
#### Cyrptography / 60pts
## Description
This time John managed to use RSA " correctly "&ellipsis; I think he still made some mistakes though. [flag.txt](https://play.icec.tf/problem-static/flag_6c0d309aff5de8e26e20afa39bd736d6bde73440f0de620e3793d4d86e3d33ca.txt)
## Solution
First of all: WTF?! Why am i so...
WTF#1: " correctly " - it is correctly, at least every provided string is correct, I spent so much time to check them
WTF#2: &ellipsis; - is it "..." or is it ["elliptic attack"](http://andrea.corbellini.name/2015/06/08/elliptic-curve-cryptography-breaking-security-and-a-comparison-with-rsa/)
Well both WTF took so much time from me before I got that 60pts chall can't be so difficult
Success:
They provided everything we need in flag file. Even more:
* N - which is modulus
* c - whichi is encrypted test
* d - which is private exponent
* e - anyway it can only 3 or 65537, so not a big deal to have it
* Phi - which is phi(N) = (p-1)*(q-1) ... and we do not need this!!!
All we really need are N, c, d
m=c^mod(N)
Using Python ```_pow(c,d,N)_``` function:
```
c=0x126c2...
d=0x12314...
N=0x1564a...
print (hex((pow(c,d,N)))[2:][:-1].decode('hex'))
```
first we use pow to decrypt message, it will be provided in INT, INT will be converted to HEX, HEX to string and we have flag
## Flag
**IceCTF{rsa_is_awesome_when_used_correctly_but_horrible_when_not}**
