Locked_Out

Locked Out

Author: Vinayak Vatsalya J

Flag: CTF{r0n_4D1_130N4rd}

Problem Statement

Coulson is locked out of Ragtag. Can you help him get back to BASE by finding the flag. He found this image in BIN.

Flag format: CTF{...}

Relevant files / links

• flag.png

Solution

• The QR code gives a string encoded in base64. After decoding this we get a link to a text file.
  
• This is in binary. After converting binary to text, we get values of n , c and e (RSA). To find the factors of n ( p and q ) this tool can be used. Using p and q values, d can be found using following script.

c = 7424699238646955201370695213431987671142812230143306867560482933056266299380926684689129315498363439046922143979269386180477235672715428337919573885741855
n = 14783703403657671882600600446061886156235531325852194800287001788765221084107631153330658325830443132164971084137462046607458019775851952933254941568056899
e = 0x10001

p = 121588253559534573498320028934517990374721243335397811413129137253981502291629 
q = 121588253559534573498320028934517990374721243335397811413129137253981502291631   #from factordb

phi = (p-1)*(q-1)

from Crypto.Util.number import inverse 
d = inverse(e, phi)
m = pow(c,d,n)

import binascii
print(binascii.unhexlify(hex(m)[2:])) #gives the flag as : 'CTF{r0n_4D1_130N4rd}'