Mesej Rahsia

Tak susah pun, run je script

Category: Crypto
Challenge file: secretMessenger.py

Solution

1. Analyze the Python script

a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z='j','b','a','c','m','n','i','p','o','q','r','t','x','z','v','s','u','y','h','g','d','e','f','k','l','w'
flag=((3108,"{",p,q,b,p,l,g,l,q,l,v,"_",d,g,h,s,v,k,"_",l,v,m,l,"}")[::-1])

From this code, we couldn’t able the see an output as there is no print() and join() method to return the flag string

2. Modify the Python script

a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z='j','b','a','c','m','n','i','p','o','q','r','t','x','z','v','s','u','y','h','g','d','e','f','k','l','w'
flag=((3108,"{",p,q,b,p,l,g,l,q,l,v,"_",d,g,h,s,v,k,"_",l,v,m,l,"}")[::-1])
print("".join(map(str,flag))) # character mapping and print as string

3. Run the Python script

$ python3 secretMessage.py
}txet_rehpic_etutitsbus{3108

It seems the flag header and flag payload string is reversed

4. Reconstruct Flag String

}txet_rehpic_etutitsbus{3108 -> 3108{substitute_cipher_text}

There you have the flag

Flag: 3108{substitute_cipher_text}