Pico CTF 2018: Caesar Cipher 2 Writeup
Points : 250
Cipher Text : 4-’3evh?’c)7%t#e-r,g6u#.9uv#%tg2v#7g’w6gA
The Pico CTF was held this month with lots of sec challenges in it.One challenge that was really solved from scratch by me was this
Caesar Cipher 2 .
A string was given which was supposed to be a ciphertext …..wait not just a normal cipher text but a cipher text involving special characters as well
The reason I had to solve it from scratch is because I couldnt find any online service to decipher it with ROTation of more than 25 …LEL …
Hint : ASCII
of course the Cipher text contained special characters so ASCII table was used for enciphering the flag.
As seen in the cipher text we do not see any characters from ASCII range 1 to 32 i.e. NULL etc.
So the best guess is it is using characters from
! (Exclaimation) whose ASCII value is 33
to
~ (Tilde) whose ASCII value is 126
That is the total characters used are 94
Here is a simple program to try all possible shifts with the cipher text until we get the flag.
After running it we can see the 60th Rotation has the flag in it . :)
Hence the Flag was : picoCTF{cAesaR_CiPhErS_juST_aREnT_sEcUrE}
Thank you for reading.
Follow me on Twitter : @vk_tushar