CodeGate Qualifiers CTF 2011 : Crypto – 200 Points

CodeGate Qualifiers CTF 2011 : Crypto – 200 Points

Hints given to us:
Find a key.
SCMPKBOUPDPHYTIAVIVRBTMVORUDNBDFNETDOIVTXROUNDKOBFWBPVOEQLTGKKARACYCGDNAECBXIZIKPTLEERZTYCYKIVXCPKPTPOVCAQRHRVKJUWMTWCMSXKADYHRVNAHCBRVSVSSCQCZQYDJXGSNRVSWCESTTBHIFCIASXRTAHKRRTUMVOKWITZPFZDISXZVVLGETPPLKSELDPGKELSHCBJBWXBIFCPEZYNBWXCDYMGAOVWNDKAKKKWBBQKPTIODKMGGHRVVNHINFCQESDYMLACVVBWBBQROPBBDFOXOSKDIGZWXFNTKFYIICWHRVVNHIYILTKHRVXPISB

This is the original file:
File:CodeGate_2011_Crypto_200.txt

Recommended Tools:
Brains – Actually, more of guesswork.
pygenere (http://smurfoncrack.com/pygenere/pygenere.php) – For cracking ciphertext using Vigenere cipher.

Finding the “Cipher” behind the Puzzle:
Looking at the given ciphertext, it seems to strongly suggest that it could be a polyalphabetic cipher.
This time round, i made use of http://www.simonsingh.net again to check which cipher it could be using.

Finally, i tried Vigenere cipher using the following link.
http://www.simonsingh.net/The_Black_Chamber/vigenere_cracking_tool.html

The returned results is as followed:

It seems to suggest that if the ciphertext is indeed using Vigenere cipher, the possible key length is 2,3 or 6.
Final Solution:
So using pygenere (http://smurfoncrack.com/pygenere/pygenere.php), i’ve tried entering explicitly 2 followed by 3 and 6 as the keylength.
Only keylength, 6, give me back sensible english words like the following picture.

On top of the page is the returned keyword that pygenere returned to me. So i’ve tried that as the key and Bingo.

Using “KRIPTO“, we solve this challenge. 😀

cheers
0x4a61636f62

Advertisements

Trả lời

Mời bạn điền thông tin vào ô dưới đây hoặc kích vào một biểu tượng để đăng nhập:

WordPress.com Logo

Bạn đang bình luận bằng tài khoản WordPress.com Đăng xuất / Thay đổi )

Twitter picture

Bạn đang bình luận bằng tài khoản Twitter Đăng xuất / Thay đổi )

Facebook photo

Bạn đang bình luận bằng tài khoản Facebook Đăng xuất / Thay đổi )

Google+ photo

Bạn đang bình luận bằng tài khoản Google+ Đăng xuất / Thay đổi )

Connecting to %s