I wrote this writeup because I have seen some guys doing this challenge by using XORTOOL, but without understanding … mister X | python xortool.py cipher.txt; cat xortool_out/000.out mister X | So hardcore That’s why I’ll try to give you a real explaination of « why xortool have worked » So, for this challenge, we were given […]

ASIS CTF Quals 2014 | Stego 100: Blocks [Write-Up]

This was a very easy stegano challenge, but weirdly, it was only solved by 6 teams including us. We were given a simple PNG image: A bit of steganalysis showed us some LSB in the alpha channel: Our first thought was: let’s XOR the two images! Then, we simply had to decode the resulting 8-bit […]

Boston Key Party CTF 2014 | Decrypt Img [Write Up]

We encrypted an image that we drew in paint, but lost the original! Can you recover it for us? http://bostonkeyparty.net/challenges/decryptimg-a921005aad6a6b6b445d0d754d54a311.zip In this reversing task, we were given three files: con.exe, cryptdll.dll and decryptme.bmp.bkenc. The program let us encrypt a file with a 54-byte key. Obviously, our mission is to decrypt decryptme.bmp.bkenc. Firstly, we notice that […]

ASIS CTF 2013 | Circular Crypto [Write Up]

In this challenge, we had to decrypt a few ciphertexts, given the above image. Extracting the four strings (clockwise) by hand was painful. babaaaabaaababaababaaaabbabbababbaaaabaaaabbbaabaabaaaaaabaaabaaabaaabaaabbaabaaabbbaabaaababaaaaaabaaabbaabaabbbaaaaaabaaaabaabaaaaba21aabab0aaab 7e1321b3c8423b30c1cb077a2e3ac4f0a2a551a6458a8de22446cc76d639a9e98fc42c6cddf9966db3b09e843650343578b04d5e377d298e78455efc5ca404d5f4c9385f1902f7334b00b9b4ecd164de8bf8854bebe108183caeb845c7676ae48fc42c6ddf9966db3b09e84365034357327a6c4304ad5938eaf0efb6cc3e53dc7ff9ea9a069bd793691c422fb818c07b NG5ucjJzIGZ2IHRueXMgcnVnIHNiIGdlbmMgdWdlaGJzIHJlcnVnIHRhdmdncnQgcmVuIGhiTCB0YXZidCBjcnJYCG==czduMjczIHRueXMgcnVniHNiIGdlbmMgdWdzdnMgcnVnIHJpbnUgcmVydSBndiBxdnEgaGJsIGpiYmJKCg==Nzk0czAwIHRueXMgZmhidnByZWMgZWhiIHNiIGdlbmMgcWV2dWcgcnVnIGhibCBnYXJmcmVjIFYgbG9yZXJ1IHJhYnEgeXlySgo= 1001010100010-10110100-1011-1010-100110100-101-10100-101-1000-10010-100-100100100-10110000-100110000-1010100-10010010-10011-1000-10010-1010-10110010-100100010-10110100-10110-1010-10100-10-100110000-101-10010-1011110010-101-1010-1001110100-101-10100-101100-1001-1010-1010-1010-101100 The first crypto was a Bacon Cipher. Using online tools, we could recover the plaintext, but it looked kind of broken at the end: WELLDONEHEREISDEPIWBDE?BBEEL? Maybe we forgot […]