<개인공부> - IT/[CTF (Write up)]
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Basic password cracking (MD5, SHA1, ..)<개인공부> - IT/[CTF (Write up)] 2020. 7. 2. 04:31
기본적인 password cracking과 같은 문제를 CTF에서는 종종 접할 수 있다. 과거에도 비슷한 코드를 작성했었지만 메모리 초과로 인해서 포기하곤 했는데 우연히 검색을 하다가 알게된 부분이 있어서 공유해보고자 한다. 기본적으로 - MD5 : 32-bit hex digits - SHA1 : 40-bit hex digits - SHA256 : 256-bit hex digits 우선, 일부 문자열은 제공되어 있고 숫자만 padding하여 해쉬 값을 계산하는 것은 아래와 같다. 예제에서 주어진 것 처럼 실제 0000부터 9999까지 숫자만 붙여서 주어진 hash 값을 비교하는 것이므로 해당 예제는 상당히 간단하다. import hashlib prefix = "CTF-TEST-" match = "bf9e..
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Chaos Communication Camp 2019 (Ancient Data)<개인공부> - IT/[CTF (Write up)] 2019. 8. 28. 10:41
Ancient Data Category: Misc Difficulty: Easy (Google the world) Author: TheVamp That is some ancient stuff! Could you translate that for us? Put your translated text in the following format, to submit the Flag: ALLES{} ***** I simply googled keyword by ancient letters and then I got the following image as below. Afterward, it is just a piece of cake. So, the flag is ALLES{ALPHABETEVOLUTION} Refe..
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Securinets Prequals 2K19 Write-up (Easy Trade)<개인공부> - IT/[CTF (Write up)] 2019. 3. 24. 13:12
This is a basic forensic question. This is my approach. I only used Wireshark Follow TCP Stream feature. Fortunately, the provided pcap file is not big so I skimmed every line. In the pcap file I found some clues for the flag. Between hosts exchanged the key and flag.txt is sent in a zip file. >> 50 40 03 04 is the signature for zip file I used the Follow TCP Stream function (Analyze >> Follow >..
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TAMUctf '19 Write-up (I heard you like files)<개인공부> - IT/[CTF (Write up)] 2019. 3. 24. 11:39
As we open the uploaded file, we can see below image. After I downloaded this file, I checked the hidden file itself by binwalk command. $ binwalk art.png DECIMAL HEXADECIMAL DESCRIPTION--------------------------------------------------------------------------------0 0x0 PNG image, 1920 x 1080, 8-bit/color RGBA, non-interlaced3408641 0x340301 PDF document, version: "1.5"3408712 0x340348 Zlib com..
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TAMUctf '19 Write-up (Hello World)<개인공부> - IT/[CTF (Write up)] 2019. 3. 24. 06:07
As we open the uploaded file, we can see a bunch of tabs and spaces. So I googled whitespace decoder on the Internet. And I got this website to decode whitespaces. >> https://vii5ard.github.io/whitespace/I simply copied and pasted the whitespaces part on the web and I got a below message.As we know we have to find a flag, however, it has nothing at all. Actually, I used this tool for the first t..
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Pragyan CTF 19' Write-up / Welcome<개인공부> - IT/[CTF (Write up)] 2019. 3. 18. 05:30
I tried this problem at first as its subject is welcome, however, I had a really hard time to solve this problem. My approach is as below. First, I assumed that it has a hidden message so I used steganography decoder right away. BUT, it has no hidden message. Afterward, I simply used fundamental forensics tools such as file and binwalk. 1) file command $ file welcome.jpeg welcome.jpeg: JPEG imag..
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UTCTF 19' Write-up / Low Sodium Bagel<개인공부> - IT/[CTF (Write up)] 2019. 3. 15. 14:16
This one is also an interesting problem. I downloaded a picture from the server and I opened it. I could see a bagel image. Actually, I am a newbie of CTF competition so whenever I see the picture I always have an assumption that picture has a hidden message, which is steganography. So I tried to decode it. There are tons of steganographic decoder website, however, below one only supports jpeg f..
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UTCTF 19' Write-up / [basics] forensics<개인공부> - IT/[CTF (Write up)] 2019. 3. 15. 13:57
[basics] forensics100My friend said they hid a flag in this picture, but it's broken!by balex This problem is the last one for the beginner. I downloaded the secret.jpg file, however, I couldn't open it. I just got "file cannot be readable" error message. So I checked the file type on linux environment (Actually, I use WSL, Windows Subsystem for Linux). And then, I found out the file's extension..