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Tag: CTF-Stego

[H4CK1T]Mozambique – 150pts

Description: EN: Implementing of the latest encryption system as alwaysbrought a set of problems for one of the known FSI services: theyhave lost the module which is responsible for decoding information.And some information has been already ciphered! Your task fortoday: to define a cryptoalgorithm and decode the message. Solution: 在查看圖片後發現被插入了一些像數 , 出現的間隔24個Pixel 在找出最後一點的像數後 , 發現是1512 , 除以24是63 , 由於是為0開始 ,所以最終圖片可能是64×64 故寫一script抽出所有像數

得到

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[H4CK1T]Crypt0P1xels – 250pt

Desciprion: EN: We have received pictures from the enemy companion of theunknown before planet. And we haven’t thought up anything better,than to construct DeathStarV3 (the general was a fan of “StarWars”) and to absorb energy of the whole planet! And again we arepursued by problems: that we don’t know coordinate! Your task is todetermine coordinates of this unique planet (which according to ourspy are ciphered in the image). Also he could steal one of thescripts intended for embedding of coordinates. All hope only foryou! Solution: 第一步是先看懂題目給予的 SECRET_TOOL.py code:

0,0這個pixel的Red value代表的是flag的長度是多少 , 經查看後發現其值是33 然後第一步是生成一個1-255的x和y , 將 (len(flag),x,y)寫入0,0 第二步是生成1-255的x1和y1 , 然後將(ascii(flag[i]),x1,y1)) 寫入 x y中 , 然後將x= x1 , y = y1 第三步是生成1-255的x1和y1 , 然後將(ascii(flag[i]),x1,y1)) 寫入 x y中 … 我們可以看清楚其pattern為 , 寫入的x y為上一個的G 和 B value , 而R value存放的是flag 第n 隻字的ascii值 所以我們可以先找出可能的pixel 和 x y值 code:

得出

然後根據pattern排序後得出

取Red value 並由ascii轉為char code:

output:

所以flag是

 

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[H4CK1T]RTFspy – 150pts

Description: Everybody likes to store passwords in txt files? And our guinea pig has gone much further! He has begun to store the information under a signature stamp “TOP SECRET” in them! Prove to him that it isn’t secure. And there are a .zip file. After unzip, there are a .rtf file included: When I open the .rtf file, can see that: We got some information in the head of the file:

Seems like a image has been encrypted. Let me try to decode with hex to text, then I got this: I got it right, it is a png file but I cannot open it correctly. When I scroll it down, I can see that:

That is a file called flag.txt inside this image. So we got: flag.txt is the flag:

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