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Engineering

2019年03月11日10:00

UTCTF wirteup [basics] re

カテゴリ: UTCTF

[basics] re

100

I know there's a string in this binary somewhere.... Now where did I leave it?

by balex

stringsコマンドでファイル中の文字列を調べます。

$ strings calculator
/lib64/ld-linux-x86-64.so.2
& 1y
libc.so.6
__isoc99_scanf
__stack_chk_fail
printf
__libc_start_main
__gmon_start__
GLIBC_2.7
GLIBC_2.2.5
GLIBC_2.4
UH-H
AWAVA
AUATL
[]A\A]A^A_
Enter an operator (+, -, *,):
Enter two operands:
%lf %lf
%.1lf + %.1lf = %.1lf
%.1lf - %.1lf = %.1lf
%.1lf * %.1lf = %.1lf
%.1lf / %.1lf = %.1lf
Error! operator is not correct
utflag{str1ng5_15_4_h4ndy_t00l}
;*3$"

フラグは、

utflag{str1ng5_15_4_h4ndy_t00l}

です。

LinuxコマンドABCリファレンス

LinuxコマンドABCリファレンス [単行本（ソフトカバー）]

中島能和

翔泳社

2018-03-01

タグ：: #Reverse; #Engineering

2019年02月10日06:00

Quals: Saudi and Oman National Cyber Security CTF writeup I love this guy

カテゴリ: Quals: Saudi and Oman National Cyber Security CTF

Quals: Saudi and Oman National Cyber Security CTF 2019 » I love this guy

Category:Malware Reverse Engineering

Level:medium

Points:100

Points

Can you find the password to obtain the flag?

Link:https://s3-eu-west-1.amazonaws.com/hubchallenges/Reverse/ScrambledEgg.exe

fileコマンドでファイルタイプを確認します。.NETアプリケーションです。

$ file ScrambledEgg.exe
ScrambledEgg.exe: PE32 executable (GUI) Intel 80386 Mono/.Net assembly, for MS Windows

dnSpyで.NETアプリケーションを逆コンパイルします。逆コンパイルされたソースコードのButton_Clickイベントの箇所を確認します。

public char[] Letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ{}_".ToCharArray();

private void Button_Click(object sender, RoutedEventArgs e)
{
string value = new string(new char[]
{
this.Letters[5],
this.Letters[14],
this.Letters[13],
this.Letters[25],
this.Letters[24]
});
if (this.TextBox1.Text.Equals(value))
{
MessageBox.Show(new string(new char[]
{
this.Letters[5],
this.Letters[11],
this.Letters[0],
this.Letters[6],
this.Letters[26],
this.Letters[8],
this.Letters[28],
this.Letters[11],
this.Letters[14],
this.Letters[21],
this.Letters[4],
this.Letters[28],
this.Letters[5],
this.Letters[14],
this.Letters[13],
this.Letters[25],
this.Letters[24],
this.Letters[27]
}));
}
}

valueとTextBoxの入力値を比較しています。valueは、

FONZY

なので、入力するとフラグが表示されます。

フラグは、

FLAG{I_LOVE_FONZY}

です。

プログラミング.NET Framework 第4版 (Microsoft Press)

プログラミング.NET Framework 第4版 (Microsoft Press) [単行本]

Jeffrey Richter

日経BP社

2013-10-10

タグ：: #Malware; #Reverse; #Engineering

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