ForbiddenBITS CTF 2013 x93 Machine

I have never participated in any CTFs after last years IFSF CTF. So I thought to start actively participate in all upcoming CTFs from this year’s ForbiddenbitsCTF. I solved two challenges in this contest. There was a service running in 95.170.83.28 3003 and we were asked to enter the restricted area by having a balance more than $5000. We were only given 100$, 100 Euros and 100 GBP as the main balance. After a lot of struggle, I found a bug in the program that if you exchange money within your account (i.e from GBP to EURO and vice-versa) after a single rotation, the balance will be increased by 100.1 EURO’s. Then I didn’t waste much time to write a script :-p I did it manually (of course it took very less time as they asked only balance above 5000 USD)

$ nc 95.170.83.28 3003
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 _    _  93   _________   ______   ______  _    _  _____  ______   ______ 
\ \  / /     | | | | | \ | |  | | | |     | |  | |  | |  | |  \ \ | |     
 >|--|<      | | | | | | | |__| | | |     | |--| |  | |  | |  | | | |---- 
/_/  \_\     |_| |_| |_| |_|  |_| |_|____ |_|  |_| _|_|_ |_|  |_| |_|____ 

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Really Wanna Trade with us ? yes/no
yes
Enter Username :
SAM

Welcome SAM

Enter your Command :

[1] balance
[2] exchange
[3] transfert
[4] restricted area
2

Enter Destination currency
EUR

Enter Source currency
GBP

Enter Amount
100

Your Balance : 100 USD , 253.85 EUR , 0 GBP

Enter your Command :

[1] balance
[2] exchange
[3] transfert
[4] restricted area
2

Enter Destination currency
GBP

Enter Source currency
EUR

Enter Amount
253.85

Your Balance : 100 USD , 0 EUR , 218.31 GBP

Enter your Command :

[1] balance
[2] exchange
[3] transfert
[4] restricted area
2

Enter Destination currency
EUR

Enter Source currency
GBP

Enter Amount
218.31

Your Balance : 100 USD , 335.86 EUR , 0 GBP

Enter your Command :

[1] balance
[2] exchange
[3] transfert
[4] restricted area
2

Enter Destination currency
GBP

Enter Source currency
EUR

Enter Amount
335.86

Your Balance : 100 USD , 0 EUR , 288.84 GBP

.
.
.
.
.
.
.

Your Balance : 6062.7 USD, 0 EUR , 0 GBP

[1] balance
[2] exchange
[3] transfert
[4] restricted area
4
FLAG{7d21ca3a7a2f068347efac7c2c9794bdb3bd0ab0}
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