[CSAW 2016] Gametime Writeup



Guess what time it is! That’s right! Gametime! Wowwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwwww!!!!!!!!!!!!

Author: Brad Antoniewicz

note: flag is not in flag{} format


To be honest, I downloaded the file, played the game once and got the key. It is possible for humans to win the game, or maybe it’s just my Super-Vegan powers LOL.
But I wanted, of course, to get the key using RE. I opened IDA and searched for interesting strings.
.rdata:00A17858 00000014 C \rGet ready to play\n                                     
.rdata:00A17970 00000033 C \rZOMGZOMG           YOU DID IT!!!        ZOMGOZMG\n      
.rdata:00A179E0 0000000F C key is %s (%s)                                            
.rdata:00A179F4 0000002C C \nWhen you see an 's', press the space bar\n\n            
.rdata:00A17A20 0000002C C \nWhen you see an '%c', press the '%c' key\n\n            
.rdata:00A17A50 00000010 C key is %s (%s)\r                                          
.rdata:00A17A60 0000002B C \rUDDER FAILURE! http://imgur.com/4Ajx21P \n              
.rdata:00A17A8C 00000024 C \r                                 \r                     
.rdata:00A17AB0 0000002A C UDDER FAILURE! http://imgur.com/4Ajx21P \n                
.rdata:00A17ADC 00000005 C %02x                                                      
.rdata:00A17B20 00000010 C \tkey is %s (%s)                                          
.rdata:00A17B30 00000034 C \r\tZOMGZOMG                                ZOMGZOMG\n    
.rdata:00A17B64 00000034 C \r\tZOMGZOMG     TAP TAP REVOLUTION!!!!!!!  ZOMGZOMG\n    
.rdata:00A17BD0 00000020 C \r\t              R U READDY?!\n\n\n                      
.rdata:00A17BF0 0000001D C \rThe game is starting in...\n                            
.rdata:00A17C10 00000033 C \rTRAINING COMPLETE!                              \n      
.rdata:00A17C48 0000002A C \rNow you know everything you need to know                
.rdata:00A17C74 0000001F C \n\n\nfor the rest of your life!\n                        
.rdata:00A17C94 0000000D C LETS PLAY !\n                                             
.rdata:00A17CA4 00000016 C \rooooh, you fancy!!!\n                                   
.rdata:00A17CBC 00000011 C NIIICE JOB)!!!!\n                                         
.rdata:00A17CD0 00000012 C \rTURBO TIME!    \n

I highlighted the important lines: The success message (I know, I got it when I played) and the failure messages. Using X-Refs I found where the failure messages are printed out and patched the program to jump to the success instead. Notice that you’ll need to change two functions.

1st jump to change:


2nd jump to change:


Now apply the patches to the program and run it. Let the game play alone and the key will be printed.

The key is: (no5c30416d6cf52638460377995c6a8cf5)


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