Category
Rev
Solution
For this challenge we get assembly source code and our task is to figure out what arithmetic operations are made on each of the variables a, b, c and d and input the result on a web page.
c$ = 0
tv64 = 4
d$ = 8
a$ = 32
b$ = 40
int mystery(int,int) PROC ; mystery
$LN3:
mov DWORD PTR [rsp+16], edx
mov DWORD PTR [rsp+8], ecx
sub rsp, 24
mov eax, DWORD PTR a$[rsp]
mov ecx, DWORD PTR b$[rsp]
sub ecx, eax
mov eax, ecx
mov DWORD PTR tv64[rsp], eax
mov eax, DWORD PTR a$[rsp]
cdq
idiv DWORD PTR b$[rsp]
mov eax, edx
mov ecx, DWORD PTR tv64[rsp]
imul ecx, eax
mov eax, ecx
mov DWORD PTR c$[rsp], eax
mov eax, DWORD PTR a$[rsp]
imul eax, DWORD PTR b$[rsp]
mov ecx, DWORD PTR c$[rsp]
add ecx, eax
mov eax, ecx
mov DWORD PTR d$[rsp], eax
imul eax, DWORD PTR b$[rsp], 5
mov ecx, DWORD PTR a$[rsp]
imul ecx, DWORD PTR c$[rsp]
add eax, ecx
mov ecx, DWORD PTR b$[rsp]
imul ecx, DWORD PTR d$[rsp]
sub eax, ecx
add rsp, 24
ret 0
int mystery(int,int) ENDP ; mystery
After going through the code we end up with the following solution.
When we submit the solution we get the flag, flag{1_c0u1d_do_7hi5_@ll_day}.