Asm2 PicoCTF Challenge

Challenge

Test.S :

asm2:

<+0>:	push   ebp          
<+1>:	mov    ebp,esp
<+3>:	sub    esp,0x10
<+6>:	mov    eax,DWORD PTR [ebp+0xc]    // 0x2e
<+9>:	mov    DWORD PTR [ebp-0x4],eax    
<+12>:	mov    eax,DWORD PTR [ebp+0x8]  // 0xb
<+15>:	mov    DWORD PTR [ebp-0x8],eax   
<+18>:	jmp    0x509 <asm2+28>          // unconditional jmp
<+20>:	add    DWORD PTR [ebp-0x4],0x1  // 0x2e + 0x1
<+24>:	sub    DWORD PTR [ebp-0x8],0xffffff80  // -128 but since two - = a + its +128
<+28>:	cmp    DWORD PTR [ebp-0x8],0x63f3      // if 0xb < 0x63f3
<+35>:	jle    0x501 <asm2+20>                 // clearly jmp to line 20
<+37>:	mov    eax,DWORD PTR [ebp-0x4]
<+40>:	leave  
<+41>:	ret    

C program to retrieve the flag

#include <stdio.h>

int main() {
    int d = 46;  // 0x2e
    int b = 11;  // 0xb

    // Loop until b is greater than 0x63f3 (25587)
    while (b <= 25587) {  // 0x63f3
        d += 1;  // Increment d by 1
        b += 128; // Increment b by 128 since two - equal a +
    }

    // Print d in hexadecimal format
    printf("d in hex: 0x%x\n", d);

    return 0;
}