I_Like_It

I Like It

Rev

Challenge

Now I like dollars, I like diamonds, I like ints, I like strings. Make Cardi like it please.

/problems/2019/i_like_it

Author: SirIan

Solution

Decompile in Hopper

int main(int arg0, int arg1) {
    puts("I like the string that I'm thinking of: ");
    fgets(&var_20, 0x14, *stdin@@GLIBC_2.2.5);
    *(int8_t *)(rbp + (strlen(&var_20) - 0x1) + 0xffffffffffffffe0) = 0x0;
    if (strcmp(&var_20, "okrrrrrrr") != 0x0) {
            puts("Cardi don't like that.");
            rax = exit(0x0);
    }
    else {
            puts("I said I like it like that!");
            puts("I like two integers that I'm thinking of (space separated): ");
            fgets(&var_2C, 0xc, *stdin@@GLIBC_2.2.5);
            __isoc99_sscanf(&var_2C, "%d %d", &var_34, &var_30);
            if (((var_30 + var_34 == 0x88) && (var_30 * var_34 == 0xec7)) && (var_34 < var_30)) {
                    puts("I said I like it like that!");
                    printf("Flag: actf{%s_%d_%d}\n", &var_20, var_34, var_30);
                    rax = 0x0;
                    rcx = *0x28 ^ *0x28;
                    if (rcx != 0x0) {
                            rax = __stack_chk_fail();
                    }
            }
            else {
                    puts("Cardi don't like that.");
                    rax = exit(0x0);
            }
    }
    return rax;
}

From the code we see that we need to put a string

okrrrrrrr

And then 2 numbers which meet the conditions

(var_30 + var_34 == 0x88)
(var_30 * var_34 == 0xec7)
(var_34 < var_30)

Using factordb.com, we get the factors

3783 = 3 * 13 * 97

We eventually get the numbers

39 and 97

Now put into the server

$ ./i_like_it 
I like the string that I'm thinking of: 
okrrrrrrr
I said I like it like that!
I like two integers that I'm thinking of (space separated): 
39 97
I said I like it like that!
Flag: actf{okrrrrrrr_39_97}

Flag

actf{okrrrrrrr_39_97}