Rating:
# Securinet Little Baby Rev Write Up
## Details:
Jeopardy style CTF
Category: Reverse Engineering
## Write up:
Running the file we see that we are in an infinite loop:
```
./warmup
I have a number from 1 to 10, what is it?
2
Try again
I have a number from 1 to 10, what is it?
6
```
Looking for these strings in the binary does not prove useful at all either but when I ctrl-c'd I noticed that it seemed to be running in a .nim file:
```
Try again
I have a number from 1 to 10, what is it?
^CTraceback (most recent call last)
/root/rev/warmup.nim(39) warmup
/root/Nim/lib/system/io.nim(491) readLine
```
Instead of going down the rabbit hole of trying to figure out what nim is I decided to do some dynamic analysis.
I found the following function which seemed to be the while loop that I wanted:
```c
while ( 1 )
{
v5 = 38LL;
v6 = "/root/rev/warmup.nim";
nimZeroMem_0(&v10, 8LL);
v10 = decodeStr__R9b5IlyQjG2mcdkp9a67LGTQ((__int64)&TM__ijE9cayl8YPnol3rizbiT0g_5, 0x3F1997CCu);
echoBinSafe(&v10, 1LL);
asgnRef_1(&guess__62AlRyOQv9cCViqvgI14ssA, 0LL);
v5 = 39LL;
v6 = "/root/rev/warmup.nim";
v1 = readLine__IfmAdseskhTUnfEYpOo5fA(stdin);
asgnRef_1(&guess__62AlRyOQv9cCViqvgI14ssA, v1);
v5 = 41LL;
v6 = "/root/rev/warmup.nim";
if ( (unsigned __int8)eqStrings(guess__62AlRyOQv9cCViqvgI14ssA, answer__2bKjAtEJJ5cp19bpmXcStjQ) )
break;
v5 = 42LL;
v6 = "/root/rev/warmup.nim";
nimZeroMem_0(&v9, 8LL);
v9 = decodeStr__R9b5IlyQjG2mcdkp9a67LGTQ((__int64)&TM__ijE9cayl8YPnol3rizbiT0g_7, 0x2149F624u);
echoBinSafe(&v9, 1LL);
}
```
After reading in my string it compared it against the answer__2bKjAtEJJ5cp19bpmXcStjQ so I took a look at that memory while the program was running.
I saw that that contained:
```
7FD1C85020A0
```
And decided to look at the memory that this pointed to where I saw the following:
```
53 65 63 75 72 69 6E 65 74 73 7B 4E 69 6D 70 65 Securinets{Nimpe
72 30 72 5F 54 68 65 5F 61 4E 69 6D 41 74 6F 72 r0r_The_aNimAtor
7D 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 }...............
```
The flag was:
```
Securinets{Nimper0r_The_aNimAtor}
```
