Honestly, this was a very easy CTF rev challenge. One of them had a flaw with there being more than 1 possible flag, while another was straight out leaking the whole flag with ltrace.
So this is the only writeup worth writing, even though it was extremely easy
Opening the binary, we see that it asks us for a password
When we run ltrace on it and enter “aaaaa” we see that it compares an empty string to “m4triaRchy”. But oddly, any strings we enter become empty.
Instead, we try to enter numbers 12345. We see now that strings appear! So its clear that its taking number, and mapping those numbers to strings, to which the final string must be “m4triaRchy”.
We see that the numbers are being mapped deterministically, meaning 1111 will always translate to “rrrr”
By trying numbers 0-9, we can get the mapping
1 = r
2 = 4
3 = c
4 = t
5 = i
6 = m
7 = a
8 = y
9 = h
0 = R
So to spell “m4triaRchy”, we need to enter 6241570398