Le Divin Crackme
In this challenge, we are given this executable.
We can guess the password L4_pH1l0soPh13_d4N5_l3_Cr4cKm3. This is because the password is stored in the memory and the use of strncmp will allow the program to get the password split in 3 blocks of 10 characters. The variables are initialized in the following order local_48, acStack_3e, acStack_34. So they will follow each other in the memory. So when we do our first strncmp, we get the 10 characters in the position of acStack_3e. acStack_3e is in the second position, so we get from the 11th character to the 21st. Same for local_48 and the first 10 characters and acStack_34 and the last 10 characters..
The flag needs also to contain the compiler used to get this executable. It was gcc, this could be found in the .comment section of the executable:
The final flag is then 404CTF{gcc:strncmp:L4_pH1l0soPh13_d4N5_l3_Cr4cKm3}