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We are going to solve the reversing challenge Zwiebel from the TUM CTF 2016 by creating a dynamic analysis script with radare. Before I knew I would write a script for radare, I had to figure out what the binary is doing. So after I downloaded the binary and checked that its a 64bit linux binary, I made sure my vagrant Linux VM is running and opened the binary for a first analysis in Binary Ninja. Lets head to main and start reversing. So first we have a printf() that is asking for the Input key. The valid input key is probably also our flag. The fflush() just makes sure that the output is displayed and not held in a buffer. After that we have an fgets(), which means here the input key string is read. The rdi register is commonly used as the Destination, so this memory with the flag symbol name is probably where our input key is stored. Funnily we can also see that its not just 0, but already initialized with some flags. Then we see an mmap(). Which is directly followed by a memcpy.
