No_Strings_Attached

by hoover Reverse Engineering beginner New to reverse engineering? This beginner challenge is an introduction to tracing the library calls a Linux program makes.

The provided x86-64 ELF asks you to guess a passphrase. The passphrase is the flag, but it is not written down anywhere in the file. Running strings on the binary only gets you guess:, correct and rejected. The program builds the real passphrase in memory first, and only then hands it to a function in the C standard library to compare against yours.

Run the program under a library call tracer such as ltrace and watch the comparison. Your goal is to read the passphrase out of the arguments the program passes to it.