ROP is a classic technique for getting around address randomization and non-executable memory. This sequence will teach you the basics.

Problem available on the shell machine in /problems/ROP_1_fa6168f4d8eba0eb , downloadable here[1] with source here[2].

If you solve the problem you will be able to read the key file by running
    cat /problems/ROP_1_fa6168f4d8eba0eb/key
on the PicoCTF shell machine

[1]https://2013.picoctf.com/problems/rop1-fa6168f4d8eba0eb
[2]https://2013.picoctf.com/problems/rop1-fa6168f4d8eba0eb.c