  Binary code similarity detection is to detect the similarity of code at
binary (assembly) level without source code. Existing works have their
limitations when dealing with mutated binary code generated by different
compiling options. In this paper, we propose a novel approach to addressing
this problem. By inspecting the binary code, we found that generally, within a
function, some instructions aim to calculate (prepare) values for other
instructions. The latter instructions are defined by us as key instructions.
Currently, we define four categories of key instructions: calling subfunctions,
comparing instruction, returning instruction, and memory-store instruction.
Thus if we symbolically execute similar binary codes, symbolic values at these
key instructions are expected to be similar. As such, we implement a prototype
tool, which has three steps. First, it symbolically executes binary code;
Second, it extracts symbolic values at defined key instructions into a graph;
Last, it compares the symbolic graph similarity. In our implementation, we also
address some problems, including path explosion and loop handling.
