+' 0) Dump the ASM from IDA, Start @ 0x40107C and the length is 0x79 (see box @ loc_401029)
+' bytes = idaapi.get_many_bytes(0x40107C, 0x79)
+' with open('/home/firefly/buffer.asm', 'wb') as f:
+' 1) Figure out what byte the code needs to be xor'ed with. Last word must match 0xfb5eL (loop at 401039, comparison check: 40105E)
+' Code to be xor'ed and add'ed is located at 40107C and the length is 0x79 (see box @ loc_401029)
+' To determine the input byte the modified (xord + add) bytes have to be passed through sub_4011E6 before the comparison check can be done
+' 2) After the check passes the state memory from angr needs to be interpreted as code, so use capstone
+' The op_str from capstone contains what looks like ASCII characters...
+' 3) Take the capstone output and interpret the ASCII codes to get the flag
+p = angr.Project('greek_to_me.exe', load_options={'auto_load_libs': False})
+# Interate through all of the possible byte values to find the correct "user" input to de-mask the flag
+for buf in xrange(0x100):
+ print("Trying buf = {0}".format(buf))
+ # Variable to store the bits written to disk using IDA
+ # Store the output from the first de-obfuscation routine
+ # Read in bytes written to file from IDA
+ with open('greek_to_me_buffer.asm', 'rb') as f:
+ # Re-implement loc_401039
+ # Set up angr to "run" sub_4011E6
+ s = p.factory.blank_state(addr=0x4011E6)
+ s.mem[s.regs.esp+4:].dword = 1 # Angr memory location to hold the xor'ed and add'ed bytes
+ s.mem[s.regs.esp+8:].dword = 0x79 # Length of ASM
+ # Copy bytes output from loc_401039 into address 0x1 so Angr can run it
+ asm = ''.join(map(lambda x: chr(x), b2))
+ s.memory.store(1, s.se.BVV(int(asm.encode('hex'), 16), 0x79 * 8 ))
+ # Create a simulation manager...
+ #import pdb; pdb.set_trace()
+ simgr = p.factory.simulation_manager(s)
+ # Tell Angr where to go, though there is only one way through this function,
+ # we just need to stop after ax is set
+ simgr.explore(find=0x401268)
+ # Once ax is set, check to see if the value in ax matches the comparison value
+ for found in simgr.found:
+ #import pdb; pdb.set_trace()
+ print(' ax = %s' % hex(found.state.solver.eval(found.state.regs.ax)))
+ if hex(found.state.solver.eval(found.state.regs.ax)) == '0xfb5eL':
+ # Upon success, dump the asm
+ code = ("%x" % found.state.solver.eval_upto(found.state.memory.load(1, 0x79), 1)[0]).decode('hex')
+ print('\n Winner is: {0}\n\n'.format(buf))
+ # Using capstone, interpret the ASM
+ md = Cs(CS_ARCH_X86, CS_MODE_32)
+ for i in md.disasm(code, 0x1000):
+ # The if statements do the work of interpreting the ASCII codes to their value counterpart
+ if i.op_str.split(',')[0].startswith("byte ptr"):
+ flag_char = chr(long(i.op_str.split(',')[1], 16))
+ if i.op_str.split(',')[0].startswith('bl'):
+ bl = chr(long(i.op_str.split(',')[1], 16))
+ if i.op_str.split(',')[0].startswith('dl'):
+ dl = chr(long(i.op_str.split(',')[1], 16))
+ if i.op_str.split(',')[1].strip() == 'dl':
+ if i.op_str.split(',')[1].strip() == 'bl':
+ flag.append(flag_char.strip())
+ print(" 0x%x\t%s\t%s\t%s" %(i.address, i.mnemonic, i.op_str, flag_char))
