Added commands for xorring regions of memory (#164)

xor: xor a region of memory with a key
    memfrob: frobnicate a memory area (https://linux.die.net/man/3/memfrob)

pwndbg/commands/xor.py

@@ -5,15 +5,46 @@ from __future__ import division
 from __future__ import print_function
 from __future__ import unicode_literals
 
+import gdb
+import six
+
 import pwndbg.commands
 import pwndbg.memory
 
+def xor_memory(address, key, count):
+    """
+    Helper function for xorring memory in gdb
+    """
+    mem = pwndbg.memory.read(address, count, partial=True)
+    
+    for index, byte in enumerate(mem):
+        key_index = index % len(key)
+        mem[index] = byte ^ ord(key[key_index])
+
+    return mem 
 
 @pwndbg.commands.Command
 @pwndbg.commands.OnlyWhenRunning
-def xor(self, address, key, count):
+def xor(address, key, count):
     '''xor(address, key, count)
 
     XOR ``count`` bytes at ``address`` with the key ``key``.
     '''
-    print(address,key,count)
+    if not isinstance(address, six.integer_types):
+        address = int(address, 16)
+
+    xorred_memory = xor_memory(address, key, count)
+    pwndbg.memory.write(address, xorred_memory)
+
+@pwndbg.commands.Command
+@pwndbg.commands.OnlyWhenRunning
+def memfrob(address, count):
+    '''memfrob(address, count)
+
+    Run the memfrob command on a region of memory
+    '''
+    if not isinstance(address, six.integer_types):
+        address = int(address, 16)
+
+    xorred_memory = xor_memory(address, '*', count)
+    pwndbg.memory.write(address, xorred_memory)