Download Introduction to Information Security - Cs Team Site | courses.cs.tau.ac.il

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts
no text concepts found
Transcript
Introduction to
Information
Security
Python
Python motivation
•
•
•
•
•
•
•
•
Python is to a Hacker what Matlab is to an engineer
Lots of built-in modules
Lots of 3rd party modules
IDA-Python!
Very popular language, very well supported
Has implementation in every OS.
Human readible
Its free
Python Diff
• In this quick overview of python:
• We will note the major differences between python
and other familiar languages.
• And talk of some useful tools
White spaces
if you can read this:
it must be python!
- Python hierarchy is defined by whitespaces
- Indentation has to be the same (3 spaces != 1 tab)
for every nest within the chain.
Hello, World
Example #1:
#!/usr/bin/python
print “Hello, World!”
Example #2:
#!/usr/bin/python
def main():
print “Hello, World!”
if __name__ == ‘__main__’:
main()
Datatype behavior
Datatypes behave differently in python:
A=5
A=6
Now A is a different variable!
Therefore if use:
A=A+5
Now A is a new variable containing the result!
Basic functions
• Using the interpreter allows us to view two basic
things:
dir(object) – shows us the structure of the object
help(object) – shows help created by the developer
of the object
Strings
•
•
•
•
•
•
•
•
•
Many builtin string machnisms.
A = “”
len(“123”) == 3
A[0] = “a” – not possible, strings are immutable.
A.find(“asd”) returns the location of asd in A
A.split()/A.join() , eg.: “\n”.join(data.split(“\n”)[0:-1])
A.lower()
replace() – returns a new string with data
Uses regular indexing.
Lists and Tuples
•
•
•
•
•
•
•
•
A = (1, 2, 3)
A is of fixed length and is immutable.
A = [ 1, 2, 3]
A is mutable, and the length can be changed by
using append:
A.append(4)
print A results in:
[1, 2, 3, 4]
A is not a new variable.
Spans
• Spans makes things very comfortable:
A = “asd”
A[0:] == “asd”
A[1:] == “sd”
A[0:-1] == “as”
A[0:1] == “a”
A[0:-2] == “a”
A[:2] == “as”
A[1:2] == “s”
• Works on tuples, and lists!!
dict()s
>>> b = dict()
>>> b["hello"] = "world"
>>> b
{'hello': 'world'}
>>> b.keys()
[‘hello’]
• [Demo dicts]
Mutable vs Immutable
• Mutable
A = [1,2,3,4]
B=A
A.append(5)
print B
[1,2,3,4,5]
• Immutable
A = “foo”
B=A
A = A + “bar”
print B
“foo”
Format conversion
• print “%d %s 0x%08X” % (0xdeadbeef, “ == “
0xdeadbeef)
• 5 / 3 == 1
• 5 / 3.0 == 1.666666…
• int(5/3.0) == 1
• str(1) == “1”
• ord(“0”) == 0x30
• chr(0x30) == “c”
File operations
• Reading from a file:
f = file(“c:\\filename”) # file(“/tmp/filename”) for linux
buf = f.read() # buf now contains entire file.
lines = buf.split(“\r\n”) # lines contains a list with all
lines excluding the “\r\n”
f.close()
• Writing to a file:
file(“filename”, “wb”).write(data) # using returning
# object to write the data
# if reference is lost file is automatically closed.
Functions
• Functions can return arbitrary objects such as:
o
o
o
o
strings
Tuples! (very common)
int
Etc.
global_var = 6
def funcname(arg1, arg2):
local_var = 5
return (var1, var2)
• Updating global variables needs special handling:
globvar = 0
def set_globvar_to_one():
global globvar # Needed to modify globvar
globvar = 1
if,else
if 1:
print “always here”
else:
print “never here”
• switch case alternative:
if key = “x”:
exit()
elif key = “z”:
suspend()
else:
print “default”
for, while
• for (i=1; i < 10; i++) alternative:
for i in range(1,10): # help(range) for more options
print A[i]
while 1:
cmd = get_next_cmd()
if cmd == “stop”:
break
elif cmd == “dothis”:
dothis()
continue
print “always here ?!?”
import,reload
• import– a way to import libraries, eg.: import sys
• Access to variables is now through the namespace:
o sys.argv[1]
• Alternatively:
• from sys import *
• Now we can access in our namespace:
o argv[1] # direct access.
• If library was modified after import we can use
reload, eg.: reload(sys)
Useful functions
• Complex binary operations:
o import struct
o struct.pack(“L”, 0xdeadbeef) – result contains DEADBEEF in little endian
(EFBEADDE) (0xdeadbeef is treated as unsigned long)
o (port) = struct.unpack(“>H”) - read unsigned short from a string
represented as bigendian
• OS operations:
o import os
o os.rename(old_name, new_name)
o os.system(“run command”)
rd
3
party modules
• You can install many modules by using pypi
• On UNIX installing modules is very easy:
o sudo pip install [modulename]
• Also available easy_install
• Useful imports:
• scapy (packet manipulation lib works with libpcap),
numpy/scipy, pylab, pylib, hashlib, socket, sqllite,
gzip, zip, bz2, html, json, wave/audioop (audio
operations), PIL (image processing), wave, pygame
• Google: [something I need] python
ipython
•
•
•
•
•
Extended interpreter capabilities
Acts almost like a shell
Adds history
Adds file completion by tab.
+ Many more features.