Introduction to Information Security

1. Introduction to Information Security Python

2. 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

3. 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

4. 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.

5. Hello, World Example #1: #!/usr/bin/python print “Hello, World!” Example #2: #!/usr/bin/python def main(): print “Hello, World!” if __name__ == ‘__main__’: main()

6. 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!

7. 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

8. 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.

9. 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.

10. 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!!

11. dict()s >>> b = dict() >>> b["hello"] = "world" >>> b {'hello': 'world'} >>> b.keys() [‘hello’] • [Demo dicts]

12. 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”

13. 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”

14. 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.

15. Functions • Functions can return arbitrary objects such as: • strings • Tuples! (very common) • int • Etc. global_var = 6 deffuncname(arg1, arg2): local_var = 5 return (var1, var2) • Updating global variables needs special handling: globvar = 0 defset_globvar_to_one(): global globvar # Needed to modify globvar globvar= 1

16. 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”

17. 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 elifcmd == “dothis”: dothis() continue print “always here ?!?”

18. import,reload • import– a way to import libraries, eg.: import sys • Access to variables is now through the namespace: • sys.argv[1] • Alternatively: • from sys import * • Now we can access in our namespace: • argv[1] # direct access. • If library was modified after import we can use reload, eg.: reload(sys)

19. Useful functions • Complex binary operations: • import struct • struct.pack(“L”, 0xdeadbeef) – result contains DEADBEEF in little endian (EFBEADDE) (0xdeadbeef is treated as unsigned long) • (port) = struct.unpack(“>H”) - read unsigned short from a string represented as bigendian • OS operations: • import os • os.rename(old_name, new_name) • os.system(“run command”)

20. 3rd party modules • You can install many modules by using pypi • On UNIX installing modules is very easy: • 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

21. ipython • Extended interpreter capabilities • Acts almost like a shell • Adds history • Adds file completion by tab. • + Many more features.