Eroman: Created page with "= Lecture 10 = Cryptopals https://cryptopals.com/ Many solution here: https://www.google.ee/search?dcr=0&source=hp&ei=k-oCWtGxJaHg6ASl0a4g&q=cryptopals+solution..."

2017-11-14T08:26:52Z

Created page with "= Lecture 10 = Cryptopals https://cryptopals.com/ Many solution here: https://www.google.ee/search?dcr=0&source=hp&ei=k-oCWtGxJaHg6ASl0a4g&q=cryptopals+solution..."

New page

= Lecture 10 =

Cryptopals

https://cryptopals.com/

Many solution here: https://www.google.ee/search?dcr=0&source=hp&ei=k-oCWtGxJaHg6ASl0a4g&q=cryptopals+solutions+python&oq=cryptopals+solutions+p&gs_l=psy-ab.3.0.0i19k1.657.4332.0.4870.17.16.1.0.0.0.124.1236.14j2.16.0....0...1.1.64.psy-ab..0.17.1235...0j0i131k1j0i22i30i19k1j33i21k1j33i160k1.0.IM86h-JeYBc

Very good solutions here (better than mine): https://github.com/ricpacca/cryptopals

== Binary, Hex, Base64 ==

Look them up if you don't know what they are. Unfortanetly, I cannot find a very good introduction to the topics in python.

In python you have integer literals in base 10, like <code>10</code> or in base 16, like <code>0xf</code> or in base 2, like <code>0b1</code>

Binary numbers can easily be representing in base 16 (called "Hex"). 8 bits (binary digits) is 2 digits in hex. Base64 is a way of storing binary data so it uses only ascii characters. A string of Base64 is shorter than a string of equivalent Hex, so Base64 is popular way to put binary data embeded in a text document.

== Problems ==

The problems are good because they require us to understand encoding in python. My solutions are poorer quality in comparison to the solutions here: https://github.com/ricpacca/cryptopals

== Problem 1-1 ==

<source lang="python">import base64

message_hex = "49276d206b696c6c696e6720796f757220627261696e206c696b65206120706f69736f6e6f7573206d757368726f6f6d"
message_bytes = bytearray.fromhex(message_hex)
message_base64 = base64.encodebytes(message_bytes)
print(message_base64)</source>
== Problem 1-2 ==

one way

<source lang="python"># Convert both hex string to bytes
hex_string_1 = '1c0111001f010100061a024b53535009181c'
hex_string_2 = '686974207468652062756c6c277320657965'

bytes_1 = bytearray.fromhex(hex_string_1)
bytes_2 = bytearray.fromhex(hex_string_2)

# Pair each byte with other byte in same position
byte_pair_list = list(zip(bytes_1, bytes_2))

# go through each bit in hex string bytes, and xor, and store result
# XOR opertator is ^
result_list = []
for b1, b2 in byte_pair_list:
xor_result = b1 ^ b2
result_list.append(xor_result)

# convert list of integers to hex
result_bytes = bytearray(result_list)
print(bytearray.hex(result_bytes))</source>

Advanced Python (Fall 2017)/lecture10 - Revision history

Eroman: Created page with "= Lecture 10 = Cryptopals https://cryptopals.com/ Many solution here: https://www.google.ee/search?dcr=0&source=hp&ei=k-oCWtGxJaHg6ASl0a4g&q=cryptopals+solution..."