Cryptography, Socket Programming, and Python OOP Concepts

Posted on Apr 7, 2025 in Computers

Cryptography, Socket Programming, and Python OOP

Base64 EncodingBase64 Decoding
import base64 #encoding
encoded_data = base64.b64encode(bytes('D','ascii'))
print("Encoded text with base 64 is")
print(encoded_data) 		import base64 #decoding
decoded_data = base64.b64decode("RW5jb2RlIHRoaXMgdGV4dA==")
print("decoded text is ")
print(decoded_data)

Ciphers and Encoding

  • Caesar’s Cipher: Simple cipher that uses an offset of 3. You just add the offset to the characters.
  • Transposition Cipher: “hello world” -> 4×4, padding=”add”
  • Base64 Encoding and Decoding: Base64 is also called PEM; it is used to convert binary to text.

Why Encode?

Some data structures might require the data to be in an 8 or 16-bit format, which would require encoding to process.

How long would it take to crack a 4-character key with no repeating characters? 26x25x24x23

Python Class Example

class Parent1:
   def __init__(self, par1):
       self.par1 = 5
class Parent2:
   def __init__(self, par2):
       self.par2 = par2
class Child(Parent1):
   def __init__(self, ch1, p1, p2):
       self.ch1 = ch1
       super().__init__(p1)
       Parent2.__init__(self, p2)
       print([self.par1, self.ch1, self.par2])
   @overload
   def method(self):
       print(self.ch1)
   @overload
   def method(self, p1):
       print(" called second implementation with "+str(p1))
firstCh = Child(4, 5, 6)
firstCh.method()
Listener Socket SetupReceiving Data
HOST = '127.0.0.1'
PORT = 65432
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
   s.bind((HOST, PORT))
   s.listen()
   conn, addr = s.accept() 		with conn:
   print(f"connected by {addr}")
   while True:
      data=conn.recv(1024)
      if not data:
         break
      conn.sendall(data)

Python Class Definitions

class Dog: #Old style, not recommended
   pass
class Dog():
   pass
class Dog(Object): #New style, best practice
   pass

Inheritance Practices

  • Good Practice:
    class Child(Parent):
       def __init__(self, arg1, arg2):
           super().__init__(arg1)
  • Bad practice:
    class Child(Parent):
       def __init__(self, arg1, arg2):
           Parent.__init__(self, arg1)

Class Attributes vs. Instance Variables

class Egg:
   color = "white" #Class attribute

   def __init__(self, size): #size is a local variable
       self.size = size #self.size is a instance variable

CIA Triad

Confidentiality: The information should only be revealed to the intended audience. Achieved through encryption.

Integrity: The data has not been altered. The sender should be who they claim to be, and the sender should not be able to deny their actions (non-repudiation). This is done through hashing, message digest, and authentication.

  • A replay would be an attack against integrity.
  • Data in processing, data in storage, data in transit.

Availability: The information/Network or service should be available for authorized users only. It should also be highly available. This is done through access control and redundancy of servers.

  • Data should be provided reliably and timely to legitimate users.

Key Management

  • Longer keys are harder for the attacker to guess, therefore less prone to brute force attacks.
  • Keys must be renewed frequently – secure against eavesdropping.
  • Keys must be revoked if required – secure against compromised accounts.
  • Must be communicated through a separate secure channel.

Encryption Considerations

  • Many encryption algorithms are prone to cryptanalysis – the art or process of deciphering coded messages without being told the key.
  • Hybrid cryptography is a process of using multiple ciphers of different types together by including the benefits of each cipher.
  • Another alternative is to use a different key for each block of data or to use a very long key.

The Map Function

  • The map() function returns a map object (which is an iterator) of the results after applying the given function to each item of a given iterable (list, tuple, etc.).
  • Syntax: map(fun, iter)