Symmetric Cryptography 🔐

Symmetric cryptography involves using the same key for both encryption and decryption processes. This section explores symmetric key algorithms, their mechanisms, and different types of ciphers.

Overview of Symmetric Cryptography 📜

• Definition: Symmetric cryptography uses a single key for both encrypting and decrypting messages. The key must remain private to ensure security.

• Key Component: The key is crucial and must be kept confidential to prevent unauthorized decryption.

Substitution Ciphers 🔄

• Definition: A substitution cipher replaces parts of plaintext with ciphertext based on a predefined mapping.

• Example:

  • Caesar Cipher: Shifts the alphabet by a fixed number of places. For example, with a shift of 3, 'A' becomes 'D'.

  • ROT13: A specific type of Caesar cipher with a shift of 13. Applying ROT13 twice returns the original plaintext.

  Example Encoding:

  • Plaintext: "Hello World"

  • Ciphertext (ROT13): "URYYB JBEYQ"

  ROT13 is its own inverse, meaning encoding and decoding use the same process.

Types of Symmetric Ciphers 🔐

1. Stream Ciphers 🎞️

   • Operation: Encrypts data one character or digit at a time.

   • Characteristics: Fast and less complex but can be less secure if key management is poor.

2. Block Ciphers 🧩

   • Operation: Encrypts data in fixed-size blocks. If the data doesn’t fill the block, it is padded.

   • Characteristics: Generally more secure but can be slower and more complex to implement.

Key Management 🔑

• Initialization Vector (IV):

  • Purpose: Prevents key reuse by introducing randomness.

  • Usage: A random IV is combined with the encryption key to create a unique key for each encryption session. The IV is sent in plaintext alongside the encrypted data.

• Example: In wireless encryption (e.g., 802.11), the IV is included in the plaintext before the encrypted data payload.

Key Takeaways

• Symmetric Key Algorithms: Use the same key for encryption and decryption.

• Substitution Ciphers: Include techniques like Caesar Cipher and ROT13, which involve replacing characters based on a key.

• Stream vs. Block Ciphers: Stream ciphers process data one unit at a time, while block ciphers process fixed-size blocks.

• Key Management: Essential to avoid key reuse, achieved using Initialization Vectors (IVs).

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