Objective: Understand and apply symmetric encryption techniques.

Overview of Symmetric Encryption

Key Concepts

  1. Encryption and Decryption:
    • Encryption: The process of converting plaintext (original data) into ciphertext (encrypted data) using a secret key.
    • Decryption: The reverse process of converting ciphertext back to plaintext using the same secret key.
  2. Block Cipher vs. Stream Cipher:
    • Block Cipher: Encrypts data in fixed-size blocks (e.g., AES operates on 128-bit blocks).
    • Stream Cipher: Encrypts data one bit or byte at a time (e.g., RC4).

Symmetric Encryption Algorithms

  1. AES (Advanced Encryption Standard):
    • Most widely used symmetric encryption algorithm.
    • Key Sizes: 128, 192, or 256 bits.
    • Use Cases: Encrypting data at rest (e.g., file encryption), secure communication (e.g., VPNs).
  2. DES (Data Encryption Standard) and 3DES (Triple DES):
    • DES is an older encryption standard, now considered insecure due to its short key length (56 bits).
    • 3DES applies DES encryption three times to each data block, increasing security.

Hands-on Exercise: Encrypting and Decrypting a Message Using AES


  1. Choose a plaintext message (e.g., “Hello, World!”).
  2. Select an AES key (e.g., 128-bit key). Ensure it’s randomly generated for security.
  3. Encrypt the plaintext using AES.
  4. Decrypt the resulting ciphertext using the same AES key.
  5. Verify that the decrypted text matches the original plaintext.

Practical Application

Further Reading and Resources