Introduction

Security Goals

The traditional goal of cryptography is to achieve CIA:

• Confidentiality: Prevent the unauthorized disclosure of information.
• Integrity: Detect the unauthorized modification or destruction of information.
• Availability: Ensure resources are accessible when required by an authorized entity.

Additional goals:

• Authentication: Process of verifying something to be true.
• Non-repudiation: Create evidence that an action has occurred, and the user cannot falsely deny the action.

Security and Obscurity

Obscurity is like hidden, while security means sharing or delivering safely.

Cryptographic Terminology

• Plaintext ($P$): The original message or data
• Encryption ($E$): Plaintext → Ciphertext
• Cryptographic Key ($K$): Secret key
• Cipher: Algorithm that transforms the message
• Ciphertext ($C$): Encrypted messages
• Decryption ($D$): Ciphertext → Plaintext

Encoding and Encryption

Encoding allows anyone who knows the corresponding decoding algorithm to decode the message or data.

    graph LR
  od["Original Data"] <--> |Algorithm| ed["Encoded Data"]
  

On the other hand, to decrypt an encrypted message, both decryption algorithm and secret key should be known.

    graph LR
  pt["Plaintext"] <-->|"Algorithm & Secret key"| ct["Ciphertext"]