Computer Science: encryption

Overview of Encryption

• Encryption: Process that transforms data into an unreadable form for unauthorized users.

  • Purpose: Protect sensitive or confidential data.

  • Limitation: Does not prevent interception but renders data meaningless to eavesdroppers.

Definitions

• Plaintext: Original data before encryption.

• Ciphertext: Data after processing through an encryption algorithm.

Types of Encryption

1. Symmetric Encryption

• Key Characteristics:

  • Utilizes a single encryption key for both encryption and decryption.

  • Key security: Keeping the key secret is a challenge, as it can be intercepted during transmission.

Example of Symmetric Encryption

• Encryption Scheme:

  • Example Encryption Key: 4 2 9 1 3 6 2 8 5 6 (Length = 10)

  • Number of possible combinations: $2^{10} = 10,000,000,000$ different keys.

  • Encryption method: Shift letters across the alphabet based on the key values (+4, +2, +9, +1…).

  • This method is termed Cyphertext.

Example of Symmetric Decryption

• Decryption Scheme:

  • Same key: 4 2 9 1 3 6 2 8 5 6.

  • Decryption method: Shift letters in reverse across the alphabet (-4, -2, -9, -1…).

  • This process results back in Plaintext.

Issues with Symmetric Encryption

• Key vulnerability: Encryption keys may be easy to crack using various tools.

• Secure Key Recommendation: Typically utilize 256-bit encryption keys.

  • Number of combinations: $2^{256} = 1.16 imes 10^{77}$ combinations, making it substantially more secure.

2. Asymmetric Encryption

• Developed to address the security weaknesses of symmetric encryption.

• Key Characteristics:

  • Utilizes two keys:

  • Public Key: Shared openly and used for encryption.

  • Private Key: Kept secret by the user and used for decryption.

Example of Asymmetric Encryption Process

1. Key Generation:

   • User (e.g., Jane) generates a matching pair of keys (public and private).

   • The keys are mathematically linked but not derivable from one another.

2. Public Key Distribution:

   • Jane shares her public key with Tom.

3. Encryption by Sender:

   • Tom uses Jane's public key to encrypt the document he wishes to send.

   • The encrypted document is referred to as ciphertext.

4. Decryption by Receiver:

   • Jane uses her private key to decrypt the ciphertext from Tom.

   • This works because only Jane's private key can decrypt the information that was encrypted with her public key.

   • Note: Jane cannot decrypt messages using the public key alone.

5. Public Key Sharing:

   • Jane can share her public key with multiple colleagues, enabling them to send her encrypted messages.

   • Each recipient must also generate their own key pairs for two-way communications.

Real-life Application of Asymmetric Encryption

Example: WhatsApp

• WhatsApp uses end-to-end encryption to ensure messages remain private between users.

  • Encryption Scope:

  • Text and voice messages.

  • Audio and video calls.

  • Shared photos, videos, and documents.

  • Location sharing and status updates.

Summary of Key Points

• Importance of encryption in protecting transmitted data.

• Understanding the operational processes behind symmetric and asymmetric encryption:

  • Asymmetric encryption: Depends on a pair of keys (public and private).