[Day 4] 1. Asymmetric Encryption Schemes

Rule:

1. Every participant has two keys:
   • Public Key: Shared with everyone.
   • Private Key: Kept secret and confidential.
2. Key properties:
   • A public key and private key form a pair and are mathematically related.
   • Private keys cannot be derived from public keys (ensuring security).
   • However, a public key is derived from its corresponding private key.
3. Both keys can be used for encryption and decryption, but:
   • Data encrypted with the public key must be decrypted using the private key.
   • Data encrypted with the private key must be decrypted using the public key.

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Understanding Through an Example:

Imagine three people: Tinku, Pinki, and Gabbar.

• Tinku and Pinki are communicating with each other.
• Gabbar is an attacker trying to intercept or interfere.

Each person has:

• A private key (kept secret).
• A public key (shared openly).

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Scenarios:

1. Encrypting Data for Personal Use

• Example: Tinku wants to secure a file on his system.
• Process:
  • Tinku encrypts the data using his public key.
  • Only Tinku can decrypt it using his private key.
• Key Point: Ensures confidentiality for personal data.

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2. Authenticating the Sender

• Example: Tinku wants to prove his identity to Pinki.
• Process:
  • Tinku encrypts the data using his private key.
  • Anyone with Tinku’s public key can decrypt it.
• Key Point: This proves that Tinku sent the data, ensuring authenticity.
• Use Case: Applications where data integrity and authenticity are crucial, e.g., election results.

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3. Ensuring Confidentiality Without Authentication

• Example: Tinku wants to send confidential data to Pinki.
• Process:
  • Tinku encrypts the data using Pinki’s public key.
  • Only Pinki can decrypt it using her private key.
• Caveat: Gabbar, who also has Pinki’s public key, could send encrypted data to Pinki.
  • Pinki cannot verify if the data is from Tinku or Gabbar.
• Key Point: Ensures confidentiality but lacks authentication.

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Message Formats

1. Secure Message Format:
   • The message is encrypted using the receiver’s public key.
2. Open Message Format:
   • The message is encrypted using the sender’s private key.

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Advantages of Asymmetric Encryption

• Better key distribution: No need to share secret keys.
• Scalability: Works well in large systems.
• Authentication & Non-repudiation: Ensures data authenticity and prevents denial of origin.

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Disadvantages of Asymmetric Encryption

• Slower compared to symmetric encryption.

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Examples of Asymmetric Encryption Algorithms

• RSA (Rivest-Shamir-Adleman)
• ECC (Elliptic Curve Cryptosystem)
• Diffie-Hellman
• El-Gamal
• DSA (Digital Signature Algorithm)
• Knapsack

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