Lecture Notes on Cryptography and Public Key Infrastructure (PKI)

Introduction to PKI

• Public Key Infrastructure (PKI) is a comprehensive term in cryptography.
  • Refers to policies, procedures, hardware, and software.
  • Involves creating, distributing, managing, storing, revoking digital certificates.
  • Essential for encryption and trust in identities (users/devices).
  • Often associated with a Certificate Authority (CA).

Symmetric Encryption

• Definition: Same key is used for encryption and decryption.
  • Known as "secret key algorithm" or "shared secret."
• Challenges:
  • Scalability issues as the number of users/devices increases.
  • Managing and sharing keys becomes complex.
• Advantages:
  • Fast and low overhead.
  • Often used alongside asymmetric encryption.

Asymmetric Encryption

• Definition: Uses two different keys - one for encryption and another for decryption.
  • The keys are mathematically related and created simultaneously.
• Keys:
  • Private Key: Kept secure by the owner, not shared.
  • Public Key: Available publicly for encrypting data.
• Process:
  • Public key encrypts data, only the corresponding private key can decrypt it.
  • Security: Public key cannot be used to derive the private key.
• Applications:
  • Used in programs like PGP, GPG.
  • Key creation involves randomization, prime numbers, cryptography.

Example of Asymmetric Encryption

• Alice's Key Generation:
  • Creates a public and private key pair.
  • Public key is distributed widely, private key is kept secure.
  • Often protected by a password for added security.
• Bob Sends a Message to Alice:
  • Encrypts "Hello Alice" using Alice's public key.
  • Creates cipher text that can only be decrypted by Alice's private key.
  • Alice decrypts the message using her private key to retrieve the plain text.

Key Management

• Individual Management:
  • Individuals manage their own key pairs.
• Enterprise Management:
  • Large organizations need robust systems to manage numerous key pairs.
  • Options include third-party management or key escrow.
  • Important for data accessibility if users leave or require organizational access.
• Considerations:
  • Sharing private keys can be controversial but may be necessary for continuity.
  • Ensures access to encrypted data beyond the original encrypter.

Conclusion

• PKI and encryption are critical for secure communications and data integrity.
• Understanding the difference between symmetric and asymmetric encryption is crucial.
• Proper key management strategies are essential for both individual and organizational security.