Course 17 - Computer Network Security Protocols And Techniques | Episode 7: Understanding Pretty Good Privacy (PGP) for Secure Email

In this lesson, you’ll learn about:

• What PGP is and where it operates in the network stack
• How PGP secures email confidentiality and authenticity
• The three-part structure of a PGP-secured message
• How session keys, public keys, and digital signatures work together
• The cryptographic algorithms supported by PGP

Introduction Pretty Good Privacy (PGP) is an application-layer security protocol designed to protect email communications. It combines symmetric encryption, public key cryptography, and digital signatures to ensure that messages remain confidential, authentic, and tamper-proof during transmission. How PGP Secures an Email PGP divides a protected email into three main components, each serving a specific security purpose. Part One: Session Key Protection

• Contains the session key and the symmetric encryption algorithm used
• The session key is a temporary, randomly generated key
• This entire part is encrypted using the recipient’s public key
• Ensures that only the intended recipient can recover the session key

Part Two: Encrypted Content and Digital Signature

• Contains the actual email message
• The message is encrypted using the session key
• Includes a digital signature created by:
  • Hashing the message to produce a digest
  • Encrypting the digest with the sender’s private key
• Provides:
  • Integrity (message was not altered)
  • Authentication (message truly came from the sender)
  • Non-repudiation
• Also specifies the hashing and encryption algorithms used

Part Three: PGP Header

• Contains protocol-related metadata
• Helps the recipient’s PGP software correctly process the message

Cryptographic Algorithms Supported by PGP PGP is flexible and supports multiple cryptographic standards:

• Public Key Algorithms:
  • RSA
  • DSS
• Hash Functions:
  • MD5
  • SHA-1
  • RIPEMD
• Symmetric Encryption Algorithms:
  • AES
  • Triple DES (3DES)

Key Takeaways

• PGP operates at the application layer
• Uses hybrid encryption for efficiency and security
• Public keys protect the session key, not the message directly
• Digital signatures ensure authenticity and integrity
• Widely used for secure email communication

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