Cryptographic key management is crucial for secure communication. This section covers key generation, exchange protocols like Diffie-Hellman, and centralized distribution through Key Distribution Centers. These processes ensure that keys are created, shared, and managed securely.

Public Key Infrastructure (PKI) provides a framework for managing digital certificates and public keys. We'll explore PKI components, certificate lifecycles, and key management practices. Understanding these concepts is essential for implementing robust cryptographic systems in real-world applications.

Key Generation and Exchange

Fundamentals of Key Generation and Exchange

• Key generation creates cryptographic keys used for encryption and decryption
• Involves complex mathematical algorithms to produce secure, random keys
• Key length determines the strength of encryption (longer keys provide stronger security)
• Key exchange securely transfers cryptographic keys between parties
• Employs various protocols to protect keys during transmission (SSL/TLS)
• Symmetric key exchange requires a pre-shared secret or secure channel
• Asymmetric key exchange uses public-private key pairs for secure communication

Diffie-Hellman Key Exchange Protocol

• Diffie-Hellman key exchange enables secure key sharing over insecure channels
• Utilizes the concept of modular arithmetic and discrete logarithms
• Process begins with two parties agreeing on public parameters (prime number and base)
• Each party generates a private key and computes a public key using the agreed parameters
• Public keys are exchanged, and a shared secret is calculated independently by both parties
• Resulting shared secret serves as the symmetric encryption key for further communication
• Provides forward secrecy, protecting past communications if keys are compromised
• Vulnerable to man-in-the-middle attacks without proper authentication

Key Distribution Center (KDC) Architecture

• Key Distribution Center centralizes key management for multiple users or systems
• Acts as a trusted third party to facilitate secure key exchange
• Maintains a database of secret keys for all users within its domain
• Implements protocols like Kerberos for authentication and key distribution
• Process involves user authentication, ticket granting, and session key generation
• Reduces the number of keys needed in a large network (n users require n keys instead of n(n-1)/2)
• Provides scalability for key management in enterprise environments
• Single point of failure can be mitigated through redundancy and backup systems

Public Key Infrastructure

Components and Standards of PKI

• Public Key Infrastructure establishes a framework for secure communication using public key cryptography
• Consists of hardware, software, policies, and procedures for managing digital certificates
• Public key certificates bind public keys to entities, verifying their authenticity
• X.509 standard defines the format and content of digital certificates
  • Includes version, serial number, signature algorithm, issuer, validity period, subject, public key info
• Certificate Authorities (CAs) issue and manage digital certificates
• Registration Authorities (RAs) verify the identity of certificate requestors
• Certificate repositories store and distribute certificates and Certificate Revocation Lists (CRLs)
• End entities (users or devices) request and use certificates for secure communication

Certificate Lifecycle and Management

• Certificate lifecycle includes issuance, usage, renewal, and revocation
• Key revocation invalidates certificates before their expiration date
  • Reasons include compromised private keys, change in affiliation, or cessation of operation
• Certificate Revocation Lists (CRLs) publish lists of revoked certificates
• Online Certificate Status Protocol (OCSP) provides real-time certificate status checks
• Key escrow involves storing private keys with a trusted third party
  • Allows key recovery in case of loss or legal requirements
  • Raises privacy concerns and potential for abuse
• Certificate chain of trust validates certificates through a hierarchy of CAs
• Cross-certification enables trust between different PKI domains

Key Management

Key Lifecycle and Rotation Practices

• Key lifecycle management encompasses the entire lifespan of cryptographic keys
• Includes key generation, distribution, storage, use, archival, and destruction
• Key rotation involves regularly changing cryptographic keys to limit exposure
  • Enhances security by reducing the impact of potential key compromises
  • Frequency depends on key usage, sensitivity of data, and organizational policies
• Automated key rotation systems streamline the process and reduce human error
• Key versioning tracks different iterations of keys throughout their lifecycle
• Cryptoperiods define the maximum time a key should be used before rotation
• Proper key destruction prevents unauthorized access to retired keys
  • Involves secure deletion methods (multiple overwrites, physical destruction of storage media)

Secure Key Storage and Hardware Security Modules

• Hardware Security Modules (HSMs) provide dedicated, tamper-resistant key storage
• HSMs perform cryptographic operations within a secure boundary
  • Protects keys from unauthorized access, even if the host system is compromised
• Offers hardware-based random number generation for high-quality key material
• Supports various cryptographic algorithms and key sizes
• Provides physical and logical access controls to restrict key usage
• Enables key backup and recovery procedures while maintaining security
• Offers audit logging capabilities for compliance and forensic purposes
• Can be used for secure boot processes and code signing in high-security environments