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Encryption and Firewalls

Encryption and Firewalls. Chapter 7. Learning Objectives. Understand the role encryption plays in firewall architecture Know how digital certificates work and why they are important security tools Analyze the workings of SSL, PGP, and other popular encryption schemes

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Encryption and Firewalls

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  1. Encryption and Firewalls Chapter 7

  2. Learning Objectives • Understand the role encryption plays in firewall architecture • Know how digital certificates work and why they are important security tools • Analyze the workings of SSL, PGP, and other popular encryption schemes • Enable Internet Protocol Security (IPSec) and identify its protocols and modes

  3. Encryption • Process of encoding and decoding information to: • Preserve its integrity • Maintain privacy • Ensure identity of users participating in the encrypted data session

  4. Why Firewalls Need to Use Encryption • Hackers take advantage of a lack of encryption • Encryption: • Preserves data integrity • Increases confidentiality • Is relied upon by user authentication • Plays a fundamental role in enabling VPNs

  5. Hackers Take Advantage of a Lack of Encryption

  6. Hackers Take Advantage of a Lack of Encryption

  7. The Cost of Encryption • CPU resources and time • Bastion host that hosts the firewall should be robust enough to manage encryption and other security functions • Encrypted packets may need to be padded to uniform length to ensure that some algorithms work effectively • Can result in slowdowns • Monitoring can burden system administrator

  8. Preserving Data Integrity • Even encrypted sessions can go wrong as a result of man-in-the-middle attacks • Encryption can perform nonrepudiation using a digital signature

  9. Maintaining Confidentiality • Encryption conceals information to render it unreadable to all but intended recipients

  10. Authenticating Network Clients • Firewalls need to trust that the person’s claimed identity is genuine • Firewalls that handle encryption can be used to identify individuals who have “digital ID cards” that include encrypted codes • Digital signatures • Public keys • Private keys

  11. Enabling VPNs • As an integral part of VPNs, encryption: • Enables the firewall to determine whether the user who wants to connect to the VPN is actually authorized to do so • Encodes payload of information to maintain privacy

  12. Digital Certificates and Public and Private Keys • Digital certificate • Electronic document that contains a digital signature (encrypted series of numerals and characters), which authenticates identity of person sending certificate • Keys • Basis of digital certificates and signatures • Enable holders of digital certificates to encrypt communications (using their private key) or decrypt communications (using sender’s public key)

  13. Digital Certificates • Transport encrypted codes (public and private keys) through the firewall from one host to another • Help ensure identity of the individual who owns the digital certificate • Provide another layer of security in firewall architecture

  14. Aspects of Digital Certificates • Establishment of an infrastructure for exchanging public and private keys • Need to review and verify someone’s digital certificate • Difference between client- and server-based digital certificates

  15. The Private Key Infrastructure • Lightweight Directory Access Protocol (LDAP) • Publicly available database that holds names of users and digital certificates • Public-Key Infrastructure (PKI) • Enables distribution of digital certificates and public and private keys • Underlies many popular and trusted security schemes (eg, PGP and SSL)

  16. Viewing a Digital Certificate

  17. Viewing a Digital Certificate

  18. Types of Digital Certificates a Firewall Will Encounter • Client-based digital certificates • Obtained by users from a Certification Authority (CA), which issues them and vouches for owner’s identity • Server-based digital certificates • Issued by a CA to a company that issues them to individuals

  19. Keys • Value generated by an algorithm that can also be processed by an algorithm to encrypt or decrypt text • Length of the key determines how secure the level of encryption is

  20. Aspects of Keys That Pertain to Firewall-Based Encryption • Public and private keys • Need to generate public keys • Need to securely manage private keys • Need to use a key server either on network or Internet • Differences between private and public key servers

  21. Public and Private Keys • Private key • Secret code generated by an algorithm • Never shared with anyone • Public key • Encoded information generated when private key is processed by the same algorithm • Can be exchanged freely with anyone online

  22. A Public Key Generated by PGP

  23. An Encrypted Communication Session

  24. Choosing the Size of Keys

  25. Generating Keys

  26. Managing Keys • Manual distribution • Use of a CA • Use of a Key Distribution Center (KDC)

  27. Using a Key Server That Is on Your Network

  28. Using an Online Key Server

  29. Analyzing Popular Encryption Schemes • Symmetric key encryption • Asymmetric key encryption • Pretty Good Privacy (PGP) • Secure Sockets Layer (SSL)

  30. Symmetric Encryption • Use of only one key to encrypt information, rather than a public-private key system • Same key is used to encrypt/decrypt a message • Both sender and recipient must have same key • Not scalable

  31. Symmetric Key Encryption

  32. Asymmetric Encryption • Uses only one user’s public key and private key to generate unique session keys that are exchanged by users during a particular session • Only the private key must be kept secret • Scales better than symmetric encryption • Disadvantages • Slower • Only a few public key algorithms are available (eg, RSA and EIGamal) that are secure and easy to use for both encryption and key exchange

  33. Asymmetric Key Encryption

  34. PGP • Hybrid system that combines advantages of asymmetric (scalability) and symmetric (speed) encryption systems

  35. PGP • Process • File/message is encrypted • Session key is encrypted using public key half of asymmetric public-private key pair • Recipient of encrypted message uses his/her private key to decode the session key • Session key is used to decode message/file • Encryption schemes used to generate public and private key pairs • Rivest-Shamir-Adleman (RSA) encryption • Diffie-Hellman encryption

  36. Using PGP

  37. Using PGP

  38. X.509 • Standard set of specifications for assembling and formatting digital certificates and encrypting data within them • A commonly used type of PKI • Widely used and well trusted

  39. X.509 and PGP Compared • X.509 • Perception of trust • PGP • Does not make use of the CA concept • Gives users ability to wipe files from hard disk (and delete permanently) • Available both in freeware and commercial versions

  40. X.509 and PGP Compared

  41. SSL • Secure way to transmit data • Uses both symmetric and asymmetric keys • Asymmetric keys start an SSL session • Symmetric keys are dynamically generated for the bulk of the transfer

  42. Using Internet Protocol Security (IPSec) Encryption • Creates a secure IP connection between two computers • Operates under the Application layer • Transparent to users

  43. Understanding IPSec • Set of standards and software tools that encrypt IP connections between computers • Allows a packet to specify a mechanism for authenticating its origin, ensuring data integrity, and ensuring privacy

  44. Modes of IPSec • Transport mode • Tunnel mode • Choice depends on type of network and whether it uses NAT

  45. Transport Mode • IPSec authenticates two computers that establish a connection • Can optionally encrypt packets • Does not use a tunnel

  46. Tunnel Mode • IPSec encapsulates IP packets and can optionally encrypt them • Encrypts packet headers rather than the data payload • Incompatible with NAT

  47. IPSec Protocols • Authentication Header (AH) • Encapsulation Security Payload (ESP)

  48. Authentication Header (AH) • Adds a digital signature to packets to protect against repeat attacks, spoofing, or other tampering • Verifies that parts of packet headers have not been altered between client and IPSec-enabled host • Incompatible with NAT

  49. AH

  50. Encapsulation Security Payload (ESP) • More robust than AH; encrypts data part of packets as well as the headers • Provides confidentiality and message integrity • Can cause problems with firewalls that use NAT

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