Lecture 7 certificates


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Network Security Course (ET1318, ET2437) at Blekinge Institute of Technology, Karlskrona, Sweden

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Lecture 7 certificates

  1. 1. Certificates
  2. 2. X.509 Authentication Service• Distributed set of servers that maintains a database about users.• Each certificate contains the public key of a user and is signed with the private key of a CA.• Is used in S/MIME, IP Security, SSL/TLS and SET.• RSA is recommended to use. 2 ET1318 - Network Security
  3. 3. 3ET1318 - Network Security
  4. 4. 4ET1318 - Network Security
  5. 5. Public-Key Certificate Use 5 ET1318 - Network Security
  6. 6. X.509 Formats 6 ET1318 - Network Security
  7. 7. Obtaining a User’s Certificate• Characteristics of certificates generated by CA:  Any user with access to the public key of the CA can recover the user public key that was certified.  No part other than the CA can modify the certificate without this being detected. 7 ET1318 - Network Security
  8. 8. Revocation of Certificates• Reasons for revocation:  The users secret key is assumed to be compromised.  The user is no longer certified by this CA.  The CA’s certificate is assumed to be compromised. 8 ET1318 - Network Security
  9. 9. CA Hierarchy 9 ET1318 - Network Security
  10. 10. Authentication Procedures 10 ET1318 - Network Security
  11. 11. Internet Key Exchange (IKE)• Protocol to manage keys in IPsec by negotiating security associations between a set of peers• Based on RFC 2409• Using a standard Diffie-Hellman exchange to obtain a shared secret• Also used to negotiate the encryption, authentication, and other cryptographic primitives that the VPN needs to create a SA• Derives from other key-exchange protocols  Internet Security Association and Key Management Protocol - ISAKMP  Oakley Key Determination protocol - Oakley  SKEME 11
  12. 12. IKE use in IPsec 12 ET1318 - Network Security
  13. 13. IKE and IPSec in Cisco ISO 13 ET1318 - Network Security
  14. 14. ISAKMP• Defines procedures and packet formats to negotiate, establish, modify, and delete SAs• UDP or TCP port 500• Establishment of SAs by using ISAKMP are achieved in two phases 1. Peers authenticate each others and establish a secure communication channel 2. ISAKMP negotiates VPN SAs 14 ET1318 - Network Security
  15. 15. ISAKMP Cookies• IKE’s goal is to prevent against DoS-attacks• An easy DoS attack against IKE could be to flood an IKE node with IKE packets with spoofed source address. Hence forcing the IKE node to do expensive, but useless, Diffie-Hellman calculations• ISAKMP uses cookies to identify the source before doing the expensive Diffie-Hellman calculation• The ISAKMP node sends a cookie that the receiver must bounce in order to start Diffie-Hellman key exchange 15 ET1318 - Network Security
  16. 16. ISAKMP 16ET1318 - Network Security
  17. 17. ISAKMP Payload Types• Key Exchange Payload• Certificate Payload (transfers a public key certificate)• Notification Payload (error messages)• Responder-Lifetime• Hash Payload• Signature Payload 17 ET1318 - Network Security
  18. 18. ISAKMP Payload Example 18 ET1318 - Network Security
  19. 19. Oakley• Three authentication methods:  Digital signatures  Public-key encryption  Symmetric-key encryption 19 ET1318 - Network Security