1. X.509 standard and CA’s operation Certificate path validation Dec. 18, 2001 2001824 C&IS lab. Vo Duc Liem

2. 2 Contents 1. Introduction 2. Previous Works 3. Proposed method 4. Assessment 5. Conclusion and further work

3. 3 Introduction Certificate path validation A & B has certificate from different CA A trust CA-B? CA-A & CA-B cross certificate  easy! Not Cross  validation path from CA-B to “most trusted” CA by A A spend time & power for verifying Root CA CA-B B CA-A A Cross ?

4. 4 Previous work Method of certificate path validation Full pathvalidation Computation O(n) Delegation certificate path validation O(1) Simple Certificate Validation Protocol O(1) Offline Path Validation* O(1) or no cost *: Method is presented in IWAP01

5. 5 Proposed method Assumption Number of CA’s not huge as user CA is stable entity and play right role, CA is responsible in law The trust between CA’s: CA trust his child

6. 6 Validating Process CA-B CA Root CA User B CA-A CA User A List of valid CAs (May sign by root CA)  ECA  ECA 1 Cert. of CA-B Cert. of B

7. 7 List of Valid CA ECA 1 : produce list of its child CA’s, sign and send to ECA 2 ECA 2 verifies ECA 1 signature; sign on list … Root CA: check signature and sign List of ECA Issuer ECA 1 … Root CA Root CA signature Alg. Root CA signature on all above fields Exp. List of valid CA

8. 8 Steps of validation A check in CRL for B certificate If not, verify by public key of CA-B (ECA) Check existence of CA-B in the list of valid CA of ECA 1 If exist, verify CA-B’s certificate by ECA 1 public key Verify the list of valid CA of ECA 1 by public key of Root CA

9. 9 Assessment Correctness Only right public key can verify signature made by respective private key Security No one can make fake certificate or change the list without knowing of private key The list of valid CA does not need change frequently Need 3 signature verification process Reduce power computing for users.

10. 10 Conclusion and further work Understand X.509 and CA’s operation Proposed method of Certificate path validation For future: Find out all possible attack Consider cross-certificate at high level

11. 11 References  Cryptography and Network Security: Principles and Practice, William Stalling, Prentice Hall 1998  ITU-T X.509 v3 recommendation (1997)  IETF – RFC 2459, Internet X.509 Public Key Infrastructure Certificate and CRL Profile, 1999  IETF – RFC 2560, Internet X.509 Public Key Infrastructure Onlin e Certificate Status Protocol – OCSP, 1999  IETF – Internet drafts, Simple Certificate Validation Protocol, 2001  NIST - Public key infrastructure study – Final report 1997  Network Security: PRIVATE Communication in a PUBLIC Worl d, C. Kaufman, R. Perlman, M, Speciner, Prentice Hall 1995.  Efficient offline path validation – Byoungcheon Lee, Kwangjo Kim, Moongseog Seo, Weonkeun Huh - IWAP 2001 document  On the complexity of Public-key Certificate Validation – Diana Berbecaru, Antonio Lioy, Marius Marian – ISC2001, LNCS 2200, p183-203, 2001