X.509 standard and CA’s operation
Certificate path validation
Dec. 18, 2001
2001824
C&IS lab.
Vo Duc Liem
Contents
 1. Introduction
 2. Previous Works
 3. Proposed method
 4. Assessment
 5. Conclusion and further work
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Introduction
 Certificate path validation
 A & B has certificate from different CA
Root 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
Cross ?
CA-A
CA-B
A
B
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Previous work
Method of certificate path validation
 Full path validation

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
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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
5
Validating Process
Root CA
List of valid CAs
(May sign by root
CA)
CA
CA-A
CA
ECA1
CA-B
ECA
Cert. of CA-B
User A
User B
Cert. of B
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List of Valid CA
 ECA1: produce list of its
child CA’s, sign and send to
ECA2
List of ECA
Issuer ECA1
…
 ECA2 verifies ECA1 signature;
sign on list
 …
 Root CA: check signature
and sign
Root CA
Root CA signature Alg.
Root CA signature on
all above fields
Exp. List of valid CA
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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
ECA1
 If exist, verify CA-B’s certificate by ECA1 public key
 Verify the list of valid CA of ECA1 by public key of
Root CA
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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.
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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
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References
①
②
③
④
⑤
⑥
⑦
⑧
⑨
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 World,
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
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