1. Introduction to PKI Novell BrainShare 2002 Tammy Green
Senior Software Engineer
Novell, Inc.
Steve Walker
Software Engineer
IO225—Introduction to PKI

2. The Problem

3. One Solution

4. Symmetric Key Cryptography
Bob and Alice agree on key
Keys can be passwords, Personal Identification Numbers (PIN), etc.
Bob encrypts message to Alice with key
Alice decrypts message with same key

5. It Works, but What If… Alice and Bob don’t know each other
Need a trusted third-party
Bob wants to send a message to 1,000 people
Need an easy way to exchange keys
Alice puts the key on a sticky note on her monitor
Need a way to notify everyone

6. Public Key Cryptography
Two keys for each person
Public key—available to everyone
Private key—kept secret
Given the public key, “hard” to find private key
Encrypt using public key
Decrypt using private key

7. Encryption/Decryption
Bob’s message
Alice’s private key A
Bob’s message
Alice’s public key A

8. Signing/Verification
Bob’s message
Bob’s message
Verified
Bob
Bob’s private key B
Bob’s public key B

9. Encryption and Signature
Bob’s private key B
Bob’s public key B
Bob
Bob’s message
Verified
Bob’s message
Alice’s public key A
Alice’s private key A

10. How Do They Exchange Keys?
Put them in the newspaper
Send them on a floppy disk
Put them in a public directory, e.g., Novell eDirectory™
“All of these methods are vulnerable
to substitution or tampering”

11. Digital Certificate Prevents tampering because it is digitally signed
Prevents substitution because it is signed by a “trusted” entity
Can put them anywhere
Web sites
Floppy disks
Directories
Etc.

12. Certificate Types X.509 PGP Simple PKI (SPKI) XML certificates
“Compact” certificates
Wireless TLS certificates
Attribute certificates

13. What Is an X.509 Certificate?
It binds a public key to a name
The name can be
A person
A group
A machine
A program
There are four versions
v1, v2—seldom used
v3—most commonly used
v4—not yet used

14. Format of a X.509 Certificate
Public Key Algorithm
Signature Algorithm
(object Identifier)
Public Key
(bit string)
Subject
(name)
Issuer
Not Before
Not After
Validity Period
(date and time) 
Signed
Optional
Extensions
Version
(Integer)

15. Who Signs a Certificate?
Self-signed
I am me because I say that I am me
Certificate Authority (CA)
Trusted third party

16. Choosing a CA Organizational CAs Commercial CAs
Trusted only within a limited domain
Self-signed
Commercial CAs
Widely trusted (e.g., by all web browsers)
Referred to as “trusted roots”

17. To Sign or Not to Sign
CAs sign certificates if predefined criteria are met
Subject name and alternative names are reasonable
Proof of possession of private key
Agrees with data in extensions
Public key not already used
Criteria are defined in Certification Practice Statement (CPS)
Validation may be done by a Registration Authority (RA)

18. Getting a Certificate 1. Generate key pair
2. Generate certificate request
4. Validate certificate
request
3. Send certificate request
8. Return certificate
5. Issue certificate
6. CA issues certificate
7. Publish certificate

19. But What If…? What if someone else claims to be me?
CA must validate identity
What if two people have the same name?
Need a global unique identifier
Qualified certificates ensure uniqueness

20. Intermediate CAs Signed by another CA Capabilities could be limited
Signed by a root CA
Signed by another intermediate CA
Capabilities could be limited
Limits put in certificate
May only sign non-CA certificates
May only sign certificates for certain names

21. CA Hierarchy

22. But What If…? How do I decide which CAs to trust?
Applications do it for you
Your company could do it for you
Can’t a CA just “trust” another CA?
CAs can cross-certify each other
Bridge CAs can bridge the gap

23. Bridging the Gap
Bridge CA

24. Certificate Extensions
Common extensions
Alternative names
Key usage
Basic constraints
CRL distribution point
Custom extensions
Picture of yourself
May be critical

25. But What If…? What if my certificate expires?
Get a new certificate
You may need a new key pair
What if the information in my certificate is incorrect?
What if someone steals my private key?
Revoke the certificate

26. Revoking a Certificate
1. Revoke certificate
2. Approve revocation
request
3. Revoke certificate
4. Publish certificate
revocation

27. Publishing Certificate Revocations
Typically done by a CA
Common methods
Certificate Revocation List (CRL)
Delta
Indirect
On-demand
Online Certificate Status Protocol (OCSP)
Simple Certificate Validation Protocol (SCVP)
Location of revocation information is in certificate

28. But What If…?
How long will it take before my certificate is actually revoked?
Depends on CA and on method of publishing
Caching can a problem
What if it takes weeks?
Revocation data may include an invalidity date
What if the CA is compromised?
CAs can be revoked
Root CA compromise is very bad

29. Validating a Certificate
Must have entire chain
For each pair of certificates make sure
Public key in issuer certificate signed other certificate
Subject and issuer names match
Certificates are within validity period
Neither certificate has been revoked
No unknown critical extensions
At least one certificate in chain is “trusted”

30. But What If… Isn’t it slow to check if every certificate is revoked?
Caching can help
OCSP and SCVP can help
Revoking certificates isn’t common yet
What if the CA doesn’t support revocation?
You could create your own revocation list

31. So, What Can I Do with a Certificate?
Sign and encrypt
Authenticate a web site
Authenticate yourself
Encrypt a data channel (e.g., SSL)
Protect data from tampering and substitution
Notarize data
Timestamp data

32. SSL Server Side Authentication
Browser
Server
Choose cipher suite
Generate R1
Generate R0
R0, cipher suites
Validate server certificate
Generate R2
Calculate symmetric key
Calculate master secret
R1, cipher suite,
certificate chain
[ R2 + … ]Server’s PubK,
[ Hash (msgs + …) ]SymK
Decrypt R2
Calculate master secret
Calculate symmetric key
Validate encrypted hash
Validate encrypted hash
[ Hash (msgs + …) ]SymK

33. SSL Mutual Authentication
Browser
Server
Choose cipher suite
Generate R1
Generate R0
R0, cipher suites
Validate server certificate
Find user certificate
Generate R2
Calculate master secret
Calculate symmetric key
R1, cipher suite,
certificate chain, trusted roots
Validate user certificate
Decrypt R2
Validate signed hash
Calculate master secret
Calculate symmetric key
Validate encrypted hash
certificate chain,
[ R2 + … ]Server’s PubK,
{ Hash (msgs + ...) }User’s PrvK,
[ Hash (msgs + …) ]SymK
Validate encrypted hash
[ Hash (msgs + …) ]SymK

34. But What If…? What if it really wasn’t me?
You must protect your client and your private key
Non-repudiation is a misnomer
What if I have a 56-bit crypto web browser?
Symmetric key will be limited to 56-bits
Unless the server has a special certificate

35. Server-Gated or Step-Up Crypto
Certificates are signed by designated CAs (e.g., VeriSign)
Called 128-bit SSL Global Server IDs
Special extensions in the certificate
OID
OID
Allows the symmetric key in the handshake to always be 128-bits

36. Benefits of Public Key Cryptography
Alice and Bob don’t know each other
A CA is a trusted third party
Bob wants to send a message to 1,000 people
Publish his certificate to a directory
his certificate to everyone
Alice puts the key on a sticky note on her monitor
CA revokes her certificate
Previous signatures still honored

37. What Is a PKI? Public Key Infrastructure
A collection of components which allow you to create, manage and use public key certificates

38. PKI Components Public/private key pairs Digital certificates
Cryptography provider
CAs
RAs
Revocation mechanism
Repository for certificates and revocation information
Management tools

39. Why Is PKI Good for eCommerce?
Data confidentiality
Data integrity
Authentication
Standards-based

40. Vision…one Net Mission
A world where networks of all types—corporate and public, intranets, extranets, and the Internet—work together as one Net and securely connect employees, customers, suppliers, and partners across organizational boundaries
Mission
To solve complex business and technical challenges with Net business solutions that enable people, processes, and systems to work together and our customers to profit from the opportunities of a networked world

42. Additional Resources www.novell.com/security IETF PKIX Working Group
RFC 2459
Net Solutions lab
Meet the Experts Night
TUT240: Configuring and Troubleshooting the Security Components of NetWare®

43. wiN big Access and Security table one Net solutions lab visit the
in the
to obtain an entry form