1. CSCD434 Network Security Spring 2019 Lecture 14
PKI

2. Overview
Public Key Infrastructure
Details

3. PKI Defined
What is PKI?

4. Public Key Infrastructure (PKI)‏
Components in General
PKI is combination of software, encryption technologies, and services
Protects business communications and transactions on Internet
PKI integrates digital certificates, public-key cryptography, and certificate authorities into
Enterprise-wide Security Architecture
Provides
A way to verify an individual’s identity and ensure that a person’s public key is bound to that identity

5. Background of PKI
PKI as we know it began with establishment of the X.509 certificate standard in 1993
RFC 1422 ,
This standard created concepts of certification authorities,
Certificate revocation lists (CRL), and
Certificate trusts that provided framework for more advanced PKI-based technologies in-use today
PKI consists of:
Software
Encryption technologies
Security services

6. PKI Components 1. Certification Authority
- Issues certificates of ownership of a public key by named entity
2. Registration Authority
- Trusted by a CA to register or vouch for users of the CA
3. Repository
- Database of active digital certificates for a CA
- Confirms status of digital certificates for individuals and businesses
4. Archive
- To store and protect sufficient information to determine if a digital
signature on an "old" document should be trusted
5. Certificates
- Includes public key, identity of party holding private key,
operational period for certificate, and the CA's own digital signature
- May contain other information about signing party or information
about recommended uses for public key

7. PKI Example Certificate
A message signed by someone that vouches for someone else’s public key
{Alice’s public key is } Bob
Encrypted with Bob’s private key
If you trust that you have Bob’s public key, and if you trust Bob, then you now trust your new knowledge of Alice’s public key
Chain of certificates:
{Carol’s key is } Damian 
{Bob’s public key is } Carol 

8. PKI Example
If Alice signs a certificate vouching for Bob’s name and key:
Alice is the Issuer
Bob is the Subject
Alice is verifying a chain of certificates:
Alice is the verifier / relying party
Anything with a public key is a principal
A Trust Anchor is a public key that the verifier has decided to trust

9. Why do we need PKI?
Why is PKI needed?
What problems does it solve?

10. Overview of PKI PKI uses public key cryptographic techniquesCA
PKI uses public key cryptographic techniques
Derives its name from public key cryptography
PKI identifies a Certificate Authority (CA) who provides public/private key pair
CA manages keys
CA is also responsible for managing Certificate Revocation List (CRL)‏

11. Digital Signatures
Created by using hash functions creates a message digest
Purpose Electronic identification of a person or thing created by using public key algorithm
Verifies integrity of data and identity of sender
Discuss digital signatures as a security feature that provides integrity, authentication, and repudiation whereas encryption primarily provides confidentiality.
Explain that digital signatures are created using hash functions, and then the message is ‘signed’ by using the user’s private key. Have students study Figure 5-2 to see how signatures are made.
The receiver uses the sender’s public key to recreate the original message digest to provide nonrepudiation.

12. Hash Functions
Message Digest is generic version of one of three algorithms, all designed to create a message digest or hash from plain text.
MD2 – produces hash of 128 bits, optimized for 8- bit machine
MD4 – optimized for 32-bit machines, fast but not secure
MD5 – created to fix security problems of MD4 and is slower
SHA – algorithm modeled on MD4. Accepts an input of up to 264 bits or less and compresses down to a hash of 160 bits.

14. Flaws of Digital Signatures
Without way to verify signer is who they say they are ... following can happen

15. Without a PKI, individuals could spoof identities
Evil
Without a PKI, individuals could spoof identities

16. Certificate Authority (CA)
Responsibilities of a CA
CA is trusted authority for certifying individuals and creating
Digital Certificates
Consists of procedures and policies plus public key algorithms to create key pair
Every CA outlines
How identities are verified,
Keys are secured,
Data placed within a digital certificate, and
How revocations will be handled

17. Hierarchical PKI
CA forms root of a tree and can sign any other key below them
These trees can be as small as a project group, or as big as the Internet

18. CA Examples VeriSign was one of first and was most dominant
Headquartered in Mountain View, California
Authentication, Validation and Payment
A 2009 market share report, VeriSign and its acquisitions (which include Thawte and Geotrust) had a 47.5% share of the certification services provider market, followed by GoDaddy (23.4%), and Comodo (15.44%)‏
In 2010, Verisign sold its CA business to Symantec

19. Top Certificate Authorities 2018

20. Digital Certificates
Binds an individual’s identity to a public key and
Contains all info needed to prove public key belongs to a legitimate owner and has not been compromised
Consists of
Owner’s public key
Information unique to owner
Digital signatures or an endorser
Explain that digital certificates are similar to digital signatures in that a public key and private key are used but with digital certificates, there is an endorser, a third party that vouches for the authenticity and identity of the public key holder.
Mention that digital signatures and digital certificates work together, where the digital certificate ensures that the public key holder’s identity is authentic.

22. Steps for obtaining a digital certificate

23. Certificate Repository
Once certificate is registered,
Identity proven, and a key pair generated, they are placed in a public repository
All certificates can be in one, large distributed database (LDAP) ‏
Each signing certificate authority can maintain its own repository and have a means of querying the other repositories for information for its users
Business communities and governments are starting to create their own CA's
Linking them by signing or cross-certifying and publishing all of their information in business- class repositories

24. Trust and Certificate Verification
If CA and integrity of certificate is trusted, still need to check:
Start and stop dates of certificates (life cycles)‏
Revocation list (CRL)‏
Lost laptop or smart card
Improper software implementation
Social engineering attack
Employee leaves company

25. Private Key Protection Recommendations
The key size should provide the necessary level of protection for the environment
The lifetime should correspond with how often it is used and the sensitivity of the data
Key should be changed and not used past its lifetime
Key should be properly destroyed at end of lifetime
Key should never be exposed in clear text
No copies of private key should be made
Key should not be shared
Key should be stored securely
Authentication should be required before it can be used
Key should be transported securely
Software implementation used for storage needs to provide the necessary level of protection

26. PKI Standards Used in Business processes Applications
Standards/protocols that use PKI
PKI implementation level
Online banking and shopping
, VPNs
S/MIME, SSL, TLS, WTLS, IPsec, PPTP
ISAKMP, CMP, SKMS, X.509, PKIX, PKCS

27. PKI Standards PKI Implementation relies on
PKIX -Public Key Infrastructure
PKCS - Public Key Cryptography
X.509
ISAKMP and XKMS are key management protocols
CMP manages certificates
S/MIME manages
SSL, TLS and WTLS for secure packet transmissions
IPSEC and PPTP for VPN
Online banking and shopping
, VPNs
S/MIME, SSL, TLS, WTLS, IPsec, PPTP
ISAKMP, CMP, XKMS, X.509, PKIX, PKCS

28. PKI Standards
PKIX/PKCS based on the X.509 standard defines four components:
The user
Certificate Authority (CA)‏
Registration authority (RA)‏
Certificate revocation lists
Online banking and shopping
, VPNs
S/MIME, SSL, TLS, WTLS, IPsec, PPTP
ISAKMP, CMP, XKMS, X.509, PKIX, PKCS

29. X.509 Certificates
Late 1980,
X.500 OSI directory standard was defined by ISO and the ITU
X.509 addresses structure of certificates used for authentication
X.509 defines a hierarchical certification structure that relies on a root certificate authority that is self- certifying
To obtain a X.509, you must ask a CA to issue you one
Explain that S/MIME offers both authentication and privacy services. Discuss briefly the four standards upon which S/MIME is built.
Explain how S/MIME is newer than PGP and supports in MIME format but the 40-bit RC2 algorithm is known to be somewhat weak. However, since S/MIME also supports 3DES, a strong algorithm, S/MIME can be used effectively and securely. Explain to students that export restrictions make S/MIME using RC2 encryption attractive when applications that use it are exported. Students should understand that the U.S. has strict restrictions over what types of encryption may be exported (for example, Windows Server versions that use 128-bit encryption cannot be exported).
You provide your public key, proof that you possess the correspingin private key and some specific info about yourself. You then ditially sign the info and send the whole package to CA. CA does due diligence and generates cert with public key.

31. Trust Models Techniques that establish how users validate certificates
Direct trust – not scalable
Hierarchical trust – based on number of root CA
Web of trust

32. Hierarchical X.509 Standard used to define hierarchy of public keys
Users trust top of tree, and which then filters down to trust of nodes farther down
Example: Paypal.com
Your computer trusts public key for a Certificate Authority such as VeriSign
Verisign certifies that Paypal, Inc. owns paypal.com, and signs their certificate for that address
Your computer sees Paypal.com’s certificate, and can trust its identity
What is the Vulnerability or Risk in this scheme?
Main Risk Very Centralized
If someone were to control VeriSign’s key, they could run a fake paypal.com, and collect usernames/passwords.

33. Hierarchical X.509

34. Hierarchical X.509 How is Trust Achieved?
Certificate is trusted because issued by a broadly accepted certificate authority ("CA")‏
You and most other Internet users accept as reliable for purpose of binding identities to credentials
CA's tend to be very careful when it comes to doing what they say they're going to do
Follow Certificate Practices Statement
If they don't, people (including browser vendors!) will stop trusting them and then they'll quickly be out of business 34

35. CA-FOO CA-BAR CA-BAR Self-Signed
If you receive Borja's certificate, and don't explicitly trust CA FOO this doesn't automatically mean certificate isn't, trustworthy, you might check to see if CA FOO's certificate was issued by a CA you do trust. If it turns out that CA BAR is in your 'trusted list', then that means that Borja's certificate is trustworthy
CA-FOO
CA-BAR
CA-BAR
Self-Signed

36. Alternative Model Web of Trust
Web of Trust concept was first proposed by
PGP creator Phil Zimmermann in 1992
Became OpenPGP standard
Based on graph of public keys, signing each other’s keys when identities are verified
Eventually, one key can ‘trust’ identity of another by tracing a path through graph of trusted keys
Depends on people verifying identity before signing someone else’s key
Today, there is a ‘strongly connected’ subgraph of keys which all trust each other
This “Strong set” contains over keys, with an average distance between keys of ~6 people.

37. Web of Trust Zimmerman believed that
“As time goes on, you will accumulate keys from other people that you may want to designate as trusted introducers.
Everyone else will each choose their own trusted introducers. And everyone will gradually accumulate and distribute with their key a collection of certifying signatures from other people, with the expectation that anyone receiving it will trust at least one or two of the signatures.
This will cause the emergence of a decentralized fault-tolerant web of confidence for all public keys”

38. Web of Trust Example

39. How Web of Trust Works You have 2 keys
Public key that you let people you trust know; and
Private key that only you know
Your public key will decrypt any information encrypted with your private key, and vice-versa
You also have key ring with group of people's public keys
You encrypt your information with a recipient's public key, and only their private key will decrypt it
You then digitally sign information with your private key, so when they verify it with your public key, they can confirm that it is you
Pretty much the same as PKI, but without the CA's

40. Summary PKI used for most of the network, web cryptography used today
Imperfect system
Many flaws
Lots of attacks against this system
Only one we have ... thats widely used to date

41. The End
No Lab this Week … Work on the Midterm