1. Public Key Infrastructure (X509 PKI) Presented by : Ali Fanian

2. Digital Signature
A Digital Signature is a data item that vouches the origin
and the integrity of a Message
The originator of a message uses a signing key (Private Key) to sign the
message and send the message and its digital signature to a recipient
The recipient uses a verification key (Public Key) to verify the origin of
the message and that it has not been tampered with while in transit
vouch
ضمانت‌ كردن‌، اطمينان‌ دادن‌، تاييد كردن‌
Intranet
Extranet
Internet
Alice
Bob

3. Digital Signature Signer Channel Receiver Message Message
Digest
Algorithm
Digest
Algorithm
Hash Function
Hash Function
Digest
Public Key
Encryption
Decryption
Private Key
Expected
Digest
Actual
Digest
Signature
Signer
Channel
Receiver

4. Digital Signature There is still a problem linked to the
“Real Identity” of the Signer.
Why should I trust what the Sender claims to be?
Moving towards PKI …

5. Digital Certificate

6. Digital Certificate
A Digital Certificate is a binding between an entity’s
Public Key and one or more Attributes relating its Identity.
The entity can be a Person, an Hardware Component, a Service, etc.
A Digital Certificate is issued (and signed) by someone
Usually the issuer is a Trusted Third Party (TTP)
A self-signed certificate usually is not very trustworthy

7. Digital Certificate CERTIFICATE Issuer Subject Subject Public Key
Signature

8. Digital Certificate How are Digital Certificates Issued? Problems
Who is issuing them?
Why should I Trust the Certificate Issuer?
How can I check if a Certificate is valid?
How can I revoke a Certificate?
Who is revoking Certificates?
Moving towards PKI …

9. Public Key Infrastructure (PKI)

10. Public Key Infrastructure (PKI)
A Public Key Infrastructure is an Infrastructure
to support and manage Public Key-based
Digital Certificates

11. Public Key Infrastructure (PKI)
“A PKI is a set of agreed-upon standards
- Certificate structure
- Structure between multiple CAs
- Methods to discover and validate Certification Paths
Operational Protocols
Management Protocols
“Digital Certificates” book – Jalal Feghhi, Jalil Feghhi, Peter Williams

12. Public Key Infrastructure (PKI)
X509 Digital Certificates standard
 Standards defined by IETF, PKIX WG:
… however X509 is not the only approach

13. X509 PKI – Technical View Basic Components: Certificate Authority (CA)
Registration Authority (RA)
Certificate Distribution System
PKI enabled applications
“Provider” Side
“Consumer” Side

14. X509 PKI – Simple Model CA RA Certification Entity Application Service
Cert. Request RA
Application
Service
Signed Certificate
Internet
Certs,
CRLs
Directory
Remote
Person
Local
Person

15. Certificate Authority (CA)
X509 PKI
Certificate Authority (CA)
Basic Tasks:
Key Generation
Digital Certificate Generation
Certificate Issuance and Distribution
Revocation
Key Backup and Recovery System
Cross-Certification

16. Registration Authority (RA)
X509 PKI
Registration Authority (RA)
Basic Tasks:
Registration of Certificate Information
Face-to-Face Registration
Remote Registration
Automatic Registration
Revocation

17. Certificate Distribution System
X509 PKI
Certificate Distribution System
Provide Repository for:
Digital Certificates
Certificate Revocation Lists (CRLs)
Typically:
Special Purposes Databases
LDAP directories

18. Certificate Revocation List
Revoked Certificates
remain in CRL
until they expire

19. Certificate Revocation List (CRL)
CRLs are published by CAs at well defined
interval of time
It is a responsibility of “Users” to “download” a CRL and verify if a certificate has been revoked
User application must deal with the revocation
processes

20. Online Certificate Status Protocol
(OCSP)
An alternative to CRLs
IETF/PKIX standard for a real-time check if a
certificate has been revoked/suspended
Requires a high availability OCSP Server

21. CRL vs OCSP Server CRL OCSP User CA Directory User OCSP Server CA
Download CRL
CRL
User CA
CRL
Directory
Certificate IDs
to be checked
Download
CRL
CRL
User
OCSP
Server CA
Answer about
Certificate States
Directory
OCSP

22. PKI-enabled Applications
X509 PKI
PKI-enabled Applications
Functionality Required:
Cryptographic functionality
Secure storage of Personal Information
Digital Certificate Handling
Communication Facilities

23. X509 PKI
Trust and Legal Issues

24. X509 PKI Trust and Legal Issues
Why should I Trust a CA?
How can I determine the liability of a CA?
Legal issues مسائل حقوقی
liability تعهد،الزام ،اسناد ديونى ،مسئوليت

25. Approaches to Trust and
X509 PKI
Approaches to Trust and
Legal Aspects
Why should I Trust a CA?
How can I determine the liability of a CA?
Certificate Hierarchies, Cross-Certification
liability
تعهد،الزام ،اسناد ديونى ،مسئوليت
Certificate Policies (CP) and Certificate Practical
Statement (CPS)

26. Certificate Hierarchies
X509 PKI
Approach to Trust
Certificate Hierarchies
and
Cross-Certification

27. CA Technology EvolutionRA
LRA
Directory
Services
Internet

28. Simple Certificate Hierarchy
Each entity has its own certificate (and may have more than one). The root CA’s certificate is self signed and each sub-CA is signed by its parent CA.
Each CA may also issue CRLs. In particular the lowest level CAs issue CRLs frequently.
End entities need to “find” a certificate path to a CA that they trust.
Root CA
Sub-CAs
End Entities

29. Simple Certificate Path*
Alice
Bob
Simple Certificate Path
Trusted Root
Alice trusts the root CA
Bob sends a message to Alice
Alice needs Bob’s certificate, the certificate of the CA that signed Bob’s certificate, and so on up to the root CA’s self signed certificate.
Alice also needs each CRL for each CA.
then Alice can verify that Bob’s certificate is valid and trusted and so verify the Bob’s signature.

30. Cross-Certification and
Multiple Hierarchies 1 2 3
Multiple Roots
Simple cross-certificate
Complex cross-certificate

31. Approach to Trust : Problems
X509 PKI
Approach to Trust : Problems
Things are getting more and more
complex if Hierarchies and
Cross-Certifications are used

32. Cross-Certification and
Path Discovery
Trusted Root
Trusted Root 3 *

33. Approach to Legal Aspects Certificate Practice Statement
X509 PKI
Approach to Legal Aspects
Certificate Policy
And
Certificate Practice Statement

34. Certificate Policy (CP)
A document that sets out the rights, duties and
obligations of each party in a Public Key
Infrastructure
The Certificate Policy (CP) is a document which
usually has legal effect
سند که مجموعه حقوق، وظایف و تعهدات هر یک از طرفین در یک زیرساخت کلید عمومی
سیاست های گواهی، سندی که معمولا دارای اثر حقوقی است.
مراجع صدور گواهي مجموعه‌اي از قواعد و سياستهاي اتخاذ شده در ارتباط با توليد و يا رده‌بندي گواهي‌ها به همراه ويژگيهاي امنيتي آنها را در قالب خط مشي و بيانيه اجرايي زير ساخت، اعلام مي‌کنند. در اين خط مشي نوع گواهي قابل ارائه به همراه ميزان امنيت و خدمات مرتبط با آنها مشخص مي‌گردد تا کاربران با آگاهي پيدا کردن از آن و با توجه به نوع فعاليتهاي آتي خود گواهي مناسب را انتخاب و دريافت نمايند. به عبارت ديگر بيانيه گواهي مشروح فعاليتهاي مرجع صدور گواهي را مشخص مي‌کند که بايد کاربران از آن آگاهي داشته باشند. در ذيل اين بيانيه آنچه که به سياستهاي صدور يک گواهي ديجيتال مربوط مي‌شود تحت عنوان سياست گواهي (CP) شناخته مي‌شود. در اين سند تعهداتي که زير ساخت کليد عمومي در قبال صدور يک گواهي بر عهده دارد به تفصيل مشخص مي‌شود. در ادامه سند کاملتر ديگري به نام احکام عملي گواهي (CPS) وجود دارد که در آن رويه‌هاي موجود در زير ساخت کليد عمومي با جزييات کامل مشخص مي‌شود. لازم است که پيشنهاد دهنده CP و CPS زير ساخت بومي را به طور کامل ارائه نمايد. در ادامه موارد مهمي که در اين سياست‌نامه‌ها بايد لحاظ شود، آمده است. Certificate Policy
Certificate Practices Statement
A CP is usually publicly exposed by CAs, for
example on a Web Site (VeriSign, etc.)

35. Policy Issues (CP) Liability Issues Repository Access Controls
Confidentiality Requirements
Registration Procedures
- Uniqueness of Names
- Authentication of Users/Organisations
مسائل مربوط به تعهدات Liability Issues
Suspension معلق کردن
Revocation (Online/CRL)
Physical Security Controls

36. Certificate Practice Statement (CPS)
A document that sets out what happens in practice
to support the policy statements made in the CP
in a PKI
سند که مجموعه آنچه در عمل اتفاق می افتد برای حمایت از سیاست اظهارات در CP در PKI ساخته شده است

37. Certificate Practice Statement (CPS)
INTRODUCTION
GENERAL
PROVISIONS
IDENTIFICATION &
AUTHENTICATION
SPECIFICATION
ADMINISTRATION
CPS
CERTIFICATE &
CRL PROFILES
OPERATIONAL
REQUIREMENTS
TECHNICAL
SECURITY
CONTROLS
PHYSICAL,
PROCEDURAL &
PERSONNEL

38. IETF (PKIX) Standards X.509 Certificate and CRL Profiles
PKI Management Protocols
Certificate Request Formats
CP/CPS Framework
LDAP, OCSP, etc.

39. Identity is Not Enough: Attribute Certificates
IETF (PKIX WG) is also defining standards for Attribute Certificates (ACs):
Visa Card vs. Passport (Identity)
Attribute Certificates specify Attributes associated
to an Identity
Attribute Certificates don’t contain a Public key
but a link to an Identity Certificate