Public Key Infrastructure

Public Key Infrastructure (X509 PKI) Marco Casassa Mont Trusted E-Services Laboratory - HP Labs - Bristol

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Outline • Basic Problem of Confidence and Trust • Background: Cryptography, Digital Signature, Digital Certificates • (X509) Public Key Infrastructure (PKI) • (X509) PKI: Trust and Legal Issues

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Confidence and Trust Issues in the Digital World Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Basic Problem

Bob

Intranet Extranet Internet

Alice

Bob and Alice want to exchange data in a digital world.

There are Confidence and Trust Issues … Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Confidence and Trust Issues • In the Identity of an Individual or Application AUTHENTICATION • That the information will be kept Private CONFIDENTIALITY • That information cannot be Manipulated

Bob

Intranet Extranet Internet

Alice

INTEGRITY • That information cannot be Disowned NON-REPUDIATION Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Starting Point: Cryptography

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Starting Point: Cryptography Cryptography It is the science of making the cost of acquiring or altering data greater than the potential value gained Cryptosystem It is a system that provides techniques for mangling a message into an apparently intelligible form and than recovering it from the mangled form Plaintext Hello World

Encryption Key

Ciphertext &$*£(“!273

Public Key Infrastructure (PKI)

Decryption Key

Plaintext Hello World

HP Laboratories, Bristol, UK

Cryptographic Algorithms All cryptosystems are based only on three Cryptographic Algorithms: • MESSAGE DIGEST (MD2-4-5, SHA, SHA-1, …) Maps variable length plaintext into fixed length ciphertext No key usage, computationally infeasible to recover the plaintext

• SECRET KEY (Blowfish, DES, IDEA, RC2-4-5, Triple-DES, …) Encrypt and decrypt messages by using the same Secret Key

• PUBLIC KEY (DSA, RSA, …) Encrypt and decrypt messages by using two different Keys: Public Key, Private Key (coupled together) Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Cryptographic Algorithms based on Private Key Plaintext

Pros

Encryption

Ciphertext

Private Key

Decryption

Plaintext

Private Key

• Efficient and fast Algorithm • Simple model  Provides Integrity, Confidentiality

Cons • The same secret key must be shared by all the entities involved in the data exchange • High risk • It doesn’t scale (proliferation of secrets)  No Authentication, Non-Repudiation

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Pros

Cryptographic Algorithms based on Public Key

• Private key is only known by the owner: less risk • The algorithm ensures Integrity and Confidentiality by encrypting with the Receiver’s Public key Intranet Extranet Internet

Bob Plaintext

Encryption

Ciphertext

Alice’s Public Key Public Key Infrastructure (PKI)

Alice Decryption

Plaintext

Alice’s Private Key HP Laboratories, Bristol, UK

Pros

Cryptographic Algorithms based on Public Key

• The algorithm ensures Non-Repudiation by encrypting with the Sender’s Private key

Intranet Extranet Internet

Bob

Plaintext

Encryption

Ciphertext

Bob’s Private Key Public Key Infrastructure (PKI)

Alice

Decryption

Plaintext

Bob’s Public Key HP Laboratories, Bristol, UK

Cons

Cryptographic Algorithms based on Public Key

• Algorithms are 100 – 1000 times slower than secret key ones They are initially used in an initial phase of communication and then secrets keys are generated to deal with encryptions

• How are Public keys made available to the other people? • There is still a problem of Authentication!!! Who ensures that the owner of a key pair is really the person whose real life name is “Alice”?

Bob

Intranet Extranet Internet

Public Key Infrastructure (PKI)

Alice

Moving towards PKI … HP Laboratories, Bristol, UK

Digital Signature

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

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

Bob

Intranet Extranet Internet

Public Key Infrastructure (PKI)

Alice HP Laboratories, Bristol, UK

Digital Signature Message

Digest Algorithm

Message

Digest

Hash Function

Algorithm

Digest

Private Key

Public Key

Encryption

Decryption

Signature

Expected Digest

Signer

Hash Function

Channel Public Key Infrastructure (PKI)

Actual Digest

Receiver HP Laboratories, Bristol, UK

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 … Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Digital Certificate

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

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 • A self-signed certificate usually is not very trustworthy Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Digital Certificate CERTIFICATE Issuer Subject Subject Public Key Issuer Digital Signature Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Digital Certificate Problems

• How are Digital Certificates Issued? • 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? Public Key Infrastructure (PKI)

Moving towards PKI … HP Laboratories, Bristol, UK

Public Key Infrastructure (PKI)

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

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

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Public Key Infrastructure (PKI) “A PKI is a set of agreed-upon standards, Certification Authorities (CA), structure between multiple CAs, methods to discover and validate Certification Paths, Operational Protocols, Management Protocols, Interoperable Tools and supporting Legislation” “Digital Certificates” book – Jalal Feghhi, Jalil Feghhi, Peter Williams Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Public Key Infrastructure (PKI)

Focus on:

• X509 PKI • X509 Digital Certificates  Standards defined by IETF, PKIX WG: http://www.ietf.org/ … even if X509 is not the only approach (e.g. SPKI) Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

X509 PKI – Technical View Basic Components: • Certificate Authority (CA) • Registration Authority (RA)

“Provider” Side

• Certificate Distribution System • PKI enabled applications Public Key Infrastructure (PKI)

“Consumer” Side HP Laboratories, Bristol, UK

X509 PKI – Simple Model CA

Certification Entity

Cert. Request

Application Service

Signed Certificate

Internet

Remote Person

RA Certs, CRLs

Directory

Local Person

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

X509 PKI Certificate Authority (CA)

Basic Tasks:

• Key Generation • Digital Certificate Generation • Certificate Issuance and Distribution • Revocation • Key Backup and Recovery System • Cross-Certification Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

X509 PKI Registration Authority (RA) Basic Tasks: • Registration of Certificate Information • Face-to-Face Registration • Remote Registration • Automatic Registration • Revocation Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

X509 PKI Certificate Distribution System Provide Repository for: • Digital Certificates • Certificate Revocation Lists (CRLs) Typically: • Special Purposes Databases • LDAP directories Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Certificate Revocation List Certificate Revocation List

Revoked Certificates remain in CRL until they expire

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

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

HP Laboratories, Bristol, UK

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

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

CRL vs OCSP Server User

Download CRL

CRL

CA

CRL

Directory Certificate IDs to be checked

User Answer about Certificate States

OCSP Server

Public Key Infrastructure (PKI)

Download CRL

CRL

Directory

CA

OCSP

HP Laboratories, Bristol, UK

X509 PKI PKI-enabled Applications Functionality Required: • Cryptographic functionality • Secure storage of Personal Information • Digital Certificate Handling • Directory Access • Communication Facilities Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

X509 PKI Trust and Legal Issues

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

X509 PKI Trust and Legal Issues • Why should I Trust a CA? • How can I determine the liability of a CA?

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

X509 PKI Approaches to Trust and Legal Aspects • Why should I Trust a CA? Certificate Hierarchies, Cross-Certification

• How can I determine the liability of a CA? Certificate Policies (CP) and Certificate Policy Statement (CPS) Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

X509 PKI Approach to Trust Certificate Hierarchies and Cross-Certification Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

CA Technology Evolution CA

CA

CA

CA

RA

CA

CA

CA

Internet

RA

RA

RA

RA

Try to reflect Real world Trust Models Public Key Infrastructure (PKI)

Directory Services

RA

CA

Internet

LRA

LRA

HP Laboratories, Bristol, UK

Simple Certificate Hierarchy Root CA Sub-CAs

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

End entities need to “find” a certificate path to a CA that they trust.

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Trusted Root

Simple Certificate Path 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.

Alice



Bob

Only then can Alice verify that Bob’s certificate is valid and trusted and so verify the Bob’s signature.

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Cross-Certification and Multiple Hierarchies 1 2

1. 2. 3.

3

Multiple Roots Simple cross-certificate Complex cross-certificate Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

X509 PKI Approach to Trust : Problems Things are getting more and more complex if Hierarchies and Cross-Certifications are used Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Trusted Root

Cross-Certification and Trusted Path Discovery Root 3

 Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

X509 PKI Approach to Legal Aspects Certificate Policy And Certificate Practice Statement Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

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 • A CP is usually publicly exposed by CAs, for example on a Web Site (VeriSign, etc.) Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Certificate Policy (CP) POLICY OUTLINE

COMMUNITY & APPLICABILITY RIGHTS, LIABILITIES & OBLIGATIONS

CERTIFICATE & CRL PROFILES

CP IDENTIFICATION & AUTHENTICATION

TECHNICAL OPERATIONAL SECURITY CONTROL REQUIREMENTS

Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Policy Issues (CP) • Liability Issues • • •

Repository Access Controls Confidentiality Requirements Registration Procedures

- Uniqueness of Names - Authentication of Users/Organisations

• • •

Certificate Acceptance Suspension and Revocation (Online/CRL) Physical Security Controls Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Certificate Policy Statement (CPS) • A document that sets out what happens in practice to support the policy statements made in the CP in a PKI • The Certificate Practice Statement (CPS) is a document which may have legal effect in limited circumstances Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Certificate Policy Statement (CPS) INTRODUCTION

SPECIFICATION ADMINISTRATION

GENERAL PROVISIONS IDENTIFICATION & AUTHENTICATION

CPS

CERTIFICATE & CRL PROFILES TECHNICAL SECURITY CONTROLS Public Key Infrastructure (PKI)

OPERATIONAL REQUIREMENTS PHYSICAL, PROCEDURA L& PERSONNEL HP Laboratories, Bristol, UK

IETF (PKIX) Standards • X.509 Certificate and CRL Profiles • PKI Management Protocols • Certificate Request Formats • CP/CPS Framework • LDAP, OCSP, etc. http://www.ietf.org/ Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK

Identity is Not Enough: Attribute Certificates IETF (PKIX WG) is also defining standards for Attribute Certificates (ACs): • Visa Card (Attribute) 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 Public Key Infrastructure (PKI)

HP Laboratories, Bristol, UK