IS/CS 698 Web Services and Authentications Digital Identification

1. IS/CS 698 Web Services and AuthenticationsDigital Identification Min Song

2. A good identification scheme is… • Sound: honest parties can successfully authenticate themselves • Non-transferable • No impersonation • All this is true even when – A large number of authentications are observed

3. Basis of identification • Something known -passwords, PINs, keys… • Something possessed -cards, handhelds… • Something inherent -biometrics

4. Passwords -weak authentication • • Usually fixed • • Stored either in the clear, or “encrypted” text • • Rules reduce the chance of easy passwords • Salt increases search space for a dictionary attack • • Pass phrases -more security

5. Biometric • • Kinds of Biometrics • Images of a person’s face, retina, or iris • Fingerprints • Hand geometry • Footprints and walking style • DNA patterns • Handwriting characteristics • Can be used for both ongoing identification and absolute identification • Advantages: • Under normal circumstances, you can’t lose or forget your biometric • Biometrics can’t readily be shared, copied, or stolen

6. Intranet Extranet Internet Bob Alice Basic Problem Bob and Alice want to exchange data in a digital world. There are Confidence and Trust Issues …

7. Intranet Extranet Internet Alice Bob 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 • INTEGRITY • That information cannot be Disowned • NON-REPUDIATION

8. Starting Point: Cryptography Cryptography Cryptography is a collection of mathematical techniques for protecting information. 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 Encryption Ciphertext Decryption Plaintext &$*£(“!273 Hello World Hello World Key Key

9. 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)

10. Plaintext Encryption Ciphertext Decryption Plaintext Private Key Private Key Cryptographic Algorithms based on Private Key Pros • 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

11. Plaintext Encryption Ciphertext Decryption Plaintext Intranet Extranet Internet Alice’s Private Key Alice’s Public Key Alice Bob Cryptographic Algorithms based on Public Key Pros • Private key is only known by the owner: less risk • The algorithm ensures Integrity and Confidentiality by encrypting with • the Receiver’s Public key

12. Plaintext Encryption Ciphertext Decryption Plaintext Intranet Extranet Internet Bob’s Public Key Bob’s Private Key Alice Bob Cryptographic Algorithms based on Public Key Pros • The algorithm ensures Non-Repudiation by encrypting with • the Sender’s Private key

13. Intranet Extranet Internet Alice Bob Cryptographic Algorithms based on Public Key Cons • 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”? Moving towards PKI …

14. 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 Intranet Extranet Internet Alice Bob

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

16. 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 …

17. 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

18. CERTIFICATE Digital Certificate Issuer Subject Subject Public Key Issuer Digital Signature

19. 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? Moving towards PKI …

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

21. 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

22. 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)

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

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

25. X509 PKI Certificate Authority (CA) • Basic Tasks: • Key Generation • Digital Certificate Generation • Revocation • Key Backup and Recovery System

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

27. Sample X509 Certificates

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

29. 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

30. Online Certificate Status Protocol (OCSP) • An alternative to CRLs • IETF/PKIX standard for a real-time check if a • certificate has been revoked/suspended • Defined in RFC 2560, June 1999 • Returns Good, Revoked or Unknown • Can run over HTTP, SMTP and Other Protocols • Requires a high availability OCSP Server

31. CRL vs OCSP Server 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

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

33. 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 Certificate Policies (CP) and Certificate Policy Statement (CPS)

34. Simple Certificate Hierarchy Root CA 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. Sub-CAs End Entities

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

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

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

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

39. 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.)

40. COMMUNITY & APPLICABILITY POLICY OUTLINE RIGHTS, LIABILITIES & OBLIGATIONS CP CERTIFICATE & CRL PROFILES IDENTIFICATION & AUTHENTICATION TECHNICAL SECURITY CONTROL OPERATIONAL REQUIREMENTS Certificate Policy (CP)