Public Key Infrastructures PKI Raj Jain Washington University in Saint Louis Saint Louis MO 63130 Jain cse wustl edu Audio Video recordings of this lecture are available at http www cse wustl edu jain cse571 07 Washington University in St Louis CSE571S 12 1 2007 Raj Jain Overview PKI X 509 and PKIX PKI Trust Models Object ID and X 509 Policies X 500 X 509 Certificate Fields and Extensions Authorizations Anonymous groups Blind Signatures Washington University in St Louis CSE571S 12 2 2007 Raj Jain What is PKI Infrastructure to find public keys S MIME PGP SSL use asymmetric cryptography and make use of PKI Certificate authorities Standards for certificates Washington University in St Louis CSE571S 12 3 2007 Raj Jain X 509 and PKIX X 509 is the ISO standard for Certificate formats PKIX is the IETF group on PKI PKIX adopted X 509 and a subset of its options PKIX is a Profile of X 509 TLS IPSec SSH HTTPS Smartcard EAP CableLabs use X 509 Washington University in St Louis CSE571S 12 4 2007 Raj Jain Concepts Subject Whose certificate is it Target Whose certificate do we want Relying Party Who wants to check the certificate Verifier Relying Party Issuer Who issued the certificate Certification Authority Issuer Trust Anchor The CA that we trust Root CA Issuer Self Principal Subject Verifier Issuer Washington University in St Louis CSE571S 12 5 2007 Raj Jain PKI Trust Models How Many CAs Monopoly One Oligarchy Many Anarchy Any How is the name space divided among CAs Top Down Bottom Up Washington University in St Louis CSE571S 12 6 2007 Raj Jain Monopoly Model Single Root CA CA Registrars to check identity Delegated CAs CA CA Issues Single point of failure Whole world cannot trust just one organization You may not want internal principals to be certified by external CA Washington University in St Louis CSE571S 12 7 2007 Raj Jain Oligarchy CA CA CA CA CA CA CA CA CA Multiple Root CA s Used in browsers Can select which root CA s to trust No Monopoly Price efficient Washington University in St Louis CSE571S 12 8 2007 Raj Jain Oligarchy Example Washington University in St Louis CSE571S 12 9 2007 Raj Jain Anarchy Model U1 U2 U6 U3 U5 U4 User driven Used in PGP Trust Ring Web of Trust Volunteer Databases Washington University in St Louis CSE571S 12 10 2007 Raj Jain Name Constraints Which part of name space 1 Top Down 2 Bottom Up Two way certification Parent Child Child Parent Cross links Washington University in St Louis CSE571S 12 11 2007 Raj Jain Relative Names A B D C E F G HIJKLMNO H to J Absolute D B E J or A B E J Relative E J No changes required if the parents change name Washington University in St Louis CSE571S 12 12 2007 Raj Jain OID Object Identifier Identify objects by a universally unique sequence of numbers Similar to what is done in SNMP to name objects Washington University in St Louis CSE571S 12 13 2007 Raj Jain Global Naming Hierarchy SNMP ccitt 0 iso 1 joint iso ccitt 2 standard 0 org 3 iso9314 9314 dod 6 fddiMIB 1 internet 1 directory 1 mgmt 2 experimental 3 private 4 mib 1 transmission 10 fddimib 73 system 1 interfaces 2 Washington University in St Louis fddi 8 CSE571S 12 14 fddi 15 2007 Raj Jain X 509 Policies Policies in X 509 are identified by OID Company X X 1 Security Level X 1 1 Confidential X 1 2 Secret X 1 3 Public Washington University in St Louis CSE571S 12 15 2007 Raj Jain X 509 Revocations Certificate Revocation Lists Too much work on the client Too much traffic on the net Not used On Line Revocation Server OLRS On line Certificate Status Protocol OCSP RFC 2560 Provides current information Saves traffic on the net Also allows chaining of OCSP responders Washington University in St Louis CSE571S 12 16 2007 Raj Jain X 500 Series of standards covering directory services Similar to white yellow pages Directory Access Protocol DAP designed by ISO Lightweight Directory Access Protocol LDAP designed by IETF LDAPv3 is RFC4510 Each entry has a Distinguished Name and a set of attributes Formed by combining Relative distinguished names X 500 Example C US O WUSTL OU CSE CN Raj Jain DNS Example jain cse wustl edu Washington University in St Louis CSE571S 12 17 2007 Raj Jain X 509 Certificate Fields Version X 509 Version 1 2 or 3 Serial Number Certificate Serial Signature Signing algorithm Issuer Validity Subject Issued to Subject Public Key Info Algorithm parameters and Public Key Issuer Unique Identifier OID of the Issuer not used Subject Unique Identifier OID of the subject not used Algorithm Identifier Signature algorithm again Encrypted Signature Extensions Only in Version 3 Specified by OID Washington University in St Louis CSE571S 12 18 2007 Raj Jain X 509 Extensions Authority Key Identifier Serial of CA s key Subject Key Identifier Uniquely identifies the subjects key Serial or hash Key Usage Allowed usage email business Private Key Usage Period Timestamps for when key can be used similar to validity Certificate Policies Policy Mappings from Issuer s domain to subject s domain Subject Alt Name Alternative name DNS Subject Directory Attributes Other attributes Washington University in St Louis CSE571S 12 19 2007 Raj Jain X 509 Extensions Cont Basic Constraints Whether CA and length of chain Name Constraints Permitted and excluded subtrees Policy Constraints OIDs Extended Key Usage Additional key usages CRL Distribution Points Inhibit Any Policy Any Policy is not allowed Freshest CRL How to obtain incremental CRLs Authority Info Access How to find info on issuers Subject Info Access How to find info on subject Washington University in St Louis CSE571S 12 20 2007 Raj Jain Sample X 509 Certificate Internet Explorer Washington University in St Louis CSE571S 12 21 2007 Raj Jain X 509 Sample Cont Washington University in St Louis CSE571S 12 22 2007 Raj Jain X 509 CRL Fields Signature Signature Algorithm for this CRL Issuer X 500 name of issuing CA This Update Time of this CRL Next Update Time next CRL will be issued For each revoked Certificate User Certificate Serial Number of revoked Certificate Revocation Date CRL Entry Extensions Reason code etc CRL Extensions optional information Algorithm Identifier Repeat of signature Encrypted Signature Washington University in St Louis CSE571S 12 23 2007 Raj Jain Entrusted Certificates Washington University in St Louis CSE571S 12 24 2007 Raj Jain Authorizations Access Control Lists List of users Groups User provides certificate of membership Role User provides credentials Washington University in St Louis CSE571S 12 25 2007 Raj Jain