Public Key Infrastructures (PKI)jain/cse571-09/ftp/l_12pki.pdf · Public Key Infrastructures (PKI) Raj Jain Washington University in Saint Louis Saint Louis, MO 63130 ... Audio/Video
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PKI, X.509 and PKIXPKI Trust ModelsObject ID and X.509 PoliciesX.500 X.509 Certificate Fields and ExtensionsAuthorizations, Anonymous groups, Blind Signatures
X.509 is the ISO standard for Certificate formatsPKIX is the IETF group on PKIPKIX adopted X.509 and a subset of its optionsPKIX is a "Profile" of X.509TLS, IPSec, SSH, HTTPS, Smartcard, EAP, CableLabs, use X.509
Subject: Whose certificate is it?Target: Whose certificate do we want?Relying Party: Who wants to check the certificateVerifier: Relying PartyIssuer: Who issued the certificate?Certification Authority: IssuerTrust Anchor: The CA that we trustRoot CA: Issuer = SelfPrincipal: Subject, Verifier, Issuer
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 2560Provides current informationSaves traffic on the netAlso allows chaining of OCSP responders
X.500X.500Series of standards covering directory servicesSimilar to white/yellow pagesDirectory Access Protocol (DAP) designed by ISOLightweight Directory Access Protocol (LDAP) designed by IETFLDAPv3 is RFC4510Each entry has a "Distinguished Name" and a set of attributesFormed by combining Relative distinguished namesX.500 Example: C= US, O=WUSTL, OU=CSE, CN=Raj JainDNS Example: [email protected]
X.509 Certificate FieldsX.509 Certificate FieldsVersion: X.509 Version 1, 2, or 3Serial Number: Certificate Serial #Signature: Signing algorithmIssuer:Validity:Subject: Issued toSubject Public Key Info: Algorithm/parameters, and Public KeyIssuer Unique Identifier: OID of the Issuer (not used)Subject Unique Identifier: OID of the subject (not used)Algorithm Identifier: Signature algorithm (again)Encrypted: SignatureExtensions: Only in Version 3. Specified by OID
X.509 ExtensionsX.509 ExtensionsAuthority Key Identifier: Serial # of CA's keySubject 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 PoliciesPolicy Mappings: from Issuer's domain to subject's domainSubject Alt Name: Alternative name. DNS.Subject Directory Attributes: Other attributes
Basic Constraints: Whether CA and length of chainName Constraints: Permitted and excluded subtreesPolicy Constraints: OIDsExtended Key Usage: Additional key usagesCRL Distribution Points:Inhibit Any Policy: “Any Policy” is not allowedFreshest CRL: How to obtain incremental CRLsAuthority Info Access: How to find info on issuersSubject Info Access: How to find info on subject
X.509 CRL FieldsX.509 CRL FieldsSignature: Signature Algorithm for this CRLIssuer: X.500 name of issuing CAThis Update: Time of this CRLNext Update: Time next CRL will be issuedFor each revoked Certificate:
User Certificate:Serial Number of revoked CertificateRevocation Date:CRL Entry Extensions: Reason code, etc.
CRL Extensions: optional informationAlgorithm Identifier: Repeat of signatureEncrypted: Signature
User could authenticate to group serverCertificate ⇒ the owner of the private key is a member of groupUser will need lots of public/private key pairsGroup servers need not know key/member associationGroup server can do a blind signature
Client wants server to sign a certificate CServer's public key is <e, n>Client picks a random number R and computes C(Re mod n)Server decrypts it with his private key Cd (Red) mod n = CdRClient just divides by R and gets Cd = Certificate signed by server
PKIX is a profile of the X.509 PKI standardBrowsers have a built-in list of root CAs⇒ OligarchyX.509 uses X.500 names. DNS names in Alternate Name field.X.509 policies are specified using OIDs.OCSP is used to check revocationAuthorization is best done by user, group, role levelAnonymous group certification is possible. Blind signatures allow even the group server to not know the public key