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1.1 Glossary

The following terms are specific to this document:

Active Directory: A general-purpose network directory service. Active Directory also refers to the Windows implementation of a directory service. Active Directory stores information about a variety of objects in the network. Importantly, user accounts, computer accounts, groups, and all related credential information used by the Windows implementation of Kerberos are stored in Active Directory. Active Directory is either deployed as Active Directory Domain Services (AD DS) or Active Directory Lightweight Directory Services (AD LDS). [MS-ADTS] describes both forms. For more information, see [MS-AUTHSOD] section, Lightweight Directory Access Protocol (LDAP) versions 2 and 3, Kerberos, and DNS.

authorization: The secure computation of roles and accesses granted to an identity.

authorization data: An extensible field within a Kerberos ticket, used to pass authorization data about the principal on whose behalf the ticket was issued to the application service.

constrained delegation: A Windows feature used in conjunction with S4U2proxy. This feature limits the proxy services for which the application service is allowed to get tickets on behalf of a user.

domain: A set of users and computers sharing a common namespace and management infrastructure. At least one computer member of the set must act as a domain controller (DC) and host a member list that identifies all members of the domain, as well as optionally hosting the Active Directory service. The domain controller provides authentication (2) of members, creating a unit of trust for its members. Each domain has an identifier that is shared among its members. For more information, see [MS-AUTHSOD] section and [MS-ADTS].

domain controller (DC): The service, running on a server, that implements Active Directory, or the server hosting this service. The service hosts the data store for objects and interoperates with other DCs to ensure that a local change to an object replicates correctly across all DCs. When Active Directory is operating as Active Directory Domain Services (AD DS), the DC contains full NC replicas of the configuration naming context (config NC), schema naming context (schema NC), and one of the domain NCs in its forest. If the AD DS DC is a global catalog server (GC server), it contains partial NC replicas of the remaining domain NCs in its forest. For more information, see [MS-AUTHSOD] section and [MS-ADTS]. When Active Directory is operating as Active Directory Lightweight Directory Services (AD LDS), several AD LDS DCs can run on one server. When Active Directory is operating as AD DS, only one AD DS DC can run on one server. However, several AD LDS DCs can coexist with one AD DS DC on one server. The AD LDS DC contains full NC replicas of the config NC and the schema NC in its forest. The domain controller is the server side of Authentication Protocol Domain Support [MS-APDS].

forwardable: A flag, as specified in [RFC4120] section 2.6, used in an S4U2self KRB_TGS_REQ message to request that the resulting service ticket be marked as forwardable, allowing it to be used in a subsequent S4U2proxy KRB_TGS_REQ message.

Kerberos principal: A unique individual account known to the Key Distribution Center (KDC). Often a user, but it can be a service offering a resource on the network.

key: In cryptography, a generic term used to refer to cryptographic data that is used to initialize a cryptographic algorithm. Keys are also sometimes referred to as keying material.

Key Distribution Center (KDC): The Kerberos service that implements the authentication (2) and ticket granting services specified in the Kerberos protocol. The service runs on computers selected by the administrator of the realm or domain; it is not present on every machine on the network. It must have access to an account database for the realm that it serves. Windows KDCs are integrated into the domain controller role of a Windows Server operating system acting as a Domain Controller. It is a network service that supplies tickets to clients for use in authenticating to services.

KRB_AP_REQ/KRB_AP_REP: The request and response messages used in the Authentication Protocol (AP) exchange.

KRB_AS_REQ/KRB_AS_REP: The request and response messages used in the Authentication Service (AS) Exchange.

KRB_TGS_REQ/KRB_TGS_REP: The request and response messages used in the ticket-granting service (TGS) exchange.

pre-authentication: In Kerberos, a state in which a key distribution center (KDC) demands that the requestor in the Authentication Service (AS) exchange demonstrate knowledge of the key associated with the account. If the requestor cannot demonstrate this knowledge, the KDC will not issue a ticket-granting ticket (TGT) ([RFC4120] sections 5.2.7 and 7.5.2).

principal: An authenticated entity that initiates a message or channel in a distributed system.

privilege attribute certificate (PAC): A Microsoft-specific authorization data present in the authorization data field of a ticket. The PAC contains several logical components, including group membership data for authorization, alternate credentials for non-Kerberos authentication protocols, and policy control information for supporting interactive logon.

realm: A collection of key distribution centers (KDCs) with a common set of principals, as described in [RFC4120] section 1.2.

security principal name (SPN): The name that identifies a security principal (for example, machinename$@domainname for a machine joined to a domain or username@domainname for a user). Domainname is resolved using the Domain Name System (DNS).

service: A process or agent that is available on the network, offering resources or services for clients. Examples of services include file servers, web servers, and so on.

Service for User (S4U): Microsoft-specific extensions to the Kerberos protocol that allow a service to obtain a Kerberos service ticket for a user that has not authenticated to the Key Distribution Center (KDC). S4U includes S4U2proxy and S4U2self.

Service for User to Proxy (S4U2proxy): An extension that allows a service to obtain a service ticket on behalf of a user to a different service.

Service for User to Self (S4U2self): An extension that allows a service to obtain a Kerberos service ticket to itself. The service ticket contains the user's groups and can therefore be used in authorization decisions.

service ticket: A ticket for any service other than the ticket-granting service (TGS). A service ticket serves only to classify a ticket as not a ticket-granting ticket (TGT) or cross-realm TGT, as specified in [RFC4120].

session key: A relatively short-lived symmetric key (a cryptographic key negotiated by the client and the server based on a shared secret). A session key's lifespan is bounded by the session to which it is associated. A session key should be strong enough to withstand cryptanalysis for the lifespan of the session.

ticket: A record generated by the key distribution center (KDC) that helps a client authenticate to a service. It contains the client's identity, a unique cryptographic key for use with this ticket (the session key), a time stamp, and other information, all sealed using the service's secret key. It only serves to authenticate a client when presented along with a valid authenticator.

ticket-granting service (TGS): A service that issues tickets for admission to other services in its own domain or for admission to the ticket-granting service in another domain.

ticket-granting ticket (TGT): A special type of ticket that can be used to obtain other tickets. The TGT is obtained after the initial authentication in the Authentication Service (AS) exchange; thereafter, users do not need to present their credentials, but can use the TGT to obtain subsequent tickets.

MAY, SHOULD, MUST, SHOULD NOT, MUST NOT: These terms (in all caps) are used as defined in [RFC2119]. All statements of optional behavior use either MAY, SHOULD, or SHOULD NOT.

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