Security service is a service, provided by a layer of communicating open systems, which ensures adequate security of the systems or of data transfersX.800 : Security architecture for Open Systems Interconnection for CCITT applications
/ref> as defined by

ITU-T The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is one of the three Sectors (branches) of the International Telecommunication Union (ITU). It is responsible for coordinating Standardization, standards fo ...

X.800 Recommendation.
X.800 and

ISO The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. Me ...

7498-2 (Information processing systems – Open systems interconnection – Basic Reference Model – Part 2: Security architecture) are technically aligned. This model is widely recognized William Stallings Crittografia e sicurezza delle reti Seconda edizione Traduzione Italiana a cura di Luca Salgarelli di Cryptography and Network security 4 edition Pearson 2006 Securing information and communications systems: principles, technologies, and applications Steven Furnell, Sokratis Katsikas, Javier Lopez, Artech House, 2008 - 362 pages A more general definition is in CNSS Instruction No. 4009 dated 26 April 2010 by Committee on National Security Systems of

United States of America The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 states and a federal capital district, Washington, D.C. The 48 contiguo ...

:CNSS Instruction No. 4009
dated 26 April 2010 :''A capability that supports one, or more, of the security requirements (Confidentiality, Integrity, Availability). Examples of security services are key management, access control, and authentication.'' Another authoritative definition is in

W3C The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working together in ...

Web service A web service (WS) is either: * a service offered by an electronic device to another electronic device, communicating with each other via the Internet, or * a server running on a computer device, listening for requests at a particular port over a n ...

Glossary adopted by

NIST The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical s ...

SP 800-95: : ''A processing or communication service that is provided by a system to give a specific kind of protection to resources, where said resources may reside with said system or reside with other systems, for example, an authentication service or a PKI-based document attribution and authentication service. A security service is a superset of AAA services. Security services typically implement portions of security policies and are implemented via security mechanisms.''

Basic security terminology

Information security Information security is the practice of protecting information by mitigating information risks. It is part of information risk management. It typically involves preventing or reducing the probability of unauthorized or inappropriate access to data ...

and

Computer security Computer security (also cybersecurity, digital security, or information technology (IT) security) is a subdiscipline within the field of information security. It consists of the protection of computer software, systems and computer network, n ...

are disciplines that are dealing with the requirements of

Confidentiality Confidentiality involves a set of rules or a promise sometimes executed through confidentiality agreements that limits the access to or places restrictions on the distribution of certain types of information. Legal confidentiality By law, la ...

Integrity Integrity is the quality of being honest and having a consistent and uncompromising adherence to strong moral and ethical principles and values. In ethics, integrity is regarded as the honesty and Honesty, truthfulness or of one's actions. Integr ...

, Availability, the so-called CIA Triad, of information asset of an organization (company or agency) or the information managed by computers respectively. There are threats that can attack the resources (information or devices to manage it) exploiting one or more vulnerabilities. The resources can be protected by one or more countermeasures or security controls. So security services implement part of the countermeasures, trying to achieve the security requirements of an organization.

Basic OSI terminology

In order to let different devices (computers, routers, cellular phones) to communicate data in a standardized way,

communication protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any variation of a physical quantity. The protocol defines the rules, syntax, semantics (computer science), sem ...

s had been defined. The

organization published a large set of protocols. The general architecture of these protocols is defined in recommendation X.200.X.200 : Information technology - Open Systems Interconnection - Basic Reference Model: The basic model
/ref> The different means (air, cables) and ways (protocols and protocol stacks) to communicate are called a communication network. Security requirements are applicable to the information sent over the network. The discipline dealing with security over a network is called Network security.Simmonds, A; Sandilands, P; van Ekert, L (2004). "An Ontology for Network Security Attacks". Lecture Notes in Computer Science 3285: 317–323 The X.800 Recommendation: #provides a general description of security services and related mechanisms, which may be provided by the

Reference Model A reference model—in systems engineering, systems, enterprise engineering, enterprise, and software engineering—is an abstract framework or domain-specific ontology (information science), ontology consisting of an interlinked set of clearly defi ...

; and #defines the positions within the Reference Model where the services and mechanisms may be provided. This Recommendation extends the field of application of Recommendation X.200, to cover secure communications between open systems. According to X.200 Recommendation, in the so-called OSI Reference model there are 7 layers, each one is generically called N layer. The N+1 entity ask for transmission services to the N entity. At each level two entities (N-entity) interact by means of the (N) protocol by transmitting Protocol Data Units (PDU). Service Data Unit (SDU) is a specific unit of data that has been passed down from an OSI layer, to a lower layer, and has not yet been encapsulated into a PDU, by the lower layer. It is a set of data that is sent by a user of the services of a given layer, and is transmitted semantically unchanged to a peer service user . The PDU at any given layer, layer 'n', is the SDU of the layer below, layer 'n-1'. In effect the SDU is the 'payload' of a given PDU. That is, the process of changing a SDU to a PDU, consists of an encapsulation process, performed by the lower layer. All the data contained in the SDU becomes encapsulated within the PDU. The layer n-1 adds headers or footers, or both, to the SDU, transforming it into a PDU of layer n-1. The added headers or footers are part of the process used to make it possible to get data from a source to a destination.

OSI security services description

The following are considered to be the security services which can be provided optionally within the framework of the OSI Reference Model. The authentication services require authentication information comprising locally stored information and data that is transferred (credentials) to facilitate the authentication: ;Authentication :These services provide for the authentication of a communicating peer entity and the source of data as described below. :;Peer entity authentication ::This service, when provided by the (N)-layer, provides corroboration to the (N + 1)-entity that the peer entity is the claimed (N + 1)-entity. :; Data origin authentication ::This service, when provided by the (N)-layer, provides corroboration to an (N + 1)-entity that the source of the data is the claimed peer (N + 1)-entity. ;Access control :This service provides protection against unauthorized use of resources accessible via OSI. These may be OSI or non-OSI resources accessed via OSI protocols. This protection service may be applied to various types of access to a resource (e.g., the use of a communications resource; the reading, the writing, or the deletion of an information resource; the execution of a processing resource) or to all accesses to a resource. ;Data confidentiality :These services provide for the protection of data from unauthorized disclosure as described below :;Connection confidentiality ::This service provides for the confidentiality of all (N)-user-data on an (N)-connection :;''Connectionless confidentiality'' ::This service provides for the confidentiality of all (N)-user-data in a single connectionless (N)-SDU :;Selective field confidentiality ::This service provides for the confidentiality of selected fields within the (N)-user-data on an (N)-connection or in a single connectionless (N)-SDU. :; Traffic flow confidentiality ::This service provides for the protection of the information which might be derived from observation of traffic flows. ; Data integrity :These services counter active threats and may take one of the forms described below. :;Connection integrity with recovery ::This service provides for the integrity of all (N)-user-data on an (N)-connection and detects any modification, insertion, deletion or replay of any data within an entire SDU sequence (with recovery attempted). :;Connection integrity without recovery ::As for the previous one but with no recovery attempted. :;Selective field connection integrity ::This service provides for the integrity of selected fields within the (N)-user data of an (N)-SDU transferred over a connection and takes the form of determination of whether the selected fields have been modified, inserted, deleted or replayed. :;Connectionless integrity ::This service, when provided by the (N)-layer, provides integrity assurance to the requesting (N + 1)-entity. This service provides for the integrity of a single connectionless SDU and may take the form of determination of whether a received SDU has been modified. Additionally, a limited form of detection of replay may be provided. :;Selective field connectionless integrity ::This service provides for the integrity of selected fields within a single connectionless SDU and takes the form of determination of whether the selected fields have been modified. ; Non-repudiation :This service may take one or both of two forms. :;Non-repudiation with proof of origin ::The recipient of data is provided with proof of the origin of data. This will protect against any attempt by the sender to falsely deny sending the data or its contents. :; Non-repudiation with proof of delivery ::The sender of data is provided with proof of delivery of data. This will protect against any subsequent attempt by the recipient to falsely deny receiving the data or its contents.

Specific security mechanisms

The security services may be provided by means of security mechanism: * Encipherment * Digital signature *

Access control In physical security and information security, access control (AC) is the action of deciding whether a subject should be granted or denied access to an object (for example, a place or a resource). The act of ''accessing'' may mean consuming ...

Data integrity Data integrity is the maintenance of, and the assurance of, data accuracy and consistency over its entire Information Lifecycle Management, life-cycle. It is a critical aspect to the design, implementation, and usage of any system that stores, proc ...

* Authentication exchange * Traffic padding * Routing control * Notarization The table1/X.800 shows the relationships between services and mechanisms Some of them can be applied to connection oriented protocols, other to connectionless protocols or both. The table 2/X.800 illustrates the relationship of security services and layers:

Other related meanings

Managed security service

Managed security service (MSS) are network security services that have been outsourced to a service provider.

References

External links

* {{usurped,
Term in FISMApedia
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List of ITU-T Security Activities and Publications
Computer network security Network protocols ITU-T recommendations ITU-T X Series Recommendations ISO standards