Security service is a service, provided by a layer of communicating open systems, which ensures adequate security of the systems or of data transfers as defined by ITU-T X.800 Recommendation.
X.800 and ISO 7498-2 (Information processing systems – Open systems interconnection – Basic Reference Model – Part 2: Security architecture) are technically aligned. This model is widely recognized
Contents
- Basic security terminology
- Basic OSI terminology
- OSI Security Services General description
- Specific security mechanisms
- Managed Security Service
- References
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:
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 Web service Glossary adopted by NIST 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 and Computer security are disciplines that are dealing with the requirements of Confidentiality, Integrity, 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 protocols had been defined.
The ITU-T organization published a large set of protocols. The general architecture of these protocols is defined in recommendation X.200.
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.
The X.800 Recommendation:
- provides a general description of security services and related mechanisms, which may be provided by the Reference Model; 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 General 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:
Specific security mechanisms
The security services may be provided by means of security mechanism:
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:
Managed Security Service
Managed Security Service (MSS) are network security services that have been outsourced to a service provider.