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Evaluation Assurance Level




Reaching a particular EAL is a process that takes time. An unrated product or system, or one with a low EAL rating, may reach a higher ranking after further testing, so these rankings are not precise indicators of their security for these reasons; a high ranking merely shows the ''minimum'' assurance level you can expect from a product or IT system. Operating System s generally called "secure" rarely reach higher rankings than EAL4. Examples of such operating systems are Novell NetWare , SUSE Linux Enterprise Server 9 , and Windows 2000 Service Pack 3.


ASSURANCE LEVELS



EAL1: Functionally Tested


EAL1 is applicable where some confidence in correct operation is required, but the
threats to security are not viewed as serious. It will be of value where independent
assurance is required to support the contention that due care has been exercised with
respect to the protection of personal or similar information.
EAL1 provides an evaluation of the TOE (Target of Evaluation) as made available to the customer, including
independent testing against a specification, and an examination of the guidance
documentation provided. It is intended that an EAL1 evaluation could be successfully
conducted without assistance from the developer of the TOE, and for minimal cost. An
evaluation at this level should provide evidence that the TOE functions in a manner
consistent with its documentation, and that it provides useful protection against
identified threats.


EAL2: Structurally Tested


EAL2 requires the cooperation of the developer in terms of the delivery of design
information and test results, but should not demand more effort on the part of the
developer than is consistent with good commercial practice. As such it should not
require a substantially increased investment of cost or time.
EAL2 is therefore applicable in those circumstances where developers or users require a
low to moderate level of independently assured security in the absence of ready
availability of the complete development record. Such a situation may arise when
securing legacy systems, or where access to the developer may be limited.


EAL3: Methodically Tested and Checked


EAL3 permits a conscientious developer to gain maximum assurance from positive
security engineering at the design stage without substantial alteration of existing sound
development practices.
EAL3 is applicable in those circumstances where developers or users require a moderate
level of independently assured security, and require a thorough investigation of the TOE
and its development without substantial re-engineering.


EAL4: Methodically Designed, Tested and Reviewed


EAL4 permits a developer to gain maximum assurance from positive security
engineering based on good commercial development practices which, though rigorous,
do not require substantial specialist knowledge, skills, and other resources. EAL4 is the
highest level at which it is likely to be economically feasible to retrofit to an existing
product line. EAL4 is therefore applicable in those circumstances where developers or users require a
moderate to high level of independently assured security in conventional commodity
TOEs and are prepared to incur additional security-specific engineering costs.


EAL5: Semiformally Designed and Tested


EAL5 permits a developer to gain maximum assurance from security engineering based
upon rigorous commercial development practices supported by moderate application of
specialist security engineering techniques. Such a TOE will probably be designed and
developed with the intent of achieving EAL5 assurance. It is likely that the additional
costs attributable to the EAL5 requirements, relative to rigorous development without
the application of specialized techniques, will not be large.
EAL5 is therefore applicable in those circumstances where developers or users require a
high level of independently assured security in a planned development and require a
rigorous development approach without incurring unreasonable costs attributable to
specialist security engineering techniques.


EAL6: Semiformally Verified Design and Tested


EAL6 permits developers to gain high assurance from application of security
engineering techniques to a rigorous development environment in order to produce a
premium TOE for protecting high value assets against significant risks.
EAL6 is therefore applicable to the development of security TOEs for application in
high risk situations where the value of the protected assets justifies the additional costs.


EAL7: Formally Verified Design and Tested


EAL7 is applicable to the development of security TOEs for application in extremely
high risk situations and/or where the high value of the assets justifies the higher costs.
Practical application of EAL7 is currently limited to TOEs with tightly focused security
functionality that is amenable to extensive formal analysis.


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