Autumn 2008 1 TM8104 IT Security Evaluation Guide on the production of Protection Profiles Reference: ISO/IEC TR 15446 Information technology - Security techniques - Guide on the production of protection profiles and security targets (Editor’s Report)
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1 Autumn 2008 TM8104 IT Security Evaluation Guide on the production of Protection Profiles Reference: ISO/IEC TR 15446 Information technology - Security.
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Autumn 20081 TM8104 IT Security Evaluation
Guide on the production of Protection Profiles
Reference: ISO/IEC TR 15446 Information technology - Security techniques - Guide on the production of protection profiles and security targets (Editor’s Report)
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Outline
Introduction
The Protection Profile (PP)
The development process
Guidance on producing a Protection Profile
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Definitions and abbreviations
DBMS – Database Management System
EAL – Evaluation Assurance Level
ISO/IEC 15408 – ”Common Criteria”
OSP – Organisational Security Policies
PP – Protection Profile
SAR – Security Assurance Requirements
SFR – Security Functional Requirements
SOF – Strength of Function
ST – Security Target
TOE – Target of Evaluation
TTP – Trusted Third Party
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Introduction
The purpose of a Protection Profile (PP) is to state a security problem rigorously for a given collection of systems or product – known as Target of Evaluation (TOE) – and to specify implementation-independent security requirements to address that issue.
The Guide provides detailed guidance relating to the various parts of a PP or ST, and how they interrelate.
This presentation, will focus on Protection Profiles and NOT Security Targets. However, the guidance for a ST is very similar to the PP guidance.
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The Protection Profile (PP)
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The development process
PPs are often developed in a logical ”top-down” manner1. identify the security concerns2. state the security objectives3. develop the IT security requirements
During an iterative development process, new requirements might surface, due to:
- new threats may be identified- organisational security policies may change- cost and time constraints may impose changes in division of responsibility between the TOE and its environment- changes in intended attack potential
The TOE might be an already developed type of product –> ”bottom-up” approach.
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The Protection Profile (PP)
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The TOE security environment
Purpose: ”define the nature and scope of the definition of the environment in which the TOE is intended to be used and the manner in which it is expected to be employed”
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Identify and specify the assumptions
”What assumptions can be made about the TOE security environment and the scope of the security concerns?”
• Aspects relating to the intended usage of the TOE
• Environmental protection of any part of the TOE
• Connectivity aspects
• Personal aspects
It is unlikely that you will completely identify all assumptions in a single attempt!
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The TOE security environment
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Identify and specify the threats
ISO/IEC 15408: the PP must contain a description of any threat to the asset against which protection will be required
However the statement of threats may be omitted if the security objectives is derived solely from the OSP and assumptions
Risk analysis may be/is an important tool!
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Identifying the threats
Definition of ”threat” (ISO/IEC 15408):an undesirable event, which is characterised in terms of a threat agent, a presumed attack method, any vulnerabilities that are the foundation for the attack and identification of the asset under attack
We need to identify- the assets- the threat agents- the attack methods
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Identifying the assets
Definition of ”assets” (ISO/IEC 15408):information and resources to be protected by the countermeasures of a TOE
Assets typically take the form of information which is stored, processed and transmitted by IT-systems
Assets may be external to the TOE (eg. firewalls)
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Identifying the threat agents
Threat agents may either be human or non-human
To identify a human threat agent, consider:
• who might want to compromise the assets and for what reasons
• who could gain access to the IT-system
• their possible level of technical expertise, opportunities, resources and motivation
Non-human sources of threats and threats arising from human sources unintentionally should also be considered.
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Identifying the attack methods
Will be based on knowledge about the TOE security environment
Potential vulnerabilities to the assets which a threat agent could exploit
The capabilities of attackers who have access to the TOE security environment
A vulnerability analysis of the TOE security environment can be useful. However, it may not identify all vulnerabilities.
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Risk analysis
Risk analysis may be helpful for threat identification.
Such methods may consider the probability and consequence of compromise of the assets, taking into account:- the possible attack methods identified- the likelihood of the attack to succeed- the consequences of any damage that may be caused
Other constraints, eg. legal requirements and cost
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Specifying the threats 1 (2)
The specification of threats in a PP should be clear:- include the threat agent- include the asset subject to the attack- include the attack method employed
Eg: An authorised user of the TOE might gain unauthorized access to information by impersonating another authorised user
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The specification of threats in a PP should be concise:
– the threat descriptions should be disjoint– specify all threats at the same level of detail– each threat should be unique labelled for ease of
reference
Specifying the threats 2 (2)
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Completing the statement of threats
The threats that are of principal interest are those that will be countered by the TOE
However, for completeness, the PP may need to include some threats that are not adressed by the TOE, eg:
- physical attack against the TOE- abuse of trust by highly privileged users- improper administration and operation of the TOE
The PP author can choose whether to include these in the enviromental assumptions or in the statement of threats
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The TOE security environment
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Identify and specify the Organisational Security Policies (OSP)
An OSP is defined as one or more rules, procedures and practices imposed by an organisation
The OSP may be omitted if the security objectives are derived soley from the threats and assumptions
Or a combination can be used (but be careful not to restate the same threats)
General rule: • Specify OSPs where the TOE is intended for use by a specific type
of organisation• There is a need for the TOE to implement a set of rules that cannot
be sensibly included within or implied by a threat description (eg. identification of acces control rules or information flow control rules)
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The Protection Profile (PP)
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The security objectives
The security objectives provide a concise statement of the intended response to the security problem
• Security objectives for the TOE• Security objectives for the environment
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Security objectives for the TOE (1)
...states what the responsibility of the TOE is in countering the threats and in supporting the OSP.
• The security objective is intended to be concise. To ”reach” an appropriate level of detail, you need a strict balance between:
• The security objectives for the TOE should be implementation-independent
• Ensure that the defined security objectives do not just repeat the information contained within the threats and the OSP
When you construct the rationale for the security objectives and the IT security requirements, you will see if you have succeeded.
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Security objectives for the TOE (2)
Three types of security objective can be identified to address the identified threats:
• preventive objectives (prevent or limit threats)• detective objectives (detect and monitor events)• corrective objectives (take action on undesirable events)
An example of a preventive security objective is:
The TOE will ensure that each user is uniquely identified and that the claimed identity is authenticated, before the user is granted accesss to the TOE facilities.
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Security objectives for the environment (1)
...will have to be identified to address those aspects of security concerns that the TOE will not (or cannot) be expected to do
• counter threats that are not countered by the TOE• help satisfy OSPs that are not fully satisfied by the TOE• ensure that the environmental assumptions are satisfied
Eg. non-IT security objective for the environment:• objectives for education and training of administrators and users
Eg. IT security objective for the environment:• a security objective for an underlying operating system to
identify and authenticate TOE users.
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Security objectives for the environment (2)
An appropriate starting point would be to compile a list of security objectives by taking each threat, OSP and assumption that is not fully addressed by the TOE and
Add a new security objective for the environment , orIf an appropriate one already has been identified, map an
existing security object to that aspect
The list should be redefined when you formulate the security objectives rationale.
The statement of security objective should be reviewed to ensure that the division of responsibilities between the TOE and its environment is appropriate.
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The Protection Profile (PP)
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The security requirements
SFR – identify the requirements for security functions which the TOE must provide to ensure that its security objectives are achieved
SAR – identify the required level of assurance in the implementation of the SFRs
SR IT-environment – define any functional and assurance requirements to be satisfied by the IT-environment (optional)
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Security functional requirements
Having defined the security objectives for the TOE in response to the identified security concerns, you need to elaborate how these security objectives are met. This is done by selecting appropriate SFR at a component level.
In the selection process it will be helpful to distinguish between
principal SFRs – which directly satisfies the identified security objectives for the TOE
supporting SFRs – to provide support for the principal SFRs
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Selecting SFRs
For each security objective for the TOE, identify the principle SFRs which directly satisfy them
Once a complete set of principle SFRs has been establish, an iterative process is used to identify a complete set of supporting SFRs.
All SFRs should (where possible) be expressed using functional components from Part 2 of ISO/IEC 15408.
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Identifying supporting SFRs
Three stages when identifying the complete set of supporting SFRsIdentify the additional SFRs needed to satisfy the dependencies of all
principal SFRsIdentify any additional SFRs that are necessary to ensure that the security
objectives for the TOE are achievedIdentify the SFRs needed to satisfy the dependencies of those supporting
SFRs selected during stage 2 and 3 (?)
This is usually an iterative process!
Eg. The PP includes a security objective for the TOE to response on detection of events indicating security violation
a principal SFR based on FAU_ARP.1 (Security Alarms) component FAU_ARP.1 has a dependency on FAU_SAA.1 (Potential Violation
Analysis) which should also be included as a supporting SFRFAU_SAA.1 has a dependency on FAU_GEN.1 (Audit Data Generation)and so on.......
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Operations on SFRs
Permitted operations on SFRs:
Assignment – specification of an identified parameter
Iteration – multiple use of the same functional component to express different requirements
Selection – specification of one or more elements from a given list
Refinement – addition of details to the security requirements
For ”assignment” and ”selection” the guidance suggest that the operations should be partially completed.
The ”iteration” can be used where the clarity of the PP can be enhanched, eg. to break down a complex SFR into distinct functional requirements
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Additional advices on SFRs
The guide also give advices on:
How to specify audit requirements
How to specify management requirements
How to specify SOF (Strength of Function)
How to specify SFRs not included in part 2 of ISO/IEC 15408
and so on....
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Security Assurance Requirements
The selection of SARs will require the balancing if several factors, e.g:
the value of the assets to be protected and the perceived risk of compromising those assets
technical feasability
likely development and evaluation costs
perceived market requirement (in the case of products)
The selection of the SARs will be relatively straight-forward if choosing an appropriate assurance packet (eg. an EAL). It is possible to include augmented SARs to the packet in order to ensure that the security objectives are satisfied.
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Additional advices on SARs
The guide also gives advices on:
How to perform operations on SARs (iterations and refinements)
How to specify SARs not included in Part 3 of ISO/IEC 15408 in a PP
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Security requirements on the environment
.. for meeting the security objectives for the environment.
SR on the IT environment.These should be specified, where feasible, using ISO/IEC 15408 functional and assurance components
SR for the non-IT environment (optional).
The guidance did not provide any clear advices (at least to me) on this topic...
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The Protection Profile (PP)
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PP rationale
Purpose:
” to demonstrate that a conformant TOE provides an effective set of IT security countermeasures within the TOE security environment”
Security objectives rationale
Security requirements rationale
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Security objectives rationale
First, show that the security objectives are necessary by (eg):Cross-reference the threats, OSPs and assumptions against the security
objectives which are intended to adress them. It should be evident thatEach security objective covers at least one threat, OSP or asumptionEach threat, OSP and assumption is covered by at least one securty
objective
Secondly, demonstrate that the security objectives are sufficient to meet the security concerns by providing informal arguments to supplement the cross-reference information
For each threat, give informal arguments why the identified security objectives will provide for effective countermeasures (detected and recovered, prevented or reduced) towards the threats
Similarily, for each identified OSP or assumption, give informal arguments…
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Security requirements rationale
Show that the IT security requirements (in particular the SFRs) are suitable to meet the identified security objectives and thereby address the security concerns.
As with the security objectives, you need to demonstrate that the security requirements are both necessary and sufficient.
Cross-reference each security objective for the TOE against the SFR which satisfies it and check that- each SFR addresses at least one security objective- each security objective for the TOE is adressed by at least one SFR
Supplement the cross reference-information with informal arguments for the sufficiency.
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Security requirements rationale
We also need to show that the assurance requirements (SAR) are appropriate for the TOE, ie:
sufficient to address the security objectives and thus meet the security concerns
not excessive (given the statement of security objectives/concerns)attainable (it should be technically feasible for the TOE to attain the
defined assurance requirements)
You also have to show that:The strength of functions (SOF) are appropriateThe security requirements (in particular the SFRs) are mutually
supportiveThe assurance measures satisfy the assurance requirements
(SAR)The IT security functions satisfy the SFRs
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The guide also includes
PPs for composite and component TOEs
Functional packages
Assurance packages
Appendices- A summary in form of a checklist- Example threats, OSPs, assumptions and security objectives and identifies appropriate ISO/IEC 15408 functional components- Special guidance for PPs which implement cryptographic functionality- Application of the guidance in various of contexts, using worked examples for different types of TOE (firewall, DBMS, TTP)