Keywords: Brewer, Chinese Wall, COI, CWSP, Nash, policy
Article : [PDF]
The Brewer and Nash1 model was constructed to provide information security access controls that can change dynamically. This security model, also known as the Chinese wall model was designed to provide controls that mitigate Conflict Of Interest (COI) in commercial organizations, and is built upon an information flow model.
In the Brewer and Nash Model, no information can flow between the subjects and objects in a way that would create a conflict of interest. This security policy was proposed initially to capture certain requirements in UK’s financial sector.
It is a real commercial policy which can be formally modeled. Its basic idea is to keep company information confidential and prevent it from unauthorized access of consulting services.
This model, similar to the Bell-LaPadula model, allows dynamically changing permissions based on rule based assess control (based on a user’s past activity). In this model, we have a wall, which segregates data types and we have a set of rules that determine what subjects can access on the other side of the wall. These dynamic rules can change as the user accesses different information.
It is based on the information flow model, where no information can flow between subjects and objects in a way that would result in a conflict of interest. The model states that a subject can write to an object if, and only if, the subject can not read another object that is in a different data set.
This model combines elements of Discretionary Access Control (DAC) and Mandatory Access Control MAC but initially Brewer and Nash formalized the Chinese Wall policy in terms of a mandatory computer security model.
The Chinese Wall policy
The chinese wall policy builds on three level of abstraction :
- Objects: contain information about only one company (for example : files)
- Company groups: collect all objects concerning a particular company
- Conflict classes: cluster the groups of objects for competing
The essentials elements are :
- Subjects: Active entities accessing protected objects
- Objects: Data organized according to 3 levels (Information; DataSet; Conflict-of-Interest (CoI) classes)
- Access Rules: Read rule, Write rule
- Read Rule: Subject S can read object O only if O is from the same company information as some object read by S, or O belongs to a COI class within which S has not read any object.
- Write Rule: Subject S can write object O only if S can read O by the Brewer-Nash Read rule, and no object can be read which is in different company dataset to the one for which write access is requested.
The Chinese Wall Policy is a combination of free choice and mandatory control. Initially a subject is free to access any object it wishes. Once the initial choice is made, a Chinese Wall is created for that user around the dataset to which the object belongs.
- Dynamically assembles ACLs based on the objects that a subject accesses
- Is built upon an information flow model
- Restricts information from flowing in a way that would create a conflict of interest.
In this model, a subject with access to one company’s data is not allowed to access a competitor’s data.
Model improvements and variants
The Chinese Wall policy was first introduced by Brewer and Nash in 1989 .
The same year, Lin  announced a new model (ACWSP: Aggressive Chinese Wall Security Policy) to fix the errors of the Brewer-Nash model. The error being that the conflict of interest is a binary relation conflict of interest, and not an equivalence class (partitions).
In 1990, Meadows  published an extension of the Brewer-Nash Model to a Multilevel Context.
In 1992, Foley  proposed a variety of approaches for implementing Chinese Wall policies using multilevel techniques.
In 1992 and 1993, Sandhu  , improved upon this model by making a clear distinction between users, principals, and subjects, defines a lattice-based security structure, and shows how the Chinese Wall Policy complies with the Bell-Lapadula model (which was erroneously indicated not feasible in the Brewer-Nash initial model).
In 1996, Foley  proposed solutions to the implementation of a wide variety of different security policies in Unix with the set-user-id facility including the chinese wall policy.
In 2001, Atluri et al.  proposed an updated model for Decentralized Workflow Systems.
In 2002, Lin  published an analysis of Symmetric Binary Relations in the context of the Chinese Wall model.
In 2003, Lin  updated the ACWSP, specially with the notion of granulation.
In 2003, Hung  proposed solutions to apply the Chinese Wall policy to Web services.
In 2004, Minsky  proposed and updated model for a decentralized treatment of a highly Distributed chinese wall policy.
In 2004, Atluri et al.  proposed a decentralized control of workflows called Decentralized workflow Chinese wall security model.
In 2005, Loock and Eloff  proposed a new model of Chinese Wall Security Policy model, for a data mining environment.
In 2007, Lin provided  a short proof of a revisited version of the chinese wall.
In 2007, Kapadia et al.  proposed a discretionary access control framework based on the chinese wall model, but for distributed environments
In 2009, Gupta  proposed and update of the Chinese wall model for cloud computing.
In 2013, a less restrictive Chinese Wall policy was proposed by Sharifi and Tripunitara .
In 2015, Fehis et al.  proposed a new chinese wall security policy model based on the subject’s wall and object’s wall
In 2015, Crampton and Sellwood  proposed The relationships, paths and principal matching model (RPPM) that supports separation of duty and Chinese Wall.
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