You have been approached by one of your clients . They are interested in doing some security re-engineering . The client is looking at various information security models. It is a highly secure environment where data at high classifications cannot be leaked to subjects at lower classifications . Of primary concern to them, is the identification of potential covert channel. As an Information Security Professional , which model would you recommend to the client?
Correct Answer: A
Securing the data manipulated by computing systems has been a challenge in the past years. Several methods to limit the information disclosure exist today, such as access control lists, firewalls, and cryptography. However, although these methods do impose limits on the information that is released by a system, they provide no guarantees about information propagation. For example, access control lists of file systems prevent unauthorized file access, but they do not control how the data is used afterwards. Similarly, cryptography provides a means to exchange information privately across a non-secure channel, but no guarantees about the confidentiality of the data are given once it is decrypted.
In low level information flow analysis, each variable is usually assigned a security level. The basic model comprises two distinct levels: low and high, meaning, respectively, publicly observable information, and secret information. To ensure confidentiality, flowing information from high to low variables should not be allowed. On the other hand, to ensure integrity, flows to high variables should be restricted.
More generally, the security levels can be viewed as a lattice with information flowing only upwards in the lattice.
Noninterference Models This could have been another good answer as it would help in minimizing the damage from covert channels.
The goal of a noninterference model is to help ensure that high-level actions (inputs) do not determine what low-level user s can see (outputs ) . Most of the security models presented are secured by permitting restricted ows between high- and low-level users. The noninterference model maintains activities at different security levels to separate these levels from each other. In this way, it minimizes leakages that may happen through covert channels, because there is complete separation (noninterference) between security levels. Because a user at a higher security level has no way to interfere with the activities at a lower level, the lower-level user cannot get any information from the higher leve.
The following answers are incorrect: Bell Lapadula
The Bell-LaPadula Model (abbreviated BLP) is a state machine model used for enforcing access control in government and military applications. It was developed by David Elliott Bell and Leonard
J. LaPadula, subsequent to strong guidance from Roger R. Schell to formalize the U.S. Department of Defense (DoD) multilevel security (MLS) policy. The model is a formal state transition model of computer security policy that describes a set of access control rules which use security labels on objects and clearances for subjects. Security labels range from the most sensitive (e.g."Top Secret"), down to the least sensitive (e.g., "Unclassified" or "Public").
The Bell-LaPadula model focuses on data confidentiality and controlled access to classified information, in contrast to the Biba Integrity Model which describes rules for the protection of data integrity. In this formal model, the entities in an information system are divided into subjects and objects. The notion of a "secure state" is defined, and it is proven that each state transition preserves security by moving from secure state to secure state, thereby inductively proving that the system satisfies the security objectives of the model. The Bell-LaPadula model is built on the concept of a state machine with a set of allowable states in a computer network system. The transition from one state to another state is defined by transition functions.
A system state is defined to be "secure" if the only permitted access modes of subjects to objects are in accordance with a security policy. To determine whether a specific access mode is allowed, the clearance of a subject is compared to the classification of the object (more precisely, to the combination of classification and set of compartments, making up the security level) to determine if the subject is authorized for the specific access mode. The clearance/classification scheme is expressed in terms of a lattice. The model defines two mandatory access control (MAC) rules and one discretionary access control (DAC) rule with three security properties:
The Simple Security Property - a subject at a given security level may not read an object at a higher security level (no read-up). The -property (read "star"-property) - a subject at a given security level must not write to any object at a lower security level (no write-down). The -property is also known as the Confinement property. The Discretionary Security Property - use of an access matrix to specify the discretionary access
control.
The transfer of information from a high-sensitivity document to a lower-sensitivity document may
happen in the Bell-LaPadula model via the concept of trusted subjects. Trusted Subjects are not
restricted by the -property. Untrusted subjects are. Trusted Subjects must be shown to be
trustworthy with regard to the security policy. This security model is directed toward access control
and is characterized by the phrase: "no read up, no write down."
With Bell-LaPadula, users can create content only at or above their own security level (i.e. secret
researchers can create secret or top-secret files but may not create public files; no write-down).
Conversely, users can view content only at or below their own security level (i.e. secret
researchers can view public or secret files, but may not view top-secret files; no read-up).
The Bell-LaPadula model explicitly defined its scope. It did not treat the following extensively:
Covert channels. Passing information via pre-arranged actions was described briefly.
Networks of systems. Later modeling work did address this topic.
Policies outside multilevel security. Work in the early 1990s showed that MLS is one version of
boolean policies, as are all other published policies.
Biba
The Biba Model or Biba Integrity Model developed by Kenneth J. Biba in 1977, is a formal state
transition system of computer security policy that describes a set of access control rules designed
to ensure data integrity. Data and subjects are grouped into ordered levels of integrity. The model
is designed so that subjects may not corrupt objects in a level ranked higher than the subject, or
be corrupted by objects from a lower level than the subject.
In general the model was developed to circumvent a weakness in the Bell-LaPadula model which
only addresses data confidentiality.
In general, preservation of data integrity has three goals:
Prevent data modification by unauthorized parties
Prevent unauthorized data modification by authorized parties
Maintain internal and external consistency (i.e. data reflects the real world)
Note: Biba address only the first goal of integrity while Clark-Wilson addresses all three
This security model is directed toward data integrity (rather than confidentiality) and is
characterized by the phrase: "no read down, no write up". This is in contrast to the Bell-LaPadula
model which is characterized by the phrase "no write down, no read up".
In the Biba model, users can only create content at or below their own integrity level (a monk may
write a prayer book that can be read by commoners, but not one to be read by a high priest).
Conversely, users can only view content at or above their own integrity level (a monk may read a
book written by the high priest, but may not read a pamphlet written by a lowly commoner).
Another analogy to consider is that of the military chain of command. A General may write orders
to a Colonel, who can issue these orders to a Major. In this fashion, the General's original orders
are kept intact and the mission of the military is protected (thus, "no read down" integrity).
Conversely, a Private can never issue orders to his Sergeant, who may never issue orders to a
Lieutenant, also protecting the integrity of the mission ("no write up").
The Biba model defines a set of security rules similar to the Bell-LaPadula model. These rules are
the reverse of the Bell-LaPadula rules:
The Simple Integrity Axiom states that a subject at a given level of integrity must not read an
object at a lower integrity level (no read down).
The * (star) Integrity Axiom states that a subject at a given level of integrity must not write to any
object at a higher level of integrity (no write up).
Lattice Model
In computer security, lattice-based access control (LBAC) is a complex access control model
based on the interaction between any combination of objects (such as resources, computers, and
applications) and subjects (such as individuals, groups or organizations).
In this type of label-based mandatory access control model, a lattice is used to define the levels of
security that an object may have and that a subject may have access to. The subject is only
allowed to access an object if the security level of the subject is greater than or equal to that of the
object.
Mathematically, the security level access may also be expressed in terms of the lattice (a partial
order set) where each object and subject have a greatest lower bound (meet) and least upper
bound (join) of access rights. For example, if two subjects A and B need access to an object, the
security level is defined as the meet of the levels of A and B. In another example, if two objects X
and Y are combined, they form another object Z, which is assigned the security level formed by
the join of the levels of X and Y.
The following reference(s) were/was used to create this question:
ISC2 Review Seminar Student Manual V8.00 page 255.
Dorothy Denning developed the information flow model to address convert channels .
and
The ISC2 Official Study Guide, Second Edition, on page 683-685
and
https://secure.wikimedia.org/wikipedia/en/wiki/Biba_security_model
and
https://secure.wikimedia.org/wikipedia/en/wiki/Bell%E2%80%93LaPadula_model and https://secure.wikimedia.org/wikipedia/en/wiki/Lattice-based_access_control
