CISSP - Biba Model (Biba Integrity Model)

Origin: Published in 1977 at the Mitre Corporation, one year after the Bell La-Padula model. While BLP model addresses Confidentiality (and nothing about Integrity), Biba proposed this model to address Integrity

Biba Integrity model describes a set of access control rules that are designed to ensure data integrity. Subjects and Objects are grouped into various ordered levels of integrity.

Access modes of Biba Model

Modify: This allows a subject to write to an object. In layman parlance, it is equivalent to write mode in other models.
Observe: This allows a subject to read an object. This command is synonymous to the read command of other models.
Invoke: This allows one subject to communicate with another subject.
Execute: This allows a subject to execute an object. The command essentially allows a subject to execute a program which is the object

This model is directed towards data integrity (rather than confidentiality). It is also called "read up, write down" model. This implies users can only write content at or below their own integrity level. Similarly, users can only read content at or above their own integrity level.

Set of rules defined by Biba model:

The Simple Integrity Property states that a subject at a given level of integrity must not read data at a lower integrity level (no read down)

Mathematically, denoted as: s ∈ S can observe o∈ O if and only if i(s) ≤ i(o)

The * (star) Integrity Property states that a subject at a given level of integrity must not write data at a higher level of integrity (no write up).

Mathematically, denoted as: s ∈ S can modify to o∈ O if and only if i(o) ≤ i(s)

Invocation Property states that a process from below cannot request higher access; only with subjects at an equal or lower level.

Mathematically, denoted as: s₁ ∈ S can invoke s₂ ∈ S if and only if i(s₂ ) ≤ i(s₁ )

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