The integrity counterpart to Bell-LaPadula. Biba prevents CORRUPTION of high-integrity data using two rules: no read down (Simple Integrity Property) and no write up (Star Integrity Property). Think of it as Bell-LaPadula flipped.
Biba fills the gap Bell-LaPadula leaves — it protects data integrity, which matters in financial, healthcare, and any environment where data accuracy is critical.
Developed by Ken Biba in 1977 at MITRE Corporation. Biba noticed that Bell-LaPadula allowed low-integrity subjects to write to high-integrity objects. Biba flipped the direction: in an integrity model, you worry about contamination coming UP from low-integrity sources.
Simple Integrity Property (no read down): A subject at integrity level L cannot read an object at a LOWER integrity level.
Star Integrity Property (no write up): A subject at integrity level L cannot write to an object at a HIGHER integrity level. This prevents contamination of trusted data by untrusted sources.
Bell-LaPadula protects confidentiality by restricting READ up and WRITE down. Biba protects integrity by restricting READ down and WRITE up. They are exact opposites.
Strict Integrity Policy: Both properties must hold at all times. Subject Low-Water Mark: A subject's integrity level degrades to the lowest level of any object it reads. Ring Policy: Subjects can read objects at any level but cannot write up.
Bell-LaPadula vs. Biba — the key comparison
| Model | Focus | No Read | No Write | Prevents |
|---|---|---|---|---|
| Bell-LaPadula | Confidentiality | Up | Down | Disclosure |
| Biba | Integrity | Down | Up | Corruption |