What is the Biba integrity model and how does it differ from Bell-LaPadula?

The Biba model enforces data integrity, the opposite focus of Bell-LaPadula's confidentiality. Its two rules are the simple integrity axiom, or "no read down," preventing subjects from reading data at a lower integrity level to avoid contamination; and the star integrity axiom, or "no write up," preventing subjects from writing data to a higher integrity level to avoid corruption. Biba prevents less trusted subjects from modifying more trusted data. While Bell-LaPadula prevents disclosure of secrets downward, Biba prevents corruption of trusted data from below.