gate0

A small, auditable, terminating, deterministic micro-policy engine.

Security Model

Gate0 is designed for high-assurance environments where policy evaluation must be deterministic and resource-bounded. See SECURITY.md for the full threat model, system invariants, and mechanical guarantees.

Architecture

Gate0 uses a linear, Deny-Overrides evaluation strategy. Each rule consists of a Target (fast-path match) and an optional Condition (deep logic).

graph TD
REQ([Request]) ==> POL

subgraph POL [Policy: Ordered Rules]
direction TB
R1[Rule 1: Deny]
R2[Rule 2: Allow]
R3[Rule 3: Allow]
end

POL ==> MATCH{Match?}

subgraph EVAL [Evaluation Logic]
direction LR
MATCH -- "Target + Condition" --> DECIDE
DECIDE{Effect?}
DECIDE -- "Deny" --> D_WIN[Deny Wins]
DECIDE -- "Allow" --> A_PEND[Allow Pending]
end

D_WIN ==> FIN([Final Decision])
A_PEND -- "Next Rule" --> MATCH
MATCH -- "No more rules" --> NO_M
NO_M[No Match] ==> D_DEF[Default Deny]
D_DEF ==> FIN

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Verification

The correctness and safety of Gate0 are mechanically verified:

• Unit Tests: Full coverage of core logic and edge cases.
• Property-Based Testing: Hundreds of adversarial scenarios generated via proptest.
• Undefined Behavior Check: Verified panic-free and UB-free using cargo miri.
• Bounded Evaluation: Worst-case inputs are tested to ensure termination.

cargo test
cargo +nightly miri test --lib

Example

use gate0::{Policy, Rule, Target, Request, ReasonCode};

let policy = Policy::builder()
.rule(Rule::allow(Target::any(), ReasonCode(1)))
.build()?;

let decision = policy.evaluate(&Request::new("alice", "read", "doc"))?;
assert!(decision.is_allow());

Examples

The examples/ directory contains illustrative scenarios demonstrating common Gate0 usage patterns:

• SaaS API: Standard RBAC/Multi-tenancy logic.
• Zero Trust Network: Attribute-Based Access Control (ABAC) with MFA and location checks.
• Complex Overrides: Demonstrating Deny-Overrides conflict resolution.

Run them with:

cargo run --example saas_api
cargo run --example zero_trust_network
cargo run --example complex_overrides

License

MIT