File size: 6,698 Bytes
b90fa8e | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 | use crate::types::{BehavioralTelemetry, TrustState};
use thiserror::Error;
#[derive(Error, Debug)]
pub enum StateMachineError {
#[error("Invalid transition from {from:?} to {to:?}: {reason}")]
InvalidTransition {
from: TrustState,
to: TrustState,
reason: String,
},
#[error("System is locked in Compromised state (T_-1). Operation rejected.")]
CompromiseLockout,
}
pub struct SystemStateMachine {
current_state: TrustState,
anomaly_threshold: f32,
}
impl SystemStateMachine {
pub fn new(anomaly_threshold: f32) -> Self {
Self {
current_state: TrustState::Unauthenticated,
anomaly_threshold,
}
}
pub fn current_state(&self) -> TrustState {
self.current_state
}
pub fn handle_device_authenticated(&mut self) -> Result<TrustState, StateMachineError> {
self.assert_not_compromised()?;
if self.current_state != TrustState::Unauthenticated {
return Err(StateMachineError::InvalidTransition {
from: self.current_state,
to: TrustState::DeviceAuthenticated,
reason: "Device authentication is only valid from T0".into(),
});
}
self.current_state = TrustState::DeviceAuthenticated;
Ok(self.current_state)
}
pub fn handle_behavioral_assertion(
&mut self,
telemetry: &BehavioralTelemetry,
) -> Result<TrustState, StateMachineError> {
self.assert_not_compromised()?;
if telemetry.anomaly_score >= self.anomaly_threshold {
self.trigger_compromise();
return Err(StateMachineError::CompromiseLockout);
}
if self.current_state == TrustState::DeviceAuthenticated && telemetry.anomaly_score < 0.25 {
self.current_state = TrustState::BehavioralContinuity;
}
Ok(self.current_state)
}
pub fn handle_step_up_auth(&mut self) -> Result<TrustState, StateMachineError> {
self.assert_not_compromised()?;
if self.current_state != TrustState::BehavioralContinuity {
return Err(StateMachineError::InvalidTransition {
from: self.current_state,
to: TrustState::HighAssurance,
reason: "Step-up authentication requires active T2 state".into(),
});
}
self.current_state = TrustState::HighAssurance;
Ok(self.current_state)
}
pub fn handle_critical_elevation(&mut self) -> Result<TrustState, StateMachineError> {
self.assert_not_compromised()?;
if self.current_state != TrustState::HighAssurance {
return Err(StateMachineError::InvalidTransition {
from: self.current_state,
to: TrustState::CriticalElevation,
reason: "Critical elevation requires active T3 state".into(),
});
}
self.current_state = TrustState::CriticalElevation;
Ok(self.current_state)
}
pub fn trigger_compromise(&mut self) -> TrustState {
self.current_state = TrustState::Compromised;
TrustState::Compromised
}
pub fn handle_hardware_recovery_reset(&mut self) -> Result<TrustState, StateMachineError> {
if self.current_state != TrustState::Compromised {
return Err(StateMachineError::InvalidTransition {
from: self.current_state,
to: TrustState::Unauthenticated,
reason: "Recovery reset is only valid from T_-1 state".into(),
});
}
self.current_state = TrustState::Unauthenticated;
Ok(self.current_state)
}
fn assert_not_compromised(&self) -> Result<(), StateMachineError> {
if self.current_state == TrustState::Compromised {
Err(StateMachineError::CompromiseLockout)
} else {
Ok(())
}
}
}
#[cfg(test)]
mod tests {
use super::*;
fn low_risk_telemetry() -> BehavioralTelemetry {
BehavioralTelemetry {
anomaly_score: 0.05,
cadence_entropy: 0.95,
spatial_risk_factor: 0.01,
timestamp: 0,
}
}
#[test]
fn starts_unauthenticated() {
let sm = SystemStateMachine::new(0.7);
assert_eq!(sm.current_state(), TrustState::Unauthenticated);
}
#[test]
fn full_happy_path_escalation() {
let mut sm = SystemStateMachine::new(0.7);
sm.handle_device_authenticated().unwrap();
assert_eq!(sm.current_state(), TrustState::DeviceAuthenticated);
sm.handle_behavioral_assertion(&low_risk_telemetry())
.unwrap();
assert_eq!(sm.current_state(), TrustState::BehavioralContinuity);
sm.handle_step_up_auth().unwrap();
assert_eq!(sm.current_state(), TrustState::HighAssurance);
sm.handle_critical_elevation().unwrap();
assert_eq!(sm.current_state(), TrustState::CriticalElevation);
}
#[test]
fn cannot_skip_states() {
let mut sm = SystemStateMachine::new(0.7);
assert!(sm.handle_step_up_auth().is_err());
assert!(sm.handle_critical_elevation().is_err());
}
#[test]
fn high_anomaly_triggers_compromise() {
let mut sm = SystemStateMachine::new(0.5);
sm.handle_device_authenticated().unwrap();
let risky = BehavioralTelemetry {
anomaly_score: 0.9,
cadence_entropy: 0.1,
spatial_risk_factor: 0.8,
timestamp: 0,
};
let result = sm.handle_behavioral_assertion(&risky);
assert!(matches!(result, Err(StateMachineError::CompromiseLockout)));
assert_eq!(sm.current_state(), TrustState::Compromised);
}
#[test]
fn compromised_state_blocks_all_transitions_until_reset() {
let mut sm = SystemStateMachine::new(0.5);
sm.trigger_compromise();
assert!(sm.handle_device_authenticated().is_err());
assert!(sm
.handle_behavioral_assertion(&low_risk_telemetry())
.is_err());
assert!(sm.handle_step_up_auth().is_err());
assert!(sm.handle_critical_elevation().is_err());
sm.handle_hardware_recovery_reset().unwrap();
assert_eq!(sm.current_state(), TrustState::Unauthenticated);
}
#[test]
fn recovery_reset_only_valid_from_compromised() {
let mut sm = SystemStateMachine::new(0.5);
assert!(sm.handle_hardware_recovery_reset().is_err());
}
}
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