Chapter 11: Capability-Based Security Framework

Advanced Capability System:

pub struct AdvancedCapability {
    capability_id: CapabilityId,
    capability_type: CapabilityType,
    signature: Ed25519Signature,
    public_key: Ed25519PublicKey,
    permissions: PermissionSet,
    restrictions: RestrictionSet,
    delegation_chain: Vec<DelegationProof>,
    max_delegation_depth: u8,
    valid_from: Timestamp,
    valid_until: Option<Timestamp>,
    security_level: SecurityLevel,
}

impl AdvancedCapability {
    pub fn create_with_cryptographic_proof(
        capability_type: CapabilityType,
        permissions: PermissionSet,
        restrictions: RestrictionSet,
        issuer_keypair: &Ed25519Keypair,
        security_level: SecurityLevel,
    ) -> Result<Self, CapabilityCreationError> {
        let capability_id = CapabilityId::generate_secure_random();
        
        let capability_metadata = CapabilityMetadata {
            id: capability_id.clone(),
            capability_type: capability_type.clone(),
            permissions: permissions.clone(),
            restrictions: restrictions.clone(),
            security_level,
            creation_timestamp: precise_timestamp(),
        };
        
        let serialized_metadata = capability_metadata.serialize_for_signing()?;
        let signature = issuer_keypair.sign(&serialized_metadata);
        
        Ok(Self {
            capability_id,
            capability_type,
            signature,
            public_key: issuer_keypair.public_key(),
            permissions,
            restrictions,
            delegation_chain: Vec::new(),
            max_delegation_depth: security_level.max_delegation_depth(),
            valid_from: precise_timestamp(),
            valid_until: None,
            security_level,
        })
    }
    
    pub fn verify_capability_chain(
        &self,
        trusted_authorities: &[Ed25519PublicKey],
        current_context: &SecurityContext,
    ) -> Result<CapabilityVerification, CapabilityVerificationError> {
        // Verify temporal validity
        let current_time = precise_timestamp();
        if current_time < self.valid_from {
            return Err(CapabilityVerificationError::NotYetValid);
        }
        
        if let Some(valid_until) = self.valid_until {
            if current_time > valid_until {
                return Err(CapabilityVerificationError::Expired);
            }
        }
        
        // Verify root capability signature
        let capability_metadata = CapabilityMetadata {
            id: self.capability_id.clone(),
            capability_type: self.capability_type.clone(),
            permissions: self.permissions.clone(),
            restrictions: self.restrictions.clone(),
            security_level: self.security_level,
            creation_timestamp: self.valid_from,
        };
        
        let serialized_metadata = capability_metadata.serialize_for_signing()?;
        
        if !self.public_key.verify(&serialized_metadata, &self.signature) {
            return Err(CapabilityVerificationError::InvalidSignature);
        }
        
        // Verify issuer is trusted
        if !trusted_authorities.contains(&self.public_key) {
            return Err(CapabilityVerificationError::UntrustedIssuer);
        }
        
        // Verify delegation chain
        let mut current_permissions = self.permissions.clone();
        let mut current_public_key = self.public_key.clone();
        
        for (index, delegation_proof) in self.delegation_chain.iter().enumerate() {
            let delegation_metadata = DelegationMetadata {
                parent_capability: self.capability_id.clone(),
                delegated_permissions: delegation_proof.delegated_permissions.clone(),
                delegation_restrictions: delegation_proof.restrictions.clone(),
                delegation_timestamp: delegation_proof.timestamp,
                delegation_depth: index as u8 + 1,
            };
            
            let serialized_delegation = delegation_metadata.serialize_for_signing()?;
            
            if !current_public_key.verify(&serialized_delegation, &delegation_proof.signature) {
                return Err(CapabilityVerificationError::InvalidDelegationSignature);
            }
            
            current_permissions = current_permissions
                .intersect(&delegation_proof.delegated_permissions)?;
            current_public_key = delegation_proof.delegate_public_key.clone();
        }
        
        // Verify delegation depth limits
        if self.delegation_chain.len() > self.max_delegation_depth as usize {
            return Err(CapabilityVerificationError::DelegationDepthExceeded);
        }
        
        Ok(CapabilityVerification {
            verified: true,
            effective_permissions: current_permissions,
            verification_timestamp: current_time,
            security_level: self.security_level,
        })
    }
}