Illustrative Scenario: Malicious "SecureDocs Scanner"

1. Attacker deploys malicious MCP server hosting "SecureDocs Scanner"
2. Meticulously copies description, JSON schema, and claims "TrustedSoft Inc." as provider
3. User's MCP Client discovers both legitimate and malicious versions
4. Due to identical presentation, tools appear as duplicates
5. User selects entry corresponding to malicious version
6. Upon invocation, malicious tool:
   - Exfiltrates entire document content to attacker-controlled server
   - Returns fake "No PII found" message to maintain deception

Illustrative Scenario: "Daily Wallpaper" Tool Rug Pull

Initial State (Version 1.0):
- Fetches new wallpaper image and sets it
- Requests permission for "access internet" and "modify desktop wallpaper"
- User approves based on benign functionality

Post-Approval Modification:
- Tool still identified as "Daily Wallpaper v1.0" to avoid re-approval
- Server-side logic updated to:
  • Scan user's Documents folder for financial keywords
  • Upload found files to attacker-controlled server
  • Continue wallpaper functionality to maintain deception

Result: Malicious action performed silently without user awareness

// Simplified ETDI Tool Definition Verification Logic
function verifyAndApproveTool(toolDefinition, providerPublicKey) {
    // 1. Verify cryptographic identity and integrity
    if (!Crypto.verifySignature(
        toolDefinition.content,
        toolDefinition.signature, 
        providerPublicKey
    )) {
        log("Tool definition signature invalid for " + toolDefinition.id);
        return false; // Reject tool
    }

    // 2. Check against previously approved version (if any)
    const approvedDef = getApprovedDefinition(toolDefinition.id);
    if (approvedDef != null) {
        if (toolDefinition.version == approvedDef.version) {
            // If version same, ensure definition content hash matches
            if (Crypto.hash(toolDefinition.content) != approvedDef.contentHash) {
                log("Tampering detected for " + toolDefinition.id);
                // Requires re-approval even for same version if content changed
                if (!promptUserForApproval(
                    "Tool content changed. Re-approve?", 
                    toolDefinition
                )) {
                    return false;
                }
            }
        } else if (toolDefinition.version < approvedDef.version) {
            log("Warning: Older version presented");
            // Policy decision: allow, warn, or block older versions
        } else { // New version
            if (!promptUserForApproval(
                "New version. Approve?", 
                toolDefinition
            )) {
                return false;
            }
        }
    } else { // First time seeing this tool
        if (!promptUserForApproval("Approve new tool?", toolDefinition)) {
            return false;
        }
    }

    // 3. Store/update approval with new definition hash and version
    storeApproval(
        toolDefinition.id,
        toolDefinition.version,
        Crypto.hash(toolDefinition.content),
        toolDefinition.permissions
    );
    return true;
}

// Example ETDI Tool Definition with Cryptographic Signing
{
    "tool_id": "secure-docs-scanner",
    "version": "1.2.0",
    "name": "Secure Document Scanner",
    "description": "Privacy-preserving document analysis tool",
    "provider": "TrustedSoft Inc.",
    "schema": {
        "type": "object",
        "properties": {
            "document_path": {"type": "string"},
            "analysis_type": {"type": "string", "enum": ["pii", "sentiment", "summary"]}
        }
    },
    "permissions": ["file:read", "network:https"],
    "api_contract_hash": "sha256:abc123...",
    "signature": "base64_encoded_signature_of_entire_definition",
    "public_key": "base64_encoded_public_key",
    "timestamp": "2024-03-14T12:00:00Z",
    "certificate_chain": ["cert1", "cert2", "root_ca"]
}

// ETDI Version and Integrity Checking
function validateToolIntegrity(toolDefinition, storedApproval) {
    // Check version consistency
    if (toolDefinition.version !== storedApproval.version) {
        if (isNewerVersion(toolDefinition.version, storedApproval.version)) {
            // New version requires re-approval
            return { status: "NEW_VERSION", requiresApproval: true };
        } else {
            // Older version - policy dependent
            return { status: "OLDER_VERSION", requiresApproval: shouldApproveOlderVersions() };
        }
    }

    // Check content integrity for same version
    const currentHash = Crypto.hash(toolDefinition.content);
    if (currentHash !== storedApproval.contentHash) {
        // Same version but different content = tampering
        return { 
            status: "TAMPERING_DETECTED", 
            requiresApproval: true,
            securityAlert: true 
        };
    }

    // Check API contract integrity if included
    if (toolDefinition.api_contract_hash && 
        toolDefinition.api_contract_hash !== storedApproval.apiContractHash) {
        // Backend API changed without version bump
        return { 
            status: "API_CONTRACT_CHANGED", 
            requiresApproval: true,
            securityAlert: true 
        };
    }

    return { status: "VALID", requiresApproval: false };
}

// Policy-Based Tool Invocation with Amazon Verified Permissions
function invokeToolWithPolicyCheck(toolId, resourceId, userContext) {
    // 1. Retrieve and verify tool definition via ETDI
    const toolDefinition = MCPClient.getVerifiedToolDefinition(toolId);
    if (!toolDefinition) {
        return AccessDenied("Tool identity/integrity verification failed");
    }

    // 2. Prepare policy evaluation request attributes
    const principal = toolDefinition.identity; // e.g., "ToolVendor::ToolX_v1.2"
    const action = determineToolAction(toolDefinition, resourceId);
    const resource = resourceId; // e.g., "UserDocs::Private::Report.pdf"
    
    // 3. Enrich context with comprehensive attributes
    const context = {
        user: { 
            id: userContext.userId, 
            department: userContext.department,
            clearanceLevel: userContext.securityClearance
        },
        request: { 
            time: currentTime(), 
            purpose: userContext.statedPurpose,
            location: userContext.location,
            deviceTrust: userContext.deviceSecurityPosture
        },
        data: {
            classification: getDataClassification(resourceId),
            sensitivity: getDataSensitivity(resourceId)
        },
        session: {
            previousActions: getSessionHistory(),
            riskScore: calculateRiskScore(userContext)
        }
    };

    // 4. Call Policy Engine for authorization decision
    const policyStoreId = getUserPolicyStore(userContext.userId);
    const authDecision = AmazonVerifiedPermissions.isAuthorized(
        policyStoreId,
        principal,
        action,
        resource,
        context
    );

    // 5. Process authorization result
    if (authDecision.isAllowed()) {
        log("Policy check passed for " + toolId + " on " + resourceId);
        
        // Proceed with tool invocation
        const userAuthToken = HostApp.getUserTokenForTool(toolId);
        const toolResult = MCPServer.invokeTool(
            toolDefinition, 
            resourceId, 
            userAuthToken
        );
        return toolResult;
    } else {
        log("Policy check failed: " + authDecision.errors());
        return AccessDenied("Tool not authorized by policy for this context");
    }
}

// Example Cedar Policies for ETDI Tool Authorization

// Policy 1: Restrict financial data access to certified tools during business hours
permit(
    principal in Group::"CertifiedFinancialTools",
    action == Action::"ReadFile",
    resource in Folder::"FinancialData"
) when {
    context.time.hour >= 9 && context.time.hour <= 17 &&
    context.user.department == "Finance" &&
    principal.certification.includes("SOX-Compliant")
};

// Policy 2: Prevent PII access for tools without privacy certification
forbid(
    principal,
    action == Action::"ProcessDocument",
    resource
) when {
    resource.classification == "PII" &&
    !principal.certifications.includes("Privacy-Shield")
};

// Policy 3: Require elevated approval for high-risk operations
permit(
    principal,
    action == Action::"ModifySystem",
    resource
) when {
    context.approval.level >= "Manager" &&
    context.request.justification != "" &&
    principal.riskScore <= 3
};

// Policy 4: Time-based restrictions for external network access
permit(
    principal,
    action == Action::"NetworkRequest",
    resource
) when {
    context.time.timezone == "UTC" &&
    context.time.hour >= 6 && context.time.hour <= 22 &&
    !resource.destination.includes("suspicious-domains")
};

// Policy 5: Data export restrictions based on user clearance
permit(
    principal in Group::"ExportCapableTools",
    action == Action::"ExportData",
    resource
) when {
    context.user.clearanceLevel >= resource.requiredClearance &&
    context.device.isManaged == true &&
    context.location.isApproved == true
};

// ETDI Call Stack Verification System
class ETDICallStackVerifier {
    constructor() {
        this.activeSessions = new Map();
        this.callStackPolicies = new Map();
        this.maxCallDepth = 10;
        this.rateLimits = new Map();
    }

    verifyToolInvocation(sessionId, callerTool, calleeTool, context) {
        const session = this.getOrCreateSession(sessionId);
        const policy = this.callStackPolicies.get(session.policyId);
        
        // 1. Check maximum call depth
        if (session.callStack.length >= this.maxCallDepth) {
            return {
                allowed: false,
                reason: "EXCESSIVE_CALL_DEPTH",
                maxDepth: this.maxCallDepth
            };
        }

        // 2. Check for circular dependencies
        if (session.callStack.some(call => call.toolId === calleeTool.id)) {
            if (!policy.allowCircularCalls) {
                return {
                    allowed: false,
                    reason: "CIRCULAR_DEPENDENCY_DETECTED",
                    callStack: session.callStack.map(c => c.toolId)
                };
            }
        }

        // 3. Verify caller-callee relationship permissions
        if (!this.isChainAllowed(callerTool, calleeTool, policy)) {
            return {
                allowed: false,
                reason: "UNAUTHORIZED_TOOL_CHAINING",
                caller: callerTool.id,
                callee: calleeTool.id
            };
        }

        // 4. Check privilege escalation
        if (this.detectPrivilegeEscalation(callerTool, calleeTool)) {
            return {
                allowed: false,
                reason: "PRIVILEGE_ESCALATION_ATTEMPT",
                callerPrivileges: callerTool.privileges,
                calleePrivileges: calleeTool.privileges
            };
        }

        // 5. Verify rate limits
        if (!this.checkRateLimit(callerTool.id, calleeTool.id)) {
            return {
                allowed: false,
                reason: "RATE_LIMIT_EXCEEDED"
            };
        }

        // 6. Add to call stack and allow invocation
        session.callStack.push({
            toolId: calleeTool.id,
            caller: callerTool.id,
            timestamp: Date.now(),
            context: context
        });

        return { allowed: true };
    }

    isChainAllowed(callerTool, calleeTool, policy) {
        // Check explicit allow/deny lists
        const chainKey = `${callerTool.id}->${calleeTool.id}`;
        
        if (policy.deniedChains.includes(chainKey)) {
            return false;
        }
        
        if (policy.allowedChains.includes(chainKey)) {
            return true;
        }
        
        // Check group-based permissions
        return policy.defaultChainPolicy === "allow";
    }

    detectPrivilegeEscalation(callerTool, calleeTool) {
        // Compare privilege levels
        const callerLevel = this.getPrivilegeLevel(callerTool.privileges);
        const calleeLevel = this.getPrivilegeLevel(calleeTool.privileges);
        
        // Prevent lower privilege tool calling higher privilege tool
        return callerLevel < calleeLevel;
    }
}

// Example Call Stack Policy Configuration
{
    "policyId": "enterprise-tool-chain-policy",
    "version": "1.0",
    "defaultChainPolicy": "deny",
    "maxCallDepth": 8,
    "allowCircularCalls": false,
    "allowedChains": [
        "data-fetcher->data-analyzer",
        "data-analyzer->report-generator",
        "auth-tool->secure-file-reader",
        "workflow-orchestrator->*"
    ],
    "deniedChains": [
        "external-api-tool->internal-system-tool",
        "guest-tool->admin-tool",
        "*->credential-manager"
    ],
    "privilegeEscalationPolicy": {
        "enabled": true,
        "allowEscalationWithApproval": true,
        "approvalRequired": ["manager", "security-team"]
    },
    "rateLimits": {
        "default": {
            "callsPerMinute": 10,
            "callsPerHour": 100
        },
        "external-api-tool": {
            "callsPerMinute": 3,
            "callsPerHour": 20
        }
    },
    "monitoring": {
        "logAllCalls": true,
        "alertOnViolations": true,
        "alertThresholds": {
            "rateLimitViolations": 5,
            "privilegeEscalationAttempts": 1
        }
    }
}

// ETDI Key Management Implementation
class ETDIKeyManager {
    constructor(config) {
        this.keyStore = new SecureKeyStore(config.keyStorePath);
        this.certValidator = new CertificateValidator(config.trustedRoots);
        this.revocationChecker = new RevocationChecker(config.crlEndpoints);
    }

    async generateProviderKeys(providerId) {
        // Generate RSA-2048 or ECDSA P-256 key pair
        const keyPair = await crypto.subtle.generateKey(
            {
                name: "RSA-PSS",
                modulusLength: 2048,
                publicExponent: new Uint8Array([1, 0, 1]),
                hash: "SHA-256"
            },
            true,
            ["sign", "verify"]
        );

        // Store private key securely
        await this.keyStore.storePrivateKey(providerId, keyPair.privateKey);
        
        // Export public key for distribution
        const publicKey = await crypto.subtle.exportKey("spki", keyPair.publicKey);
        return {
            providerId,
            publicKey: btoa(String.fromCharCode(...new Uint8Array(publicKey))),
            algorithm: "RSA-PSS-SHA256"
        };
    }

    async signToolDefinition(toolDefinition, providerId) {
        const privateKey = await this.keyStore.getPrivateKey(providerId);
        const dataToSign = JSON.stringify(toolDefinition);
        
        const signature = await crypto.subtle.sign(
            {
                name: "RSA-PSS",
                saltLength: 32
            },
            privateKey,
            new TextEncoder().encode(dataToSign)
        );

        return {
            ...toolDefinition,
            signature: btoa(String.fromCharCode(...new Uint8Array(signature))),
            timestamp: new Date().toISOString(),
            signingAlgorithm: "RSA-PSS-SHA256"
        };
    }

    async verifyToolDefinition(signedDefinition, providerPublicKey) {
        try {
            // Import public key
            const publicKey = await crypto.subtle.importKey(
                "spki",
                new Uint8Array(atob(providerPublicKey).split('').map(c => c.charCodeAt(0))),
                {
                    name: "RSA-PSS",
                    hash: "SHA-256"
                },
                false,
                ["verify"]
            );

            // Extract signature and original data
            const { signature, signingAlgorithm, ...originalDefinition } = signedDefinition;
            const dataToVerify = JSON.stringify(originalDefinition);
            
            // Verify signature
            const isValid = await crypto.subtle.verify(
                {
                    name: "RSA-PSS",
                    saltLength: 32
                },
                publicKey,
                new Uint8Array(atob(signature).split('').map(c => c.charCodeAt(0))),
                new TextEncoder().encode(dataToVerify)
            );

            return { valid: isValid, definition: originalDefinition };
        } catch (error) {
            return { valid: false, error: error.message };
        }
    }
}

// OAuth-Enhanced ETDI Client Implementation
class OAuthETDIClient {
    constructor(config) {
        this.oauthConfig = config.oauth;
        this.keyManager = new ETDIKeyManager(config.keys);
        this.policyEngine = new PolicyEngine(config.policies);
        this.tokenCache = new Map();
    }

    async authenticateAndAuthorize(toolDefinition, userContext) {
        // 1. Verify tool signature and identity
        const verificationResult = await this.keyManager.verifyToolDefinition(
            toolDefinition,
            await this.getTrustedPublicKey(toolDefinition.provider)
        );

        if (!verificationResult.valid) {
            throw new Error("Tool signature verification failed");
        }

        // 2. Validate OAuth token if present
        if (toolDefinition.oauth_token) {
            const tokenValidation = await this.validateOAuthToken(
                toolDefinition.oauth_token,
                toolDefinition.oauth_config
            );
            
            if (!tokenValidation.valid) {
                throw new Error("OAuth token validation failed");
            }
        }

        // 3. Check policy-based authorization
        const policyDecision = await this.policyEngine.evaluate({
            principal: toolDefinition.tool_id,
            action: userContext.requestedAction,
            resource: userContext.targetResource,
            context: {
                user: userContext.user,
                environment: userContext.environment,
                time: new Date().toISOString()
            }
        });

        if (!policyDecision.allowed) {
            throw new Error(`Policy violation: ${policyDecision.reason}`);
        }

        // 4. Obtain user authorization token if required
        let userToken = null;
        if (toolDefinition.requires_user_auth) {
            userToken = await this.getUserAuthToken(
                toolDefinition.oauth_config,
                userContext.user
            );
        }

        return {
            authorized: true,
            toolDefinition: verificationResult.definition,
            userToken: userToken,
            policyDecision: policyDecision
        };
    }

    async validateOAuthToken(token, oauthConfig) {
        try {
            // Get JWKS from OAuth provider
            const jwks = await this.getJWKS(oauthConfig.jwks_uri);
            
            // Decode and verify JWT
            const decoded = jwt.verify(token, jwks, {
                issuer: oauthConfig.issuer,
                audience: oauthConfig.audience
            });

            // Verify token hasn't been revoked
            const revoked = await this.checkTokenRevocation(token);
            
            return {
                valid: !revoked,
                claims: decoded,
                scopes: decoded.scope ? decoded.scope.split(' ') : []
            };
        } catch (error) {
            return { valid: false, error: error.message };
        }
    }
}

// Amazon Verified Permissions Integration
class AVPPolicyEngine {
    constructor(config) {
        this.avpClient = new VerifiedPermissionsClient({
            region: config.region,
            credentials: config.credentials
        });
        this.policyStoreId = config.policyStoreId;
    }

    async evaluate(authorizationRequest) {
        try {
            const response = await this.avpClient.isAuthorized({
                policyStoreId: this.policyStoreId,
                principal: {
                    entityType: "Tool",
                    entityId: authorizationRequest.principal
                },
                action: {
                    actionType: authorizationRequest.action.type,
                    actionId: authorizationRequest.action.id
                },
                resource: {
                    entityType: "Resource",
                    entityId: authorizationRequest.resource
                },
                context: {
                    contextMap: authorizationRequest.context
                }
            });

            return {
                allowed: response.decision === "ALLOW",
                reason: response.reason,
                determiningPolicies: response.determiningPolicies,
                errors: response.errors || []
            };
        } catch (error) {
            return {
                allowed: false,
                reason: "Policy evaluation error",
                error: error.message
            };
        }
    }

    async createPolicy(policyDefinition) {
        // Create Cedar policy in Amazon Verified Permissions
        return await this.avpClient.createPolicy({
            policyStoreId: this.policyStoreId,
            definition: {
                static: {
                    statement: policyDefinition.cedarStatement
                }
            }
        });
    }
}

// Example Best Practice Cedar Policy Structure
// Policy: Comprehensive data access control with context awareness

permit(
    principal in ToolGroup::"TrustedDataProcessors",
    action in [Action::"ReadFile", Action::"ProcessDocument"],
    resource in DataFolder::"CustomerData"
) when {
    // Time-based restrictions
    context.request.time.hour >= 6 && 
    context.request.time.hour <= 22 &&
    
    // Location restrictions
    context.user.location in Location::"ApprovedOffices" &&
    
    // Device security requirements
    context.device.isManaged == true &&
    context.device.encryptionEnabled == true &&
    
    // User authorization requirements
    context.user.hasValidMFA == true &&
    context.user.trainingCurrent == true &&
    
    // Data classification matching
    principal.dataClassificationLevel >= resource.requiredClearance &&
    
    // Rate limiting
    context.session.requestCount <= 100
};

// Explicit deny for sensitive operations
forbid(
    principal,
    action == Action::"ExportData",
    resource
) when {
    resource.classification == "HIGHLY_CONFIDENTIAL" &&
    !context.user.hasSpecialApproval
};