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sec-design.md

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BUSINESS POSTURE

  • Business Priorities and Goals:

  • Provide a secure and private note-taking application.

  • Offer end-to-end encryption to protect user data.

  • Ensure accessibility across multiple platforms (web, desktop, mobile).

  • Maintain user trust by prioritizing data security and privacy.

  • Offer a reliable and stable note-taking service.

  • Business Risks:

  • Data breach leading to exposure of user notes.

  • Loss of user trust due to security vulnerabilities.

  • Service unavailability impacting user productivity.

  • Compliance issues related to data privacy regulations (e.g., GDPR, CCPA).

  • Supply chain attacks compromising the application or its dependencies.

SECURITY POSTURE

  • Existing Security Controls:

  • security control: End-to-end encryption of notes (described in application documentation and likely implemented within the client applications).

  • security control: Password-based authentication (standard authentication mechanism for user accounts).

  • security control: Secure software development lifecycle (inferred from the project's focus on security and privacy, although specific details are not provided in the input).

  • security control: HTTPS for communication (standard practice for web applications, assumed for Standard Notes web and API interactions).

  • accepted risk: Reliance on user-generated passwords for account security (inherent risk with password-based authentication).

  • accepted risk: Potential vulnerabilities in third-party dependencies (common risk in software development, requires ongoing dependency management).

  • Recommended Security Controls:

  • security control: Implement multi-factor authentication (MFA) to enhance account security.

  • security control: Regularly perform penetration testing and vulnerability scanning to identify and address security weaknesses.

  • security control: Implement a robust security incident response plan to handle potential security breaches effectively.

  • security control: Conduct regular security awareness training for developers and operations teams.

  • security control: Implement static application security testing (SAST) and dynamic application security testing (DAST) in the CI/CD pipeline.

  • security control: Implement software composition analysis (SCA) to manage and monitor third-party dependencies for known vulnerabilities.

  • Security Requirements:

  • Authentication:

  • Requirement: Securely authenticate users accessing the application.

  • Requirement: Support strong password policies and consider passwordless authentication options.

  • Requirement: Implement session management to control user access after successful authentication.

  • Authorization:

  • Requirement: Implement role-based access control (RBAC) if different user roles or access levels are required (although not explicitly stated as needed for a note-taking app, it's good practice for future scalability).

  • Requirement: Ensure users can only access and modify their own notes and data.

  • Input Validation:

  • Requirement: Validate all user inputs to prevent injection attacks (e.g., XSS, SQL injection if a database is directly accessed from the client - unlikely in this architecture, but relevant for backend services).

  • Requirement: Sanitize user-generated content before rendering it in the application to prevent XSS.

  • Cryptography:

  • Requirement: Utilize strong encryption algorithms for end-to-end encryption of notes (likely AES-256 or similar).

  • Requirement: Securely manage encryption keys, ensuring they are not accessible to unauthorized parties.

  • Requirement: Use HTTPS for all communication channels to protect data in transit.

DESIGN

  • C4 CONTEXT
flowchart LR
    subgraph "Standard Notes Ecosystem"
        center "Standard Notes Application"
    end

    u1["User"] -- "Uses" --> center
    center -- "Syncs data with" --> bs["Backend Services"]
    center -- "Uses" --> os["Operating System"]
    center -- "Uses" --> db["Local Device Storage"]

    style center fill:#f9f,stroke:#333,stroke-width:2px
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  • C4 Context Elements:

  • Element:

  • Name: User

  • Type: Person

  • Description: Individual user who uses the Standard Notes application to create, manage, and access notes.

  • Responsibilities: Creates, reads, updates, and deletes notes. Manages their account and preferences.

  • Security controls: Strong password or MFA for account access. Responsible for keeping their encryption key secure (if applicable to their setup).

  • Element:

  • Name: Standard Notes Application

  • Type: Software System

  • Description: The note-taking application itself, available on web, desktop, and mobile platforms. Provides the user interface and core note-taking functionalities.

  • Responsibilities: Allows users to create, edit, and organize notes. Encrypts and decrypts notes. Synchronizes notes with backend services. Manages local data storage.

  • Security controls: End-to-end encryption of notes. Input validation on user inputs. Secure storage of encryption keys locally (protected by OS mechanisms). HTTPS for communication with backend services.

  • Element:

  • Name: Backend Services

  • Type: Software System

  • Description: Cloud-based services that handle user account management, note synchronization, and potentially other features like extensions or subscriptions.

  • Responsibilities: Authenticates users. Stores encrypted notes. Manages user accounts and subscriptions. Provides API for application to interact with.

  • Security controls: Secure authentication and authorization mechanisms. Encryption of data at rest and in transit. Access control to backend resources. Regular security updates and patching.

  • Element:

  • Name: Operating System

  • Type: Technology

  • Description: The operating system on which the Standard Notes application runs (e.g., Windows, macOS, iOS, Android, Linux).

  • Responsibilities: Provides the environment for the application to run. Manages system resources. Provides security features like file system permissions and process isolation.

  • Security controls: OS-level security controls (firewall, antivirus, access controls). Application sandboxing (depending on OS and platform).

  • Element:

  • Name: Local Device Storage

  • Type: Data Store

  • Description: Local storage on the user's device where the Standard Notes application stores notes and application data locally.

  • Responsibilities: Persistently stores notes and application settings locally. Provides fast access to notes when offline.

  • Security controls: Encryption of local storage (depending on OS capabilities and application implementation). File system permissions to restrict access to application data.

  • C4 CONTAINER

flowchart LR
    subgraph "Standard Notes Ecosystem"
        subgraph "Client Applications"
            wa["Web Application"]
            da["Desktop Application"]
            ma["Mobile Application"]
        end
        subgraph "Backend Services"
            api["API Gateway"]
            auth["Authentication Service"]
            sync["Synchronization Service"]
            db["Database"]
        end
    end

    u1["User"] -- "Uses via Browser" --> wa
    u1 -- "Uses Native App" --> da
    u1 -- "Uses Native App" --> ma

    wa -- "API Requests (HTTPS)" --> api
    da -- "API Requests (HTTPS)" --> api
    ma -- "API Requests (HTTPS)" --> api

    api -- "Authenticates User" --> auth
    api -- "Manages Notes" --> sync
    sync -- "Stores/Retrieves Notes" --> db

    style wa fill:#f9f,stroke:#333,stroke-width:2px
    style da fill:#f9f,stroke:#333,stroke-width:2px
    style ma fill:#f9f,stroke:#333,stroke-width:2px
    style api fill:#ccf,stroke:#333,stroke-width:2px
    style auth fill:#ccf,stroke:#333,stroke-width:2px
    style sync fill:#ccf,stroke:#333,stroke-width:2px
    style db fill:#ccf,stroke:#333,stroke-width:2px
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  • C4 Container Elements:

  • Element:

  • Name: Web Application

  • Type: Container

  • Description: Browser-based client application built using web technologies (likely JavaScript, HTML, CSS). Provides access to Standard Notes features through a web browser.

  • Responsibilities: User interface for note creation, editing, and management. Handles note encryption and decryption in the browser. Communicates with the API Gateway for backend services.

  • Security controls: Input validation in the browser. Secure handling of encryption keys in the browser's memory or local storage. HTTPS for all communication. Content Security Policy (CSP) to mitigate XSS.

  • Element:

  • Name: Desktop Application

  • Type: Container

  • Description: Native desktop application for Windows, macOS, and Linux, providing access to Standard Notes features. Likely built using technologies like Electron or native platform frameworks.

  • Responsibilities: User interface for note creation, editing, and management. Handles note encryption and decryption within the application. Communicates with the API Gateway for backend services. Manages local data storage.

  • Security controls: Input validation within the application. Secure storage of encryption keys using OS-specific secure storage mechanisms. HTTPS for all communication. Code signing of the application to ensure integrity.

  • Element:

  • Name: Mobile Application

  • Type: Container

  • Description: Native mobile application for iOS and Android, providing access to Standard Notes features on mobile devices.

  • Responsibilities: User interface for note creation, editing, and management on mobile. Handles note encryption and decryption within the application. Communicates with the API Gateway for backend services. Manages local data storage.

  • Security controls: Input validation within the application. Secure storage of encryption keys using mobile OS secure storage mechanisms (Keychain, Keystore). HTTPS for all communication. Application signing and permissions management.

  • Element:

  • Name: API Gateway

  • Type: Container

  • Description: Entry point for all API requests from client applications to the backend services. Routes requests to appropriate backend services. May handle rate limiting, authentication, and other cross-cutting concerns.

  • Responsibilities: API request routing. Authentication and authorization of requests. Rate limiting and traffic management. SSL termination.

  • Security controls: Web Application Firewall (WAF) to protect against common web attacks. DDoS protection. Secure configuration of API gateway. Access control lists (ACLs) to restrict access to backend services.

  • Element:

  • Name: Authentication Service

  • Type: Container

  • Description: Service responsible for user authentication and session management. Verifies user credentials and issues authentication tokens.

  • Responsibilities: User authentication (username/password, MFA if implemented). Session management. Token generation and validation. Password management (hashing, storage).

  • Security controls: Secure password hashing algorithms. Protection against brute-force attacks. Secure storage of authentication secrets. Regular security audits of authentication logic.

  • Element:

  • Name: Synchronization Service

  • Type: Container

  • Description: Service responsible for synchronizing encrypted notes between user devices and the backend database. Handles conflict resolution and data consistency.

  • Responsibilities: Receives encrypted notes from clients. Stores encrypted notes in the database. Retrieves encrypted notes for clients. Handles synchronization logic and conflict resolution.

  • Security controls: Secure communication channels (HTTPS). Access control to the database. Input validation on data received from clients. Rate limiting to prevent abuse.

  • Element:

  • Name: Database

  • Type: Container

  • Description: Persistent storage for encrypted notes and user account data. Likely a relational database or NoSQL database.

  • Responsibilities: Stores encrypted notes and user data. Provides data persistence and retrieval. Ensures data integrity and availability.

  • Security controls: Encryption at rest for stored data. Database access controls and authentication. Regular database backups. Security hardening of the database server.

  • DEPLOYMENT

Deployment Solution: Cloud-based Deployment (Common for SaaS applications)

flowchart LR
    subgraph "Cloud Provider"
        subgraph "Region"
            subgraph "Availability Zone 1"
                lb1["Load Balancer"]
                api_instance1["API Gateway Instance"]
                auth_instance1["Authentication Service Instance"]
                sync_instance1["Synchronization Service Instance"]
                db_instance1["Database Instance"]
            end
            subgraph "Availability Zone 2"
                lb2["Load Balancer"]
                api_instance2["API Gateway Instance"]
                auth_instance2["Authentication Service Instance"]
                sync_instance2["Synchronization Service Instance"]
                db_instance2["Database Instance (Replica)"]
            end
        end
        cdn["CDN"]
    end

    Internet -- "HTTPS Requests" --> cdn -- "HTTPS Requests" --> lb1
    Internet -- "HTTPS Requests" --> cdn -- "HTTPS Requests" --> lb2

    lb1 -- "Requests" --> api_instance1
    lb2 -- "Requests" --> api_instance2

    api_instance1 -- "Authentication" --> auth_instance1
    api_instance2 -- "Authentication" --> auth_instance2

    api_instance1 -- "Note Sync" --> sync_instance1
    api_instance2 -- "Note Sync" --> sync_instance2

    sync_instance1 -- "Data Storage" --> db_instance1
    sync_instance2 -- "Data Storage" --> db_instance2

    db_instance1 -- "Data Replication" --> db_instance2

    style lb1 fill:#aaf,stroke:#333,stroke-width:2px
    style lb2 fill:#aaf,stroke:#333,stroke-width:2px
    style api_instance1 fill:#eee,stroke:#333,stroke-width:2px
    style api_instance2 fill:#eee,stroke:#333,stroke-width:2px
    style auth_instance1 fill:#eee,stroke:#333,stroke-width:2px
    style auth_instance2 fill:#eee,stroke:#333,stroke-width:2px
    style sync_instance1 fill:#eee,stroke:#333,stroke-width:2px
    style sync_instance2 fill:#eee,stroke:#333,stroke-width:2px
    style db_instance1 fill:#ddd,stroke:#333,stroke-width:2px
    style db_instance2 fill:#ddd,stroke:#333,stroke-width:2px
    style cdn fill:#aaf,stroke:#333,stroke-width:2px
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  • Deployment Elements:

  • Element:

  • Name: CDN (Content Delivery Network)

  • Type: Infrastructure

  • Description: Global network of servers that caches static content (e.g., web application assets) to improve performance and availability for users worldwide.

  • Responsibilities: Caching and serving static content. Reducing latency for users. Providing DDoS protection.

  • Security controls: DDoS mitigation. Secure configuration of CDN. HTTPS support.

  • Element:

  • Name: Load Balancer (LB)

  • Type: Infrastructure

  • Description: Distributes incoming traffic across multiple instances of backend services (API Gateway). Improves availability and scalability.

  • Responsibilities: Traffic distribution. Health checks of backend instances. SSL termination.

  • Security controls: Secure configuration of load balancer. SSL/TLS encryption. Protection against common load balancer vulnerabilities.

  • Element:

  • Name: API Gateway Instance

  • Type: Infrastructure

  • Description: Virtual machine or container instance running the API Gateway software.

  • Responsibilities: API request routing, authentication, rate limiting.

  • Security controls: Security hardening of the instance. Regular security patching. Network security groups/firewalls to restrict access.

  • Element:

  • Name: Authentication Service Instance

  • Type: Infrastructure

  • Description: Virtual machine or container instance running the Authentication Service software.

  • Responsibilities: User authentication and session management.

  • Security controls: Security hardening of the instance. Regular security patching. Network security groups/firewalls to restrict access.

  • Element:

  • Name: Synchronization Service Instance

  • Type: Infrastructure

  • Description: Virtual machine or container instance running the Synchronization Service software.

  • Responsibilities: Note synchronization logic. Data handling.

  • Security controls: Security hardening of the instance. Regular security patching. Network security groups/firewalls to restrict access.

  • Element:

  • Name: Database Instance

  • Type: Infrastructure

  • Description: Managed database service instance (e.g., AWS RDS, Google Cloud SQL, Azure Database) or self-managed database server.

  • Responsibilities: Persistent storage of encrypted notes and user data. Data replication for high availability.

  • Security controls: Database access controls. Encryption at rest. Regular backups. Security hardening of the database instance. Network security groups/firewalls to restrict access.

  • Element:

  • Name: Availability Zone

  • Type: Infrastructure

  • Description: Isolated location within a cloud region. Using multiple availability zones provides redundancy and fault tolerance.

  • Responsibilities: Physical isolation and redundancy.

  • Security controls: Physical security of data centers. Redundancy to improve resilience against infrastructure failures.

  • Element:

  • Name: Region

  • Type: Infrastructure

  • Description: Geographical area containing availability zones.

  • Responsibilities: Geographical location for infrastructure deployment.

  • Security controls: Data residency compliance (depending on region and regulations).

  • BUILD

flowchart LR
    dev["Developer"] -- "Code Changes" --> vc["Version Control (GitHub)"]
    vc -- "Code Push" --> ci["CI/CD Pipeline (GitHub Actions)"]
    ci -- "Build & Test" --> build_artifacts["Build Artifacts"]
    ci -- "SAST/SCA" --> security_scan["Security Scan Results"]
    security_scan -- "Pass/Fail" --> ci
    ci -- "Publish" --> artifact_repo["Artifact Repository"]
    artifact_repo -- "Deployment" --> deployment_env["Deployment Environment"]

    style dev fill:#fff,stroke:#333,stroke-width:2px
    style vc fill:#ccf,stroke:#333,stroke-width:2px
    style ci fill:#ccf,stroke:#333,stroke-width:2px
    style build_artifacts fill:#ddd,stroke:#333,stroke-width:2px
    style security_scan fill:#ddd,stroke:#333,stroke-width:2px
    style artifact_repo fill:#ddd,stroke:#333,stroke-width:2px
    style deployment_env fill:#eee,stroke:#333,stroke-width:2px
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  • Build Elements:
  • Element:
  • Name: Developer
  • Type: Person
  • Description: Software developer who writes and modifies the application code.
  • Responsibilities: Writing secure code. Following secure coding practices. Committing code changes to version control.
  • Security controls: Security awareness training. Secure coding guidelines. Code review process.
  • Element:
  • Name: Version Control (GitHub)
  • Type: Tool
  • Description: System for tracking changes to the codebase. Provides collaboration and version history.
  • Responsibilities: Source code management. Access control to codebase. Audit logging of changes.
  • Security controls: Access control to repository (role-based access). Branch protection rules. Audit logs.
  • Element:
  • Name: CI/CD Pipeline (GitHub Actions)
  • Type: Tool
  • Description: Automated pipeline for building, testing, and deploying the application.
  • Responsibilities: Automated build process. Automated testing (unit, integration, etc.). Security scanning (SAST, SCA). Artifact publishing. Deployment automation.
  • Security controls: Secure pipeline configuration. Access control to pipeline configuration and secrets. Security scanning tools integration. Audit logging of pipeline activities.
  • Element:
  • Name: Build Artifacts
  • Type: Data
  • Description: Output of the build process, e.g., compiled code, packaged applications, container images.
  • Responsibilities: Deployable application components.
  • Security controls: Integrity checks of build artifacts (e.g., checksums, signatures). Secure storage of build artifacts.
  • Element:
  • Name: Security Scan Results
  • Type: Data
  • Description: Output of security scanning tools (SAST, SCA) indicating potential vulnerabilities.
  • Responsibilities: Identification of security vulnerabilities in code and dependencies.
  • Security controls: Automated security scanning tools. Vulnerability reporting and tracking.
  • Element:
  • Name: Artifact Repository
  • Type: Tool
  • Description: Storage for build artifacts (e.g., container registry, package repository).
  • Responsibilities: Secure storage of build artifacts. Versioning of artifacts. Access control to artifacts.
  • Security controls: Access control to artifact repository. Encryption at rest for stored artifacts. Vulnerability scanning of stored artifacts (if applicable).
  • Element:
  • Name: Deployment Environment
  • Type: Environment
  • Description: Target environment where the application is deployed (e.g., cloud infrastructure, staging environment, production environment).
  • Responsibilities: Running the application. Providing runtime environment.
  • Security controls: Security hardening of deployment environment. Network security controls. Monitoring and logging.

RISK ASSESSMENT

  • Critical Business Processes:

  • User note creation, editing, and deletion.

  • Note synchronization across devices.

  • User authentication and account management.

  • Subscription management (if applicable).

  • Data to Protect and Sensitivity:

  • User notes: Highly sensitive. Contain personal thoughts, ideas, and potentially confidential information. Confidentiality and integrity are critical.

  • User credentials (passwords): Highly sensitive. Confidentiality and integrity are critical to prevent unauthorized access.

  • User metadata (account information, settings): Sensitive. Confidentiality and integrity are important to protect user privacy and account security.

QUESTIONS & ASSUMPTIONS

  • Questions:

  • What type of database is used for the backend? (Relational, NoSQL?)

  • What specific cloud provider is used for deployment (if any)?

  • Are there any specific compliance requirements (e.g., GDPR, HIPAA)?

  • What is the process for managing and rotating encryption keys?

  • Are there any third-party integrations that need to be considered from a security perspective?

  • What is the current level of security awareness training for developers?

  • Assumptions:

  • BUSINESS POSTURE: The primary business goal is to provide a secure and private note-taking application. User privacy and data security are paramount.

  • SECURITY POSTURE: End-to-end encryption is a core security control. HTTPS is used for all communication. Secure software development lifecycle practices are followed.

  • DESIGN: The application uses a cloud-based backend architecture with separate services for API gateway, authentication, and synchronization. A relational or NoSQL database is used for persistent storage. Client applications handle end-to-end encryption. Deployment is likely on a major cloud provider using multiple availability zones for high availability. GitHub Actions or similar CI/CD is used for build and deployment automation.