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Zstandard Project Design Document

BUSINESS POSTURE

Zstandard (Zstd) is a fast, lossless compression algorithm and implementation developed by Facebook. It aims to provide a combination of high compression ratios and very fast compression/decompression speeds, filling a gap between traditional algorithms like zlib (which prioritizes compatibility and decent compression) and newer algorithms like LZ4 (which prioritizes speed above all else).

Business Priorities and Goals:

  • Reduce storage costs: By achieving high compression ratios, Zstd can significantly reduce the amount of storage space required for data, leading to cost savings, especially at Facebook's scale.
  • Improve data transfer speeds: Faster compression and decompression speeds translate to quicker data transfers over networks, reducing latency and improving application performance.
  • Enhance data processing efficiency: Faster data access allows for quicker processing of compressed data, benefiting various applications like databases, search indexes, and big data analytics.
  • Open Source and Community Adoption: Promote widespread adoption of Zstd by making it open-source and encouraging community contributions. This fosters innovation and ensures the algorithm's long-term viability.
  • Wide Applicability: Design the algorithm and library to be versatile and applicable across a wide range of use cases, from embedded systems to large-scale data centers.

Business Risks:

  • Data Loss: Although Zstd is designed for lossless compression, bugs in the implementation could potentially lead to data corruption or loss. This is a critical risk that must be mitigated through rigorous testing and quality assurance.
  • Performance Degradation: Unexpected performance issues in specific scenarios or with particular data types could negate the intended benefits of Zstd.
  • Security Vulnerabilities: Vulnerabilities in the compression/decompression library could be exploited by attackers to compromise systems or data.
  • Adoption Challenges: Lack of widespread adoption could limit the benefits of Zstd, especially in scenarios requiring interoperability with other systems.
  • Intellectual Property Issues: Potential patent or copyright issues could hinder the development or use of Zstd. (This is less likely given Facebook's open-source approach, but still a consideration).

SECURITY POSTURE

Existing Security Controls:

  • security control: Fuzzing: Extensive fuzzing is used to test the robustness of the Zstd library against unexpected or malformed input. This helps prevent crashes, buffer overflows, and other potential security vulnerabilities. (Described in the fuzz/ directory and related documentation).
  • security control: Static Analysis: Static analysis tools are likely used to identify potential coding errors and security vulnerabilities before runtime. (Mentioned in various parts of the documentation and build process).
  • security control: Code Reviews: All code changes undergo thorough code reviews by other developers to ensure code quality and security. (Standard practice for open-source projects on GitHub).
  • security control: Memory Safety: The code is written in C, which is not inherently memory-safe. However, careful coding practices and the use of tools like AddressSanitizer (ASan) and Valgrind help mitigate memory safety issues. (Implied by the project's focus on robustness and the use of fuzzing).
  • security control: Regular Updates: The Zstd team actively maintains the library and releases updates to address bug fixes and security vulnerabilities. (Evidenced by the release history on GitHub).
  • security control: Community Scrutiny: Being an open-source project, Zstd benefits from scrutiny by the wider security community, which helps identify and address potential vulnerabilities.

Accepted Risks:

  • accepted risk: Complexity of C Code: The use of C, while providing performance benefits, introduces inherent risks related to memory management and potential vulnerabilities that are harder to completely eliminate compared to memory-safe languages.
  • accepted risk: Zero-Day Vulnerabilities: Despite all precautions, there's always a risk of undiscovered (zero-day) vulnerabilities that could be exploited before a patch is available.
  • accepted risk: Dependence on External Libraries: While Zstd minimizes external dependencies, any vulnerabilities in those dependencies could potentially impact Zstd's security.

Recommended Security Controls:

  • security control: Continuous Fuzzing: Integrate fuzzing into the continuous integration (CI) pipeline to ensure that every code change is automatically tested for vulnerabilities.
  • security control: Static Analysis Integration: Formally integrate static analysis tools into the CI pipeline and establish clear rules for addressing identified issues.
  • security control: Software Composition Analysis (SCA): Implement SCA to identify and track any third-party libraries used by Zstd, and monitor them for known vulnerabilities.
  • security control: Security Audits: Conduct periodic independent security audits of the Zstd codebase to identify potential vulnerabilities that might be missed by internal reviews.

Security Requirements:

  • Authentication: Not directly applicable to a compression library.
  • Authorization: Not directly applicable to a compression library.
  • Input Validation:
    • The library must handle malformed or corrupted compressed data gracefully, without crashing or exhibiting undefined behavior.
    • The library should validate the integrity of compressed data using checksums (already implemented).
    • The library should protect against decompression bombs (maliciously crafted compressed data that expands to an extremely large size).
  • Cryptography:
    • While Zstd itself is not an encryption algorithm, it should be compatible with encryption. It should be possible to compress data and then encrypt it, or vice versa, without issues.
    • If any cryptographic features are added (e.g., for integrity checks), they must use well-established and secure cryptographic algorithms.
  • Memory Management:
    • The library must handle memory allocation and deallocation safely to prevent memory leaks and buffer overflows.
    • The library should be robust against out-of-memory conditions.

DESIGN

C4 CONTEXT

graph LR
    User(("User\n(Application/System)")) --> Zstd((Zstd\n(Compression Library)))
    Zstd --> FileSystem((File System))
    Zstd --> Network((Network))
    Zstd --> OtherSystems((Other Systems\nusing Zstd))
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Element Descriptions:

  • Element:

    • Name: User
    • Type: Application/System
    • Description: Any application or system that utilizes the Zstd library for compression or decompression.
    • Responsibilities: Calls the Zstd API to compress or decompress data.
    • Security controls: Depends on the specific application; not directly controlled by Zstd.

  • Element:

    • Name: Zstd
    • Type: Compression Library
    • Description: The Zstandard compression library.
    • Responsibilities: Provides functions for compressing and decompressing data.
    • Security controls: Fuzzing, static analysis, code reviews, memory safety practices, regular updates, community scrutiny.

  • Element:

    • Name: File System
    • Type: External System
    • Description: The file system where compressed or uncompressed data is stored.
    • Responsibilities: Stores and retrieves data.
    • Security controls: File system permissions, access controls, encryption (if used).

  • Element:

    • Name: Network
    • Type: External System
    • Description: The network over which compressed or uncompressed data is transmitted.
    • Responsibilities: Transmits data between systems.
    • Security controls: Network security protocols (TLS/SSL), firewalls, intrusion detection systems.

  • Element:

    • Name: Other Systems
    • Type: External System
    • Description: Other systems or applications that also use Zstd and may interact with the primary user.
    • Responsibilities: Compress or decompress data using Zstd.
    • Security controls: Similar to the "User" element; depends on the specific system.

C4 CONTAINER

Since Zstd is a library, the container diagram is essentially an expanded view of the context diagram.

graph LR
    User(("User\n(Application/System)")) --> ZstdAPI((Zstd API))
    ZstdAPI --> CompressionModule((Compression\nModule))
    ZstdAPI --> DecompressionModule((Decompression\nModule))
    ZstdAPI --> DictionaryBuilder((Dictionary\nBuilder\n(Optional)))
    CompressionModule --> FileSystem((File System))
    DecompressionModule --> FileSystem((File System))
    CompressionModule --> Network((Network))
    DecompressionModule --> Network((Network))
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Element Descriptions:

  • Element:

    • Name: User
    • Type: Application/System
    • Description: Any application or system that utilizes the Zstd library.
    • Responsibilities: Calls the Zstd API.
    • Security controls: Application-specific.

  • Element:

    • Name: Zstd API
    • Type: API
    • Description: The public interface of the Zstd library.
    • Responsibilities: Provides functions for compression, decompression, and dictionary building.
    • Security controls: Input validation, error handling.

  • Element:

    • Name: Compression Module
    • Type: Library Component
    • Description: The core logic for compressing data.
    • Responsibilities: Implements the Zstandard compression algorithm.
    • Security controls: Fuzzing, static analysis, memory safety practices.

  • Element:

    • Name: Decompression Module
    • Type: Library Component
    • Description: The core logic for decompressing data.
    • Responsibilities: Implements the Zstandard decompression algorithm.
    • Security controls: Fuzzing, static analysis, memory safety practices, decompression bomb protection.

  • Element:

    • Name: Dictionary Builder
    • Type: Library Component (Optional)
    • Description: Functionality for creating custom compression dictionaries.
    • Responsibilities: Builds dictionaries to improve compression ratios for specific data types.
    • Security controls: Input validation, memory safety practices.

  • Element:

    • Name: File System
    • Type: External System
    • Description: The file system.
    • Responsibilities: Stores and retrieves data.
    • Security controls: File system permissions, access controls.

  • Element:

    • Name: Network
    • Type: External System
    • Description: The network.
    • Responsibilities: Transmits data.
    • Security controls: Network security protocols.

DEPLOYMENT

Zstd is a library, and its deployment is typically integrated into the deployment process of the application that uses it. There are several possible deployment scenarios:

  1. Static Linking: The Zstd library is compiled directly into the application executable.
  2. Dynamic Linking: The Zstd library is compiled as a shared library (e.g., .so, .dll) and loaded by the application at runtime.
  3. System-Wide Installation: The Zstd library is installed as a system-wide library, making it available to all applications on the system.
  4. Containerization: The application and the Zstd library (either statically or dynamically linked) are packaged together within a container (e.g., Docker).

We'll describe the Dynamic Linking scenario in detail, as it's a common and illustrative approach.

graph LR
    AppServer(("Application Server")) --> ZstdLib((Zstd Shared Library\n(e.g., libzstd.so)))
    AppServer --> App((Application\nusing Zstd))
    OS((Operating System)) --> AppServer
    OS --> ZstdLib
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Element Descriptions:

  • Element:

    • Name: App Server
    • Type: Server
    • Description: The server where the application is deployed.
    • Responsibilities: Runs the application.
    • Security controls: Operating system security, firewall, access controls.

  • Element:

    • Name: Zstd Shared Library
    • Type: Shared Library
    • Description: The compiled Zstd library (e.g., libzstd.so on Linux, libzstd.dll on Windows).
    • Responsibilities: Provides compression/decompression functionality.
    • Security controls: Regular updates, code signing (if applicable).

  • Element:

    • Name: Application
    • Type: Application
    • Description: The application that uses the Zstd library.
    • Responsibilities: Performs its intended function, utilizing Zstd for compression/decompression.
    • Security controls: Application-specific security measures.

  • Element:

    • Name: Operating System
    • Type: Operating System
    • Description: The underlying operating system.
    • Responsibilities: Manages system resources, loads shared libraries.
    • Security controls: OS security updates, security hardening.

BUILD

The Zstd build process is automated and uses a combination of Makefiles and CMake. The process generally involves the following steps:

  1. Developer: A developer writes code and commits changes to the GitHub repository.
  2. Continuous Integration (CI): A CI system (e.g., GitHub Actions, Travis CI, CircleCI) is triggered by the commit.
  3. Source Code Checkout: The CI system checks out the source code from the repository.
  4. Build Environment Setup: The CI system sets up the build environment, including installing necessary dependencies (e.g., compiler, build tools).
  5. Compilation: The source code is compiled using the chosen build system (Make or CMake).
  6. Testing: The compiled library is tested using a suite of unit tests and integration tests. This includes fuzzing.
  7. Static Analysis: Static analysis tools are run to identify potential code quality and security issues.
  8. Artifact Creation: If all tests pass, build artifacts are created (e.g., static libraries, shared libraries, executables).
  9. Artifact Storage/Publication: The build artifacts are stored or published (e.g., to a release on GitHub, to a package repository).
graph LR
    Developer((Developer)) --> GitHub((GitHub Repository))
    GitHub -- Trigger --> CI((CI System\n(GitHub Actions, etc.)))
    CI --> Checkout((Checkout Source Code))
    Checkout --> Setup((Setup Build Environment))
    Setup --> Compile((Compile Code))
    Compile --> Test((Run Tests\n(Unit, Integration, Fuzzing)))
    Test --> StaticAnalysis((Static Analysis))
    StaticAnalysis -- Pass --> Artifacts((Create Artifacts\n(libzstd.a, libzstd.so, etc.)))
    Artifacts --> Publish((Publish/Store Artifacts))
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Security Controls in the Build Process:

  • security control: CI/CD: Automation of the build process ensures consistency and reduces the risk of manual errors.
  • security control: Fuzzing: Fuzzing is integrated into the testing phase to identify vulnerabilities.
  • security control: Static Analysis: Static analysis tools are used to detect potential coding errors and security issues.
  • security control: Dependency Management: The build process should manage dependencies securely, ensuring that only trusted and up-to-date libraries are used. (This is an area for potential improvement using SCA).
  • security control: Code Signing: Build artifacts (especially shared libraries) can be code-signed to ensure their authenticity and integrity. (This is not explicitly mentioned in the Zstd documentation but is a recommended practice).

RISK ASSESSMENT

Critical Business Processes:

  • Data Storage: Efficient and reliable storage of large amounts of data.
  • Data Transfer: Fast and efficient transfer of data over networks.
  • Data Processing: Quick access to and processing of compressed data.

Data Sensitivity:

  • The Zstd library itself does not handle sensitive data directly. It operates on byte streams. The sensitivity of the data being compressed or decompressed depends entirely on the application using Zstd.
  • Therefore, the data sensitivity is classified as variable, ranging from non-sensitive (e.g., public datasets) to highly sensitive (e.g., user data, financial records, proprietary information). The application using Zstd is responsible for protecting the data appropriately, before and after compression/decompression.

QUESTIONS & ASSUMPTIONS

Questions:

  • Are there any specific compliance requirements (e.g., FIPS 140-2) that Zstd needs to meet in certain deployment scenarios?
  • What is the process for reporting and handling security vulnerabilities discovered in Zstd?
  • What are the specific static analysis tools used in the build process, and what rules are enforced?
  • Are there any plans to formally integrate Software Composition Analysis (SCA) into the build pipeline?
  • Are there any plans to conduct regular independent security audits of the Zstd codebase?

Assumptions:

  • BUSINESS POSTURE: Facebook (Meta) prioritizes performance, efficiency, and open-source collaboration.
  • SECURITY POSTURE: The Zstd development team follows secure coding practices and is responsive to security concerns.
  • DESIGN: The library is designed to be modular and extensible, allowing for future enhancements and optimizations. The primary use case is within Facebook's infrastructure, but it's also intended for broad adoption.