Introduction

SymCrypt is the core cryptographic function library currently used by Windows.

History

The library was started in late 2006 with the first sources committed in Feb 2007. Initially the goal was limited to implement symmetric cryptographic operations, hence the name. Starting with Windows 8, it has been the primary crypto library for symmetric algorithms.

In 2015 we started the work of adding asymmetric algorithms to SymCrypt. Since the 1703 release of Windows 10, SymCrypt has been the primary crypto library for all algorithms in Windows.

Goals

Like any engineering project, SymCrypt is a compromise between conflicting requirements:

• Provide safe implementations of the cryptographic algorithms needed by Microsoft products.
• Run on all CPU architectures supported by Windows.
• Good performance.
• Minimize maintenance cost.
• Support FIPS 140-2 certification of products using SymCrypt.
• Provide high assurance in the proper functionality of the library.

Clone the Repo

In some of our Linux modules, SymCrypt uses Jitterentropy as a source of FIPS-certifiable entropy. To build these modules, you will need to ensure that the jitterentropy-library submodule is also cloned. You can do this by running git submodule update --init -- jitterentropy-library after cloning.

The SymCryptDependencies submodule provides the RSA32 and msbignum implementations which are used as benchmarks in the unit tests when compiled on Windows. Due to licensing restrictions, we cannot release these libraries publicly, so this submodule will only be cloneable by Microsoft employees with access to our private Azure DevOps repository. If you are external to Microsoft, you can ignore this submodule. It is only used in the unit tests and does not change the behavior of the SymCrypt product code.

Build and Test

SymCrypt can be compiled with CMake >= 3.13.0 and Visual Studio 2019 (with Windows 10 SDK version 18362) on Windows or gcc 7.4.0 or clang 10.0.0 on Linux. Note that CMake ships with Visual Studio 2019.

Python3 is also required for translation of SymCryptAsm, and for building the SymCrypt module with integrity check. The integrity check additionally requires pip and pyelftools: pip3 install -r ./scripts/requirements.txt

1. Optionally use CMake from Visual Studio $env:PATH="C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\Common7\IDE\CommonExtensions\Microsoft\CMake\CMake\bin\;${env:PATH}"
2. For Microsoft employees building the library internally, to include msbignum and RSA32 implementation benchmarks in the unit tests:
   1. Make sure the SymCryptDependencies submodule is initialized by following the steps above (git submodule update --init)
   2. In step 4 below, add the additional cmake argument -DSYMCRYPT_INTERNAL_BUILD=1
3. mkdir bin; cd bin
4. Configure CMake compilation:
   • For x86 Windows targets: cmake .. -DCMAKE_TOOLCHAIN_FILE="../cmake-toolchain/WindowsUserMode-X86.cmake" -A Win32
   • For x86-64 Windows targets: cmake .. -DCMAKE_TOOLCHAIN_FILE="../cmake-toolchain/WindowsUserMode-AMD64.cmake"
   • For x86-64 Linux targets: cmake .. -DCMAKE_TOOLCHAIN_FILE="../cmake-toolchain/LinuxUserMode-AMD64.cmake"
   • For ARM64 Linux targets: cmake .. -DCMAKE_TOOLCHAIN_FILE="../cmake-toolchain/LinuxUserMode-ARM64.cmake"
   • For no CPU optimizations: cmake ..
   • Optionally, for a release build, specify -DCMAKE_BUILD_TYPE=Release
5. cmake --build .
   • Optionally, for a release build on Windows, specify --config Release
   • Optionally specify -jN where N is the number of processes you wish to spawn for the build

If compilation succeeds, the output will be put in the exe subdirectory relative to where compilation occurred (i.e. bin/exe if you followed the instructions above).

The SymCrypt unit test is in the unittest directory. It runs extensive functional tests on the SymCrypt library. On Windows it also compares results against on other implementations such as the Windows APIs CNG and CAPI, and the older crypto libraries rsa32 and msbignum, if they are available. It also provides detailed performance information.

Versioning and Servicing

As of version 101.0.0, SymCrypt uses the version scheme defined by the Semantic Versioning 2.0.0 specification. This means:

• Major version changes introduce ABI and/or API breaking changes
• Minor version changes introduce backwards compatible additional functionality or improvements, and/or bug fixes
• Patch version changes introduce backwards compatible bug fixes

The initial open source release started at version 100 for compatibility with our previous internal versioning scheme.

Regarding servicing, our strong recommendation is that distro vendors and application developers regularly update to the latest version of SymCrypt and SymCrypt engine for both security fixes and functionality/performance improvements. We take care to maintain a stable API and ABI for SymCrypt and have a suite of strong regression tests, and staying on the current version prevents the need for complex and potential riskier backports.

We will support long-term servicing of specific releases for security fixes. Details of this plan will be released publicly in the future.

Security Bugs

If you believe you have found a problem that affects the security of this code, please do NOT create an issue or pull request, but instead email your comments to secure@microsoft.com.

Contribute

We love to receive comments and suggestions. Unfortunately we cannot accept external code contributions at this time. Cryptographic code is considered highly sensitive by many of our large customers. We have some very big customers who put great value in the assurance of the crypto code used in their organization. By restricting the coding to a handful of employees we can greatly reduce the (perceived) risk of malicious contributions.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.