November 3, 2019

461 words 3 mins read



Cryptographic library

repo name microsoft/SymCrypt
repo link
language C
size (curr.) 28962 kB
stars (curr.) 489
created 2019-03-15
license MIT License


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


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.


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.

Build and Test

SymCrypt can be compiled with CMake >= 2.8.9 and Visual Studio 2019 (with Windows 10 SDK version 18362) on Windows or gcc 7.4.0 on Linux. Note that CMake ships with Visual Studio 2019.

  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. git submodule update --init
  3. mkdir bin; cd bin
  4. Configure CMake compilation:
    • For 32-bit Windows targets: cmake .. -DCMAKE_TOOLCHAIN_FILE=../cmake-toolchain/windows-x86.cmake -A Win32
    • For 64-bit Windows targets: cmake .. -DCMAKE_TOOLCHAIN_FILE=../cmake-toolchain/windows-amd64.cmake
    • For Linux (or Windows with no CPU optimizations): cmake ..
  5. cmake --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.

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


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 with any additional questions or comments.

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