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Cryptographic library
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NielsFerguson Merged PR 3206192: Publish new version 2019-04-29
Various fixes

Related work items: #20814154, #21329664
Latest commit 13e3c0c May 1, 2019


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

At the moment this library only compiles with the Windows build system. Unfortunately this toolchain is not available outside Microsoft. We expect to have a Linux port working in the near future.

The SymCrypt unit test is in the \unittest directory. It runs extensive functional tests on the SymCrypt library, as well as on other implementations such as the Windows APIs CNG and CAPI, and the older crypto libraries rsa32 and msbignum. 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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