The openssl package implements Go crypto primitives using OpenSSL shared libraries and cgo. When configured correctly, OpenSSL can be executed in FIPS mode, making the openssl package FIPS compliant.
The openssl package is designed to be used as a drop-in replacement for the boring package in order to facilitate integrating openssl inside a forked Go toolchain.
A program directly or indirectly using this package in FIPS mode can claim it is using a FIPS-certified cryptographic module (OpenSSL), but it can't claim the program as a whole is FIPS certified without passing the certification process, nor claim it is FIPS compliant without ensuring all crypto APIs and workflows are implemented in a FIPS-compliant manner.
FIPS 140-2 is a U.S. government computer security standard used to approve cryptographic modules. FIPS compliance may come up when working with U.S. government and other regulated industries.
The Go crypto package is not FIPS certified, and the Go team has stated that it won't be, e.g. in golang/go/issues/21734 Adam Langley says:
The status of FIPS 140 for Go itself remains "no plans, basically zero chance".
On the other hand, Google maintains a branch that uses cgo and BoringSSL to implement various crypto primitives: https://github.com/golang/go/blob/dev.boringcrypto/README.boringcrypto.md. As BoringSSL is FIPS 140-2 certified, an application using that branch is more likely to be FIPS 140-2 compliant, yet Google does not provide any liability about the suitability of this code in relation to the FIPS 140-2 standard.
The openssl package has support for multiple OpenSSL versions, namely 1.0.2, 1.1.0, 1.1.1 and 3.0.2.
All supported OpenSSL versions passes an small set of automatic tests that ensure they can be built and that there are no major regressions.
These tests do not validate the cryptographic correctness of the openssl package.
On top of that, the Microsoft CI builds and tests a subset of the supported OpenSSL versions as part of the Microsoft Go fork release process. These tests are much more exhaustive and validate a specific OpenSSL version can produce working applications. Currently only OpenSSL 1.1.1 goes through this process.
Versions not listed above are not supported at all.
The OpenSSL shared library libcrypto is loaded at runtime using dlopen when calling openssl.Init. Therefore, dlopen's shared library search conventions also apply here.
The libcrypto shared library file name varies among different platforms, so a best effort is done to find and load the right file:
- The base name is always
libcrypto.so. - Well-known version strings are appended to the base name, until the file is found, in the following order:
3->1.1->11->111->1.0.2->1.0.0.
This algorithm can be overridden by setting the environment variable GO_OPENSSL_VERSION_OVERRIDE to the desired version string. For example, GO_OPENSSL_VERSION_OVERRIDE="1.1.1k-fips" makes the runtime look for the shared library libcrypto.so.1.1.1k-fips before running the checks for well-known versions.
The openssl package does not use any symbol from the OpenSSL headers. There is no need that have them installed to build an application which imports this library.
Microsoft CI verifies that all the functions and constants defined in our headers match the ones in the OpenSSL headers for every supported OpenSSL version.
The OpenSSL bindings are implemented in such a way that the OpenSSL version used when building a program does not have to match with the OpenSSL version used when running it.
This feature does not require any additional configuration, but it only works with OpenSSL versions known and supported by the Go toolchain.
OpenSSL is used for a given build only in limited circumstances:
- The platform must be GOOS=linux.
- The build must have cgo enabled.
- The android build tag must not be specified.
The work done to support FIPS compatibility mode leverages code and ideas from other open-source projects:
- All crypto stubs are a mirror of Google's dev.boringcrypto branch and the release branch ports of that branch.
- The mapping between BoringSSL and OpenSSL APIs is taken from Fedora's Go fork.
- The portable OpenSSL implementation is ported from Microsoft's .NET runtime cryptography module.
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