mbedtls

This is an idiomatic Rust wrapper for MbedTLS, allowing you to use MbedTLS with only safe code while being able to use such great Rust features like error handling and closures.

Additionally, building on MbedTLS's focus on embedded use, this crate can be used in a no_std environment.

Building

This crate depends on the mbedtls-sys-auto crate, see below for build details.

Features

This is a list of the Cargo features available for mbedtls. Features in bold are enabled by default.

• aesni Enable support for the AES-NI instructions. On SGX, this feature is enabled automatically.
• debug Enable debug printing to stdout. You need to configure the debug threshold at runtime.
• dsa Enable support for DSA signatures
• force_aesni_support MbedTLS normally uses runtime detection of AES-NI support. With this feature, always use AES-NI. This will result in undefined instruction exceptions on unsupported processors. On SGX, this feature is enabled automatically.
• mpi_force_c_code Enables the mpi_force_c_code feature in mbedtls-sys
• legacy_protocols Enable support for SSLv3, TLSv1.0 and TLSv1.1
• no_std_deps On no_std, you must enable this feature. It enables optional dependencies needed on no_std. If the std feature is enabled, this feature is ignored.
• padlock Enable support for VIA padlock.
• pkcs12 Enable code to parse PKCS12 files using yasna
• pkcs12_rc2 Enable use of RC2 crate to decrypt RC2-encrypted PKCS12 files
• rdrand Enable the RDRAND random number generator. On SGX, this feature is enabled automatically.
• std If this feature is not enabled, this crate is a no_std crate. (An allocator is required) The necessary C functions to make MbedTLS work without libc will be provided.
• time Enable time support in mbedtls-sys.
• zlib Enable zlib support in mbedtls-sys.

PRs adding new features are encouraged.

mbedtls-sys-auto

Unfortunately, the mbedtls-sys crate on crates.io is claimed by another, apparently inactive, project.

To use this crate, you will need to have clang and cmake installed, see below for details.

Configuring and linking MbedTLS

MbedTLS has a plethora of compile-time configuration options that significantly impact what functionality is available. To make sure Rust's view of MbedTLS matches up with what's built in C, MbedTLS must be configured using Cargo features (see next section) and built using mbedtls-sys's build script.

The mbedtls-sys crate includes the MbedTLS source code, the MbedTLS version will have the same major.minor version as the crate. Instead of using the provided source, you can specify the path to your own source tree using the RUST_MBEDTLS_SYS_SOURCE environment variable. It is not recommended to use a custom source that is based on a different version of MbedTLS than the one provided in the crate.

The build script will perform the following steps:

1. generate an appropriate config.h (any existing config.h is ignored),
2. compile a statically-linked MbedTLS, this requires cmake to be installed,
3. generate Rust bindings based on the configuration, this requires clang to be installed.

Features

This is a list of the Cargo features available for mbedtls-sys. Features in bold are enabled by default.

• aesni Enable support for the AES-NI instructions. On SGX, this feature is enabled automatically.
• aes_alt Allow an alternative implementation of AES, replacing the T-tables code.
• custom_has_support Override runtime feature detection. In a dependent crate, you must define the functions mbedtls_aesni_has_support and mbedtls_padlock_has_support following the MbedTLS function signatures. On SGX, this feature is enabled automatically.
• custom_printf Provide a custom printf implementation. printf is only used for the self tests. In a dependent crate, you must define the mbedtls_printf function with the standard printf signature.
• debug Enable debug callbacks.
• havege Enable the Hardware Volatile Entropy Gathering and Expansion (HAVEGE) algorithm.
• legacy_protocols Enable support for SSLv3, TLSv1.0 and TLSv1.1
• mpi_force_c_code MbedTLS uses assembly code for MPI functions, when available. In some situations we may prefer C code instead. This is in particular the case on x86 platforms where compile-time mitigation for speculative execution is required (e.g., LVI). Letting the compiler insert the required lfences during C-code compilation may result in faster code than letting the compiler apply mitigations on assembly code.
• padlock Enable support for VIA padlock.
• pkcs11 Enable PKCS#11 support. This requires pkcs11-helper to be installed.
• std If this feature is not enabled, this crate is a no_std crate. In a no_std configuration without libc, you need to provide your own versions of the following standard C functions: calloc()/free(), and strstr()/strlen()/strncpy()/strncmp()/strcmp()/ snprintf(), and memmove()/memcpy()/memcmp()/memset(), and rand()/printf(). For printf(), you can optionally use the custom_printf feature. rand() is only needed for the selftests. On UNIX platforms, this also enables networking, filesystems and OS entropy.
• threading Enable threading support. On cfg(unix) platforms, this uses pthreads. On other platforms, you need to provide a custom threading implementation. In a dependent crate, you must define the functions mbedtls_mutex_init(), mbedtls_mutex_free(), mbedtls_mutex_lock(), and mbedtls_mutex_unlock() following the MbedTLS function signatures.
• time Enable time support. On cfg(unix) platforms, this uses libc. On other platforms, you need to provide your own implementations of mbedtls_platform_gmtime_r(const long long*, struct tm*) and mbedtls_time(long long*).
• trusted_cert_callback Enable trusted certificate callback support.
• zlib Enable zlib support.

For the complete mapping of features to config.h defines, see [mbedtls-sys/build/config.rs]. PRs adding new features are encouraged.

MbedTLS version updates

Instructions for updating to new MbedTLS source code releases in mbedtls-sys/:

1. Wipe out vendor/ and replace it with the contents of the distribution tarball.
2. Cherry-pick any local changes from the previous version.
3. Use the command in build/headers.rs to generate the list of headers, and update that file as appropriate.
4. Check build/config.rs vs. vendor/include/mbedtls/config.h.
5. Update Cargo.toml version number.

Contributing

We gratefully accept bug reports and contributions from the community. By participating in this community, you agree to abide by Code of Conduct. All contributions are covered under the Developer's Certificate of Origin (DCO).

Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I have the right to submit it under the open source license indicated in the file; or

(b) The contribution is based upon previous work that, to the best of my knowledge, is covered under an appropriate open source license and I have the right under that license to submit that work with modifications, whether created in whole or in part by me, under the same open source license (unless I am permitted to submit under a different license), as indicated in the file; or

(c) The contribution was provided directly to me by some other person who certified (a), (b) or (c) and I have not modified it.

(d) I understand and agree that this project and the contribution are public and that a record of the contribution (including all personal information I submit with it, including my sign-off) is maintained indefinitely and may be redistributed consistent with this project or the open source license(s) involved.

License

This project is primarily distributed under the terms of the Apache License version 2.0 and the GNU General Public License version 2, see LICENSE-APACHE and LICENSE-GPL for details.

A note about licensing

MbedTLS is dual-licensed Apache-2.0 / GPL-2.0+, and so are the mbedtls and mbedtls-sys-auto crates. However, the sources are distributed in two different single-licensed tarballs. The authors of the mbedtls and mbedtls-sys-auto crates do not warrant that the two versions of the MbedTLS code are exactly the same. This repository includes the Apache-2.0 version. Since Apache-2.0 is compatible with GPL-3.0+ this is probably not an issue for people whishing to use mbedtls-sys in a GPL-3.0+-licensed project, but if you want to use it in a GPL-2.0-licensed project, you should probably manually specify the GPL-2.0 source when building.