Mbed Crypto

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The cryptography library in Mbed TLS is a reference implementation of the cryptography interface of the Arm Platform Security Architecture (PSA). This cryptography library is called Mbed Crypto and used to be developed in its own github repository.

The development of Mbed Crypto has moved to Mbed TLS. No updates will be made to the mbed-crypto repository anymore.

Mbed TLS and Mbed Crypto have the same APIs, and the same build system, so most users only need to change the URL to clone or download the library from.

To save build time and possibly avoid system dependencies, you may want to exclude the X.509 and TLS parts of the library by running

scripts/config.py crypto

or

scripts/config.py crypto_full

before building Mbed TLS.

The rest of this document gives more details on this migration.

Building Mbed/PSA Crypto from the mbedtls repo

This document explains how to build the Mbed Crypto library (the current incarnation of the PSA Crypto library) from the mbedtls repository.

The intended audience is users of Mbed Crypto or PSA Crypto who used to get it from the mbed-crypto repository, and will now need to get it from the mbedtls repository. Users who have always been getting Mbed Crypto from the mbedtls repository and building it as part of Mbed TLS are unaffected.

Summary

• Run` scripts/config.py crypto` before you build;
• build as usual;
• keep libmbedcrypto.a or libmbedcrypto.so;
• discard the other library files if you don't need them.

When using the default config.h

You can just build as usual (using make or cmake+make) and only keep libmbedcrypto.a from the build results, discarding the other libraries.

Alternatively, if you want to avoid building the X.509 and TLS libraries before discarding them, you can run scripts/config.py crypto before running make (possibly after cmake). This will still create empty files for the
X.509 and TLS libraries, but not waste resources building them.

When starting from the default config.h and adapting it with config.py

If you're using a custom config.h derived from the default one by running a number of scripts/config.py set/unset XXX commands, then you can just append scripts/config.py crypto to your list of existing calls to config.py and
build as usual.

Again, this will create empty files for the X.509 and TLS libraries, but not waste resources building them. Just discard those files and use libmbedcrypto.a as usual.

Unlike the case of using the default config, running scripts/config.py crypto is required here, to avoid check_config.h complaining if your custom crypto build is not compatible with the default TLS options.

When using a user config file

If you're starting from the default config.h but customizing it using a user config file, by setting the MBEDTLS_USER_CONFIG_FILE, then you can just run cripts/config.py crypto before your build as usual. This will modify the default config.h but will keep your user config file unchanged.

Again, this will create empty files for the X.509 and TLS libraries, but not waste resources building them. Just discard those files and use libmbedcrypto.a as usual.

Unlike the case of using the default config, running scripts/config.py crypto is required here, to avoid check_config.h complaining if your custom crypto build is not compatible with the default TLS options.

When using a standalone config.h

If you're using a custom stand-alone config.h, that is one that's maintained independently and replaces the default one (either by overwriting it with your file, or setting MBEDTLS_CONFIG_FILE in your build environment), then you
can just keep your file as is (assuming you're only setting crypto options in it) and build as usual.

Again, this will create empty files for the X.509 and TLS libraries, but not waste resources building them. Just discard those files and use libmbedcrypto.a as usual.

If your custom standalone config.h was not clean and included X.509 or TLS settings despite targeting Mbed Crypto, you might get errors from check_config.h. These would be resolved by running scripts/config.py -f <path_to/your_config.h> crypto just one time. After that you can keep using and maintaining your standalone config.h as usual.