README for TF-PSA-Crypto

The TF-PSA-Crypto repository provides an implementation of the PSA Cryptography API version 1.2, with the limitation that the implementation of the PAKE extension still has minor non-compliances, such as returned error codes.

The PSA Cryptography API implementation is organized around the PSA Cryptography driver interface aiming to ease the support of cryptographic accelerators and processors.

PSA Cryptography API

The PSA Cryptography API provides access to a set of cryptographic primitives. It has a dual purpose. First, it can be used in a PSA-compliant platform to build services, such as secure boot, secure storage and secure communication. Second, it can also be used independently of other PSA components on any platform.

The design goals of the PSA Cryptography API include:

• The API distinguishes caller memory from internal memory, which allows the library to be implemented in an isolated space for additional security. Library calls can be implemented as direct function calls if isolation is not desired, and as remote procedure calls if isolation is desired.
• The structure of internal data is hidden to the application, which allows substituting alternative implementations at build time or run time, for example, in order to take advantage of hardware accelerators.
• All access to the keys happens through key identifiers, which allows support for external cryptoprocessors that is transparent to applications.
• The interface to algorithms is generic, favoring algorithm agility.
• The interface is designed to be easy to use and hard to accidentally misuse.

We welcomes feedback on the design of the API. If you think something could be improved, please open an issue on our Github repository. Alternatively, if you prefer to provide your feedback privately, please email us at [email protected]. All feedback received by email is treated confidentially.

PSA Cryptography API implementation in TF-PSA-Crypto

TF-PSA-Crypto includes an implementation of the PSA Cryptography API. It covers most, but not all algorithms.

PSA Cryptography driver interface

TF-PSA-Crypto supports drivers for cryptographic accelerators, secure elements and random generators. This is work in progress. Please note that the driver interfaces are not fully stable yet and may change without notice. We intend to preserve backward compatibility for application code (using the PSA Cryptography API), but the code of the drivers may have to change in future minor releases of TF-PSA-Crypto.

Please see the PSA driver example and guide for information on writing a driver.

Configuration

The TF-PSA-Crypto repository should build out of the box on most systems. Its configuration is based on C preprocessor macros defined in include/psa/crypto_config.h.

These configuration options are organized into seven groups:

1. Cryptographic mechanism selection (PSA API): PSA_WANT_xxx macros that specify which parts of the PSA Cryptography API the user wants to enable, e.g. cryptographic algorithms, key types, elliptic curves.
2. Platform abstraction layer: Options to port the library to different platforms.
3. General and test configuration options: Options that are test-specific or not related to a particular part of the library.
4. Cryptographic mechanism selection (extended API): Options to enable cryptographic mechanisms beyond the current PSA Cryptography API, such as LMS or key wrapping.
5. Data format support: Options to enable support for various data formats, such as ASN.1 or PEM.
6. PSA core: Options to configure components other than cryptographic mechanisms, such as key management and random number generation.
7. Built-in drivers: Options to configure non-functional aspects of built-in cryptographic mechanisms such as performance/size trade-offs.

The file include/psa/crypto_config.h can be edited manually, or in a more programmatic way using the Python script scripts/config.py (use --help for usage instructions).

We provide some non-standard configurations focused on specific use cases in the configs/ directory. You can read more about those in configs/README.txt.

Documentation

Documentation for the PSA Cryptography API is available on GitHub.

To generate a local copy of the library documentation in HTML format:

1. Make sure that Doxygen is installed.
2. Run cmake -B /path/to/build_dir /path/to/TF-PSA-Crypto/source
3. Run cmake --build /path/to/build_dir --target tfpsacrypto-apidoc
4. Open one of the main generated HTML files:
   • apidoc/index.html
   • apidoc/modules.html or apidoc/topics.html

Compiling

The build system is CMake. The CMake build system creates one library: libtfpsacrypto.

Tool versions

You need the following tools to build the library from the main branch with the provided CMake files. TF-PSA-Crypto minimum tool version requirements are set based on the versions shipped in the latest or penultimate (depending on the release cadence) long-term support releases of major Linux distributions, namely at time of writing: Ubuntu 22.04, RHEL 9, and SLES 15 SP4.

• A C99 toolchain (compiler, linker, archiver). We actively test with GCC 5.4, Clang 3.8 and Arm Compiler 6.21. More recent versions should work. Slightly older versions may work.
• Python 3.8 or later to generate some source files (see below), the test code, and to generate sample programs.
• CMake 3.20.2 or later.
• A build system like Make or Ninja for which CMake can generate build files.
• Microsoft Visual Studio 2019 or later (if using Visual Studio).
• Doxygen 1.8.14 or later.

Git usage

The supported branches (see BRANCHES.md) use a Git submodule, framework. Release tags also use Git submodules.

After cloning or checking out a branch or tag, run: git submodule update --init to initialize and update the submodule before building.

However, the official source release tarballs (e.g. tf-psa-crypto-1.0.0.tar.bz2) include the content of the submodule.

Generated source files in the development branch

The source code of TF-PSA-Crypto includes some files that are automatically generated by scripts and whose content depends only on the TF-PSA-Crypto source, not on the platform or on the library configuration. These files are not included in the development branch of TF-PSA-Crypto, but the generated files are included in official releases. This section explains how to generate the missing files in the development branch.

The following tools are required:

• Python 3 and some Python packages, for some library source files, sample programs and test data. To install the necessary packages, run:

  python3 -m pip install --user -r scripts/basic.requirements.txt
  

  Depending on your Python installation, you may need to invoke python instead of python3. To install the packages system-wide or in a virtual environment, omit the --user option.
• A C compiler for the host platform, for some test data.

The scripts that generate the configuration-independent files will look for a host C compiler in the following places (in order of preference):

1. The HOSTCC environment variable. This can be used if CC is pointing to a cross-compiler.
2. The CC environment variable.
3. An executable called cc in the current path.

Note: If you have multiple toolchains installed, it is recommended to set CC or HOSTCC to the intended host compiler before generating the files.

Any of the following methods are available to generate the configuration-independent files:

• On non-Windows systems, when not cross-compiling, CMake generates the required files automatically.
• Run framework/scripts/make_generated_files.py to generate all the configuration-independent files.

CMake

In order to build the source using CMake in a separate directory (recommended), just enter at the command line:

mkdir /path/to/build_dir && cd /path/to/build_dir
cmake /path/to/tf/psa/crypto/source
cmake --build .

In order to run the tests, enter:

ctest

The test suites need Python to be built. If you don't have Python installed, you'll want to disable the test suites with:

cmake -DENABLE_TESTING=Off /path/to/tf/psa/crypto/source

To configure CMake for building shared libraries, use:

cmake -DUSE_SHARED_TF_PSA_CRYPTO_LIBRARY=On /path/to/tf/psa/crypto/source

There are many different build modes available within the CMake build system. Most of them are available for gcc and clang, though some are compiler-specific:

• Release. This generates the default code without any unnecessary information in the binary files.
• Debug. This generates debug information and disables optimization of the code.
• ASan. This instruments the code with AddressSanitizer to check for memory errors. (This includes LeakSanitizer, with recent version of gcc and clang.) (With recent version of clang, this mode also instruments the code with UndefinedSanitizer to check for undefined behaviour.)
• ASanDbg. Same as ASan but slower, with debug information and better stack traces.
• MemSan. This instruments the code with MemorySanitizer to check for uninitialised memory reads. Experimental, needs recent clang on Linux/x86_64.
• MemSanDbg. Same as MemSan but slower, with debug information, better stack traces and origin tracking.
• Check. This activates the compiler warnings that depend on optimization and treats all warnings as errors.
• TSan. This instruments the code with ThreadSanitizer to detect data races and other threading-related concurrency issues at runtime.
• TSanDbg. Same as TSan but slower, with debug information, better stack traces and origin tracking.

Switching build modes in CMake is simple. For debug mode, enter at the command line:

cmake -D CMAKE_BUILD_TYPE=Debug /path/to/tf/psa/crypto/source

To list other available CMake options, use:

cmake -LH

Note that, with CMake, you can't adjust the compiler or its flags after the initial invocation of cmake. This means that CC=your_cc make and make CC=your_cc will not work (similarly with CFLAGS and other variables). These variables need to be adjusted when invoking cmake for the first time, for example:

CC=your_cc cmake /path/to/tf/psa/crypto/source

If you already invoked cmake and want to change those settings, you need to invoke the configuration phase of CMake again with the new settings.

Note that it is possible to build in-place, use:

cmake .
cmake --build .

Regarding variables, also note that if you set CFLAGS when invoking cmake, your value of CFLAGS doesn't override the content provided by CMake (depending on the build mode as seen above), it's merely prepended to it.

Consuming TF-PSA-Crypto

TF-PSA-Crypto provides a CMake package configuration file for consumption as a dependency in other CMake projects. You can load its CMake library target with:

find_package(TF-PSA-Crypto)

You can help CMake find the package:

• By setting the variable TF-PSA-Crypto_DIR to ${YOUR_TF_PSA_CRYPTO_BUILD_DIR}/cmake, as shown in programs/test/cmake_package/CMakeLists.txt, or
• By adding the TF-PSA-Crypto installation prefix to CMAKE_PREFIX_PATH, as shown in programs/test/cmake_package_install/CMakeLists.txt.

After a successful find_package(TF-PSA-Crypto), the target TF-PSA-Crypto::tfpsacrypto is available.

You can then use it directly through target_link_libraries():

add_executable(xyz)

target_link_libraries(xyz PUBLIC TF-PSA-Crypto::tfpsacrypto)

This will link the TF-PSA-Crypto library to your library or application, and add its include directories to your target (transitively, in the case of PUBLIC or INTERFACE link libraries).

TF-PSA-Crypto as a subproject

The TF-PSA-Crypto repository supports being built as a CMake subproject. One can use add_subdirectory() from a parent CMake project to include TF-PSA-Crypto as a subproject.

Microsoft Visual Studio

The TF-PSA-Crypto library can be built with Microsoft Visual Studio Community suitably installed as a CMake project. For a general documentation about CMake projects in Visual Studio, please refer to its documentation.

The following instructions have been tested on Microsoft Visual Studio Community 2019 Version 16.11.26. The TF-PSA-Crypto library and its tests build out of the box with:

• Visual Studio Community installed with the default "Desktop development with C++" and "Python development" workloads.
• Python libraries needed for code and test generation installed as defined in basic.requirements.txt. Refer to the Visual Studio documentation of Python environments.
• When cloning the TF-PSA-Crypto repository in Visual Studio, a CMakeSettings.json is created at the root of the repository. In that file, add the line "environments": [ {"CC" : "cl"} ] to the configuration. That way when building the library and its tests, a CC environment variable is set with value "cl". This is needed by Python scripts that generate test cases. The CMakeSettings.json file can be edited in Visual Studio by following Project > CMake Settings for TF-PSA-Crypto > Edit JSON.
• If necessary (it may have been done automatically when updating CMakeSettings.json), generate the CMake cache: Project > Generate Cache
• Build the library: Build > Build All
• The test suites can then be run: Test > Run CTests for TF-PSA-Crypto

Example programs

We've included example programs for different features and uses in programs/. Please note that the goal of these sample programs is to demonstrate specific features of the library, and the code may need to be adapted to build a real-world application.

Tests

The TF-PSA-Crypto repository includes an elaborate test suite in tests/ that initially requires Python to generate the tests files (e.g. test_suite_psa_crypto.c). These files are generated from a function file (e.g. suites/test_suite_psa_crypto.function) and a data file (e.g. suites/test_suite_psa_crypto.data). The function file contains the test functions. The data file contains the test cases, specified as parameters that will be passed to the test function.

Porting TF-PSA-Crypto

TF-PSA-Crypto can be ported to many different architectures, OS's and platforms. Before starting a port, you may find the following Knowledge Base articles useful:

• Porting Mbed TLS to a new environment or OS
• What external dependencies does Mbed TLS rely on?
• How do I configure Mbed TLS

TF-PSA-Crypto is mostly written in portable C99; however, it has a few platform requirements that go beyond the standard, but are met by most modern architectures:

• Bytes must be 8 bits.
• All-bits-zero must be a valid representation of a null pointer.
• Signed integers must be represented using two's complement.
• int and size_t must be at least 32 bits wide.
• The types uint8_t, uint16_t, uint32_t and their signed equivalents must be available.
• Mixed-endian platforms are not supported.
• SIZE_MAX must be at least as big as INT_MAX and UINT_MAX.

License

Unless specifically indicated otherwise in a file, TF-PSA-Crypto files are provided under a dual Apache-2.0 OR GPL-2.0-or-later license. See the LICENSE file for the full text of these licenses.

Third-party code included in TF-PSA-Crypto

This project contains code from other projects. This code is located within the drivers/ directory. The original license text is included within project subdirectories, where it differs from the normal Mbed TLS license, and/or in source files. The projects are listed below:

• drivers/everest/: Files stem from Project Everest and are distributed under the Apache 2.0 license.
• drivers/p256-m/p256-m/: Files have been taken from the p256-m repository. The code in the original repository is distributed under the Apache 2.0 license. It is distributed in TF-PSA-Crypto under a dual Apache-2.0 OR GPL-2.0-or-later license with permission from the author.

Contributing

We gratefully accept bug reports and contributions from the community. Please see the contributing guidelines for details on how to do this.

Contact

• To report a security vulnerability in TF-PSA-Crypto, please email [email protected]. For more information, see SECURITY.md.
• To report a bug or request a feature in TF-PSA-Crypto, please file an issue on GitHub.
• Please see SUPPORT.md for other channels for discussion and support about TF-PSA-Crypto.