Mbed TLS is an implementation of the TLS and SSL protocols and the respective cryptographic algorithms and support code required. It is dual-licensed with the Apache License version 2.0. Stated on the website is that Mbed TLS aims to be "easy to understand, use, integrate and expand".
History
The PolarSSL SSL library is the official continuation fork of the XySSL SSL library. XySSL was created by the French "white hat hacker" Christophe Devine and was first released on November 1, 2006, under GPL and BSD licenses. In 2008, Christophe Devine was no longer able to support XySSL and allowed Paul Bakker to create the official fork, named PolarSSL. In November 2014, PolarSSL was acquired by ARM Holdings. In 2011, the Dutch government approved an integration between OpenVPN and PolarSSL, which is named OpenVPN-NL. This version of OpenVPN has been approved for use in protecting government communications up to the level of Restricted. As of the release of version 1.3.10, PolarSSL has been rebranded to Mbed TLS to better show its fit inside the Mbed ecosystem. It was also announced that the licence would change from GPL to Apache License later in 2015.
Library
The core SSL library is written in the C programming language and implements the SSL module, the basic cryptographic functions and provides various utility functions. Unlike OpenSSL and other implementations of TLS, Mbed TLS is like wolfSSL in that it is designed to fit on small embedded devices, with the minimum complete TLS stack requiring under 60KB of program space and under 64 KB of RAM. It is also highly modular: each component, such as a cryptographic function, can be used independently from the rest of the framework. Versions are also available for Microsoft Windows and Linux. Because Mbed TLS is written in the C programming language, without external dependencies, it works on most operating systems and architectures without any trouble. Later versions of PolarSSL than 1.3.0, add abstraction layers for memory allocation and threading to the core "to support better integration with existing embedded operating systems".
The following documentation is available for developers:
High Level Design: a high level description of the different modules inside the library, with UML diagrams, use cases and interactions in common scenarios.
API documentation: Doxygen-generated documentation from the header files of the library.
Source code documentation: The source code of the library is documented to clarify structures, decisions and code constructs.
Automated testing
Mbed TLS provides automated testing of the code and of PolarSSL's compatibility as follows:
A test framework is included with the source code that contains over 5000 automated tests to test for regressions and compatibility on different platforms.
Mbed TLS is currently available for most Operating Systems including Linux, Microsoft Windows, OS X, OpenWrt, Android, iOS and FreeRTOS. Chipsets supported at least include ARM, x86, PowerPC, MIPS.
Algorithms
Mbed TLS supports a number of different cryptographic algorithms: ;Ciphers: ;Cryptographic hash functions: ;Public-key cryptography:
