How is Mbed TLS (formerly PolarSSL) protected legally?
Copyright
Mbed TLS (formerly known as PolarSSL) is, like most software, protected by copyright. It is licensed for use under a dual open-source Apache 2.0 OR GPL 2.0-or-later license. The project is owned by TrustedFirmware.org, and the code is owned by all the people and companies who have contributed to it, collectively known as The Mbed TLS Contributors. (Note: some files in the 3rdparty directory, not used in the default build, have a different copyright as noted in the file headers, and are licensed under only the Apache 2.0 license).
When contributing code to us, the author is required to sign off all commits with a Developer Certificate of Origin line, confirming that the code submitted can (legally) become part of the project, and be subject to the same Apache 2.0 or GPL 2.0-or-later license.
Trademark
The PolarSSL brand name is trademarked in the US. You can see the trademark at USPTO for yourself.
You can also find more information about using the Mbed trademark.