Add feature to choose Ecc, Micro-ecc or Cryptoauthlib to manage ecc

[LizzieDE110]

I had noticed that the handshake was very slow on a SAMR21-xpro board, and I discovered that it was because ECC management (key generation, signature, and verification) was very slow.

I am working with RIOT (which supports Micro-ecc), so I created a small program to compare execution times between the current ECC API and Micro-ecc. Here are my results:

Example using ECC from tinydtls/ecc:

2024-02-08 11:34:16,670 # DTLS sock example to generate key and see if it takes a long time
2024-02-08 11:34:23,755 # Keys generated
2024-02-08 11:34:30,593 # Signature created

Similar example using Micro-ecc:

2024-02-08 11:32:39,924 # ECDSA key generation example
2024-02-08 11:32:40,336 # Keys generated
2024-02-08 11:32:40,773 # Signature created

So Micro-ecc is much faster than the current ECC API and I decided to add the feature of tinydtls to use Micro-ecc (and thus accelerate the handshake).

Additionally, on another board, I have a secure element (ATECC608A) which is even faster than Micro-ecc and adds a very secure environment to work with private keys and secrets, so I decided to integrate it as well.

For now, I know that I have to add documentation. Examples using Micro-ecc and Cryptoauthlib require that those libraries are installed on your development environment before compiling.

[LizzieDE110]

Todo :

• add function to set slots to use for ECC and ECDH
• May be also add feature to store peer keys into ATECC?