Added ecc/ecc-export-Qx-Qy example program

[danielinux]

Example on how to convert a ASN.1 ECC key into [Qx,Qy] raw form, used e.g. in wolfBoot.

Minor extra change: added -pthread to the LDFLAGS otherwise ecc-stack example in the same directory would not link (gcc9.2.1/GNU-Linux).

[kaleb-himes]

Daniele,

Thanks! Just a few things:

• Can you add a ecc-export-Qx-Qy section to the README.md (Example: https://github.com/danielinux/wolfssl-examples/tree/ecc-export-qx-qy/ecc#ecc-key-decode)?
• Can you add a macro guard such that if appropriate configuration is not used the example will still build and run simply outputting the line "please configure wolfSSL with --enable-xxx and try again (Example: https://github.com/danielinux/wolfssl-examples/blob/ecc-export-qx-qy/ecc/ecc-verify.c#L115)

[danielinux]

Kaleb,
Thank you!

Added description in README.md and ifdef guards as suggested.

[kaleb-himes]

Thanks Daniele, looks great! I would note only one minor thing we can improve in a future PR, you have the POINT_SIZE set to 32 which only allows this app to work with the following ECC key sizes:

112, 128, 160, 192, 224, 239, 256.

I tested with key sizes 320, 384, 512, and 521 but all failed. If we set POINT_SIZE to 69 it can be used with any supported ECC key size between 112 and 521!

Thanks for the great example!

• KH