The following link is to our wolfssl users manual. Chapter seven talks about certificates and key generation. Specifically Chapter 7 section 7 (7.7) directly addresses your concerns regarding RSA keys.

http://wolfssl.com/wolfSSL/Docs-wolfssl … cates.html

Example code of generating the "der":

byte der[4096];
int  derSz = RsaKeyToDer(&genKey, der, sizeof(der));
if (derSz < 0)
   /* derSz contains error */;

The buffer der now holds a DER format of the key.

The question  I have is, how do I(a embedded device on myside) or any peer embedded device generate the parameter "der" in "RsaPublicKeyDecode(der, &idx, &key, (word32)derSz);"

Is there any specific function that I would have to use?

Thanks!