We've been asked to generate a certificate signing request using elliptic curve and we can't use any third-party library as it's an embedded application with very limited resources).
We are used to generating CSR using RSA, but we can't find any documentation on how to do that with an elliptic curve; specifically, which data to use for the signing part. Studying OpenSSL-generated CSR it looks like there are multiple signatures generated, or a hash of some kind, but we don't know. And OpenSSL source code is quite difficult to read when you're not used to it.
Can anyone point us in the right direction?