Document how to get SubjectPublicKey form from SubjectPublicKeyInfo

[lawliet89]

I guess this is similar to #470.

I have computed an EC private key: openssl ecparam -name prime256v1 -genkey -noout -outform der -out ecdsa_private_key.der and the corresponding public key: openssl ec -in ecdsa_private_key.der -inform der -pubout -out ecdsa_public_key.der -outform der.

As far as I can tell, (by converting the DER public key to PEM), the public key from this is in SubjectPublicKeyInfo. I understand that ring works with the "traditional" form (is this PKCS#1?)

Is there any command line tool I could use to perform this conversion? openssl ec does not seem to have the RSAPublicKey_{in|out} analogue.

[briansmith]

I don't know. It's better to ask on openssl-users; see https://www.openssl.org/community/mailinglists.html.

Once #378 is fixed, you'll be able to parse a SubjectPublicKeyInfo in ring to get the raw SubjectPublicKey that sing::signature::verify() uses.

[briansmith]

Closing as a duplicate of #370 (edit: was #378).