Details-on-ARKG-instance-output

This is a first draft of text that exemplifies what I meant with clarifying the use of the blind tau. It is not possible to use a generic approach for all keys since the keys differ based both on use and curve.

draft-bradleylundberg-cfrg-arkg.md

@@ -330,8 +330,8 @@ A concrete ARKG instantiation MUST specify the instantiation
 of each of the above functions and values.
 
 The output keys of the `BL` scheme are also the output keys of the ARKG instance as a whole.
-For example, if `BL-Blind-Public-Key` and `BL-Blind-Secret-Key` output ECDSA keys,
-then the ARKG instance will also output ECDSA keys.
+An ARKG derived blinded private public key pair enables use cases where any procedure that involves the private key and the blinding key generates an output that is independent from one involving only the private key. Each blinding key is also a private key for a given procedure over a particular curve. 
+For example, the blinding key for EdDSA using Ed25519 or Ed448 is generated by invoking the required routines in RFC 8032 [section 5.1](https://www.rfc-editor.org/rfc/rfc8032#section-5.1) and [section 5.2](https://www.rfc-editor.org/rfc/rfc8032#section-5.2) respectively, and a blinding key for ECDH over X25519 assumes a suitably generated X25519 key pair. Relatedly, for ECDSA over NIST curves the blinding key is generated by invoking the key generation routine specified in ANSI X9.62, and ECDH over NIST curves uses the key generation routine specified in [NIST SP 800-56A](https://csrc.nist.gov/pubs/sp/800/56/a/r3/final).
 
 Instantiations MUST satisfy the following compatibility criteria: