How secure is rndc?

[Len Conrad]

>I suppose the question to be answered is why RNDC does not encipher
>the payload.

RNDC is used primarily to secure control signals to named.

What's to encrypt when the packet content is a generic signal?

When TSIG is used to secure dynamic updates (payload is DNS record), 
the DNS records themselves are most often public, so why encrypt them 
in the update query?

Len