So I'll send 2 transaction, is this possible ?
input ( a1=5 XMR, a2=5XMR ) output( g1=2 XMR, a3= 8 XMR ) -> ring-sing with a1
Let's do one at at time. This one needs to be signed using
both inputs. so
input ( a1=5 XMR, a2=5XMR ) output( g1=2 XMR, a3= 8 XMR ) -> ring-sing with a1 + ring-sign with a2
You can't spent a2 without a valid signature (ring or otherwise)
OK np, I have both private keys, so I'll sing(ring or otherwise). What will be content ? (what I'm signing)
Now you are getting into an area the details of which I'm still working to fully understand in the code. But you are signing at least some portion of the transaction you create to spend the outputs, if not all of it.
But if I'm able to ring-sign input then I can use my old pubic key (I know private key) sing your input (I do not have private key only public) :-)
No, you can't sign with a public key by itself. You can only
add one or more public keys to an otherwise valid signature, but there has to be a private key already present to make the signature valid. You can't sign my output without my private key. I can do it and add
your public key, but without my private key, you can't.
This is the
SIG step on page 9 of the CN whitepaper if you want to read it. You need a valid key pair (puiblic
and private) for the output, plus a set (possibly empty) of other public keys.