My understanding of the paper is that the blinding factor would be included in the extra data which is incorporated into the ring signatures used in the range proof.

Although, since I think the range proof is optional for single output transactions (or at least, one output per transaction doesn't require a range proof since there's only one possible value that it can be to make the whole thing work, and that value must be in range, I'm not entirely sure how you'd transmit it then, though in any case, since using it will pretty much require segwit, adding extraneous data isn't much of a problem. In both cases, I imagine the blinding factor would be protected from outside examination via some form of shared secret generation... Although that would require the sender to know the recipient's unhashed public key; I don't know of any shared secret schemes that will work on hashed keys.

Jeremy Papp

On 2/9/2016 7:12 AM, Henning Kopp via bitcoin-dev wrote:
Hi all,

I am trying to fully grasp confidential transactions.

When a sender creates a confidential transaction and picks the blinding
values correctly, anyone can check that the transaction is valid. It
remains publically verifiable.
But how can the receiver of the transaction check which amount was
sent to him?
I think he needs to learn the blinding factor to reveal the commit
somehow off-chain. Am I correct with this assumption?
If yes, how does this work?

All the best
Henning


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