In confidential transaction proposed by Maxwell, instead of transaction amounts we use pedersen commitments to hide the amount and add the range proof to the transaction to prevent overflow. A simple commitment with one input and one output C1 and C2 is as follow: (Ignore the fee for simplicity)
C1 = C2 => BF1*G + a*H = BF2*G + a*H
where in this example
BF1 = BF2 obviously since it only has one input and output.
How does the sender send the amount and blinding factor to the receiver? Receiver can check if the amount is correct! I noticed Maxwell said they use ECDH. I assume there is no additional communication channel for ECDH. Then how does the sender get receivers public key? and does sender need to reveal both blinding factor and amount in the ECDH?