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As I know from the Elliptic Curve Diffie Hellman (ECDH), you can create a "Shared Key": https://asecuritysite.com/encryption/ecdh2
This will look like this:
dA × dB × G = Shared Key
QB = dB × G
QA = dA × G
But is it possible to get the sum of dA and dB? (Plusing the value of each private key?)
dA + dB × G = ???
How to get a "Shared Key" when adding each private key (plus)?
QA + QBcan not be calculated by third parties? That is, the point G does not allow this to be done. Or how canQA + QBbe calculated? Maybe in a different way? – Izi Tors – 2019-10-25T10:24:25.593If you know the points QA and QB, what you should do is draw the curve, mark the points QA and QB, connect them with a line, find where the line intersects the curve (apart from QA and QB). The third intersection will be -(QA + QB). You can then reflect the point over the X axis to find the point QA + QB. You can read more about addition here. (note that there are also some modulo operations) @IziTors
– MCCCS – 2019-10-25T10:45:12.803How on the graph of the curve can they get the sum of the total private keys (dA + dB) by calculating QA + QB? – Izi Tors – 2019-10-25T11:19:06.393
It’s assumed to be impossible to find dA + dB from QA + QB, but you can find (dA + dB) x G if you know QA and QB by adding them. If you know QA and QB or QA + QB you can’t find dA or dB or their sum. – MCCCS – 2019-10-25T12:03:18.450
And there are minus points QA - QB, and accordingly minus (dA - dB) x G ? – Izi Tors – 2019-11-01T12:27:02.017
@IziTors Yes. it's correct. – MCCCS – 2019-11-01T15:03:41.363