user81435: 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)?

user38618: Yes, QA + QB = (dA + dB) × G, but this isn't used in ECDH as QA + QB can be calculated by third parties.
You can read about this property here.

81435: <p>As I know from the Elliptic Curve Diffie Hellman (ECDH), you can create a "Shared Key": <a href="https://asecuritysite.com/encryption/ecdh2" rel="nofollow noreferrer">https://asecuritysite.com/encryption/ecdh2</a></p>

<p>This will look like this:</p>

<pre><code>dA × dB × G = Shared Key

QB = dB × G

QA = dA × G
</code></pre>

<p>But is it possible to get the sum of dA and dB? (Plusing the value of each private key?)</p>

<pre><code>dA + dB × G = ???
</code></pre>

<p>How to get a "Shared Key" when adding each private key (plus)?</p>
 38618: <p>Yes, <code>QA + QB = (dA + dB) × G</code>, but this isn't used in ECDH as QA + QB can be calculated by third parties.</p>

<p>You can read about this property <a href="https://crypto.stackexchange.com/a/53980/">here</a>.</p>
