Two transactions are signed by different private keys, and the value of "R" for these two transactions is the same? Everyone knows an error in the Blockchain when the same value of "R" can be calculated and find out the private key of the transaction:

ECDSA Signature and the &quot;z&quot; value

But I have a question. Can I find two private keys with the same value of "R"?
Can you please tell if you can get the value "K" if you know that two transactions signed different private keys, and the value "R" on these two transactions is the same?
Assuming the two private keys are unrelated, the answer is no.

The reason for this is simple: there are 3 unknowns (the two private keys, and the single secret k value), but only two equations (the ECDSA validation equation for both signatures).

If a relation is known between the two private keys (like one is twice the other, or one is one higher than the other, ..), another equation becomes known, and the system becomes solvable.