I wonder if it is possible to break the encryption on a password by such encryption:
Where E is the encryption function that uses a known public key of the server.
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I wonder if it is possible to break the encryption on a password
No, it is not possible to recover the value of pwd, unless the public key scheme used by the server is weak (or if you also have the server's private key).
Here is the demonstration of that: suppose you did have a method that, given $< E_s(k), k \oplus pwd >$, would recover $pwd$. Then, here is how you could recover the value $x$ given $E_s(x)$:
Select a random $r$
Create the pair $< E_s(x), r >$, and give it to your recovery method
The recovery method would return the value $x \oplus r$.
Since you know $r$, that gives you the original plaintext $x$.
Thus demonstrating that the public key method used by the server was weak.