Hi,

I would like to understand how one can verify that bitcoins in a given address are unspendable.

To me, there are N points on the field of the elleptic curve. That makes (N+1)/2 points with distinct x coordinates (=half side of the symetrical field)

Therefore, there are (N+1)/2 points left, such as (x,y)!=k*G with k in [0,N].

For example:

If I pick x=0 (for which I'm almost sure it cannot result from k*G), we can derive two points :

P1=(0 , 64828261740814840065360381756190772627110652128289340260788836867053167272156)
Adress1=15wJjXvfQzo3SXqoWGbWZmNYND1Si4siqV

P2=(0 , 50963827496501355358210603252497135226159332537351223778668747140855667399507)
Adress2=1MqALQs6ea1ACgwRurqgaBDWzxYPoXCXzu

These adresses are valid (even active in the blockchain). However, they don't have a private key.

Then, is it possible to know if a public key has a private key (i.e. derived from k*G) ?

Regards,

Mr. Akaki