Question

For example, how can the owner of list A compare identify how many of their strings exist in List B without ever seeing List B?

List A            List B
abcdef            abcdef
ghijkl            mnopqr
stuvwx            stuvwx
yz0123            

The result should be two. As in, List A has 2 strings found in List B. This is easy enough if lists are shared in open text. But how can this answer be found without the owner of List A seeing List B?

Answer 1

You can hash the strings in the two lists and then compare the hashes.