I will explain this one using only privatekeys. But remember that those calculations depend only if you already have the TARGET PUBLICKEY. if you don't have the publickey this example doesn't apply.

Lets to asume that we have the key like you example:

We divide it in two pats, most significative bytes and less significative bytes.

Part 1 less significative bytes:


We calculate and store the publickeys  from

to


In this example is 2^24 publickeys (16777216 publickey) this can be done in seconds, this part is the precalculated data it can be more but all depend of how much memory do you have.

now the second part:

This part must be brute force from


to


We need to add the remaining bytes filled as ZERO

Example:


We need to calculate each of those public key, this is again 2^24 public keys to be calculate.
For EACH of those "TEMP PUBLICKEY" values we need to do a Public keys subtraction


Now we need to compare the NEW PUBLICKEY against our precalcualted data if there is a match then we only need to concatenate or Add our partials privatekey to get the real one.

Example, lets to say that the TARGET PRIVATEKEY is e3b0c441234c1c149afbf4c8996fb56ab7ae41e4649b934ccdef991b7852b855

In that case in some point our subtraction  will be something like this:


If there is a match our privatekey will be:



NO, there is no public program that do that actually, because those examples of missing characters are unlikely to happen.


Is exactly the same but with the advantage that we can use BSGS at full capacity