Many security algorithms today have such a large key length, that there’s just no use in trying to brute-force a key. For example to find one AES-256 key you would have to try 2^128 keys on *average*.

My question is, if there’s a special name for a brute-force attack where you would somehow know that a key “lies” in a specific range, which would reduce the amount of calculations so drastically that a brute-force attack suddenly becomes feasible.

An example about simple brute-force RSA-factorization might make it more clear:

We have a 2048-bit RSA key. Way too large to just try one number at a time to brute-force it.

But we assume now that I have a special algorithm that doesn’t directly return one of the factors, but can tell us that one of the factors lies in a certain range **k (plus / minus 1,000,000,000)**. Then we would only have to try the possibilities from **k – 1,000,000,000** up to **k + 1,000,000,000** and this is probably quite possible to brute-force.

No matter if such algorithms exist or not, is there a special name for this specific attack (reducing the possible key range to make a brute-force attack feasible)?