I think it is a fair assumption that an attacker trying to learn a seed would know the seed size, and most people use the same derivation path for the same coin, even if it is technically possible to use an arbitrary path.
That would only lower the complexity by a little. It is still more timeconsuming to bruteforce seeds via its entropy as compared to the addresses itself. While if you succeed in bruteforcing the seeds, you'll access more than a singular address, you're far more likely to succeed in bruteforcing addresses as most of the addresses out there are generated before HD wallet became a thing and that you need additional steps to go from a seed to an address. Hence, it wouldn't make a difference to how many addresses you can access with a successful attempt.
It is quite futile to target specific groups of people, unless you know for a fact that their generation
if is flawed or if majority of the users are using the same parameters for their seeds.
For all intents and purposes, you are not going to successfully brute force anything with 128 bits of entropy. The same is probably true for anything with somewhere in the range of mid 70's bits of entropy, and I would argue it would be impossible to brute force anything with somewhere between the mid 80's to mid 90's bits of entropy, assuming the laws of physics as we know them hold true.
If you assume a "secret" is generated in a way without flaws (such as flawed RNG), you will receive no additional security (regarding brute force attacks) by having your secret having 129 bits of entropy versus it having 128 bits of entropy because in both cases, it is impossible to brute force the secret. The only reason you would want to generate a secret that would have more than 128 bits of entropy if you assume no flaws in the generation process is if you are making the assumption there may flaws in the process.
Yes. Same holds true for addresses and infact, people should be more likely to succeed at bruteforcing an address as compared to seeds.
