3 ms·
It doesn't sound too hard to generate an RSA "vanity key", with any value you want for some of the bytes. You can't control _all_ of the bytes, because it stil
by tux3 3y ago
It doesn't sound too hard to generate an RSA "vanity key", with any value you want for some of the bytes.
You can't control _all_ of the bytes, because it still needs to have the right structure and for you to have the corresponding private key, but 40 bytes of your choosing seems completely doable.
And if you can do that, you can impersonate someone else whose pubkey has the same 40 bytes. With a hash, any bit difference in any part of the key should result in a completely different fingerprint (hash collisions being extremely hard to find).
- lucb1e 3y agoNote that this is specific to RSA keys. In no scenario (that doesn't involve extraterrestrial resources or perhaps nuclear fusion) can you create an ECC key, let alone a hash fingerprint, with 40 bytes of vanity. Afaik ECC keys are considered to be half the strength of a symmetric key (pre-quantum), so that's 20 fully random bytes or 160 bits of entropy. The sun simply doesn't hit the earth with enough energy even if you'd capture 100% of that and starve all life for it to do a computation of that magnitude. (The boundary is around the standard 128-bit key size iirc; I keep forgetting if the sun's energy would be sufficient for like ~120 bits or more like ~140 bits... and that's assuming perfectly efficient computational machines.) Since the person you're responding to didn't specify which public key type, and since it's not obvious that your mention of RSA is to the exclusion of other algorithms such as ECC, I felt like the comment is a bit misleading