Are HSDirs stable or there is a chance to lose my hidden service if HSdirs shuts down? Also Why there is no way to make a hidden service use ECC instead of RSA?
Are HSDirs stable or there is a chance to lose my hidden service if HSdirs shuts down?
If your HSDirs decide to die for whatever reason then your hidden service will be unavailable to most clients, at least for a time. Clients can still access your service, but only if they already know the information in your hidden service descriptors.
Hidden services get new descriptor-ids and therefore new sets of HSDirs every 24 hours, so the problem will eventually resolve itself.
Additionally each hour a hidden service checks to see if it needs to re-upload its descriptors; at this point if network status documents imply that one of your service's HSDirs are down then they'll choose a replacement . This protects against HSDirs vanishing from the network, but doesn't necessarily defend against a HSDir attempting to censor your service.
I'm fairly sure methods of detecting such censorship have been proposed, such as your hidden service periodically downloading its own descriptors to confirm that they're still available. I'm not sure if any have actually been implemented however.
Also keep in mind that to become a HSDir an onion-router needs a considerable amount of uptime, so it would be very unusual if they all decided to die at once. (dir-spec says it takes 25 hours to earn the HSDir flag, but I've heard that's been increased.)
Also Why there is no way to make a hidden service use ECC instead of RSA?
I believe there's a push to switch over to elliptic curve cryptography in the next version of the hidden services protocol. Take that will a grain of salt though, someone else might know better.