Have just recalled BitCoinVanityGen website - can anyone recall the URL (dot com??) - I vaguely recall they had the PrivateKeys and emailed them to a user, hence it was considered unsafe.
It's heavily promoted on
Beginners & Help (which doesn't show Trust ratings) by user/scammer
Velkro.
I'm just leaving
Pretty Addy Giveaway - part 2 here, up to you if you want to add it
I remember a very impressive idea presented by gmaxwell to improve split-key generation:
Say you have N people who each want to find a vanity tweak of their pubkeys which will roughly take M million tries to find.
You can find all N of them with just ~M million tries, instead of the N*M million tries if they were to do them themselves alone.
Here is how. Each person has a pubkey P_i, they all come up with uniformly random tweaks T_i. They tweak their keys, and send these resulting public keys to the hashing server. They keep the tweak and original pubkey private. They also send the string(s) they want to match. They stay connected.
The sever takes all the strings and compiles them into a single match expression (which can be matched in log() operations at worst, probably better).
Then the server sums all the tweaked pubkeys and grinds on it comparing the output with the omnibus matcher.
When it gets a hit it then demands all clients except the one with the match to tell them the private keys for their tweaked keys (this reveals nothing about the original private key, since it's been tweaked). It then sums up the tweak it found and everyone elses private keys and gives that to the lucky user.
Everyone remaining sends new tweaked pubkeys (probably in the same message they sent their prior private keys). They get summed and the process continues with the new basepoint.
If someone fails to send their private key, you kick them off and ban them and you lose that result because you cannot reconstruct the tweaks without everyone elses keys.
Implemented correctly this is completely secure.
(click the quote to read the full post/context)
As far as I know, this hasn't been implemented yet.
