Split-key vanity address
A split-key vanity address is a type of vanity address generated from one or more ECDSA private keys. The general use case is when a user generates a key-pair and only shares his public key. Everybody can use this public key to find the complementary public key leading to a vanity address. The user can than merge his private key with the complementary private key, leading to the private key of the vanity address. The security of such solution is guaranteed by the properties of the Elliptic Curve Cryptography .
A split-key vanity address is generated by a specialised software, called a generator. One such sample generator is available as a part of the Vanitygen program suite. Bitaddress can be used for this purpose as well as explained in this video
In order to create a usable vanity address, one needs to merge two or more private keys. This can be done with specialised software, such as the GoBit Testing Suite. Another option is using the Vanity Wallet tool of Bitaddress.
Address generation outsourcing
Generating a split-key vanity address can be outsourced to a third party miner without risking your final private key being compromised. Moreover, work on such address generation can be distributed to many miners simultaneously through a use of a pooling service. One example of such a service is Vanity Pool.
Another option for outsourcing your Vanity Address generation in this manner is Vante. This service generates your service on an on-demand basis.