I have not found a whitepaper, but there is this very informative blog post: What is Lisk?
This note from the blog post sheds light on the Lisk approach:
There are ongoing discussions about public, private, and consortium blockchains. With Lisk you can build whatever you want and need. However, in order to attract startups and developers we are putting our main focus on public consortium blockchains. That means federated blockchains which are secured by delegates chosen from a public marketplace which are being paid for generating blocks, either by the blockchain application owner or its users. Continue reading in order to learn more about the Lisk delegate marketplace.
Lisk uses Delegated Proof of Stake for it's consensus algorithm, for sidechains this creates a marketplace for securing your applications ledger, from the blog post:
The Lisk delegate marketplace is a way to connect blockchain application developers and sidechain delegates. This is necessary, because every sidechain is an independent blockchain which needs its own set of nodes to secure it. If blockchain application developers don’t use our default consensus algorithm (e.g. PoS or PoW) they will have to take care of the sidechain miners/forgers themselves, which might be a better option for some use-cases. However, if the blockchain application developer is using our default consensus algorithm (DPoS) he will be able to rent delegates from the delegate marketplace for a recurring fee.
Project Home Page: https://lisk.io/
Lisk Blog: https://blog.lisk.io/