This blog post is based on a twitter thread that I published here.

One class of protocols that I mention in the appendices of http://bitcoinrollups.org are what I call “validia chains”. Validia chains share similarities with both sidechains and validity rollups, with interesting tradeoffs.

A validia chain is a blockchain that:

1) Fully inherits double-spend security from a parent chain,
2) Has its state transitions verified by the parent chain using validity proofs, and
3) Stores its state data outside of the parent blockchain aka “offchain data availability” (DA)

Validia chains and sidechains both do offchain DA.

Validia chains and validity rollups both inherit double-spend security from a parent chain and have their state transitions verified by the parent chain using validity proofs.

What are the implications of these features?

Validia chains & sidechains both trust 3rd parties (TTPs) with security of funds transferred in from the parent chain, but the exact security model differs:

• TTPs in validia chains can freeze but not steal funds
• TTPs in sidechains can both freeze and steal funds

Several offchain DA models have been proposed for validia chains to reduce the risk of frozen funds:

• Validium: DA committee
• Valutia: Collateralized DA (bonds are slashed if data is unavailable)
• Adamantium: Data self-custody with onchain escape hatch if user goes offline

There is also a DA model called a “Volition” where users can choose on a per-tx basis which DA model to use. If a user needs to send a high value tx, they can use expensive onchain DA rollup mode. If a user needs to send a low value tx, they can use cheap offchain DA validia chain mode.

Here’s the full lineup of offchain DA options:

With validia chains we can create layered networks that serve a diverse spectrum of user preferences. L3 validia chains with lower cost & higher throughput can be built on L2 rollups that provide max security but limited throughput (yet still higher throughput than L1).