Ofelimos is a novel blockchain protocol introduced by Input Output Global research. The protocol is based on proof of useful work (PoUW) to provide a sustainable alternative to proof of work’s (PoW) high energy cost and carbon footprint.


PoW protocols capitalize on the work performed by miners. Furthermore, PoW protocols ensure security through competition between miners to solve computational problems to produce a new block. Unfortunately, this requires significant power and resource usage. For example, bitcoin’s energy expenditure is on par with many small to medium countries.

Conversely, PoUW protocols would ensure that at least some of PoW protocol’s computational effort required to maintain security is repurposed to solve real-world problems.

This would require computational problems to be hard, yet divisible into small uniform steps.

Each such step would essentially correspond to a single PoW query in the sense that each such step may qualify to publish a block.

PoUW protocols would implement stochastic local search (SLS) algorithms to attempt to find good solutions rather than optimal ones.

SLS can compute solutions for real-economy applications in various areas (ie logistic planning, event scheduling, urban planning, etc.)

Put simply, PoUW enables the use of computational work to solve real-world problems (ie optimizing company logistics or event scheduling) while also mining blocks. The key term in proof of useful work is “useful.”

PoUW properties

How does a PoUW ensure blockchain security?

It achieves this by applying the following mechanisms:

Anti-grinding: In a competition to solve queries and mine blocks, miners could attempt to exclusively solve instances that are faster to solve than others, rejecting more complex ones-as a special form of so-called grinding attacks.

Knowledge advantage resistance: Some miners may wish to solve queries at no cost and faster rate than honest miners through knowledge advantage.

PoUW limits this threat by separating block minting success from the amount of work it takes to solve queries, and by pre-hashing at a specified threshold. This ensures that all miners have the same likelihood of minting a block and that each computation comes at a cost.

Maintained variable difficulty: In PoW consensus protocols, the difficulty to find a block, as determined by the hashing threshold, mush be continuously adapted to the level of computational power that is globally applied to the blockchain.

Ofelimos enables this by adapting the post-hash threshold such that the block rate per time remains constant.

Frequent updates: To ensure that the miners can catch up with improved solutions quickly, the miners must have the opportunity to share good solutions with the rest of the network rapidly.

Ofelimos ensures this by differentiating between (slow) ranking blocks (responsible for blockchain security) and (fast) input blocks (which are essentially transactions), enabling state updates to be disseminated fast.

Usefulness: Lack of usefulness in proof of work leads to an unnecessary loss of computing power.

For good characteristics of the applied optimization algorithm, roughly half of the overall computing power applied to PoUW is dedicated to useful computation. Additionally assuming that the competing miner is not very powerful, almost all invested computing power is dedicated to useful computation.

The choice of SLS algorithms to be embedded into the PoUW is therefore crucial to ensuring that the protocol is reasonably useful.


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