Pantos Project Update: Eighth TAST Technical White Paper

Feb 21, 2020 · 5 min read
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In the eighth TAST Technical White Paper, we were able to further reduce operating costs for our existing blockchain relay solution by applying the content-addressable storage pattern. Overall, we achieved a significant cost reduction of up to 92% over traditional blockchain relays. Furthermore, we outline how relays can be leveraged to enable blockchain interoperability applications such as cross-blockchain token transfers. The devised protocol shows that most requirements for cross-blockchain token transfers can be fulfilled.

To not only write about it on a theoretical level, we also present a proof-of-concept implementation on GitHub of the PAN token for Ethereum-based blockchains on our decentralised blockchain relay prototype.

Key facts of White Paper VIII:

  • The prototype published in September is a blockchain relay enabling a blockchain to verify the inclusion of transactions in another blockchain in a fully decentralised manner.
  • We further improved the prototype (available on GitHub) by reducing the amount of data stored, yielding a cost reduction of up to 53%, so as compared to our previous prototype with 84% we now stand at a 92% cost reduction when compared to traditional relay solutions.
  • The relay can be used to implement true cross-blockchain token transfers as envisioned by Pantos.
  • Proof of Concept for such token transfers has been realised within the new Pantos prototype.
  • In future work, we will continue this approach as well as look into blockchain interoperability beyond individual applications and blockchains.
  • Download fact sheet PDFs in English, German and French.

Recapping the work on the prototype so far
With the sixth TAST Technical White Paper we introduced a novel blockchain relay design. Basically, the relay optimistically accepts newly received block headers without fully validating them. A full validation is only carried out if off-chain clients deem the received block headers to be illegal. With this novel design we were able to set the foundation to replicate the state of one blockchain within another one in a cost-efficient way.

In the seventh TAST Technical White Paper we further refined this approach and developed an incentive structure encouraging off-chain clients to participate. In a preliminary cost analysis, we saw that with our relay design we can drastically reduce operational costs.

Further Optimising the Blockchain Relay

Fig. 1

A blockchain relay is operated by off-chain clients who continuously submit block headers from the source blockchain to the destination blockchain (see Fig. 1). This way, the source blockchain is essentially replicated within the destination blockchain.

It becomes possible from within the destination blockchain to make queries such as “What is the branch of the source blockchain with the highest total difficulty (i.e. the main chain)?”, “Was transaction x included in block B of the source blockchain?” and so on.

For blockchain relays to work reliably, they need to have access to all the block headers of the source blockchain from within the destination blockchain.

Usually, these block headers are stored within the relay smart contract deployed on the destination blockchain. However, smart contract storage is very costly.

We can reduce storage cost by storing the bulk of the data in the blockchain’s transaction history instead and only storing the hash of that data within the contract. Clients that wish to interact with the contract need to retrieve the data from the transaction history and present it to the smart contract. By comparing the hashes, the smart contract can verify that the provided data is valid.

Implementing this pattern further reduces the operational cost of our relay by up to 53%. Overall, our blockchain relay now achieves a cost reduction of up to 92% over traditional relay designs.

Cross-Blockchain Token Transfers

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Fig. 2

We leverage the functionality offered by blockchain relays to create blockchain interoperability solutions such as cross-blockchain token transfers as envisioned by Pantos. A Proof of Concept for such cross-blockchain token transfers has been realised in the new Pantos prototype.

Let’s consider the example in Fig. 2. Imagine Bob wants to transfer some tokens from his account on blockchain A to Alice’s account on blockchain B.

At first, Bob submits a transaction txburn to the source blockchain (A) (Step 1). Eventually, txburn is included in a new block and appended to blockchain A. When this happens, off-chain clients operating the blockchain relay are notified of the new block and relay the corresponding block header to the relay contract deployed on blockchain B (Step 2).

Since Alice is the intended recipient of the cross-blockchain transfer, she waits until the relay contract has received the header of the block containing txburn (Step 3).

She then creates a Merkle proof of membership for txburn (Step 4) and submits the proof to the token contract deployed on blockchain B (Step 5). Since the relay contract on blockchain B has already received the corresponding block header, the token contract can request the verification of the Merkle proof from the relay contract (Step 6).

If the verification of the Merkle proof is successful, the token contract can be sure that txburn is a valid “burn” transaction which has been successfully included in blockchain A. The contract subsequently creates the amount of tokens that were burned and assigns them to Alice.

Conclusion and next steps

The outlined interaction provides an example of how cross-blockchain token transfers can be carried out using blockchain relays. In the future, we will further secure these token transfers, as well as explore blockchain interoperability beyond individual applications and blockchain platforms.

For more information, check out the eighth TAST Technical White Paper.

Pantos AMA coming up in March 2020

We used to cover Pantos related topics in Bitpanda AMAs (you can find the latest one here). Now that we’ve made significant progress with our prototype approach and want to be more active in our communication in general, we will host a Pantos-only AMA in March 2020. Follow us on Facebook, Twitter and join the Pantos community on Telegram (Pantos announcements, official English group, official German group) to not miss the exact date and time for the AMA.

About Pantos

As the first multi-blockchain token system, Pantos aims to bring blockchain projects closer together, improve communication between developers, researchers and users, and set innovative standards for cross-chain token transfers.

The goal is to serve as a lighthouse project in an increasingly fragmented blockchain space. With multiple blockchains serving all kinds of different purposes, Pantos is seeking to allow these projects to talk to one another in a standardised way. This will speed up innovation by creating a link between blockchains which then can scale together.

To get the latest news on the progress of the Pantos project you can follow our official channels:


The first multi-blockchain token system.

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