New blackany are born all the time. Bitcoin was the only bloccano for many years, but now hundreds of them. The problem is that, if you want to use functions provided by other bloccano, you have to buy tokens. But that could soon change. One of the emerging technologies called sicani (eng. sidechains – side chain), promises to facilitate the movement of tokens between different chains and, as a consequence, open the doors to a world of possibilities, including the creation of bridges to integrate conventional financial and banking systems.
In October 2017, Agelos Kias (Aggelos Kiayias), Professor at the University of Edinburgh and chief science officer of the research company IOGK; Andrew Miller (Andrew Miller), Professor, University of Illinois at Urbana-Champaign; and Dionysus, Zindros (Dionysis Zindros), a researcher from the University of Athens issued an article «Non-Interactive Proofs of Proof-of-Work» — NiPoPoW («non-interactive confirmation of proof of completion of work»), which were presented absent for three years part of the puzzle Saidjanov.
One coin different circuit
Saidchina is a technology that allows you without the involvement of a third party to move tokens from one blockchain to another, use them there, and then return back.
Initially, the «progenitor» was Bitcoin, but it could be any other circuit. In addition, when a token is moved to another blockchain, it needs to maintain its value. In other words, bitcoin and Ethereum remains sidechained with bitcoin.
The main advantage of Saidjanov is that the technology allows users to access a variety of new services. For example, you can move bitcoins to a third-party chain to use its special privacy features, faster transactions or smart contracts.
Saidjanov there are other uses. This technology could offer a safer method of updating Protocol or to act as a kind of firewall, so that in the event of a disaster in the sidechained main chain will remain unaffected.
«It’s kind of a limitation of liability,» he said Sandros in a video explaining the technology.
Finally, if banks will create their own baccani, technology Saidjanov will allow users of the cryptocurrency to keep in touch with them, implementing and tracking deposits, debt securities and other assets.
How it all began
For the first time the cryptocurrency community to talk about siddaiah in 2012 when Bitcoin Core developers are looking for ways to secure updates of the Bitcoin Protocol.
One of the ideas was to «unilateral communication», in which users can transfer bitcoins to a separate blockchain for testing. However, after moving it was impossible to bring back.
«I thought of it as a software tool that could be used to make large-scale changes,» — said in an interview with Bitcoin Magazine, Adam Buck (Adam Back), CEO of Blockstream. «We can say that we are going to make a new version of Bitcoin, and I think it will be ready in a year, but to test it you can early.»
According to buck next year on the IRC channel Bitcoin Bitcoin Core developer Gregory Maxwell proposed the idea of «two way communication», with which there is a possibility to transmit the token on the alternative chain, and then back to Bitcoins at a later block.
The development of bilateral relations is also consistent with the interests of the Bitcoin Core team. Alternative coins such as Litecoin and Namecoin, have become increasingly popular. The danger lies in the fact that these altcoins are «diluted» the value of bitcoin. The Bitcoin Core developers decided that it would be prudent to maintain bitcoin as a reserve currency and neutralize the advantages of Saidjanov on altonah.
To translate the concept of Saidjanov in reality, in 2014, Back together with Maxwell and a few other Bitcoin Core developers formed a company Blockstream. In October of the same year, the band released «Enabling Blockchain Innovations with Pegged Sidechains» — a document describing new features that will the introduction of Saidjanov, and revealing the essence of technology in a broad sense. Co-author of the document was made by Miller.
How does the technology of Saidjanov
One of the important technology components of Saidjanov is the simplified payment verification (SPV), which shows that the tokens are blocked in the same chain, so the validators can safely unlock the equivalent value in the alternate circuit. But for sidename proof of the SPV should be concise enough to fit in a single transaction with coins – a transaction that rewards the miner for a new coin.
At a time when researchers Blockstream released a document, they understood that Saidjanov they need a concise proof of the SPV, but they have not yet developed the necessary cryptography. So they are outlined only General ideas.
The document submitted to the Blockstream, describes two types of bilateral linkages: two-way symmetrical, where both circuits are independent from their own mining; and asymmetrical two-way, where the miners are full of Saidjanov validators of the original chain.
When symmetrical bilateral when the user sends their bitcoins to a special address. This means basically the Bitcoin blockchain is blocked. They remain locked during the competition period, which lasts approximately one hour (about six blocks), proof of completion of the transaction. Then, you create an SPV proof to send to a sidechained.
At this point in the sidechained the corresponding transaction with an SPV proof confirming that the money was locked in the Bitcoin blockchain. After that the same value of coins razblokirovat the sidechained.
Coins are used, pass from hand to hand and back to the main circuit. The process then repeats itself, the coins are locked in sidechained, is the waiting period creates an SPV proof and sent back to unlock coins in the main chain.
Process asymmetrical two-way communication is a little different. The transition from the main chain to the side does not require SPV proofs, because the validators sidechained aware of the state of the main chain. However, when coins are returned to the original chain, the SPV proof is still needed.
In search of a compact proof
In the side chain compact SPV proof should contain a compressed version of all header blocks of the chain which blocked funds from the Genesis block and to the tender period as well as transaction data and some other data. Thus, the SPV proof can also be seen as confirmation «PoW» for each specific withdrawal.
The inspiration for the compressed proof SPV was a technique known as «skip list» («admission list»), developed 25 years ago. The trick of applying this method to the compact SPV proof was to find a way to skip the record header blocks, while maintaining a high level of security, without the possibility of tampering with the evidence by the other party.
Working on issue Blockstream presented to the Miller, who for several years thought about compact SPV, early draft of a document describing technology Saidjanov.
In August 2012, the forum BitcoinTalk, in the message called «High-Value-Hash Highway» («Fast path highly significant hash»), Miller described «the merkle skip list» («admission list Merkle»), which could use a light version of the Bitcoin client to quickly determine the longest chain. In this article, Miller described the value of the data structure as «absolutely stunning».
After reviewing the project submitted by the company Blockstream, Miller found a vulnerability in a compact SPV proof described in the document. Discussions continued, but «it did not help to find a way to solve the problem without sacrificing efficiency,» said Miller.
Non-trivial contributions of the Miller article in Blockstream are several paragraphs in Appendix B, which describes the problem of creating a compact SPV proof.
«It should be possible to significantly compress the headers, while maintaining the same amount of work, but optimization of these trade-offs and the formation of security guarantees beyond the scope of this article and the theme of the current work.»
This work has been delayed for three years.
Meanwhile, growing interest in shadchanim by researchers from IOHK, whose plan was to create Cardano – a new «proof-of-stake» (PoS) blockchain, which IOHK signed a contract.
Cardano was to consist of two levels: the operating level for the storage of cash receipts, launched in September 2017; and the level of smart contracts. These levels would be two blockchains, supported by sidename. Thus, the calculations could be simple and at the same time protected from any attacks that may occur at the level of smart contracts. But if IOHK wanted to pursue the work of Cardano in accordance with the plan, it was necessary to allow the side chain.
In February 2016, Kias, at that time Professor at the University of Athens and two of his disciples, Nikolaos, Lamprou (Nikolaos Lamprou) and Aikaterini-Panagiota from Stoke’s (Aikaterini-Panagiota Stouka) – released the «Proofs of Proofs of Work with Sublinear Complexity» — PoPoW («evidence of working with sublinear complexity»).
This article was the first official statement on establishing a compact SPV proof. However, the proof described in the document was interactive, while for sidename it was not interactive.
In the interactive proof verifier and check the join in the negotiations, there can be more than one round of message exchange. A non-interactive proof, by contrast, is a simple short line of text that will neatly fit into a single transaction the blockchain.
Report of the PoPoW was presented at the seminar Bitcoin’16, combined with the conference «Financial cryptography and data security», International Association of financial cryptography (IFCA). Miller, who was at the conference, approached Kiasu and shared the idea to make the Protocol non-interactive.
«It was a remarkable observation,» he said Kias, «but the protection of evidence is absolutely not obvious and will require significant efforts.»
Zindros, who had just started work on his PhD thesis under the guidance of Kiasu, also attended the conference, and he needed a topic for a dissertation. Kias decided that this is just what you need, so that «three of them dropped the hammer and adapted Protocol PoPoW and evidence of safety to non-interactive settings,» as said Kias.
In October 2016, Kias officially joined IOHK. A year later, along with Miller and Sindroom, he released NiPoPoW, adding a concise proof of the SPV. It happened five years after the first discussions of Saidjanov on the forums of the developers of Bitcoin.
«I don’t know, would work technology if the evidence was interactive, but not interactive it really works well,» said Sandros.
There is still a lot of work
Even with all NiPoPoW saidonly still not fully fleshed out. There are a number of open questions. For example:
How tight can be the evidence?
After the transaction has been locked in the same chain, how much time must pass before it can be sent to another?
Is it possible to move a token directly from one side chain to another?
«Many theories have yet to give a clear definition,» said CEO IOHK Charles Hoskinson (Charles Hoskinson).
In addition, although NiPoPoW and is intended to evidence the work performed in the blockchains, some believe that if the blockchain will take its place in the world on a larger scale, the future will be for protocols such as Ouroboros, Algorand or Snow White, which promise to be more energy efficient than Bitcoin.
In particular, if Cardano, based on Ouroboros, will work in accordance with the plan, researchers IOHK will need to examine NiPoPoS.
Hoskinson, confident in their own abilities. «We can do it,» he said. «We can definitely use NiPoPoS. The only question is, how many megabytes or kilobytes it would take? If we can bring it down to 100 KB? It is really a question.»