Federated Sidechains Are Bitcoin’s Original Upgradeable Sidechain Implementation

To je mnenjski uvodnik Shinobija, samouka, izobraževalca v Bitcoin prostoru in tehnološko usmerjenega voditelja podcasta Bitcoin.

Zvezne stranske verige are currently the only deployed type of Bitcoin sidechain (the most recent paper tukaj). Zamisel o uporabi zveznega sistema vezave in soglasja je bila pravzaprav dodatek v izvirna bela knjiga stranskih verig. Ni bilo konkretne zasnove za nobeno vrsto dvosmernega klina, ki bi vključeval rudarje, zato je bil zvezni klin opisan kot način za uvedbo stranske verige zdaj in nadgradnjo na dvosmerni preverjeni klin z uporabo dokazov za preprosto preverjanje plačil (SPV), podobnih kaj mehke verige do, when something was concretely designed that was safe and deployable. It was also pointed out that in terms of incentives, for very small systems it might be dangerous to use a miner-based peg as they could steal from a very small group of people without much consensus on doing anything about it from the wider Bitcoin system. Federations could be useful for smaller systems where the group of users isn’t big enough to be a disincentive for miners to steal coins.

The general idea is to effectively have a blockchain where a selected group of trusted parties custody bitcoin pegged into the system using multisig, and produce the blocks on the sidechain, signing them with cryptographic keys instead of using proof-of-work. The entire security model is based on having a decently large set of distinct participants in the group, or federation, that are very geographically distributed and are publicly known.

Federations use a threshold of members for both the custody of bitcoin on the mainchain and blocksigning, i.e., a 5-of-7 multisig. This is done instead of requiring all seven of the members to sign in order to balance the two major risks of such a system: theft versus loss. The federation together can steal all of the funds locked in a federated sidechain if they choose to cooperate together to do so; this is why the entire security model is based around many different actors in many different legal jurisdictions. You want it to be exceedingly difficult and unlikely that many different governments all cooperate in order to force a federation to do something malicious, so you want a large number of people needed to sign things. On the other hand, if you require all seven members to sign everything, then all it takes is a single member to lose access to their keys to result in permanent loss of all funds in the sidechain. Hence requiring a majority of members to sign, but not all of them. This leaves some margin of error for key loss while also still requiring a high number of members to be coerced or to conspire to result in a theft of funds.

Zaradi tega je varnostni model sistema dvosmeren glede varnostnih pragov. Kot je bilo že omenjeno, se mora pet od sedmih udeležencev v tej hipotetični situaciji dogovarjati ali biti prisiljeni k sodelovanju, da bi lahko ukradli sredstva stranske verige, da bi bila sredstva aktivno ukradena. Vendar pa morajo le trije od sedmih udeležencev izgubiti, uničiti ali biti prisiljeni onesposobiti svoje ključe, da bodo sredstva stranske verige ostala zamrznjena in jih ni mogoče premakniti — po možnosti trajno. Mejne vrednosti so ravnotežje med tema dvema tveganjema.

Oba hkrati morata biti dovolj visoka, da je malo verjetno, da bi prišlo do obeh najhujših primerov.

Poleg teh osnovnih lastnosti obstaja velika stopnja svobode pri tem, kako lahko implementirate zvezno stransko verigo, tako v smislu oblikovanja same stranske verige kot tudi glede upravljanja ključev za ključe za podpisovanje blokov in skrbniške ključe.

Tekočina

Liquid was the first federated sidechain deployed on Bitcoin, designed for private transactions between exchanges for trading and issuance of other assets like stablecoins or equity tokens. Its codebase is built almost entirely on that of Bitcoin itself. One of the core features of the Liquid network was the implementation of Zaupne transakcije, funkcija, ki uporablja kriptografske dokaze obsega za skrivanje zneskov, poslanih v transakcijah, vendar še vedno zagotavlja jamstvo pod določenimi predpostavkami, da se ne porabi denar, ki ne obstaja. Izvedena tudi tekočina Zaupna sredstva, razširitev zaupnih transakcij. Zaupna sredstva skrivajo, kateri žeton je porabljen poleg zneska.

Ti dve funkciji v kombinaciji zagotavljata močno rešitev za eno od velikih pomanjkljivosti, ki jih je možna z zvezno stransko verigo: cenzuro. Pražna večina (v naši hipotetični zvezi 5 od 7 zgoraj) bi se lahko vsi strinjali s cenzuro določenih transakcij ali UTXO, če bi vsi imeli razlog za to, kot je sum ali potrjena nezakonita dejavnost. V takem primeru bi imeli celo razumno spodbudo, da to storijo, da vladam ne bi dali razloga, da bi sledile celotnemu sistemu. Zaupne transakcije/sredstva lahko zagotovijo dovolj visoko raven zasebnosti, da bi zveza zelo težko izbrala določene vrste transakcij, tudi če ima razlog za cenzuro.

Transakcija vezave na Liquid je razmeroma preprost postopek v dveh korakih. Uporabnik, ki se želi priključiti, vzame multisig naslov federacije in nato "popravi" vsak javni ključ, ki je v njem vključen, z uporabo plačilo po pogodbi z naslovom Liquid, ki ga nadzorujejo, za ustvarjanje novih javnih ključev. Člani zveze lahko izpeljejo ustrezne zasebne ključe, ko izvedo uporabljen naslov Liquid. Dokler te informacije niso razkrite, nihče, niti zveza, ne ve, da je transakcija na ta spremenjeni naslov Liquid Peg-in. Nato uporabnik odda transakcijo v glavni verigi in počaka na 100 potrditev. Ko so potrditve zbrane, lahko uporabnik odda transakcijo v omrežju Liquid in pošlje svoje kovance sebi. Ta transakcija uporablja poseben vnos, ki vsebuje naslov Liquid, s katerim so prilagodili ključe zveze, podpis, ki dokazuje, da jo nadzorujejo, in dokaz Merkle, ki kaže, da ima transakcija priklopa v glavno verigo vsaj 100 potrditev.

The peg-out process is much simpler. A user constructs a transaction that burns bitcoin on Liquid using OP_RETURN, contains an address to send to on the mainchain, and a special zero-knowledge proof from one of the federation members (which one is hidden). When federation members see such a transaction with a valid member proof, they will sign a withdrawal on the mainchain. The proof is implemented to prevent fraudulent or invalid withdrawals and allows whichever federation member is providing the proof to enforce whitelisting or restrictions on peg-outs. Anyone can freely peg bitcoin into the Liquid network, but a relationship with a federation member is required to peg-out.

Kar zadeva varnost upravljanja ključev in rokovanja, je Blockstream razvil varnostne module strojne opreme (HSM) za upravljanje ključev in izvajanje operacij podpisovanja. Te naprave ščitijo ključe, ki se uporabljajo za podpisovanje blokov in vpenjanje/izstopanje, ter jih varujejo pred posegi ali ekstrakcijo ključev. Da bi zagotovili nekatera sredstva za obnovitev v primeru, da okvarjene naprave izgubijo ključe, pa tudi za zaščito pred ekstrakcijo ključev za zlonamerne namene, se varnostne kopije ključa vsakega člana vzdržujejo šifrirane na način, ki zahteva sodelovanje tako člana kot Blockstreama. dešifrirajte ključ za nalaganje v nov HSM. Nobena stran ne more dešifrirati varnostne kopije sama. Zadnja obrambna linija pred izgubo ključa so ključi za dvig v sili. Vsak naslov, na katerega zveza vrže kovance za vezavo, ima dve poti porabe: zahtevani prag zveze in po približno enomesečnem časovnem zaklepu (čeprav se lahko čas spremeni) zahtevani prag za ključe v sili. To je drugi niz ključev, ki jih lahko vzdržuje zveza, druga stranka ali njihova kombinacija, da se zagotovi povrnitev kovancev, če se izgubi preveč zveznih ključev. Zveza redno premika kovance po glavni verigi v svojem skrbništvu, preden poteče časovna zapora, tako da dokler zveza ni spodletela, te nujne poti nikoli ne bo mogoče porabiti. Blockstream trenutno vzdržuje obnovitvene ključe, ki so geografsko porazdeljeni.

Na koncu je tu še funkcija, imenovana »Dinamične federacije«. To omogoča veliki večini federacije posodobitev članstva, dodajanje ali odstranjevanje članov. To se naredi s posodobitvijo programske opreme programske opreme za podpisovanje po odločitvi, katere nove člane dodati ali obstoječe odstraniti, in nato enomesečno obdobje signalizacije. Če se v enem mesecu štiri petine blokov, ki so signalizirali spremembo federacije, omrežje »razcepi«, da prepozna novo zvezo kot podpisnike blokov. Omrežje nato začne uporabljati nove priključne naslove z novo zvezo, vendar še vedno prepoznava stare še dodaten mesec, da zagotovi, da nobena vezava med spremembo zveze ni razveljavljena. Prav tako ni dovoljeno odstraniti toliko članov zveze, da jih ne ostane dovolj za podpisovanje izpisov s starih naslovov. Vsi ti vidiki zveznih nadgradenj so del pravil soglasja in jih uveljavljajo/potrjevajo HSM.

Podlaga (RSK)

Rootstock is a federated sidechain with many design differences versus Liquid. Firstly, it is essentially a copy-paste clone of Ethereum in terms of functionality. It fully supports Solidity, the scripting language used by Ethereum, so that any contract deployed on Ethereum is trivially portable to Rootstock. The rationale for doing this is obviously that Ethereum has a lot of demand and can deliver functionality that Bitcoin is not capable of. Obviously, there are many downsides and risks to Ethereum’s architecture, but you can’t deny there is demand for it.

Another major difference in terms of architecture is what the federation does — they collectively manage a multisig that custodies the funds on the mainchain, but the federation does not in normal circumstances participate in minting blocks. This is done by Bitcoin miners through merged mining, allowing them to mine Bitcoin and Rootstock at the same time. While this provides no meaningful security difference for Bitcoin pegged into the Rootstock chain, it does provide some for other assets issued on the sidechain. The federation can always steal the Bitcoin on the mainchain if enough collude, but because miners actually mine the sidechain it can continue and allow the other assets to keep being transacted. If those other assets have enough value, even without being backed by real bitcoin, the Rootstock BTC token should still have enough market demand to pay fees to utilize other assets to incentivize miners to keep mining.

The involvement of miners isn’t absolute, though. As long as a majority of Bitcoin miners are also mining Rootstock, they are in total control of organizing transactions and mining them into blocks, but if that percent of miners drops into the range of half (or slightly lower), there are consensus rules allowing the federation to sign checkpoints preventing reorgs back before the checkpoint. If the hash rate drops more drastically than that they are even capable of taking over as blocksigners, like Liquid’s federation members. It’s a very dynamic system that can function both without miners and without the federation in order to keep the blockchain progressing forward.

The peg-in process is very simple: send bitcoin to the RSK peg-in address and then wait for enough confirmations. After enough confirmations have built up, a Solidity smart contract on the sidechain will recognize the transaction and credit it to an account on the sidechain controlled by the same key that the UTXO you pegged-in was locked to. Pegging-out is also controlled by a smart contract, which will communicate with the federation’s HSMs, which will sign a mainchain withdrawal transaction when told to by the contract.

Ko je Roostock prvič predstavil vse, kar je bilo potrebno za vezavo, je bila večina federacijskih HSM-jev, ki so podpisali transakcijo, potem ko jim je to naročila pametna pogodba na stranski verigi. Leta 2020 so implementirali nov mehanizem klinov, imenovan POWPeg. Ta nadgradnja je HSM-jem omogočila, da dejansko potrdijo dokazila SPV rudarjev. HSM-ji zdaj zavračajo podpis transakcij vezave, razen če večina trenutnega nabora rudarjev RSK gradi na transakciji iz iniciacije vezave. Varnostni model se na koncu skrči na to, da HSM-ji ostanejo varni, vendar se ne bodo podpisali brez ustreznega dokazila o delu, ki potrjuje izklope, razen če je večina od njih spremenjena in ključi ekstrahirani.

Zaprto

Ljudje že osem let delajo na oblikovanju stranskih verig in medtem ko smo so šli skozi štiri different designs (and there are a few more out there: these are just the ones that have gotten traction with technical Bitcoiners), there is nothing currently deployed except federated chains. Federated systems might not be the trustless sidechain that many people want, but they are still very useful systems — especially in any context where the only way to meet a market demand is to trust a single custodian to arbitrate something. Federations immediately become a default improvement by spreading the counterparty risk around to multiple players.

No, to so na kratko zvezne stranske verige. Zadnji del, ki sledi, obravnava vse slabosti in negativne strani glavnih trenutnih predlogov, vsaj nekaj misli na visoki ravni o tem, kaj si ljudje resnično želijo od »popolne« stranske verige in kako to potencialno doseči.

To je gostujoča objava avtorja Shinobija. Izražena mnenja so v celoti njihova lastna in ne odražajo nujno mnenj BTC Inc ali Bitcoin Magazine.