ZK light client bridges: Succinct Telepathy and zkBridge versus multisig bridges
Thread906 words
Surveys the bridge spectrum from CEXs to multisig and MPC bridges, then argues light client bridges with zk state verification are the gold standard. Explains proof of consensus in Telepathy and zkBridge's header relay.
Key claims
Committee-based bridges are prone to exploits
Light client bridges via ZKPs are the gold standard
ZK bridging should become more established over the next 3-6 months
0/ bridges enable interoperability & capital flow across chains 🌉
but committee-based bridges have proven to be a security risk & have been often been the target of exploits ⚠️
That's why we need light client based bridges relying on state verification via #ZKPs ✨
🧵 (0/30)
1/ this 🧵 primarily focuses on @SuccinctLabs Telepathy bridge & @zkcollective's zkBridge. But to get started, let's have a more holistic at the bridging space
2/ when looking at the bridging space more broadly, at one end of the spectrum, we find centralized exchanges acting as asset bridges for many users, offering exits to various chains
3/ another prevalent bridge architecture involves multisig bridges, which are managed by a multisig of validators that oversee one chain’s deposits and authorize withdrawals on a different chain
4/ some examples of classic multisig bridges include @wormholecrypto, @harmonyprotocol's original Horizen bridge or the @avax bridge
5/ @MultichainOrg and @SynapseProtocol are also examples of committee-based bridging solutions. However, they use multi-party computation for added security
6/ want to know more about secure multi-party computation? 🔒👇
x.com/expctchaos/status/1608855450606526470
7/ but the concept of centralization is not only at odds with the core principles of cryptocurrency, but also bears significant risks. Centralized structures lack censorship resistance & require users to trust a lot in a few trusted parties
8/ as mentioned initially, these types of centralized bridges have proven to be rather prone to attacks and generally provide much lower levels of security than the fundamental blockchains they are meant to connect
9/ that's why we need more secure bridging technology. And personally, I would argue that the “gold standard” of bridging is light client based state verification via zero knowledge proofs
one example is @SuccinctLabs’ #Telepathy bridge 🌉
10/ #Telepathy is as a unique decentralized communication protocol that involves no central trusted authority for relaying messages between #Ethereum and various destination chains
11/ it is designed with a permissionless light client smart contract and incorporates #zkSNARK circuits that are open source. This allows any participant to generate necessary proofs to update the light client
12/ the challenge in bridging lies in the case of two chains without shared security - meaning their validator sets and consensus mechanisms can vary and often do
13/ hence, the verification of the source chain’s state on the target chain becomes equivalent to validating the source chain’s consensus in the target chain’s execution environment
14/ this principle is precisely what light clients leverage to efficiently manage the state of a blockchain concerning computation & storage
15/ for effective blockchain interoperability, given two chains with differing validator sets, an ideal setup includes an on-chain light client for the source chain operating on the target chain
16/ this approach is for example embodied in the Inter-Blockchain Communication (#IBC) protocol. The design eliminates extra trust assumptions for cross-chain communication, apart from trusting the economic security of each participating chain’s consensus
17/ for more on #IBC (and zkIBC), check my thread below 👇
x.com/expctchaos/status/1641530762305630208
18/ once an on-chain light client can monitor another chain’s block headers, any participant can provide state proofs to authenticate any information (such as balances, storage, transactions, events) about the source chain in the context of the target chain
19/ consequently, creating cross-chain applications, such as a token bridge, becomes easier
then why don't we do this already?
well historically, implementing such a system was a challenging task though
20/ however, recent advancements in zero-knowledge proof systems have made it feasible
these systems, capable of succinctly verifying computation, will undoubtedly revolutionize the bridging field.
okay that might have been a bit too quick. Let's unpack this
21/ #zk proofs such as zkSNARKs are by definition succinct. This means that the proofs are small in size & can be quickly verified. Hence, ZKPs can compress large quantities of data into just a small proof
22/ using #zkSNARKs hence allows users can generate proof of a computationally expensive operation in an off-chain environment, which can then be cheaply verified on-chain due to its succinctness property
23/ this concept of verifiable computation, which is currently allowing zk rollup teams to scale the execution throughput. ofthe Ethereum ecosystem, can also be used to scale verification of consensus (or state)
24/ @SuccinctLabs' calls this “proof of consensus” allows to concisely express the above idea:
using zero-knowledge proofs to generate a validity proof of a chain’s state according to its consensus protocol
25/ this validity proof can power a gas-efficient light client, paving the way for trust-minimized interoperability (at least depending on the terminology as one still has to "trust" in the consensus of the corresponding chain)
26/ how @SuccinctLabs' Telepathy bridge compares. toother bridging solutions, is well summarized in the below table 📊👇
27/ another example of a ZKP-based bridge is @zkcollective's #zkBridge, which runs a highly optimized #zkSNARK scheme for block header relay, which helps achieve cryptographic security assurance...
28/ ...without any external trust assumptions such as a central or PoS committee, thereby significantly reducing on-chain verification cost, similar to how it was described above
29/ the validity of block headers on remote chains is proven by #zkSNARKs, thus requiring no external trust. Hence, as long as the connected chains and light-client protocols are secure, and there is one honest relayer, @zkcollective's #zkBridge is secure and live
30/ I think this kind of technology will profoundly reshape the bridging space and increase cross-chain security
would expect to become more established over the next 3-6 months
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What came next · since 30 May 2023
Since then
Zero has written 2 more pieces on Succinct since this one.