NFT Platform Security Guide (1)

For any software company , Fundamentally speaking, security is a difficult and asymmetric problem . There is no panacea for this —— Only last month , Several technology companies have obvious loopholes (e.g. Okta, HubSpot). However , The unmanaged and tamper proof nature of cryptocurrency itself means that security vulnerabilities can lead to billions of dollars in permanent losses . This persistent risk is for ambitious NFT It's a huge challenge for the project .

The loss of hundreds of millions of dollars in user assets has greatly damaged the reputation of the industry , And seriously damage the companies and projects involved . This risk is unacceptable for many enterprises entering the industry , Especially those who already have a certain user base 、 Enterprises with reputation and legal responsibility . therefore , Security as NFT A judgment criterion for project selection platform , Becoming more and more important .

Every platform has a strong incentive to be safe . But the truth is , All solutions have their own trade-offs —— It is important to ,NFT The project should clearly understand what trade-offs they and their platform have made .

This article will review some of the most popular NFT Make a detailed and fair evaluation of the choices made by the platform , Include Ronin、Polygon、Immutable、Solana and Optimism. The focus will be on the underlying security of the platform from the following two core elements .

• Consensus security ： By attacking the nodes of the platform / Verifier ( Such as , adopt 51% attack ) With the difficulty of stealing assets
• Bridging safety ： Security of the mechanism for transferring assets out and into Ethereum . This is usually a more worrying point , Because once there is a loophole in the bridge , Usually Make the user's assets directly at risk .

This article will explore these security issues in depth , Provide necessary technical details , Let the project leader get comprehensive information and make a choice . If you just want to briefly understand their similarities and differences , You can look at this form ：

Ronin

Ronin It's a  Sky Mavis Labs  Blockchain created , Currently dedicated to Axie Infinity And its ecological support .

Consensus security

Ronin It's a piece. “ Side chain ” —— A blockchain with its own nodes and consensus mechanism , But there is an official line between it and Ethereum “ The bridge ”.Ronin Use certificate of authorization (proof-of-authority, POA) Mechanism , have 10 Nodes , These nodes pledge their reputation , To make sure they don't abuse their rights . This is similar to Ethereum's test network, such as  Goerli ( have 20 Of nodes POA chain )  Quite a . If any of these nodes 5 Nodes (50%) Do evil or be attacked , They can launch 51% attack And steal the user's assets through Shuanghua or other attack means . Generally speaking , This scale can be said to be a particularly small number of nodes ( Bitcoin has 15000 Nodes , Ethereum has nearly 6000 Nodes ). They built a more centralized network , In exchange for faster 、 A cheaper deal . Besides , Users cannot run their own nodes , also Ronin The source code of the node is not disclosed , Therefore, users cannot audit it .

Bridging safety  

 

Ronin The official Ethereum bridge of is 5/9 Of “ Multiple signatures ”(multisig) control .“ Multiple signatures ” A total of n One of the private key holders m A signer signs to authorize each transaction . stay Ronin In the network , Every bridge deal needs to get “ Multiple signatures ” Authorization of . However , There is no mechanism to check whether deposits or withdrawals are really effective —— Anyone who can access 5/9 Anyone with a private key can Ronin Any number of tokens in the bridge are put into any Ethereum address . in other words , Any user on the bridge directly entrusts all their assets to this “ Multiple signatures ” System .

2022 year 3 month , This trust setting is exploited by hackers ,6.25 $billion stolen . Hackers were able to access by Axie The team holds 4 A private key and Axie DAO The verifier is leased to Axie Team 1 Private key ( common 5/9 Private key ). As far as we know , It shows that this is a Typical network security vulnerabilities ： Due to the centralization of these verifiers' private keys , There are serious consequences .Sky Mavis Has promised to Compensate users who have lost money , and Increase to... In the next three months 21 A verifier , In order to ensure that Ronin More resilient to future attacks . Although they need to do so in a more robust consensus / Make a trade-off between bridging mechanism and scalability .

Polygon

Polygon At present, an Ethereum PoS Side chain (Polygon PoS), And a special NFT Service business (Polygon Studios), by Skyweaver and ZED RUN And other major projects .Polygon It is developing towards providing different capacity expansion solutions , Most of them are based on  zk-rollup technology  ( Discussed later ), But at present, there is only Polygon PoS As NFT The platform goes online and the main network .

Consensus security

Polygon PoS It's a side chain , Its basic mode is similar to Ronin be similar , It's just Polygon It's a kind of “commit sidechain” ( Submission chain )： It regularly submits the check points of the status on the chain to Ethereum .Polygon PoS Consensus consists of two main parts . The first is Bor chain (Block Producer chain, Blockchain production ), This is a Polygon Where the transaction actually took place ： Pick from the larger pool of verifiers A rotating subset of production blocks , Let this subset run a Adjusted PoA The Internet , This network determines the packaging and sequencing of transactions . However , There is only one block producer in this subset ( see  PolygonScan Browser's block verifier ) Selected to propose 64 Consecutive blocks ( One sprint).

Next is  Heimdall Checkpoint system , More verifiers ( at present Cap of 100) I'll just Bor At the end of the block 30 Minutes of summary snapshots ⅔ “PoS” Consensus , And publish the snapshot as a checkpoint on Ethereum . However , Although the system now has 100 A verifier , But before 4 The pledge proportion of verifiers is 53%, front 7 The pledge proportion of verifiers is 67% ( See here , Click on “ Show all ” And sort by pledge weight ). also ,⅔ The majority consensus requirement refers to the weight of the pledge , Not the number of verifiers . It means , Just attack and control 7 Private key , All assets in the chain ( Not just bridging assets ) Can be stolen through malicious checkpoints —— And the pledgor must always keep their private key online . Besides , because ⅔ The pledge proportion of is the requirement for reaching a consensus , and 43% The pledge weight of is determined by 3 A verifier controls , Just attack 3 A hot wallet is enough to completely freeze withdrawals and checkpoints .

 

The total amount of pledge is 2,307,879,127 MATIC, The top seven verifiers pledged 1,540,761,159 MATIC (~67%)

Contract upgrades can be used to defend against evil checkpoints ( Assuming that the perpetrator can be detected quickly ) —— But this has its own security risks , We'll talk about this next .

Bridging safety

Polygon Bridging and Ronin The difference between bridging is , The checkpoint system eliminates the need for independent verifiers to sign each deposit and withdrawal . However , This means that the security of the bridge depends entirely on Heimdall Systems and Bor Consensus , This is vulnerable to the above attacks .

 

  Besides ,Polygon Use one  5/8  Multi sign system to manage their bridging smart contracts , And the contract upgrade can be carried out immediately without time lock . This can resist the vulnerability of smart contract or the attack on the verifier with high pledge weight discussed above .4 A private key consists of Polygon The founder holds , This architecture has been used by security researchers in the community Strong criticism , Because only one more private key is needed, it is possible to upgrade Polygon All assets of the contract (50 Over US $100 million ) Steal away . However , because Polygon The signer does not need to sign every deposit and withdrawal transaction , These administrator private keys can be kept offline , Make them less likely to be attacked .