What Does Mutable Mean?


Heard people talking about the case for mutable blockchains and not sure what they are on about? In this blog we will simply define and explain it.

A Simple Explanation Of Mutable

“Mutable” means “able to be changed”. Blockchains are immutable by nature – they cannot be changed. But there is growing discussion about the benefits of making some blockchains mutable.

The Mutability Debate

By definition, a blockchain is immutable. Or is it? Some things disappear or expire on a blockchain. A smart contract may end a service which is no longer being paid for. That, in effect, is mutability. Even the concept of immutability only has integrity if the original data, entered by a human, can be trusted. What of the code written to execute smart contracts on the blockchain? It too is written by humans. Any chain, including the blockchain, is only as strong as its weakest point. Hence the question is being asked, should blockchains, by design, be given extra functionality and made mutable? Could one of the blockchain’s greatest strengths also be its greatest weakness? Or will the discussion to make blockchains mutable compromise the very reason for their existence?

How Blockchains Work

The immutability of the blockchain is achieved because every new block is cryptographically tied to its predecessor by way of a timestamp and hash. If any data on a block in the chain is changed, it will generate a new hash not compatible with the previous block and break the chain. This would then be flagged to every node in the network. Immutability is one of the fundamental features and strengths of the blockchain. But there are arguments for making them mutable.

Benefits Of Making Blockchains Mutable

It is ironic that some of the industries calling for blockchain mutability are the very ones that were the motivation for its invention. Distrust in central banks triggered the arrival of the world’s first cryptocurrency, Bitcoin. Yet the financial services industry is one of the loudest in its desire to rewrite blockchains. The GDPR’s (General Data Protection Regulation) “Right to be Forgotten” (RtbF) provision calls on blockchain data to be editable in certain circumstances, upholding the right of someone’s private information to disappear from search engines for good. This is already presenting an enormous challenge to the technology. Certainly, there are benefits to being able to make corrections to the blockchain.

Data privacy – the use of blockchain to store sensitive information such as healthcare and criminal records demands the need to be selectively available in an anonymous fashion.

Data access control – blockchain allows users to have total control over their own data and specifically which data is made available to another at any one time. Hence the ability to hide some of that data is needed.

Malicious content – a decentralized system is vulnerable to the uploading of malicious and libelous content from anyone. A mechanism to remove such content would be valuable.

Fraudulent transactions – in the event a network was attacked and funds stolen, the ability to reverse that transaction from within the blockchain would be beneficial.

Problems With Making Blockchain Mutable

Selecting a correction mechanism – who in a decentralized network plays Judge and jury and is given the power to make decisions on behalf of all? Which correction mechanism is best? The very notion of making a blockchain mutable flies in the face of the reason for their invention. It essentially becomes a centralized network.

Weakening the platform – a lack of understanding fuels much skepticism about the security and power of blockchain technology. To trade away one of the core planks of its very foundation is likely to do more harm than good.

Mechanisms Being Considered

One of the biggest issues with making blockchains mutable is deciding who has the authority and in what circumstances an edit should be allowed. It is generally accepted that this would occur only in exceptional circumstances and under strict policy guidelines. Some mechanisms being considered are:

Voting based redaction – a request is submitted to the miners or validators of the blockchain who would consider the policy guidelines and vote on whether to execute it. This method however still results in a breaking of the blockchain and a compromise of its integrity as the hash of the modified block will no longer match the previous block.

Chameleon hash – a hash that looks like a hash but instead also generates a “trapdoor” key which can be used to remove malicious content without breaking the chain. A request is made to miners or validators who use the trapdoor key to annul the transaction.

µchain – µ is the Greek letter “mu”. Hence this mechanism uses a mutant. A problem with the chameleon hash is that because one single key is used to encrypt all the transactions of a user, that key can then be accessed by others to mutate any of their transactions without leaving any footprints. µchain solves this problem by using multi-key encryption. It allows a mutated version of a block to effectively replace the original block, without breaking the chain.

Want To Know More About Mutable Blockchains?

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