A Guide to Blockchain Immutability and Challenges

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A Guide to Blockchain Immutability and Challenges

Immutability means it is hard to make changes without collusion — not that data is unchangeable.

· Security Zone ·
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There are thousands of tales spread throughout the world about blockchain. It is true that this technology is premier among all. Not only did it give birth to cryptocurrencies but it also resolved various security issues.

As I mentioned, a number of tales are there, but the most questioned and discussed tale is the immutability of a blockchain. In this post, I am shedding some light on this aspect. So, let's take a glimpse.

What Is Blockchain Immutability?

Immutability can be defined as the ability of a blockchain ledger to remain unchanged, for a blockchain to remain unaltered and indelible. More succinctly, data in the blockchain cannot be altered.

Each block of information, such as facts or transaction details, proceed using a cryptographic principle or a hash value. That hash value consists of an alphanumeric string generated by each block separately. Every block not only contains a hash or digital signature for itself but also for the previous one. This ensures that blocks are retroactively coupled together and unrelenting. This functionality of blockchain technology ensures that no one can intrude in the system or alter the data saved to the block.

It is also important to know that blockchains are decentralized and distributed in nature, where a consensus is made among the various nodes that store the replica of data. This consensus ensures that the originality of data must be maintained. Undoubtedly, immutability is a definitive feature of this technology. This concept has the ability to redefine the overall data auditing process and makes it more efficient, cost-effective, and brings more trust and integrity to the data.

How Immutability Is Achieved

As I explained above, the hash value secures each block of code separately. Though, the point of interest is how it establishes immutability. To comprehend this scenario, you need to understand cryptographic hashing.

Cryptographic Hash Basics

Today, generating a cryptographic isn't dreadful, as modern programming languages are provided with several "hash functions." With these, one simply needs to pass a set of bytes and the function will return a checksum signature.

There is no dearth of functions under this umbrella; however, the SHA-256 is popular in the blockchain space. Let's better understand with an example.

For instance, you want to generate a cryptographic hash in Python code. For this, you need to import the hashlib package from the standard library of Python, which offers access to the sha256 function. Let's look at the code.

>>> import hashlib

>>> h = hashlib.sha256(' Dummy Data')

>>> h.hexdigest()


These functions are generating a string of 64 characters. Irrespective of the size of the input, you will always get the same fixed length of the string, which is known as the digital signature.

This digital signature points to the exact data that you input. The key utility of this hash that you can't reverse-engineer it. It means you will not be able to use this output string to find the input data. It simply results in the immutability.

Cryptography + Blockchain Hashing Process = Immutability

In this system, transactions verified by a blockchain network include blocks of information embedded with timestamps, which is secured by a hashing process. It links together and incorporates the hash of the previous block. This mechanism develops the chronological chain that joins each block.

The hashing always includes the meta-data of the previous block while generating a new hash for it, which establishes a link between the block and the chain then becomes " unbreakable." After this, nobody can delete and alter the data of the block placed in the blockchain, because if somebody attempts this, the subsequent block rejects the modification (as the hash of block wouldn't be valid anymore).

It is true that this is a robust mechanism. However, there are several challenges that this mechanism has to overcome.

Challenges to Immutability of Blockchain

51 Percent Attack

There are numbers of challenges for this mechanism. However, the chief weakness can be the possibility of a “51 percent attack.” What is this? Well, this term signifies that an attacker can acquire huge computing power over all other members of the network. In short, it can be referred to as "controlling interest of generating power."

As I mentioned above, it is a decentralized form of a network where no single entity is in charge. Yet, miners together can spell death for the immutability of the blockchain system by just creating a majority of hashing power. Now, owing to the upsurge in mining marketplaces and the accessibility to renting mining capacity, there is no difficulty for people to carry out such attack.

This allows attackers to alter the transaction data that is supposed to be "immutable" first. By this facility, attackers can reverse the high-value transaction, spend the money the second time, and secure the profit. 

Quantum Computing

Another big challenge in this space is quantum computing, which is threatening blockchain's trait of immutability. Experts at IBM have asserted that quantum computing has the ability to reverse-engineer the public key of the blockchain network, which can find the private keys to break the system. There is no doubt in saying that this is a real and credible threat in the space, which is capable of affecting almost 50 percent of blockchains.


Experts suggest that the “51 percent attack” can be tackled by creating a stronger protocol and by using a consensus algorithm such as delegated proof-of-stake” or just “proof-of-stake” algorithm.

Why is this needed? Well, it is hard to stake numbers of tokens on a network instead of renting out computing power. Though, it is hard to say that these solutions are reliable enough in such a threat.

For the threat of quantum computing, many application developers have recommended integration of quantum cryptography into the core of blockchain. In the upcoming years, the blockchain architecture created with quantum particles will be able to record all history in a more secure way.

The solutions to these are quite futuristic. So, for now, be mindful of adopting blockchain and the benefits available to create robust application solutions.


Making changes in both offline and live blockchain technologies is extremely difficult. When people refer to blockchain as immutable, it means that it is difficult to make changes without collusion, not that the data cannot be changed. And remember: This technology has both positive and negative implications for data privacy.

51 percent attack, blockchain, changes, data, digital signature, dlt, hash, immutablility, security, technology

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