The concept of immutability has become one of the pillars that define the strength and core value of Blockchain technology since the birth of Bitcoin. However, according to experts at Tan Phat Digital, in a real technical environment, the question of whether data on the Blockchain can be modified cannot be answered with a simple assertion. Blockchain's immutability is not an absolute physical barrier but the result of a sophisticated combination of cryptographic data structures, distributed consensus algorithms and huge economic barriers.
To understand the ability to modify data, it is necessary to consider Blockchain from many angles: from natural technical phenomena such as chain reorganization, targeted attack scenarios such as 51% attacks, to administrative interventions such as chain splits (hard forks) or new research on redactable Blockchain to meet modern legal requirements.
Security mechanism and cryptographic nature of Blockchain immutability
Blockchain immutability is built on a multi-layer architecture, where each component plays a role in preventing unauthorized attempts to change data. The foundation of this security lies in how data is encrypted and linked together in chronological order.
Cryptographic hash function system and linked chain structure
Each block of data in the Blockchain does not exist independently but is closely linked to the previous block through a hash function. A hash function, such as SHA-256, works in a one-way manner: it converts any amount of data into a fixed-length string of characters. An important characteristic of the hash function is the avalanche effect: just by changing a single bit in the input data, the hash result will change completely and unpredictably.
In the Blockchain structure, the header of the current block (Block $n$) always contains the hash code of the previous block header (Block $n-1$). This creates a chain of cryptographic logic. If an entity wants to modify the data in Block $k$, the hash code of Block $k$ will change. Since this hash code is stored in Block $k+1$, Block $k+1$ also becomes invalid. To maintain the validity of the entire chain after modification, the entity is forced to recalculate the hash for Block $k$ and all blocks from $k+1$ up to the latest block at the beginning of the chain.
In systems using Proof of Work, this recalculation requires a huge amount of computing power, because miners must find a $Nonce$ value such that the block's hash code satisfies the difficulty of the network. The energy and time costs of doing this for blocks deep in the chain are an economic barrier that makes modifying data practically impossible for single individuals or organizations.
Merkle Tree Structure and Transaction Integrity
Within each block, thousands of transactions are summarized through a Merkle Tree structure. The Merkle Root is the final hash representing all transactions in that block and is included in the block header. This structure allows nodes in the network to check the integrity of a specific transaction without downloading the entire block's data, and also enhances tamper resistance because any change at the transaction level will change the Merkle Root and lead to invalidation of the entire block.
Decentralized network and consensus mechanism
Different from traditional databases with centralized storage, Blockchain operates on a peer-to-peer (P2P) network of thousands of independent nodes. Each node maintains a full or partial copy of the ledger, and no node has absolute control. When a new block is proposed, it must undergo validation by other nodes based on a certain consensus protocol such as Proof of Work (PoW) or Proof of Stake (PoS).
The consensus mechanism ensures that even if a few nodes are attacked or intentionally change data, the rest of the network will recognize the discrepancy and reject that invalid version of the ledger. Immutability here is not only a technical characteristic but also an equilibrium state of game theory, where participating agents tend to comply with the rules to receive rewards instead of attacking the system to receive the valuelessness of destroyed data.
Ability to change data through chain reorganization (Chain Reorganization)
Although Blockchain is considered immutable, in technical reality, transaction history can be "rewritten" to a certain extent through the phenomenon of chain restructuring (reorg). This is a natural process of the network to maintain global consensus, but it also brings risks to the authenticity of data.
Reorg mechanism
The reorg phenomenon often occurs when the network is temporarily split into two branches (forks) due to information transmission delay. This is most common when two miners find two valid blocks at almost the same time in different geographical locations. One half of the network may receive Block A first and consider it the top of the chain, while the other half receives Block B first.
This disagreement is only resolved when a subsequent block (e.g. Block C) is mined. If Block C is built upon Block B, then the chain containing Blocks B and C becomes the longer chain (the chain with the most effort). According to Satoshi Nakamoto's rules, nodes across the network will automatically switch to accepting this longest chain and abandon the shorter chain containing Block A. The process of nodes deactivating blocks in the old chain to accept blocks in the new chain is called chain restructuring.
Impact of Reorg on Data Integrity
When a reorg occurs, the discarded blocks are called "stale blocks". Transactions contained in these blocks, which were previously considered confirmed, are now excluded from the official blockchain. If those transactions do not appear in the new longer chain, they are considered never to have occurred and are sent back into the mempool to wait to be mined again.
This leads to uncertainty about the status of the most recent transactions. This is why users and exchanges are often recommended to wait for a transaction to go at least 2 to 6 blocks into the chain (confirmations) before considering it final. The deeper the reorg, the greater the risk to data integrity and user trust.
See also: What is Merkle Tree? Core role in Blockchain security 2026
51% attack: Risk of intentional data alteration
If reorg is a probabilistic technical phenomenon, then 51% attack is a deliberate attempt to manipulate and modify data on the Blockchain by taking control of the majority of network power.
Method of implementation and ability to reverse transactions translation
A 51% attack occurs when one entity controls more than 50% of the computing power (hashrate) in a PoW network or more than 50% of the stake (stake) in a PoS network. With this advantage, an attacker can create a private blockchain at a faster rate than the public chain of the rest of the network. After some time, the attacker publishes this private string. Since the attacker's chain is longer (more effort involved), the entire network will be forced to perform a large-scale restructuring to accept that chain as the official history.
Cost and economic feasibility 2025-2026
The ability to modify data through a 51% attack depends directly on the value of the network. For large networks like Bitcoin or Ethereum, the cost of carrying out this attack is extremely large. According to the latest estimated data from Tan Phat Digital in mid-2025, the cost to attack 51% of the Bitcoin network is about 10 billion USD. For the Ethereum (PoS) network, the attacker needs to own nearly 45 billion USD worth of ETH at stake.
Detailed characteristics of the 51% attack:
Double-spending:An amount of money is spent twice by reversing the block containing the first transaction. The actual probability of execution is high for small networks, but extremely low for BTC or ETH.
Confirmation prevention: Transactions of some users are denied inclusion in the block. Can be done if the 51% control threshold is maintained.
History Overwrite (Deep Reorg): Replaces a long segment of existing blocks to modify past information. Extremely difficult, requiring maintaining 51% strength for a very long time.
"Nothing at Stake" attack: Miners mine on multiple chain branches at the same time to maximize profits in PoS. Currently effectively limited by the slashing mechanism (stake penalty).
See more: What is Chain in Blockchain? The secret to data immutability
Interfering with immutability through Hard Fork: Lessons from The DAO
In addition to technical methods, data on the Blockchain can be modified through social consensus. The most typical example is The DAO hack on the Ethereum network in 2016. When 3.6 million ETH was appropriated by hackers, the community was faced with a choice: keep immutability or change history to refund the money.
To resolve, a Hard Fork was carried out at block number 1,920,000. Bản cập nhật này can thiệp vào trạng thái của Blockchain, chuyển số ETH bị đánh cắp vào một hợp đồng rút tiền mới. This action proves that immutability is not absolute but can be changed if the majority of stakeholders agree to intervene in the system.
Editable Blockchain: New Trends and Solutions
In the context of regulations such as GDPR requiring the "right to be forgotten", absolute immutability becomes a legal barrier. This led to the development of controlled editable Blockchain technology.
Details of data editing mechanisms:
Chameleon Hashing: Uses a hash function containing a "trapdoor" key. Helps preserve chain structure and smooth modifications at the block level, but requires extremely secure key management to avoid abuse.
Fine-grained Redaction: Allows deletion or modification at the level of data as small as individual transactions. However, it increases algorithmic complexity and computational resources.
Threshold Consensus: Modifications are only allowed when the consensus of a certain group of trusted nodes is reached. The disadvantage is that it reduces the decentralization of the system.
Off-chain Storage: Store the original data off-chain and only store the hash code on the chain for easy replacement when needed. Đòi hỏi sự tin cậy cao vào hệ thống lưu trữ ngoại khối.
So sánh khả năng sửa đổi giữa Public Blockchain và Private Blockchain
Dưới góc nhìn quản trị của Tấn Phát Digital, sự khác biệt về mô hình dẫn đến khả năng sửa đổi dữ liệu rất khác nhau:
Public Blockchain: Dữ liệu phi tập trung cao độ. The amendment requires a 51% attack or a global-scale Hard Fork consensus, which is extremely difficult to achieve. The data here has the highest immutability.
Private Blockchain: Systems like Hyperledger Fabric allow operators to control read/write permissions. In particular, the "Private Data Purge" feature allows sensitive data to be permanently deleted from storage history to comply with the law, which is almost impossible to do on public chains.
The current status of Blockchain applications in Vietnam and data security until 2026
Vietnam is entering a period of accelerating Blockchain application into the national digital infrastructure. By 2026, this technology will be widely present in many key fields.
National Infrastructure NDAChain and VNeID
Tan Phat Digital recognizes NDAChain (National Data Association Chain) as an important milestone, playing the role of "backbone infrastructure" for national digital data. With the capacity to process more than 5 million authenticated transactions, this platform ensures transparency of public administrative data. Integrating Blockchain into VNeID helps the Ministry of Public Security trace the origin of precursors and chemicals, preventing all attempts to delete illegal records.
Details of Blockchain application in Vietnamese organizations:
VPBank & Banks:Applied in interbank payments and foreign trade financing. Helps significantly increase transaction speed and reduce operating costs from 5-7 days to 24 hours.
Ministry of Public Security (VNeID): Trace the origin of chemicals and precursors. Helps make state management transparent and prevent fraud in sensitive fields.
Agridential.vn (VBC): Trace the origin of agricultural products such as Sagrifood pork and ST25 rice. Enhance the value of Vietnamese agricultural products and create absolute trust for international consumers.
Cryptographic Technical Academy: Authenticate diplomas and certificates. Completely eliminate the problem of fake degrees and modernize the educational management process.
VBSN (National): Provides shared Blockchain infrastructure (BaaS). Ensuring data sovereignty and the ability to master Vietnam's core technology.
The Potential and Challenges of Blockchain in Vietnam
Despite the great potential for breakthroughs in the digital economy, the roadmap to popularizing Blockchain in Vietnam still faces legal barriers. Vietnam is currently developing specific regulations on digital assets and a Sandbox mechanism to create a safe corridor for businesses.
Technically, cybersecurity risks and attacks on smart contracts still require large investments. Experts at Tan Phat Digital recommend that it is necessary to soon complete the legal framework and focus on training high-quality human resources to fully master this technology.
10 Typical Case Studies on practical Blockchain applications
Below are typical application cases that demonstrate data integrity and operational efficiency in practice:
VNeID (Ministry of Public Works an): Integrating Blockchain to trace the origin of precursors and toxic chemicals. This system helps prevent unauthorized deletion or modification of records, ensuring every chemical journey is controlled transparently on a national identification platform.
NDAChain (National Data Association) infrastructure: The "backbone" platform for Vietnam's data economy, which has processed more than 5 million authenticated transactions by the end of 2025. NDAChain creates a unified authentication layer that makes all public administrative transactions verifiable and unforgeable.
Sagrifood (Pork traceability): Deploying a closed Blockchain system in March 2024 to monitor the clean meat production process. Data from farm to shelf is permanently recorded, helping consumers authenticate quality through QR codes.
ST25 Rice (Brand Protection): Pilot project in collaboration with USAID LinkSME uses Blockchain to prevent counterfeiting of ST25 rice. Storing unchangeable farming information helps increase the reputation and export value of Vietnamese rice in the international market.
VPBank (Foreign Trade Finance): Applying Blockchain to digitize the Letter of Credit (L/C) and trade finance process. This technology helps eliminate manual data errors, shortening international transaction processing time from 5 days to less than 24 hours.
Cryptographic Engineering Academy (Diploma authentication): Use the VBSN network to store and authenticate degrees and certificates. This system helps employers look up accurate information immediately, completely eliminating fake diplomas.
Da Nang Digital Map (Urban Management): Pilot digital map project in Da Nang uses Blockchain to manage planning and infrastructure data. Blockchain's immutability ensures historical records of land ownership and zoning are always transparent.
Wagyu Beef (Vietnam - Japan cooperation): VBC cooperates with Scalably Inc. Deploying Blockchain to manage quality and trace the origin of Wagyu cattle in Japan. This is a testament to cross-border data security and interoperability.
OCOP Ca Mau (Special products): Complete the origin traceability system for regional specialty products (OCOP) by 2023. Blockchain helps limit the situation of poor quality products with brands being swapped, protecting farmers' rights.
EUBIZ (Enhancing agricultural exports): Piloting Blockchain in the supply chain of cashew nuts and agricultural products exported to the EU. Transparency of product journeys helps meet strict international food safety standards.
Frequently Asked Questions (FAQs)
1. Is the Blockchain really 100% unmodifiable? In fact, data on the Blockchain is almost impossible to delete or modify once it has been authenticated thanks to the federated hashing mechanism and decentralized consensus. However, in private networks (Private Blockchain), administrators have the right to overwrite or purge certain data to meet internal requirements.
2. If I transfer the wrong money or write down the wrong data, can I "cancel" the transaction? Wrong transactions cannot be deleted directly. Instead, you must add a new transaction to correct or reverse the error, and both transactions (the incorrect transaction and the correction transaction) will exist forever in the ledger history.
3. Is a 51% attack easy on large networks like Bitcoin? Extremely difficult. To control more than 50% of the Bitcoin network's computing power by 2026, attackers would need to invest around $10 billion in equipment and electricity alone, making the endeavor economically impractical.
4. Why is data on Private Blockchain easier to modify than Public Blockchain? Because Private Blockchain is managed by a single entity or organization. They take control of authentication nodes and can set up policies like "Private Data Purge" to delete sensitive data to comply with the law.
5. How does Vietnam's NDAChain protect data? NDAChain uses a 3-layer security architecture and connects millions of national authenticated transactions, helping to prevent any fraud or unauthorized changes to public and commercial administrative information.
6. Can quantum computers break Blockchain by 2026? By 2026, experts say quantum computers are still not strong enough to directly threaten cryptographic algorithms such as Bitcoin's SHA-256. However, the technology industry is gradually turning to post-quantum encryption (PQC) standards to hedge against long-term risks.
7. Does "reorg" lose my data? In theory, reorg could make a just-confirmed transaction "void" if the block containing it is removed from the longest chain. However, these transactions are often sent back to the "mempool" to wait to be mined again in the next block.
8. Does an editable blockchain (Redactable) reduce security? It does not corrupt the chain because it uses a Chameleon hash function with a trapdoor key for modifications without changing the hash code of the block. However, it requires absolute trust in the administrative key holder.
9. How did The DAO hack change Blockchain history? To get back the stolen 3.6 million ETH, the Ethereum community performed a Hard Fork to change transaction history. This shows that immutability can be interfered with by social consensus in emergency situations.
10. How does the Digital Technology Industry Law 2025 in Vietnam affect Blockchain?This law (effective in early 2026) provides a legal framework and Sandbox mechanism, allowing testing of digital asset and Blockchain applications in a controlled environment, ensuring investor rights and data security.
Can Blockchain have its data modified? The answer is "Yes" technically, but "Extremely difficult" in practice for public systems, and "Administrative" for private systems.
In Vietnam, the period 2025-2026 is the golden time to complete the national Blockchain ecosystem. We need to balance immutability for trust and editability for privacy compliance. Blockchain is not just a storage technology, but a technology that creates sustainable digital trust for the future.
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