Innovations & Trends

How Does a Block of Data on a Blockchain Get Locked?

Blockchain technology is revolutionizing various industries with its inherent security, decentralization, and immutability. But how exactly does blockchain accomplish the tamper-proof security of data that it is renowned for?

The answer lies in the processes surrounding the creation of sequential blocks that make up the blockchain ledger. Specifically, the cryptographic operations involved in “locking” blocks of transactions to permanently seal and secure the data stored within.

This article will explore the technical mechanisms that enable the locking of blocks in a blockchain, enabling immutable storage of information.

What is a Block in a Blockchain?

A blockchain is composed of a continuous sequence of smaller data structures called blocks that each contain batches of transactions. For example, a single block on the Bitcoin blockchain typically contains around 500 to 2,000 transactions that occurred on the network.

The block also contains other key information including the cryptographic hash of the previous block, a timestamp, and a nonce number. Once created, these blocks get added linearly to the existing blockchain by network participants through the mining process.

Block in a Blockchain

How Are Blocks Created?

For a new block of transactions to be created and added to a blockchain, the following process occurs:

  • Transactions are initiated by users and broadcast to the peer-to-peer network of nodes.
  • Network nodes collect these transactions into a candidate block.
  • Miners validate the transactions inside the candidate block verifying signatures, balances, etc.
  • The validated block of transactions is permanently “sealed” through encryption.
  • The sealed block is broadcast to all nodes and mined onto the existing blockchain.

This establishes the complete record of the transactions in a tamper-evident manner through the block-sealing process.

How Does a Block Get Locked on a Blockchain?

Locking or sealing a block on a blockchain involves cryptography that permanently preserves the block’s contents in a way that cannot later be altered. This is accomplished through creating a cryptographic hash digest of the block’s contents.

Cryptographic Hash Function

A cryptographic hash function takes an input of any length, like a block of blockchain transactions, and converts it into a fixed-length alphanumeric string called a hash digest. This hash is unique to the specific contents of the input.

Even the smallest change to the input data results in a completely different hash output. Hashes are consistently reproducible – meaning the same input always generates the identical hash output.

Locking Process

Once a candidate block of transactions is validated by miners, locking the block simply involves calculating the hash digest of its contents including the transaction data and metadata.

This locking hash is included in the block itself when it gets permanently added to the chain. Future blocks will incorporate this hash to link everything together in an immutable chain.

Tamper Evidence

If anyone later attempts to modify the contents of a particular block in the chain, this will alter its hash. The next block still retains the original hash before modification.

This mismatch in hashes reveals the unauthorized tampering, making the blockchain effectively immutable due to hashes cementing the state of each block as it was sequenced onto the chain.

Characteristics of a Locked Block

Some key qualities of a block that has been securely locked into the blockchain through cryptography are:

  • The block contents cannot be altered without invalidating hashes
  • The block transactions are permanently recorded in order
  • The sequence of blocks remains verifiable using hashes
  • The entire blockchain history remains auditable
  • Mismatches in hashes anywhere reveal tampering
  • New transactions get added via new sequential blocks

These attributes create a solid audit trail enabling the decentralized blockchain ledger to be trusted for recording data and events in a verifiable and incorruptible manner.

What is the Significance of Locking Blocks?

Locking each block using cryptographic hashes delivers some significant advantages that underpin blockchain’s game-changing potential across industries:

  • Trust – Enforces integrity without centralized control
  • Transparency – Records remain verifiable and auditable
  • Security – Contents cannot be forged or secretly modified
  • Decentralization – No single point of failure for the ledger
  • Accuracy – Transactions remain unchanged over time
  • Immutability – Blocks cannot be deleted or altered
  • Automation – Consensus algorithm seals blocks at intervals

These capabilities unlocked by cryptographically chaining blocks together enable blockchains to foster trusted collaboration, create transparency, automate processes, and disrupt traditional business models.

Real-World Applications

Securely and irrevocably locking blocks has enabled some profound blockchain use cases:

  • Cryptocurrencies – Cementing records of coin transactions
  • Financial services – Settlement of trades, payments
  • Supply chains – Tracking authenticity of goods
  • Healthcare – Storing patient medical records
  • Government – Digital identity records, documenting votes
  • Real estate – Recording property deeds and titles

Across industries, the immutability derived from chaining locked blocks allows blockchains to provide strong integrity, security, and legal suitability to various kinds of records and transactions.

Frequently Asked Questions

What is inside a typical blockchain block?

A standard block contains a batch of transactions, timestamp, nonce number, hash of the previous block, and the hash that locks the block. The hash locks in the contents permanently.

What is the core process that allows a block to be locked?

Locking a block involves calculating the cryptographic hash digest of its contents including transaction data. This immutable hash seals the block and gets included when chaining it to the blockchain.

How are hashes used in blockchain block locking?

Hashes create tamper-evidence by cascading from one block to the next. If a past block’s contents are altered, its recalculated hash won’t match the hash stored in the next chained block, revealing manipulation.

Can a locked block ever be modified on a blockchain?

No, the cryptographic hashes permanently lock in the state of each block at the time it was sealed, making the blockchain history irreversible and verifiable. No locked block can be secretly altered.

What are the main benefits of cryptographically locking blockchain blocks?

Locking blocks enable trust, transparency, decentralization, security, and immutability in the blockchain ledger, which can digitally verify records, transactions, identities, and other data robustly.


In summary, cryptographic hashes are the fundamental mechanism that enables blockchain blocks to be irreversibly sealed, preserving the correctness and sequence of data stored in the decentralized ledger across time and participants. This locking process is central to blockchain’s ability to offer trusted collaboration, automation, and disruption of conventional processes. By immutably chaining blocks, blockchains provide a platform for securely recording and sharing data at scale without centralized control.

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