SegWit Explained: Enhancing Bitcoin Transactions and Network Efficiency

SegWit Explained: Enhancing Bitcoin Transactions and Network Efficiency

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In this guide, we will explore SegWit’s origins, workings, and impact, shedding light on how it has shaped the Bitcoin blockchain and what it means for the future of digital currency. 

Understanding SegWit

Segregated Witness, commonly known as SegWit, is an enhancement to the Bitcoin blockchain. It was proposed by developer Pieter Wuille in 2015 and implemented in 2017.

SegWit’s primary function is to separate the witness data from the main block, reflected in the term “Segregated Witness.”

This separation creates additional space within the block, allowing more transactions to be processed without changing the original 1MB block size.

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The Purpose of SegWit

SegWit was introduced to address two significant issues within the Bitcoin network: transaction malleability and scalability limitations.

Transaction malleability allowed the alteration of transaction data, posing a security threat. SegWit mitigated this by separating the witness data from the main transaction data, effectively resolving the malleability issue.

Moreover, Bitcoin’s scalability was constrained by the limited block size, which restricted the number of transactions processed per block. SegWit addressed this by creating additional space within each transaction block, potentially increasing the network’s capacity.

How SegWit Works

SegWit segregates witness data from transaction data and stores it in a distinct data structure. When a Bitcoin transaction is broadcast, nodes upgraded to SegWit can validate the transaction without downloading the witness data until it is required later.

This segregation increases the effective block size limit, including more transactions in a single block. This can impact transaction fees and the speed of transaction validation.

How SegWit Addressed Transaction Malleability

SegWit addressed transaction malleability by detaching the signatures from the transaction data. Transaction malleability can occur in two ways: first, by adding extra data to the script that holds the signature and other unlocking data after a transaction is signed; second, by altering the signature within the script.

Since the script, known as ScriptSig, and its signatures form part of the transaction ID, any modifications alter it.

SegWit resolved this issue by removing all data, including signatures and public keys, from ScriptSig and relocating it to the witness, a new component of SegWit transactions not included in the transaction ID. Consequently, ScriptSig became immutable after signing, preventing any changes to the transaction ID without invalidating the entire transaction.

How SegWit Increased the Block Size

SegWit enhanced the block size by introducing a novel measurement system known as block weight. This new metric enabled more transactions to be accommodated within each block without directly raising the block size limit.

Before SegWit, Bitcoin constrained each block to 1MB of data, typically fitting around 1,650 transactions per block. The concept of block weight, quantified in weight units, supplanted the block size as the primary constraint, allowing a complete block to hold up to approximately 2,700 transactions.

Applications of SegWit

Segregated Witness, or SegWit, offers several important functionalities within the Bitcoin network:

  • Addressing Transaction Malleability: SegWit’s main objective was to correct the flaw in transaction malleability in Bitcoin and similar cryptocurrencies. This flaw permitted the alteration of transaction IDs before confirmation, thereby complicating transaction tracking and security. By relocating the signature data to a separate segment of the transaction, which is excluded from the transaction ID computation, SegWit rendered the transactions immutable once signed.
  • Enhancing Transaction Throughput: SegWit effectively increases the capacity of each block, thereby allowing a greater number of transactions per block. This improvement boosts the network’s ability to process higher transaction volumes, particularly during periods of increased activity.
  • Lowering Transaction Fees: With the capacity to include more transactions in each validated block, the availability of transaction space rises, potentially reducing transaction fees during times of high demand.
  • Facilitating Layer-2 Solutions: SegWit laid the groundwork for Layer-2 (L2) solutions like the Lightning Network by resolving transaction malleability and improving scalability. These solutions, which build on the Bitcoin blockchain, aim to enable faster and more cost-effective transactions, enhancing Bitcoin’s utility for everyday use.
  • Increasing Network Flexibility: The SegWit upgrade simplified the implementation of future enhancements and modifications to the Bitcoin protocol. It introduced a more modular transaction structure, facilitating the integration of new features and optimizations without necessitating disruptive changes to the network.
  • Boosting Security: SegWit made the Bitcoin network more resistant to various attacks and vulnerabilities by addressing malleability and optimizing transaction efficiency.

Advantages and Disadvantages of SegWit

While SegWit has conferred numerous benefits to the Bitcoin network, it also presents certain challenges and criticisms. Here are the key points:


  • Scalability: SegWit increases the number of transactions processed per block, reducing network congestion.
  • Reduced Fees: Efficient use of block space often results in lower transaction fees.
  • Enhanced Security: SegWit eliminates malleability, improving the security of Bitcoin transactions, particularly those involving multiple signatures.
  • Future Upgrades: SegWit facilitates future protocol enhancements and innovations, such as the Lightning Network, which aims to improve Bitcoin’s scalability and speed further.


  • Adoption Rate: SegWit’s initial adoption was slow, with many users and services, including Bitcoin wallets, taking time to upgrade. Even now, not all Bitcoin services have integrated SegWit changes.
  • Complexity: The alterations introduced by SegWit are complex and require significant adjustments from developers and service providers.
  • Block Size Debate: SegWit led to divisions within the Bitcoin community, with some members arguing that simply increasing the block size would have been a more straightforward solution to scalability issues. This debate resulted in several hard forks, including Bitcoin Cash.
  • Reduced Miner Income: The potential for lower transaction fees due to SegWit might reduce miners’ profits. Additionally, supporting the sidechain that stores witness data might be viewed as a burden since it does not generate revenue.


Segregated Witness, or SegWit, represents a crucial upgrade for Bitcoin, addressing significant issues such as malleability and scalability. By separating witness data from transaction data, SegWit allows more transactions to be included in each block, thereby enhancing transaction throughput and reducing fees. This separation has inadvertently increased Bitcoin’s block size, improving scalability and efficiency and facilitating the development of Layer-2 networks on the Bitcoin blockchain.

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Phillip Scarbrough
About Author

Phillip Scarbrough

Phillip Scarbrough, a prominent figure in crypto analysis, brilliantly navigates the labyrinth of blockchain technology. With a knack for distilling complex subjects into comprehensible prose, Phillip's articles enlighten a vast audience about the crypto universe. As digital currencies evolve, his seasoned insights remain invaluable to readers worldwide.

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