What is SegWit? an introduction to Bitcoin's clever on-chain scaling approach

When Satoshi Nakamoto designed Bitcoin, he implemented a fundamental constraint: each block could not exceed one million bytes in capacity. This limitation meant that the number of transactions that could be recorded in each block was extremely limited. In Bitcoin's earliest days, this one-million-byte capacity was sufficient to handle the transaction volume of a niche market. However, as the number of Bitcoin users surged dramatically, the network became particularly congested.

The Bitcoin network updates with a new block approximately every ten minutes. Due to the one-million-byte capacity constraint, each block could contain no more than a few dozen transactions at most. Currently, Bitcoin can process an average of seven transactions per second. Under special circumstances, this limitation creates a backlog of tens of thousands of transactions on the Bitcoin blockchain, with transaction fees for Bitcoin transfers reaching as high as tens of dollars. During periods of network congestion, Bitcoin transactions can take several days to be packaged and confirmed.

This inefficiency created an urgent need within the cryptocurrency community for an efficient technical solution to solve the problem of slow Bitcoin transaction processing. The solution needed to help users receive their Bitcoin faster while paying lower transaction fees to miners. The answer came in the form of Segregated Witness, commonly known as Bitcoin SegWit.

Introducing SegWit

Bitcoin SegWit technology was proposed in 2015 by Bitcoin developer Pieter Wuille and other Bitcoin Core contributors as a comprehensive solution to the transaction processing speed problem. In 2017, SegWit was officially implemented through a soft fork on the Bitcoin network, increasing the information processing capacity of a single Bitcoin block by 1.7 times.

Currently, major cryptocurrencies including Bitcoin, Litecoin, and Bitcoin Cash have adopted SegWit technology. The primary benefits of implementing Bitcoin SegWit include expanding block capacity, increasing transaction speed, and optimizing transaction scalability. These improvements have made Bitcoin transactions more efficient and cost-effective for users worldwide.

The technical principles of SegWit

To understand how Bitcoin SegWit works, it's essential to examine the structure of Bitcoin transaction information. Every piece of transaction information in Bitcoin is divided into two parts: basic transaction data and witness data. Transaction data records the account balance and transfer details, while witness data verifies the user's identity through digital signatures.

Users generally care most about the core information related to their assets, such as account balances and transaction amounts. The verification of user identity, while necessary for security, does not need to occupy as much space in the transaction structure. In simple terms, the recipient of a transfer only needs to confirm that the assets are available and authentic; they do not need to know all the detailed verification information about the sender.

In the traditional Bitcoin transaction structure, witness data—specifically the signature information—takes up a significant amount of storage space, which delays transfer efficiency and increases packaging costs. According to statistics, signature information can occupy up to 65% of the space in a Bitcoin transaction block. Bitcoin SegWit technology addresses this inefficiency by extracting the witness data from the transaction information and storing it separately. This separation speeds up transaction processing and allows more transactions to fit within each block.

The main advantages of SegWit

Bitcoin SegWit provides several significant advantages that improve the Bitcoin network's overall performance and usability.

Increased block capacity: After adopting Bitcoin SegWit, the original block storage space is effectively released because the witness data is stored separately. This means more transaction information can be processed within the same one-million-byte limit. The separation of witness data effectively increases the block's capacity for actual transaction data, allowing more transactions to be included in each block.

Faster transaction rate: Similar to Ethereum's layer-2 scaling approach, Bitcoin SegWit processes Bitcoin data in layers to increase the transaction rate. After implementing SegWit, the Bitcoin transaction system concentrates more computing power and larger storage capacity on processing transaction information rather than signature verification. This dramatically reduces the burden on the network, and theoretically, the transactions per second (TPS) rate increases significantly. Data shows that after adopting Bitcoin SegWit, the average cost per transaction has been significantly reduced, making Bitcoin more accessible for everyday use.

Favorable for Lightning Network: The Lightning Network is one of the most discussed Bitcoin layer-2 protocol expansion solutions, designed to solve Bitcoin's scalability problem through off-chain transactions. The Lightning Network creates an additional layer of network on top of the Bitcoin blockchain and establishes payment channels that enable large transfer transactions to be completed quickly and smoothly under any circumstances. Bitcoin SegWit complements the Lightning Network by quickly processing the data with the highest priority on-chain, relieving pressure from the main blockchain and indirectly creating favorable conditions for Lightning Network implementation.

Additionally, under Bitcoin SegWit's technical framework, transaction data and signature data are completely separated. Throughout the entire transaction processing system, the user's signature data is excluded from the transaction malleability calculation, eliminating the possibility of transaction information being tampered with. This innovation prevents incorrect information from being permanently recorded on-chain and provides positive benefits for the expansion and application of transaction information repair programs.

Furthermore, Bitcoin SegWit is considered a precursor to Bitcoin Ordinals, as it expanded the limit on how much arbitrary data can be placed in a transaction. This expansion allows for inscriptions to be engraved on each satoshi of Bitcoin. In 2021, the Taproot upgrade built upon this foundation by creating a system that makes it easier to store arbitrary witness data and continued to expand the data limit placed in Bitcoin transactions, ultimately enabling the birth of Bitcoin Ordinals non-fungible tokens that exist today.

How SegWit is applied

For ordinary users, Bitcoin SegWit technology provides three main benefits: enhanced security with higher security than ordinary addresses, faster transactions through expandable block capacity and quicker transaction verification, and cheaper fees that are lower than ordinary wallet addresses.

Users can take advantage of Bitcoin SegWit by using a SegWit-compatible wallet address to receive Bitcoin transfers. Data has shown that Bitcoin's SegWit utilization rate has exceeded 67% and continues to grow, demonstrating widespread adoption across the network.

Bitcoin addresses are currently divided into several main formats, each with distinct characteristics:

Legacy (P2PKH) format: These traditional addresses start with the number 1 (for example: 1Fh7ajXabJBpZPZw8bjD3QU4CuQ3pRty9u). P2PKH stands for Pay To PubKey Hash, and this was Bitcoin's original address format, which is still in use today.

Nested (P2SH) format: These multi-signature addresses start with the number 3 (for example: 3EktnHQD7RiAE6uzMj2ZifT9YgRrkSgzQX). P2SH stands for Pay-to-Script-Hash, which uses redemption scripts and redemption script hashes. This address structure is similar to P2PKH but supports more complex functions than traditional addresses. P2SH script functions are most commonly used with multi-signature addresses, which can specify multiple digital signatures to authorize transactions. For example, an address starting with 3 might be controlled by three people, requiring any two of them to agree to initiate a transfer.

Nested SegWit (P2SH) format: These Bitcoin SegWit-compatible addresses also start with 3 (for example: 3KF9nXowQ4asSGxRRzeiTpDjMuwM2nypAN). Because the P2SH method is used for packaging, SegWit-compatible addresses also start with 3, making them recognizable by old nodes and ensuring backward compatibility.

Native SegWit (Bech32) format: These native segregated witness addresses start with bc1 (for example: bc1qf3uwcxaz779nxedw0wry89v9cjh9w2xylnmqc3). The Bech32-encoded address format was specially developed for Bitcoin SegWit and was defined in BIP173 at the end of 2017. One of the main features of this format is that it is case-insensitive, containing only characters 0-9 and a-z, which effectively avoids confusion and improves readability when inputting addresses. Since fewer characters are required, the address uses Base32 encoding instead of the traditional Base58, making calculations more convenient and efficient. Bech32 addresses provide higher security, better optimized checksum error detection, and minimize the chance of invalid addresses. They are natively compatible with Bitcoin SegWit and require no additional space to embed SegWit addresses into P2SH addresses, resulting in lower handling fees.

For version 0 segwit addresses, they always start with bc1q. Pay-to-Witness-Public-Key-Hash (P2WPKH) addresses have a fixed length of 42 characters, while Pay-to-Witness-Script-Hash (P2WSH) addresses have a fixed length of 62 characters. P2WPKH is typically used for ordinary addresses, and P2WSH is usually used for multi-signature addresses.

P2TR (Bech32m) format: These Taproot addresses start with bc1p (for example: bc1pqs7w62shf5ee3qz5jaywle85jmg8suehwhaOawnqxevre9k7zvqdz2mOn). To fix a bug in the original Bech32 specification where certain character combinations could pass checksum verification incorrectly, a new standard called Bech32m was proposed. Bech32m adds an extra constant to the Bech32 checksum formula to ensure that any additional characters will generate an invalid checksum. This new standard applies to Taproot addresses and future address versions, while version 0 Bitcoin SegWit addresses continue to use the original Bech32 format, as they are already protected by length limits.

The subtle differences between addresses

Different Bitcoin address formats offer varying levels of efficiency and cost savings when using Bitcoin SegWit. Understanding these differences helps users optimize their transaction fees:

• SegWit-compatible addresses (starting with 3) save approximately 24% in transfer fees compared to traditional addresses (starting with 1)
• Native Bitcoin SegWit addresses (starting with bc1) save approximately 35% in transfer fees compared to traditional addresses (starting with 1)
• Bitcoin SegWit addresses (starting with bc1 or 3) can save up to 70% in transfer fees compared to multi-signature addresses (starting with 3)
• Taproot addresses (starting with bc1p) support BTC NFT holding and Ordinals NFT functionality, with transfer fees similar to addresses starting with 3

These differences demonstrate the practical benefits of adopting newer Bitcoin SegWit address formats, particularly for users who conduct frequent transactions or want to minimize their transaction costs.

Conclusion

Bitcoin SegWit represents a crucial development in Bitcoin's evolution, significantly increasing the number of transactions each block can process on the Bitcoin network. By separating witness data from transaction data, Bitcoin SegWit effectively expanded block capacity without requiring a hard fork, maintaining backward compatibility while improving efficiency. This innovative approach addressed the rare exploit relating to transaction malleability, where transaction IDs could be altered before confirmation, which previously caused complications for multi-signature wallets and layer-2 solutions.

Beyond immediate capacity improvements, Bitcoin SegWit added greater programmability to Bitcoin, enabling further scaling solutions like the Lightning Network and ultimately paving the way for innovations such as Taproot and Bitcoin Ordinals. The widespread adoption of Bitcoin SegWit, with utilization rates exceeding 67% and continuing to grow, demonstrates the cryptocurrency community's recognition of its benefits.

Today, major cryptocurrency platforms and wallets have fully integrated Bitcoin SegWit support across Bitcoin, Litecoin, and Bitcoin Cash, optimizing user experience, reducing transaction fees, and increasing transfer speeds. Modern wallets also support Taproot addresses, which enable Ordinals inscriptions, BRC-20 tokens, and BTC NFTs, expanding Bitcoin's functionality beyond simple value transfers. As Bitcoin continues to evolve, Bitcoin SegWit stands as a foundational upgrade that successfully balanced network efficiency, backward compatibility, and future expandability, demonstrating that significant improvements can be achieved through clever engineering rather than contentious hard forks.

FAQ

What is SegWit in Bitcoin?

SegWit (Segregated Witness) is a Bitcoin upgrade implemented in 2017 that separates transaction signatures from transaction data. This increases block capacity, improves transaction speed, and resolves transaction malleability issues.

What is the difference between BTC and BTC SegWit?

BTC SegWit offers lower transaction fees and faster confirmation times compared to standard BTC. SegWit uses a different address format, so verify exchange compatibility before sending funds to avoid transaction failures.

What happens if I send Bitcoin to a SegWit address?

Your Bitcoin will be received directly in the SegWit address. The transaction processes normally on the network with reduced fees due to SegWit's efficient data structure.

What is a Bitcoin SegWit address?

A Bitcoin SegWit address is a transaction format using Segregated Witness protocol to reduce fees and increase speed. It starts with 'bc1' prefix and separates transaction signature data from transaction data.