What is Bitcoin Segregated Witness? SegWit technical improvements

SegWit, activated in 2017, improves Bitcoin's scalability and efficiency by separating signature data from transaction blocks, enabling more transactions per block and lower fees.

Jun 17, 2025 at 07:21 pm

Understanding the Basics of Bitcoin Segregated Witness (SegWit)

Bitcoin Segregated Witness, commonly referred to as SegWit, is a protocol upgrade implemented on the Bitcoin network in August 2017. Its primary goal was to address scalability issues and improve transaction efficiency. The term "Segregated" refers to separating, while "Witness" pertains to the digital signatures included in transactions. By segregating signature data from the main transaction block, SegWit enables more transactions to be processed within the same block size limit.

The original Bitcoin block size was capped at 1 MB, limiting the number of transactions that could be confirmed per second. As Bitcoin adoption grew, this limitation led to higher transaction fees and slower confirmation times. SegWit introduced a new structure that allowed for the effective increase in block capacity without altering the actual block size limit.

How Does SegWit Reconfigure Transaction Data?

In traditional Bitcoin transactions, each transaction contains both transaction data (such as sender, receiver, and amount) and signature data (also known as the witness). Signature data can account for up to 65% of the total transaction size. With SegWit, this signature data is moved outside of the main transaction block.

• Instead of being stored within the transaction itself, witness data is stored separately.
• A new field called the witness block is introduced, which is not subject to the 1 MB block size limit in the same way as the base block.
• This reconfiguration increases the effective block size to approximately 1.8 MB, allowing more transactions to be processed per block.

This structural change also resolved a long-standing issue known as transaction malleability, where third parties could alter transaction IDs before confirmation, potentially causing disruptions in smart contracts or second-layer solutions like the Lightning Network.

Benefits of Implementing SegWit

SegWit brought several notable improvements to the Bitcoin ecosystem:

• Increased Block Capacity: By removing signature data from the main transaction block, more transactions can fit into a single block. This directly improves throughput and reduces congestion on the network.

• Lower Transaction Fees: With more space available per block, users are less likely to bid aggressively for limited block space. As a result, average transaction fees decreased after SegWit activation.

• Improved Security: SegWit enforces stricter validation rules for transaction signatures, reducing the risk of invalid transactions propagating through the network.

• Support for Second-Layer Solutions: SegWit fixed transaction malleability, enabling the development of advanced off-chain protocols such as the Lightning Network, which allows for near-instant and low-cost Bitcoin transfers.

• Better Hardware Efficiency: SegWit transactions are structured in a way that optimizes processing on mining hardware, leading to faster verification times and improved overall network performance.

Technical Changes Introduced by SegWit

From a technical standpoint, SegWit modified how transactions are serialized and hashed. It introduced a new transaction format and updated the way block weight is calculated:

• New Version Field: SegWit added a version byte to transactions, allowing for future upgrades without breaking compatibility with older nodes.

• Merkle Tree for Witnesses: A new Merkle tree is used specifically for witness data, ensuring integrity and efficient verification.

• Block Weight Calculation: Instead of measuring block size in bytes alone, SegWit uses a concept called block weight, where:

  • Base data (excluding witness) is multiplied by 4
  • Witness data is multiplied by 1
  • Total weight must not exceed 4,000,000 weight units

This flexible system maintains backward compatibility while effectively increasing capacity.

SegWit Adoption and Wallet Compatibility

After its activation, SegWit adoption gradually increased across wallets, exchanges, and services. However, not all Bitcoin addresses initially supported SegWit. Users had to ensure their wallets were compatible with SegWit addresses, which typically begin with bc1 instead of 1 or 3.

To enable SegWit:

• Update wallet software to a version that supports SegWit
• Generate a Bech32 address (e.g., bc1...)
• Ensure receiving parties also support SegWit to benefit from lower fees

Many major wallets, including Electrum, Blockchain.com, BitPay, and Coinbase, now fully support SegWit. Exchanges also widely adopted it to reduce costs and improve transaction speeds for users.

Frequently Asked Questions (FAQs)

Q: Can non-SegWit wallets receive Bitcoin from SegWit addresses?

A: Yes, they can. SegWit is backward compatible, meaning funds sent from a SegWit address can be received by a legacy address. However, the sender will still benefit from lower fees, while the recipient does not need to upgrade unless they want to send SegWit transactions themselves.

Q: What is the difference between P2SH-P2WPKH and Bech32 addresses?

A: P2SH-P2WPKH addresses start with a '3' and wrap SegWit functionality inside a legacy script format. They offer some fee savings but are less efficient than Bech32 addresses (starting with 'bc1'), which are native SegWit and provide optimal fee reductions and error detection capabilities.

Q: How does SegWit affect miners?

A: SegWit gives miners the ability to include more transactions per block, which can lead to higher fee revenue due to increased throughput. Additionally, it reduces the computational load during transaction verification, improving mining efficiency.

Q: Is SegWit mandatory for using Bitcoin?

A: No, SegWit is optional. Users can continue using legacy addresses and transactions. However, those who adopt SegWit benefit from lower fees and faster confirmations, making it increasingly advantageous over time.