What is Bitcoin's segregated witness address?

SegWit improves Bitcoin's scalability by separating signature data from transactions, enabling more transactions per block and reducing fees.

Jun 16, 2025 at 04:14 pm

Understanding the Concept of Segregated Witness (SegWit)

Bitcoin's Segregated Witness (SegWit) is a protocol upgrade implemented in 2017 to improve the scalability and efficiency of Bitcoin transactions. SegWit addresses were introduced as part of this upgrade, designed to separate (or "segregate") signature data from transaction data. This separation allows more transactions to be included in a single block, effectively increasing the network’s throughput without changing the block size limit.

The core idea behind SegWit was to fix a long-standing issue known as transaction malleability, where third parties could alter transaction IDs before confirmation. By moving signature data outside the main transaction block, SegWit ensured that transaction IDs remained immutable once created. This change also paved the way for future upgrades like the Lightning Network.

How Does a SegWit Address Work?

A SegWit address functions differently from legacy Bitcoin addresses such as P2PKH (Pay-to-Public-Key-Hash) or P2SH (Pay-to-Script-Hash). The most common types of SegWit addresses are:

• Bech32 addresses (starting with "bc1"): These are native SegWit addresses and are considered the most efficient format.
• P2SH-SegWit addresses (starting with "3" or "2"): These are wrapped in a P2SH structure for backward compatibility.

In a standard Bitcoin transaction, signature data (witness data) takes up a significant portion of the transaction size. With SegWit, this data is stored separately, allowing for more transactions per block. As a result, block space utilization becomes more efficient, reducing fees during high network congestion.

Technical Structure of a SegWit Transaction

When analyzing a SegWit transaction, one can observe two primary components: the base transaction data and the witness data.

• Base transaction data includes inputs, outputs, and metadata but excludes signatures.
• Witness data contains all the cryptographic signatures required to validate the transaction.

This structure leads to the concept of block weight, which replaced the traditional block size limit. A block's maximum weight is 4,000,000 weight units, where witness data is counted at a quarter of the cost of other data. This means SegWit blocks can hold more transactions while remaining within the same physical block size constraints.

Additionally, SegWit enables features like script versioning, allowing developers to implement new functionalities without hard forks. It also improves verification efficiency by making it easier for nodes to process transactions quickly.

Generating and Using a SegWit Address

To generate a SegWit address, follow these steps:

• Choose a wallet that supports SegWit functionality.
• Navigate to the receiving section of your wallet.
• Look for an option labeled “SegWit” or “Bech32” when generating a new address.
• Select it to create a native SegWit address starting with "bc1".

Using a SegWit address ensures lower transaction fees due to reduced data size. If you're sending Bitcoin to a SegWit address, ensure your wallet supports sending to Bech32 or P2SH-SegWit formats.

Some wallets allow users to choose between different address types:

• Legacy (P2PKH): High fees
• P2SH-SegWit: Lower fees than legacy
• Bech32: Lowest fees and optimal performance

Always verify the recipient’s address type before initiating a transfer, especially if they specify a preferred format.

Compatibility and Adoption of SegWit Addresses

Since its activation in August 2017, SegWit adoption has steadily increased across major wallets and exchanges. Most modern wallets support both P2SH-SegWit and Bech32 address formats.

However, some older systems or services may not yet fully support SegWit addresses. In such cases, using a P2SH-SegWit address offers a compromise — it provides some SegWit benefits while maintaining backward compatibility with non-upgraded systems.

Exchanges have also embraced SegWit for several reasons:

• Reduced withdrawal fees for users
• Faster confirmations due to smaller transaction sizes
• Enhanced security against transaction malleability attacks

Despite widespread support, users should always check their service provider's documentation to confirm SegWit compatibility before depositing or withdrawing funds.

Frequently Asked Questions

Q: Can I send Bitcoin from a legacy address to a SegWit address?

Yes, you can send Bitcoin from a legacy address to a SegWit address without any issues. The receiving end will benefit from lower fees upon spending, but the sending transaction itself does not gain SegWit advantages unless sent from a SegWit-enabled wallet.

Q: Are Bech32 addresses safe to use?

Yes, Bech32 addresses are safe and recommended for use. They offer better error detection capabilities compared to older formats, reducing the risk of fund loss due to mistyped addresses.

Q: Why do some wallets still use P2SH-SegWit instead of Bech32?

Some wallets use P2SH-SegWit to maintain compatibility with older systems that haven't updated to support Bech32. While Bech32 is superior in efficiency and safety, P2SH-SegWit remains widely supported.

Q: What happens if I send Bitcoin to a SegWit address but my wallet doesn’t support SegWit?

You can still receive Bitcoin on a SegWit address even if your wallet doesn’t support SegWit. However, when you spend those funds later, your wallet might not take advantage of SegWit's fee savings unless it supports the appropriate address type.