What is a Legacy Bitcoin Address?

Bitcoin addresses allow users to transact with their BTC. Whether you're using a hardware wallet or an extension wallet like Leather, it's important to understand how different Bitcoin addresses work as you'll need one to send funds, interact with other wallets, and more. This is especially true as the Bitcoin blockchain ecosystem continues to grow.

A Bitcoin address is a unique identifier that consists of a string of 34 to 62 letters and numbers that acts as a secure destination for users to both send and receive bitcoin, functioning very similarly to an email address as one is required to both send and receive email. While there are different kinds of Bitcoin addresses, this Leather Learn Center piece will primarily focus on one of the earliest and most recognizable ones: Legacy Bitcoin addresses. 

What to Know About Legacy Bitcoin Addresses

A legacy Bitcoin address is the original address format that was first introduced when Bitcoin launched in 2009 and has been in use since. Bitcoin users can distinguish legacy addresses from other types of addresses because they always start with the number “1”. 

For example, a typical legacy address looks like this: 15e15hWo6CShMgbAfo8c2Ykj4C6BLq6Not.

However, the difference between legacy addresses and other types of Bitcoin addresses (like Taproot addresses) runs deeper than just appearances. Compared to more modern address types, legacy addresses have both higher transaction fees and larger transaction sizes due to how they are optimized. This is because when a legacy address is used, both the entire script and signature data are included when a transaction is made.

These factors have made legacy addresses much less efficient compared to their modern counterparts, one of them being Segregated Witness addresses. 

Segregated Witness (SegWit) was the last significant upgrade to the Bitcoin network itself and led to an improvement on legacy addresses. SegWit raised the transaction capacity of Bitcoin by increasing its block size from 1 MB to 4 MB. Additionally, unlike the traditional Bitcoin transactions that had been associated with legacy addresses (which included both the entire script and signature data), SegWit separated the signature data from the transaction data and placed it in a different part of the block, thereby lowering transaction sizes. Both of these changes meant lower fees for users since a larger block size meant more transactions could take place within a single block.

While this increase in transaction size does not directly affect legacy addresses as they remain popular, the notable advantages that SegWit addresses boast may entice users to make the transition from legacy to SegWit. Additionally, SegWit addresses do feature backwards compatibility, meaning that users can send and receive bitcoin from a SegWit address to a legacy address. 

How Legacy Bitcoin Addresses Are Generated with Bitcoin Wallets

To generate an address, a private and public key are required. A private key is a hexadecimal 256-bit number that is randomly generated when a user creates a Bitcoin wallet. To create this hexadecimal 256-bit number, the Bitcoin network generates a random decimal number between 1 and 2^256, and once that decimal number has been selected, it goes through the SHA-256 algorithm. This results in the creation of the private key, which is formatted as a combination of digits between 0 and 9 and letters between A and F. 

A public key is then created based on the private key’s hexadecimal number using elliptic curve multiplication. Elliptic curve manipulation (ECDSA) is an algorithm that multiplies the private key by a variable in an elliptic curve, which results in an output that serves as the public key. The public key is then shortened using two hashing algorithms: SHA-256 and RIPEMD160 (also known as RACE Integrity Primitives Evaluation Message with 160-bit length).

Firstly, SHA-256 hashes the public key, which is vital for security purposes because by producing a randomly generated hash, it reduces the chances of creating an identical Bitcoin address and prevents reversing. Once the output has been created, it gets hashed again, or “double-hashed”, this time by the RIPEMD160. This algorithm shortens the output to 160 bits, making it both shorter and easier to read. Once this public key hash (which is the output from the RIPEMD 160) has been created, a version byte is attached to the front of it, and in the case of legacy addresses, that byte is 0x00. 

A checksum is then calculated by using the SHA-256 algorithm twice to hash out the public key hash with the version byte, and the first 4 bytes from that calculated value act as the checksum, which is used to detect errors. Finally, the checksum, version byte, and public key hash are combined into one value and then encoded into a scheme called Base58. Base58 makes the Bitcoin address more legible and freer from errors by adding more letters and removing the characters 0 (zero), O (capital o), l (lower L), and I (capital i) as these characters are seen as almost identical and difficult to differentiate. Once that’s done, the legacy Bitcoin address has been generated. 

How Does a Legacy Bitcoin Address Differ From Other Address Types?

When comparing legacy addresses with newer address formats, each has its unique advantages and characteristics, and it is up to the individual user to decide which address is best for them, based on how they'd like to use their assets (and the type of assets they may have). In the case of legacy addresses, while they have higher transaction fees than any of the newer address formats, they have remained a consistently reliable option for Bitcoin users to send and receive crypto.

While newer address types like Native SegWit and Taproot have their advantages, they have not been fully integrated into all Bitcoin wallets as some may only have the capacity to support and send bitcoin to specific address formats. Legacy addresses are universally supported because they have been around since the inception of Bitcoin, so while they may have higher transaction costs, they are also consistently reliable for sending and receiving bitcoin. 

Overall, these are all the main information you need to know about legacy Bitcoin addresses. Since their inception alongside the launch of Bitcoin back in 2009, legacy Bitcoin addresses have remained a popular address format for users thanks to their advantages and real-world applications. 

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