P2PKH (Legacy Address)

P2PKH (Pay to Public Key Hash) is Bitcoin's original standard address type, the default wallets used from 2009 until SegWit arrived in 2017. A P2PKH address is the Base58Check encoding of a 20-byte HASH160 of a public key, carrying a 0x00 version byte that makes every mainnet P2PKH address begin with the numeral 1. Because it predates Segregated Witness, it is commonly called a legacy address.

How the lock works

The output's locking script (scriptPubKey) is OP_DUP OP_HASH160 <pubKeyHash> OP_EQUALVERIFY OP_CHECKSIG. To spend, the owner supplies a signature and the full public key in the input's scriptSig. The script duplicates and hashes the supplied key, checks it against the committed hash, then verifies the signature. Committing to a hash rather than the key itself was an early design choice with two virtues: addresses stay a manageable length, and the public key is revealed only at spend time. HASH160 — SHA-256 followed by RIPEMD-160 — and the Base58Check alphabet, which drops easily confused characters like 0, O, I, and l and appends a four-byte checksum, both date from this format and shaped everything that followed.

The fee cost of being first

Legacy outputs are heavier to spend than witness outputs because the unlocking data — signature plus full public key — lives in the scriptSig, which is counted at full weight, rather than in the discounted witness field that SegWit introduced. A typical P2PKH input weighs roughly half again as much as its P2WPKH (Native SegWit) equivalent, so a wallet full of type-1 UTXOs pays a permanent fee premium every time it spends. Legacy addresses also lack the error-detecting strength of the Bech32 checksum and its typo-locating guarantees — Base58Check detects errors but cannot point to them.

Why it still matters

P2PKH is far from dead. Many older wallets, exchanges, paper wallets, and hardware devices still generate and accept type-1 addresses, and an enormous amount of value — including coins untouched since the earliest years — sits in legacy outputs. Every full node validates them today and will indefinitely; nothing about newer formats invalidates old ones. For a self-sovereign operator auditing holdings, the prefix is a practical signal: type-1 UTXOs are the expensive ones to move, so they are the natural candidates for consolidation during a low-fee period, swept into a modern output type in one deliberate transaction rather than dragged along input by input at high-fee moments. As with any consolidation, mind the privacy cost of linking inputs, and never undo good hygiene around address reuse just to tidy a wallet.

Reading the address landscape

Recognizing formats at a glance is a small skill that pays constantly: 1 means P2PKH, 3 means script-hash (often wrapped SegWit), bc1q means native SegWit, and bc1p means Taproot. Each step in that lineage bought lighter spends, better error detection, or stronger privacy. P2PKH is where the lineage starts — the format every later design was measured against, and the one that proved hash-based addressing could carry real value for decades.

There is a quiet lesson in how gracefully P2PKH has aged. Seventeen years of protocol evolution — script versioning, witness restructuring, an entirely new signature scheme — and a coin locked to a key hash in 2010 still spends today with the same private key, no migration required. Bitcoin's upgrade discipline treats old outputs as permanent obligations, which is precisely the property that makes long-horizon savings credible: the format you choose today can be conservative or cutting-edge, but nothing you hold becomes unspendable because the network moved on. For an operator managing keys across decades, that guarantee — not any particular address format — is the foundation. Choose modern formats for new receives, keep legacy keys backed up exactly as carefully as new ones, and let fee conditions dictate when the old coins finally move.