P2WPKH

P2WPKH, or Pay-to-Witness-Public-Key-Hash, is a type of Bitcoin transaction output introduced with Segregated Witness (SegWit). It represents a shift from the traditional P2PKH scheme by placing the witness data outside the base transaction, improving efficiency and allowing future protocol extensions. P2WPKH outputs are commonly used on the Bitcoin network where SegWit is supported.

The scriptPubKey for P2WPKH is a witness program consisting of OP_0 followed by a 20-byte push, written as OP_0 <20-byte-hash>. The 20-byte hash is the key hash derived from the recipient’s public key (RIPEMD160(SHA256(pubkey))). The recipient’s address is encoded as a Bech32 string with version 0 and a 20-byte program; on mainnet the human-readable part is "bc" and on testnet it is "tb".

Spending a P2WPKH output differs from legacy scripts. There is no traditional scriptSig; instead, the input includes a witness consisting of two items: a digital signature and the public key. The signature proves ownership of the corresponding private key, and the public key is used to verify the 20-byte key hash stored in the output.

Advantages of P2WPKH include reduced transaction weight due to the separation of witness data, which can lower fees and increase effective throughput in blocks. It also fixes transaction malleability associated with older formats and enables more flexible protocol development.

For compatibility, native Bech32 P2WPKH is supported by SegWit-aware wallets and nodes. To maintain compatibility with older software, P2WPKH can be nested inside P2SH, forming P2SH-P2WPKH, which allows SegWit spending in environments that do not yet support native Bech32 addresses.