P2PK: Pay-to-Public-Key (The Original Script)

Before Bitcoin had addresses, it had P2PK (Pay-to-Public-Key). This was the first script type used by Satoshi Nakamoto to send the very first bitcoins. While rarely used today, understanding P2PK is essential for understanding how Bitcoin's scripting language evolved.

1. Locking to the Key, Not the Hash

In modern Bitcoin, we send money to a hash of a public key (an address). In P2PK, the coins are locked directly to the raw public key bytes.

• Legacy Method: "Here are 50 BTC. Only the person who owns this specific 65-byte public key can spend them."

• Modern Method: "Here are 50 BTC. Only the person who can provide a public key that hashes to this 20-byte string can spend them."

2. No Human-Readable Addresses

P2PK does not have a standard "address" format like 1BvBM... or bc1q....

• If you wanted to receive a P2PK payment in 2009, you had to send your full 65-byte (uncompressed) public key to the sender.

• The sender's wallet would then construct a script specifically for that key.

3. Why it was Phased Out

P2PK was quickly replaced by P2PKH (Pay-to-Public-Key-Hash) for two main reasons:

1. Size: A public key is 33 or 65 bytes. A hash is only 20 bytes. P2PKH saves significant block space.

2. Quantum Security: In P2PK, your public key is visible on the blockchain the moment you receive money. In P2PKH, your public key is hidden behind a double-hash until the moment you spend the coins.

4. The Genesis of the Chain

The first 50 BTC ever created (the Genesis Block reward) and thousands of early mining rewards are locked in P2PK scripts. Because these coins have never been moved, their public keys remain exposed on the ledger today.

Feature	P2PK (Legacy)	P2PKH (Standard)
Locked To	Raw Public Key	Public Key Hash
Address Format	None	Base58 (Starts with 1)
Space Usage	High (65 bytes)	Low (20 bytes)
Primary Use	Early Mining / Coinbase	Daily Transactions

In the next section, we will analyze the ScriptPubKey Structure of P2PK.