P2PKH

Pay To Pubkey Hash

This script pattern is used to “send” someone bitcoins. It’s the most common script used for locking an output to someone’s public key.

It is similar to P2PK, but the lock contains the hash of a public key instead (and not the public key itself).

How does P2PKH work?

The P2PKH script pattern contains a hashed public key surrounded by these opcodes:

scriptPubKey	76a91412ab8dc588ca9d5787dde7eb29569da63c3a238c88ac	OP_DUP OP_HASH160 12ab8dc588ca9d5787dde7eb29569da63c3a238c OP_EQUALVERIFY OP_CHECKSIG	P2PKH
hex | opcodes	inline | stack

To solve this script, the owner of the hashed public key above needs to provide the original public key, along with a valid signature for it:

scriptSig	48304502203f004eeed0cef2715643e2f25a27a28f3c578e94c7f0f6a4df104e7d163f7f8f022100b8b248c1cfd8f77a0365107a9511d759b7544d979dd152a955c867afac0ef7860141044d05240cfbd8a2786eda9dadd520c1609b8593ff8641018d57703d02ba687cf2f187f0cee2221c3afb1b5ff7888caced2423916b61444666ca1216f26181398c	304502203f004eeed0cef2715643e2f25a27a28f3c578e94c7f0f6a4df104e7d163f7f8f022100b8b248c1cfd8f77a0365107a9511d759b7544d979dd152a955c867afac0ef78601 044d05240cfbd8a2786eda9dadd520c1609b8593ff8641018d57703d02ba687cf2f187f0cee2221c3afb1b5ff7888caced2423916b61444666ca1216f26181398c
hex | opcodes	inline | stack

In short, when this script runs:

• The original public key is DUPlicated and then HASH160’ed.
• This hashed value is compared with the hashed public key in the scriptPubKey to make sure it is EQUALVERIFY.
• If it matches, the script continues and the CHECKSIG checks the signature against the public key (just like a P2PK script).

Where can you find P2PKH scripts?

P2PKH is the default script used by wallets when you want to “send” someone bitcoins, so you can find it in most blocks in the blockchain.

Here are some interesting transactions that use P2PKH:

• 6f7cf9580f1c2dfb3c4d5d043cdbb128c640e3f20161245aa7372e9666168516 - First P2PKH Transaction (16th January 2009)
• a1075db55d416d3ca199f55b6084e2115b9345e16c5cf302fc80e9d5fbf5d48d - Pizza Transaction (10,000 BTC)

Why do we have P2PKH as well as P2PK?

If P2PK does a good job of locking up bitcoins to a public key, why do we have the more complex P2PKH script?

Only Satoshi knows why we started using P2PKH, but the reason probably goes something like this…

Satoshi wanted a easier way for people to be able to share their public keys with each other. Satoshi knew that you could make public keys:

• Safer by adding a checksum (to detect errors)
• Shorter by converting the public key to base58

However, the result was still pretty big:

Therefore, a solution for getting an even shorter result is to hash the public key first:

So there we have a much shorter version of our public key (we call it an address) that we can easily share with other people. Any wallet software can then take this address and decode it from base58 to get the public key hash, which can then be set inside a locking script.

Now, the only thing we have to do to make this work is to change the locking mechanism so that we lock an output to the hash of a public key. Then, we provide the original public key we come to unlock it, and the hash of that will be checked before carrying on with the signature check as normal:

It’s a bit more complex from a programming perspective, but it does allow for the use of shorter and more convenient addresses for sending and receiving bitcoins.

I think Satoshi ultimately had usability in mind for Bitcoin, and that’s why we have P2PKH.

Would we still use P2PKH if Satoshi knew about compressed public keys?

References

• https://bitcoin.stackexchange.com/questions/3600/why-are-bitcoin-addresses-hashes-of-public-keys