# 302.4 Lesson - publicKey

**Screen:** publicKey

**Headline:** Bitcoin Addresses and the Master Public Key

**Reward:** 3

**Text:** A master public key in Bitcoin is a key that is cryptographically derived from a Bitcoin private key and is used to generate Bitcoin addresses that payers can send Bitcoin to.

It can be used to generate an unlimited number of Bitcoin addresses from a single master public key.

While the private key is used to authorize Bitcoin transactions and therefore needs to be kept private, the Bitcoin addresses derived from the public key can be shared with a payer to receive payments from them.

Master public keys consist of a long sequence of numbers and letters and begin with xpub, ypub or zpub.

A Bitcoin address for receiving payments starts with either 1, 3 or bc1.

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## QUIZ

**Question:** What is the purpose of a master public key in Bitcoin?

**Answer:** To generate an unlimited number of Bitcoin addresses from a single key

**Feedback:** Correct! It's worth noting that, while funds can only be moved with the private key, it might be a good idea to not share the master public key on a public forum to preserve financial privacy. Only share Bitcoin addresses with payers to receive payments

**Correct:** true

**Answer:** To authorize Bitcoin transactions

**Feedback:** No, the master public key is not used to authorize Bitcoin transactions. That's the job of the private key. Try again

**Correct:** false

**Answer:** To verify that the supply of all bitcoin in existence does not exceed 21 million

**Feedback:** No. While every user can independently verify the monetary supply of in the bitcoin network with a bitcoin node, this is not what the master public key is used for. Try again.

**Correct:** false

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