Bitcoin Q&A: Public Keys vs. Addresses

What is the difference between public keys and addresses? How are new addresses generated? How are change addresses generated? Why have two outputs? Do you still pay fees if you are sending bitcoin to new addresses in your own wallet? What is the VanityGen command? What does the SIG_HASH flag do?

Chapters
0:00 What is the difference between public keys and addresses?
0:57 If my wallet automatically generates a new address for each transaction, will bitcoin previously sent to me on a different address be transferred to the new address just generated? If someone is going to send me funds to a previously-used address, will I still receive them?
3:54 How can we generate a new address to receive change?
4:17 Why not have a single output with the exact amount of BTC, instead of two outputs, one of which is change?
5:17 Do transactions with multiple inputs and one output pay a fee, even if the wallet is just reorganizing funds?
7:00 Can you explain the VanityGen command? What is a vanity address?
10:55 SIGHASH_ALL is for signing all inputs and outputs. How can all inputs be signed with one signature, when each of the inputs have a different private key?

These questions are from the MOOC 9.3 and 9.5 sessions which took place on March 2nd and March 16th, 2018 respectively. Andreas is a teaching fellow with the University of Nicosia. The first course in their Master of Science in Digital Currency degree, DFIN-511: Introduction to Digital Currencies, is offered for free as an open enrollment MOOC course to anyone interested in learning about the fundamental principles.

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Andreas M. Antonopoulos is a technologist and serial entrepreneur who has become one of the most well-known and respected figures in bitcoin.

He is the author of two books: “Mastering Bitcoin,” published by O’Reilly Media and considered the best technical guide to bitcoin; “The Internet of Money,” a book about why bitcoin matters.

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[BitcoinOnlyCentral]

The fact that andreas has only 147k subscribers let’s you know how truly early we still are.

[yohan]

OMG! I've spent days trying to find information on the topic of addresses and all is here explained clearly. Liked and subscribed!

[livingbeings]

Looking forward to your upcoming Joe Rogan appearance

[Garfi]

The parent public key, chain code, and the index number are combined and hashed with the HMAC-SHA512 algorithm to produce a 512-bit hash. This 512-bit hash is split into two 256-bit halves. The right-half 256 bits of the hash output become the chain code for the child. The left-half 256 bits of the hash are added to the parent private key to produce the child private key.

Why is this last step needed? why not just take left-half 256 bits of the hash as child private key?

[joehernandez]

I have a question about getting your crypto from blockchain

[cryptowelt]

how can i generate a vanitiy adress and be sure that is safe?

[vishnuvarma]

Is there a vanity gen command in the Bitcoin client or is it the website only that provides it? And if so, is it legitimate????

[dereenaperi]

Hi Andreas could you help me get my Bitcoin address.

[ChiIeboy]

I have never listened to anyone so smart, yet _so very adept_ at explaining technical concepts in such an understandable manner.

[leapbtw]

oh boy did this not age well, 10:50
i genned a vanity address with 8 chars in two hours with my 5800X lmao

[wesleyashley]

I think of it like this. The public key is what ties together all the generated addresses where you receive from others who send to those multiple addresses. So the public key is like your home address. You don't want people who send you stuff to know where you live so you give them a PO box address. Thats like a wallet address. It ends up at your house which is like it being connected to your public key.

[EDUCACAOFINACEIRACOMECAREMCASA]

It looks like you've provided a Bitcoin address. Is there something specific you'd like assistance with regarding this address?

[desther]

Andreas is so amazing speaker. I can listen to his talks all day and i always learn something new.

[chetandosco]

I love you andreas but i didnt understand anything. I think i should just give up and buy Doge

[Chris-zues]

if I generate a watch only wallet will it show all my addresses together or will every new address be separate?

[JoeKazemi]

This is very insightful and helpful. Thank you so much.

[michaelsane]

Especially with Vanity address creation, wont we run out of possible addresses? How many possible addresses can there be.. 58 to the power of 58?

[cooldog]

I did not label some of my address and keys for some tokens. How can I tell which is the addresses and which are the keys?

[bitmau]

What happens when I use multiple wallets? How do I consolidate all of my transactions?

[TheMiamiTiger]

Can somebody give this man a microphone and some egg cartons for echo dampening?