Bitcoin Q&A: What is Segregated Witness?
Channel: aantonop
Date: 2018-04-28

What is Segregated Witness (SegWit)? How do you know you’re using SegWit? SegWit fixes transaction malleability and enables further upgrades towards Bitcoin smart contracts. Can transaction malleability lead to denial-of-service (DoS) attacks? Does SegWit put witness data in a different block? Did SegWit change transaction validation? versus? Are there any security risks of invalid blocks?

CORRECTION: At ~2:07, I stated the incorrect BIP number for the Bech32 address format, which should be BIP173. BIP176 is about "bits" denomination. https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki

More on SegWit: https://bitcoincore.org/en/2016/01/26/segwit-benefits/

Chapters
0:00 What is Segregated Witness (SegWit)?
3:06 How would you know that you are using Segregated Witness?
5:20 What type of malleability and scalability issues can Bitcoin present without using Segregated Witness?
7:17 Why is nobody exploiting the malleability bug in Bitcoin or Bitcoin Cash, if you can interject a change with the signatures, pay a higher fee, and broadcast it again?
8:22 If we are making two different blocks, a transaction and witness block, are they still the same size?
9:28 How is the witness part included in add-on blocks and verified in the coinbase transaction?
10:53 SegWit security. Are there any concerns about the potential increase in the number of invalid blocks propagated, if not enough people are storing the unhashed signature data on their nodes?
11:59 If I don't store signature data on my node, could I not verify previous transactions? If that is the case, should large transactions remain off SegWit or the Lightning Network, insofar as you not personally storing signature data?

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.

If you want early-access to talks and a chance to participate in the monthly live Q&As with Andreas, become a patron: https://www.patreon.com/aantonop

RELATED:
The Lightning Network - https://www.youtube.com/playlist?list=PLPQwGV1aLnTurL4wU_y3jOhBi9rrpsYyi
SegWit adoption - https://youtu.be/KCsTVTRk6I4
Advanced Bitcoin Scripting Part 1: Transactions and Multi-sig - https://youtu.be/8FeAXjkmDcQ
Advanced Bitcoin Scripting Part 2: SegWit, Consensus, and Trustware - https://youtu.be/pQbeBduVQ4I
How do I choose a wallet? - https://youtu.be/tN6b62sEpsY
Hot vs. cold wallets - https://youtu.be/Aji_E9sw0AE
SegWit adoption - https://youtu.be/KCsTVTRk6I4
Secure, tiered storage system - https://youtu.be/uYIVuZgN95M
Decentralised exchanges and counterparty risk - https://youtu.be/hi_jaw0dT9M
Decentralised exchanges with fiat - https://youtu.be/3Url8tbQEkA
How do I secure my bitcoin? - https://youtu.be/vt-zXEsJ61U
How do mnemonic seeds work? - https://youtu.be/wWCIQFNf_8g
HODLing and the "get free" scheme - https://youtu.be/MhOwmsW1YNI
How to get people to care about security - https://youtu.be/Ji1lS9NMz1E
Bitcoin as everyday currency - https://youtu.be/xYvvSV4mjH0
Irreversibility and consumer protection - https://youtu.be/R107YWu5XzU
Hyperbitcoinization - https://youtu.be/AB5MU5fXKfo
Job opportunities with cryptocurrencies - https://youtu.be/89_p4pDlQtI
How long until mainstream adoption? - https://youtu.be/y3cKBDBabtA
What is the biggest adoption hurdle? - https://youtu.be/jHgyHF3F2TI

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

Follow on Twitter: @aantonop https://twitter.com/aantonop
Website: https://antonopoulos.com/

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.

THE INTERNET OF MONEY, v1: https://www.amazon.co.uk/Internet-Money-collection-Andreas-Antonopoulos/dp/1537000454/ref=asap_bc?ie=UTF8

[NEW] THE INTERNET OF MONEY, v2: https://www.amazon.com/Internet-Money-Andreas-M-Antonopoulos/dp/194791006X/ref=asap_bc?ie=UTF8

MASTERING BITCOIN: https://www.amazon.co.uk/Mastering-Bitcoin-Unlocking-Digital-Cryptocurrencies/dp/1449374042

[NEW] MASTERING BITCOIN, 2nd Edition: https://www.amazon.com/Mastering-Bitcoin-Programming-Open-Blockchain/dp/1491954388

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