What is Segwit? Segregated Witness Explained Simply - YouTube

What is Segwit?

Will it truly allow for Bitcoin to scale for mass adoption?

And how does it even work?

Well stick around,

in this episode of Crypto whiteboard Tuesday

we’ll answer these questions and more.

Hi, I’m Nate Martin from 99Bitcoins.com

and welcome to Crypto Whiteboard Tuesday

where we take complex cryptocurrency topics,

break them down

and translate them into plain English.

Before we begin, don’t forget to subscribe to the channel

and click the bell so you’ll immediately get notified

when a new video comes out.

Today’s topic is Segregated Witness, or Segwit for short.

Segwit is an upgrade to the Bitcoin network

that was activated in August of 2017.

It was first introduced by Developer Pieter Wiulle

at the Scaling Bitcoin conference in December 2015.

Segwit aims to solve several issues:

one of which is Bitcoin’s scalability.

Bitcoin transactions are written on a Blockchain,

an immutable ledger

on which transactions are bundled together into blocks

that are chained one to the other, in order to determine their order.

A new block is created roughly every 10 minutes.

Additionally,

Bitcoin’s protocol limits the capacity of a block to 1mb,

which limits a Bitcoin block to around 2700 transactions on average.

This creates a problem

when a lot of people are trying to send Bitcoins simultaneously

as the queue of transactions waiting to enter the blockchain

gets longer and longer..

While Visa can process 1,700 transactions per second,

Bitcoin can process only 4,

not nearly a scale that could handle mass adoption.

In order for Bitcoin to truly become usable on a worldwide scale,

it needs to find a way to increase its transaction capacity.

Another issue Segwit addresses is transaction malleability.

Every Bitcoin transaction has 3 parts -

who sent it (also known as input), who receives it (output),

and a digital signature

that verifies that the sender is eligible to send the coins.

It turns out that Bitcoin’s code allows digital signatures to be altered

while a transaction is still waiting to get confirmed.

The signature alteration can be done in such a way that

if you run a mathematical check on it, it is still valid according to the network.

But if you run a hashing algorithm on it,

it gives a different result.

Let me explain with an example:

For the sake of simplicity

let’s say that the signature value was “3”,

but instead of “3” I change it to “03” or “3+7-7”.

While mathematically, the values are all the same,

so it’s still a valid signature,

if I hash these different versions I will get different results,

since hashing depends on how you write the value

and not just the value itself.

Since the hash is the transaction’s id in the blockchain,

this means I can effectively change any unconfirmed transaction’s id

to a different id and it will still be valid.

Creating a new transaction id for an existing transaction

can be problematic for a number of reasons:

First, if you want to build second layer solutions

on top of the Bitcoin network, like the Lightning Network,

you need to make sure no one can alter the first layer

since the one relies on the other.

If you want to learn more about the Lightning Network

make sure to catch our episode about it as well.

Second, altering transaction ids can cause issues

if you’re spending or accepting unconfirmed funds.

Let’s go through another example:

Alice pays Bob in transaction X which is currently unconfirmed.

Bob uses these unconfirmed funds

to pay for a product online from Charlie (transaction Y).

Meanwhile, Charlie sends Bob his product

before waiting for confirmation on transaction Y.

After receiving his product,

Bob does some technical tinkering, and maliciously changes,

or malleates, Alice’s payment

so that her transaction, X gets confirmed

but with a different transaction id.

Transaction Y, which is what Bob sent to Charlie,

is now invalid

since it relies on transaction X’s original transaction id

that now no longer exists.

So Charlie won’t get paid

even though he’s already delivered the goods to Bob.

Bad Bob...

While scalability and malleability

are the two most burning issues that Segwit addresses,

there are a variety of other technical issues

that Segwit tackles

that don’t necessarily affect the end user directly.

Now that you know what Segwit is,

let’s talk a bit about how it actually works.

Segregated Witness is a proposed change

to how blocks are structured.

Non segwit blocks, also known as legacy blocks,

have a total of 1mb space for all of the block data:

inputs, outputs, signatures and additional scripts.

Segwit blocks, on the other hand,

are in fact large 4mb blocks that consist of a base transaction block

and an extended block.

So contrary to popular opinion, Segwit is indeed a block size increase.

Segwit blocks move the digital signature

and other data known as “the witness” outside of the base transaction block.

The witness data will still be transmitted,

but it is placed inside the extended block.

So the base transaction block includes the information about the sender

and the receiver

and the witness data is left blank and doesn’t take up any more space.

This allows for more transactions to fit inside

the 1mb base transaction block.

The extended block (the additional 3mb)

include all of the witness data that isn’t mandatory

in the base transaction block.

The new block format Segwit introduces

achieves two major goals:

First, it moves the digital signature outside of the base transaction block.

This way,

if someone changes the signature on the transaction,

it won’t affect the transaction id.

This in effect solves the transaction malleability issue....

you know...Bob.

Second, it shrinks down the base transaction data.

Since the witness data takes up to 65% of the transaction size,

moving it outside of the base transaction block

allows more transactions to fit inside that 1mb block.

I know what you’re probably thinking.

If Segwit is in fact a block size increase,

why not just increase the block size to 4mb in the first place?

Why all of this hassle and block size debate

if the end result is in fact bigger blocks.

The answer is really quite simple -

developers wanted to avoid a contentious hard fork

in the Bitcoin network.

You see, Bitcoin’s protocol specifically states that

blocks can’t exceed 1mb.

So, developers had to find a solution

that will allow the network to accept both Segwit and Non Segwit blocks

if a hard fork were to be avoided.

The solution of a 1mb block with an “extension” of another 3mb

is something that is still acceptable under the existing protocol.

Legacy nodes receive only the 1mb base transaction block

without the extended block.

They still consider them valid.

Segwit nodes receive both the base and extended block

(up to 4mb in total)

and can validate the transactions in full.

This backwards compatibility is also known as a soft fork.

This approach is a lot less risky

since it doesn’t require nodes to update their software to support Segwit.

It means that even if it takes years for all of the nodes to upgrade,

the network will still function.

Now let’s move on to how Segwit blocks are measured by miners.

While legacy blocks are measured in size,

Segwit blocks are measured in weight.

Block Weight is a new concept introduced in Segwit,

and it’s calculated on a per-transaction basis.

Each transaction has a “weight” which is defined this way:

The size of your Base Tx

(meaning that which doesn’t include the witness data) *3

+ the Full Tx size, that = your transaction weight.

Legacy transactions

don’t have the ability to strip away the witness data from the base transaction,

so their weight will always be 4 times the tx size.

For example, a legacy TX of 1000 bytes

will have a weight of 1000*3 + 1000 = 4000.

Segwit transactions, on the other hand,

are going to have a weight of less than 4 times the tx size.

For example,

a 1200 byte Segwit transaction comprised of 400 bytes of witness data

will have a weight of

(1200 (the total transaction size)-400 (the size of the witness data))

leaving the base transaction size of 800, times 3,

making 2400,

add the total transaction size of 1200, and that = 3600.

In short,

the larger the size of the witness data, the lighter the tx weight will be.

This incentivizes miners to prefer ‘lighter’ Segwit transactions

over ‘heavier’ ones,

since they can fit more of them inside a base transaction block,

which increases the potential miner’s fee,

should that block be accepted and confirmed.

While in theory Segwit transactions can create a block up to 4mb in size,

in practice the average block size that includes Segwit transactions

is around 2mb.

Today, almost 50% of all Bitcoin transactions

are Segwit transactions.

Since legacy transactions are larger in size,

they require higher network fees to get confirmed faster.

And finally,

Segwit addresses start with a “3” while legacy addresses start with a “1”.

Thanks to its advantages,

more and more popular wallets and exchanges support Segwit.

Ledger, TREZOR, Electrum, Exodus and Coinomi

are just some of the major wallet brands

that have already adopted Segwit.

It’s important to note that if you have a legacy wallet

and you want to move to a Segwit wallet

you will need to create a brand new Segwit wallet

and move all of your funds to its address.

There’s no way to just upgrade your existing legacy wallet

to work with Segwit.

Segwit is the first of many upgrades

that will gradually allow for Bitcoin to scale for mass adoption.

It’s a fundamental change that will allow further developments

down the road

like the Lightning Network, Schnorr Signatures and more.

As more and more wallets adopt Segwit,

it will soon become the standard for any Bitcoin transaction.

Well, that’s it for today’s episode of Crypto Whiteboard Tuesday.

Hopefully by now you understand what Segwit is -

An upgrade to the Bitcoin protocol

that Segregates the witness data from the base transaction data,

hence achieving a smaller transaction size,

securing transactions from malleability issues and more.

You may still have some questions.

If so, just leave them in the comment section below.

And if you’re watching this video on YouTube,

and enjoy what you’ve seen,

don’t forget to hit the like button.

Then make sure to subscribe to the channel

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as soon as we post new episodes.

Thanks for watching me here at the Whiteboard.

For 99bitcoins.com, I’m Nate Martin,

and I’ll see you…in a bit.