Understanding SegWit2X & Replay Attacks

in bitcoin •  last year

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Segwit2X hard fork will occur in about a month.

This is the hard fork that most of the Bitcoin community is unenthusiastically waiting for.

So if you’ve been wondering what’s the big deal about it, let’s take a look at SegWit2X.

This is an attempt to address the scaling issues currently plaguing Bitcoin by increasing the size or more specifically, the weight of the blocks of the Bitcoin blockchain.
The reason this change can only be implemented as a hard fork is due to the fact that this change requires the legacy nodes to upgrade.
You can think of legacy nodes as the original nodes of the bitcoin blockchain that have never upgraded.
This means they follow the original protocols set in place when Bitcoin was first created.
SegWit2X would require these nodes to accept blocks that they otherwise would have rejected prior to the hard fork.
Because this change would ultimately increase what is being called the weight of a block, this in turn increases the workload for the nodes of the Bitcoin Network. It will also affect the miners.
(I’ll include links down below that go much more in depth on how exactly the nodes and miners will be effected so you can get a better idea of how this hard fork will change things.)

This may sound like a simple and logical move to help the network deal with the increase of transactions, but it’s important to note that like everything else involving Bitcoin things get technical and philosophical.

There is a very important issue with SegWit2X that I think everyone who uses Bitcoin needs to be aware of, and that is the threat of replay attacks.

If a hard fork occurs and neither the new or original blockchain implement protocols and protect against replay attacks, things can go south.
When a blockchain splits, the original blockchain or legacy blockchain and all of its past transactions are the same on the newly split blockchain. This is why we are able to receive an equal amount of the newly created coin if we were holding the original coin at the time of the split.

At the time of the split however, if there is no replay protection protocol implemented by either the legacy blockchain, or the new one, new transactions that occur on either chain could be copied and sent on the other chain. This would cause anyone sending BTC or the new hard forked coin to accidentally send both coins to a lucky recipient.

This also opens the door for malicious actors to receive both coins when the intention was to send only one.

Enter: Replay Protection- a protocol that ensures that new transactions are valid on one blockchain and not the other.

It’s true that either the original blockchain or the newly formed blockchain can implement this replay protection to prevent this type of double spending.
However it would be much easier for the new blockchain to implement this security. This is because the original Bitcoin blockchain network is so widely spread the likelihood that this security protocol would be implemented in time is very slim.

This can be quite confusing to understand so you can find links down below for additional articles and blog posts that go much more into detail on how exactly this hard fork will effect the blocks and how replay attacks happen and how they can be prevented.

Additional Reading/Sources:

Explaining SegWit2X Replay attacks

More on block size vs block weight

Basic Layout of SegWit2X

List of supporters for SegWit2X (includes exchanges and wallets)

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Great job explaining everything Heidi

These forks are sort of out of control. Here was the picture I made of what CoinMarketCap is going to look like in 2018.


Love it!


daamn thats sick! .. do I see a steem fork there? shouls i be worried?


That looks like the original steem , not fork


We should all be worried. I put ShitConnect in the #3 spot and UET (Useless Ethereum Token) in the #8th spot. Yikes!!!!!!


This can already happen -- not via hard forks but by normal people forking the BTC code and establishing their own coins.


The scary thing about that-- even though said jokingly-- is that IT MIGHT JUST HAPPEN!


Yeah I made one like that too, only the first 100 coins are all bitcoin forks. lol


great graphic!


thats really made, kinda takes the shine off our precious bitcoin to! feel bad

Excellent description of the upcoming hard fork. Much appreciated.

Great post. Thanks for the valuable information.

Thanks for the overview of some of the mechanics involved there. I have been learning the mechanics of a few different blockchains recently in preparation for launching my own Steem Witness server - which I have just done.

I would be honored and greatly helped if you would consider voting for me as witness here at Steemit - My witness application post is here.

The more votes I get, the more time I can invest in helping improve Steemit. :)

Great info

Very detailed info about SegWit2X. My quetion is: how are the miners going to be affected, positive or negative?


Considering 85% of the hashpower on the network supports 2x, they obviously think it is in their interests.

thanks @heiditravels very helpful post for someone new like me in Bitcoin and cryptocurrency

Since when are twitter polls indicative of community support in one direction or another. In Bitcoin there are exactly 2 metrics that cannot be faked, and one is a centralized bolt-on. The first is obviously hashpower - which has been signalling overwhelming support for 2x.

Additionally, signatures made by BTC addresses containing funds (stakeholders) also cannot be faked. These poll results appear to be more or less in agreement with the hashpower.

It's absurd that anyone would take claims that 2X lacks community support seriously.

Great stuff as always, Heidi.

I looked at the list of supporters that you linked to and laughed when I saw the "LOL" response for SegWit2x. So great.

Andreas Antonopoulos basically seems to prefer Lightning network and off chain solutions saying that in engineering often times the simple way is the wrong way...

Great breakdown on seg 2x 👍

Thanks so much for the summary. Very helpful.

Hey Heidi and thank you for the post! After reading through it (I admit I didn't read the additional sources), I'm left with one main question: If we presently hold Bitcoin, and the replay protections are NOT implemented in time for the split on the SegWit2X fork, what is the best way for one to protect one's interest?

Is it as simple as NOT making transfers until it is implemented? Take the "wait-n-see" approach?

Thanks again!

Thanks for the video. Heidi, do you think that the new SegWit2x coin could take the "bitcoin" name? I know that Garzik is getting ridiculed for advocating SegWit2x, but could it actually turn out that the new coin ends up being the more legitimate successor to bitcoin? Just interested in your thoughts.


If it becomes the chain with the most cumulative proof of work, it should. The same goes for Bitcoin Cash.

great post

BTC or the new hard forked coin to accidentally send both coins to a lucky recipient.

Good review👌

Thanks for your good information i really love it and thanks to you

Good review

very informative, thank you for sharing this.
You have made it simpler than it sounds. *thumbs up

Let's keep Satoshi's revolution alive with these t-shirts


Thanks for the overview

SegWit: An optimization proposed by Bitcoin Core developer Pieter Wuille at the end of 2015, SegWit increases the volume of transactions that fit into each block without raising the block size parameter. Specifically, it also removes transaction malleability, an issue that once resolved could lead to a number of network improvements.


Yes, SegWit was implemented as a soft fork recently, now this new segwit2x is mostly rejected by the Core dev team.

Good post bro

Isn't this like central bankers sitting at the top deciding what interest rate and money supply should be?

I think if you already hold BTC and have no intention to sell it in the short term, the best strategy is to hold onto your coins and stay calm.

People are not going to support new coins going further. Bitcoin will remain the king !!!

Great post Heidi! Thank you for the information, best wishes to you always :)
- @splendorhub

I like this

hy @heiditravels
I am new to steemit can you help me please


that's very nice post great job @heiditravels hey i request u to check out my traveling blog i post very nice contants there i hope u like it i am so thankfull if u did

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Hi I upvoted this post could you please upvote my post thanks :)


Everybody should just lie low with these upcoming forks. Don't understand how a fork cannot have replay attack protection and that you have to "opt-in" for it. Should be a feature by default.

Keep your BTC safe and don't spend your BTC until the dust has settled.

I also think we are going to be seeing more and more forks appearing.

Me parecio muy interesante

Great post, nice summary. Not sure why after reading some of the comments i feel more scared though

Hello @heiditravels hi how are you now, before i want to introduce myself first, @ bilqis07 and i want to thank you for your help to vote me and also follow me

Very interesting post !

I liked your post and learned a lot about blockchains. and how repetitive attacks can be avoided

great post

Great ! We are waiting !!
Thanks for sharing my friend !!

You say Bitcoin Cash started 4 months ago but it started August 1 which was less than 3 months ago, it is October 24.


Whoops. Thanks for the correction.

Good post

Great job simplifying a complicated issue. Especially for a newbie like me.


this is very nice and helpful topic. Thanks again

Hi heiltravel i read your blog and its nice. Welcome to steemit and I'm Sakib from Bangladesh. I'm also new in steemit. I'm also vote and followed you. So can you please vote and follow me also ?? Best of luck.

whooooaaa nice jobe girl, ur awesome

Bravo mademoiselle
Excellent post

Thank you for the "warning"! :)

Great post and nice information about coming fork...


Great post and nice information about coming fork...


Congratulations @heiditravels!
Your post was mentioned in the hit parade in the following category:

  • Pending payout - Ranked 5 with $ 179,45

Upvoted! Well done, I'm new on here so find your blog posts incredibly informative! Thanks :)

I see people just buying bitcoins at 5600$+ to just get the new fork coins but eventually they will be at loss because after the hard fork the btc price will be going down it may stay up for sometime but eventually it will be that 4400$ mark. So that extra bait of bitcoin gold you get will not cover up . It is good to have something free but dont buy btc inorder just to have some free lunch


Yes I agree that it it isn't wise to purchase Bitcoin just to receive Bitcoin gold. But why do you see BTC getting stuck at $4,400?

Bitcoin hard fork is become a tradition, almost every month there is a new shitcoin out of bitcoin. It looks like scam already. Try to lure all the money to one useless crypto.

Thanks for the information. I am a newbie, so it is hard for me to digest all of this now. I will need to come back to your links later. By the way, I believe I saw you on YouTube. Was that you being interviewed. Just asking. Thank you.

Thanks for the information.

could you please add me to your list i am new here and i loved your article!! it's really awesome...


I'm happy you enjoyed learning from it :) you can follow my profile by clicking on the "follow" button near the top right of my profile :)

Hey great post! Thank you for explaining it in layman terms. I am a noob in crypto world

Very informative and a lot to learn.

Verry nice post..

Bitcoins keeps having more and more siblings, maybe SMTs are Steem's siblings too, Come Next year Quick lets see some Magics!

Excelente post, felicitaciones, tienes mi upvote.


thinks for the info helps mush

With segwit 2x are the mining fees going to be less cause currently with bitcoin I believe that is a downfall of it being used more as a digital currency.

you got my full uv and i resteemed you, thx for adding value!

Nicely explained! To be honest, I fear more about what "big money"(aka the traditional stock market financial terrorists) could do with bitcoin if they decide to attack during that point for vulnerability. Maybe I´m just too paranoid, never mind. Hey, if you want to do some interesting reading while you travel, I write about history humorously, and sometimes even about bitcoin. Stroll thru my blog and check out if its your cup of tea. Bye!

Nice point of view, I like your comments.

Nice point of view, I like your comments.

Great info, thanks for sharing!

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Bitcoin Gold...ugh. SegWit2X...ugh. lol **LEAVE MY BITCOIN alone!

Great video, thanks. Upvoted, and you have a new follower.

Bitcoin Gold...ugh. SegWit2X...ugh. lol **LEAVE MY BITCOIN alone!

Great, informative video, thanks. Upvoted, and you have a new follower.

Bitcoin Gold...ugh. SegWit2X...ugh. lol **LEAVE MY BITCOIN alone!

Great, informative video, thanks. Upvoted, and you have a new follower.

Bitcoin Gold...ugh. SegWit2X...ugh. lol **LEAVE MY BITCOIN alone!

Great, informative video, thanks. Upvoted, and you have a new follower.

great article , thanks for sharing

Fine post. I like the way you condense a wealth of information into a brief post. Always appreciated.

And it looked like a nice sunset. Don't let the sun go down, and Full Steem Ahead.

Fine post. I like the way you condense a wealth of information into a brief post. Always appreciated.

And it looked like a nice sunset. Don't let the sun go down, and Full Steem Ahead.

Very clear explanation. Thanks :-)

Bitcoin Gold was not such a success. I wonder how SegWit2x will be?