Bitcoin Attacks that are Probably not a problem - Discussion

Welcome to this discussion thread. Feel free to ask questions or discuss things related to this section.


I am wondering that since the SHA256 hash function is often doubled hashed in Bitcoin (e.g. address creation, Merkle Tree of transactions) does this not mean that in the event that SHA256 is broken then there is adequate time to upgrade to a new more secure hash function?

Nothing to add other than this course is very useful!


Hi, an hash function is not same as encryption one.
Search the web to learn more about this difference, example at

A broken hash function would only mean it’s hash result could give a same output but for 2 different inputs, double hashing would mean the same for the broken prove, because in the event that there is a not equal to b and if A=hash( a ) and B = hash ( b ) and if A=B then hash(hash(a)) = hash(hash(b))

So I would left here your question in other words would perhaps be: Why Bitcoin uses double hashes sometimes in its operation?

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I notes a lot of people say it the only way to keep your funds save from government and etc. But when FBI tracks criminal they still find a way to find out information to theirs wallets and confiscate theirs BTC. So it still big change if government want they can take it from you.

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So if Ray is right will monero be the only decentralized coin?

How can you connect to a satellite?!

1st, you need to get tracked. Don’t let them find you. Use TOR networks, which provide multiple bifurcation of your online address.

2nd, encrypt your data. They may find you and hold your data, but without your password, your BTC will be immovable.

3rd, don’t put all your eggs in 1 basket. Use multiple wallets/addresses and diversify your hodlings.

4th, don’t engage in criminal activities!


Thank you cme for your information and the link. I will definitely check it and try to read more about it. Interesting.

And I also would like to know why Bitcoin sometimes uses double hashes in its operations?

my 1st search was lost so
after new search on google I found

and also

and also from CW (pseudo-Satoshi) one pseudo-answer:

I can see why this is going to be a dispute reason between public-open-source against try to have sw-patent.

TLDR: “So why does he hash twice? I suspect it’s in order to prevent length-extension attacks.”


Thank you so much for the reply and the links. I really appreciate it.

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what of the prospect of Quantum computing overcome some of these: coulds but probably nots?

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I have a few curiosities/questions regarding the Segmentation Attack.
In the case a part of the Bitcoin network gets segmented, the nodes continue communicating within that segmented network creating their own separate blockchain with lower difficulty, and some point later regain connection with the rest of the network, why is it so sure that the network outside of this segmented network will have the valid blockchain and reverse all transactions happened in the segmented network? Wouldn’t both chains be equally long (as blocks get produced every 10 minutes in both networks)? And wouldn’t the nodes of the segmented network adjust to the difficulty of the larger network (with higher difficulty) as soon as they regain contact with it? Could it happen then that by chance one of the nodes of the segmented network mines the next block right after they regain contact and thus all transactions of the larger network get reversed (as the longer blockchain will be the one that had been mined in the segmented network)?
If anybody could clarify if that is correct or if I don’t completely understand something that would be great!

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At the end of the day I think it unwise to use any cryptocurrency for any sort of improper uses. Not only is it on a public network but it also seem rather pointless at this time to spend crypto currency except in the rare event that you live in one of the few small countries or places that are now using a digital fiat currency. I feel this way of course because it is simply not worth it to to pay for things in an asset that could literally be worth so much more the very next day. In regards to the privacy based coins that are currently out there I struggle to see how these coins will survive through the process of global regulations regarding digital assets. the idea of a peer to peer financial system is interesting but the geopolitics around around regulating such a financial system are here to stay I believe.

In regards to the attacks I am very curious about what I have heard called a 51% attack. In what situations would a group of validators choose to do such a thing and why?

Any others have any thoughts or opinions.

@Alko89 @thecil

the malicious client video presents, for lack of a better term, “culture” or “community values” as a solution to malicious dev code: “closed source software will just never be accepted in crypto. i mean and it’s all about open source… i can not imagine in my wildest dreams…” - ivan ~3:45-4:00

this is understandable to me and probably most people here, but aside from certain changes in culture becoming more likely as crypto gains more mainstream adoption, this highlights to me one of the most important but least discussed aspects of the entire space: social constructionism.

social construction is the reason you know what i mean when i use the word “crypto” (simply a prefix by itself but imbued with an entire value system of our community/ies when interpreted by each other), it’s the reason bitcoin is now worth “dollars” (itself a social construction of currency used as a store of value to become money), and it’s the reason the 2016 DAO attack was mitigated ("[we the community don’t like this version of the blockchain; time for a fork]").

the DAO attack was resolved by a what essentially came down to a political division among those who wanted to protect a certain culture/ideals from dissidents. Now because humans not only write but also interpret code AND interpret whatever the code presents them, they are in the position to extract any value they want from it (which will be more valuable the more people agree on it as valuable); i think this problem of knowledge context (i.e. perspective/worldview, itself dependent on backgrounds, naitonal/educational/etc) is likely to resurface more and more often as more socially engineered attacks become common.

to me, this is an extremely fascinating issue at the core of blockchain vulnerabilities (think also of oracle integrity, social/network oracles, i.e. where we get the “ground truth” that yet still depends on human input) and where the hard and soft sciences meet; advances here might resolve long-standing questions in epistemology, and i want to be there for that!

anyone else??

In regards to a 51% attack, Ivan mentions that a malicious group could mine blocks faster simply by not announcing their blockchain. And by not announcing their blockchain their difficulty does not increase.

How does one, or a group of nodes mine without announcing? Is every node in the malicious part, producing the exact same blocks with the same transactions without propagating them, leading to 51% of the nodes having identical but isolated blockchains?

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The consensus algorithm is more complicated than simply ‘the longest chain’ wins. In reality is it the chain with the most Proof-of-work. So because the segmented nodes will be operating at a lower difficulty level, their blocks will have less work put in than the non-segmented nodes.
Hence when they rejoin the network, it would not be possible for their chain to be ‘heavier’ i.e. have more PoW than the other.

Hope that makes sense and answers your question!


I thought i would have questions by now but, i had no issue understanding the lecture and find this very useful. See y’all again!

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Yes that makes sense, thank you for taking the time to answer!

In regards of the segmentation part. I have 2 questions.

When the smaller region connects to the main blockchain again, is the bitcoin they mined lost, unless maybe they exchange it before that?

Second, would it be possible to create your own network with a few nodes, so you can then get the mining reward every single 10 minutes?