Can the blockchain be outpaced by a chain of low-difficulty blocks?


Let's say someone creates a blockchain fork starting from the genesis block, when the difficulty was absurdly low compared to today; then he starts mining new blocks from there up to the current block index.

Normally, this would require such an amount of time to make it completely impossibile to catch up with the real blockchain; even if he used today's powerful mining hardware, the difficulty increase would compensate for it quickly. But, here's the catch: he customizes his mining software to not ever increase the difficulty, even if it's mining hundreds of blocks per second; block timestamps are simply faked in order to make it seem they were generated at ~10 minutes interval.

When the fake blockchain is longer then the real one (currently ~300000 blocks), he starts broadcasting it; it appears to conform to all rules, and it's longer than the current one, thus all clients and miners treat this as a winning fork and switch to working on it. Of course, difficulty...

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It is technically possible that all copies of the blockchain are lost...but extremely unlikely. Also, I see no reason why such a massive data loss would be restricted to a single historical block, rather than the whole blockchain.

For a cool visualization of the number of full nodes on the network, look here:

Keep in mind that there are probably a lot more copies of the entire blockchain than there are full nodes. For example, I run 1 full node from my house, but also have 3 full copies of the blockchain backed up (so I don't have to download again). It would take a cataclysmic event to destroy all the world's backups.

Also, having worked IT for a bank, I can assure you that your bank account doesn't have nearly this many redundant...

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Short answer:

Technically possible? Yes. Likely? No.

It would be possible to modify the protocol to include other types of transactions -- such things have been proposed for a wide variety of issues, including being able to lockdown stolen coins, timestamp messages, etc.

It is highly unlikely they will ever make it in, at least not anytime soon, because changing the blockchain is a Big Deal and we are already dealing with "block chain bloat" and many of them have other possible solutions that don't involve modifying the block chain.

Your particular suggestion (in the other thread) seems incredibly unlikely to ever make it as part of the protocol since there is just no need for it to be. Trading exchanges can easily implement futures, options, and all sorts of derivatives if they want - no changes to blockchain...

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The steps to run the network are as follows:

1) New transactions are broadcast to all nodes.

2) Each node collects new transactions into a block.

3) Each node works on finding a difficult proof-of-work for its block.

4) When a node finds a proof-of-work, it broadcasts the block to all nodes.

5) Nodes accept the block only if all transactions in it are valid and not already spent.

6) Nodes express their acceptance of the block by working on creating the next block in the chain, using the hash of the accepted block as the previous hash.

Nodes always consider the longest chain to be the correct one and will keep working on extending it. If two nodes broadcast different versions of the next block simultaneously, some nodes may receive one or the other first. In that case, they work on the first one they received, but save the other branch in case it becomes longer. The tie will be broken when the next proofof- work is found and...

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Let's say an attacker connects to the Bitcoin network. Let's say this attacker possesses an old ASIC HW and she used it to generate a blockchain of half a million blocks, with faked timestamps and really low difficulty, but otherwise valid. So, this chain is longer than the Bitcoin blockchain, but is shorter difficulty-wise.

How does the attacker presents this version of blockchain to the network and how much work will the network nodes spend on finding out that that blockchain is difficulty-wise shorter. Do they need to (and will they) download the whole chain from the attacker? Or is there any information on the top of the blockchain that can be used as hint on how much total work was spent in the entire...

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This article is a gentle introduction to blockchain technology and assumes minimal technical knowledge. It attempts to describe what it is rather than why should I care, which is something for a future post.

Shorter companion pieces to this are:


People use the term ‘blockchain technology’ to mean different things, and it can be confusing. Sometimes they are talking about The Bitcoin Blockchain, sometimes it’s The Ethereum Blockchain, sometimes it’s other virtual currencies or digital tokens, sometimes it’s smart contracts. Most of the time though, they are talking about distributed ledgers, i.e. a list of transactions that is replicated across a number of computers, rather than being stored on a central server.

The common themes seem to be a data store which:

usually contains financial transactions is replicated across a number of systems in almost real-time usually exists over a peer-to-peer network uses cryptography...
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Blocks are found in the Bitcoin block chain. Blocks connect all transactions together. Transactions are combined into single blocks and are verified every ten minutes through mining. Each subsequent block strengthens the verification of the previous blocks, making it impossible to double spend bitcoin transactions (see double spend below).


Bitcoin Improvement Proposal or BIP, is a technical design document providing information to the bitcoin community, or describing a new feature for bitcoin or its processes or environment which affect the Bitcoin protocol. New features, suggestions, and design changes to the protocol should be submitted as a BIP. The BIP author is responsible for building consensus within the community and documenting dissenting opinions.

Block Chain

The Bitcoin block chain is a public record of all Bitcoin transactions. You might also hear the term used as a “public ledger.” The block chain shows every single record...

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Public vs. Private Ledgers
What is the future of Distributed Ledgers?

While many crypto-technologies, such as Bitcoin, are permissionless, much of the legacy infrastructure is permissioned. Ongoing discussion regarding integration of distributed ledgers into legacy systems has brought attention to a growing divide:

Permissionless Ledgers (Public Blockchains) vs. Permissioned Ledgers (Private Blockchains)

Permissionless Ledgers

Also called unpermissioned ledgers, allow anyone to contribute data to the ledger with all participants possessing an identical copy of the ledger. Since there is no single owner of the ledger, this methodology is more suitable for censorship resistant applications (e.g. Bitcoin).

Permissioned Ledgers

Sometimes called private blockchains, allow for distributed identical copies of a ledger, but only to a limited amount of trusted participants only. As the...
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This article is intended to be an introduction to the blockchain technology that was introduced with the Bitcoin currency. Some details I believe are not important will be deliberately omitted to ease the understanding of this article. I will try to keep a technological approach rather than a financial/ethical one. You will not find any discussion about how to buy/ manage Bitcoins or my personal opinion on whether you should invest in that currency.

Is a database

A blockchain is a way to store data. It can be compared to a new type of database. It is composed of blocks that are chained together thus forming a block-chain. Each block is linked to the previous block of the chain. A block contains data or even programs in some recent implementations.

The blockchain was the technological innovation behind the first decentralized digital currency, the Bitcoin. Nevertheless other types of blockchains have been created since which are not targeted to be...

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Blocks in the main chain (black) are the longest series of blocks that go from the genesis block (green) to the current block. Purple blocks are blocks that are not in the longest chain and therefore not used.

A block chain is a transaction database shared by all nodes participating in a system based on the Bitcoin protocol. A full copy of a currency's block chain contains every transaction ever executed in the currency. With this information, one can find out how much value belonged to each address at any point in history.

Every block contains a hash of the previous block. This has the effect of creating a chain of blocks from the genesis block to the current block. Each block is guaranteed to come after the previous block chronologically because the previous block's hash would otherwise not be known. Each block is also computationally impractical to modify once it has been in the chain for a while because every block after it would also have to be regenerated. These...

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There’s been a bit of a buzz recently about using blockchains, one of the approaches used within the Bitcoin protocol, to support things other than the bitcoin currency.

Honduras is reportedly piloting a land register using blockchain technologies. On a smaller scale, the Isle of Man is piloting a registry of digital currency companies, again using blockchain. There are articles and videos that claim that blockchain can be used in the internet of things, for health records, and to track votes.

I want to dig a bit deeper and try to work out the practical application of blockchain for sharing registries, with a particular eye on open data. But before I can start looking at how those kinds of applications might work, I needed to understand how the Bitcoin blockchain works, at a technical level.

Note that this is written based only on a couple of days of research. I might well have missed things and certainly haven’t gotten into the arguments and subtleties within...

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I’ve had a look around and can’t find an answer to this.

Is it possible to attack the current Bitcoin blockchain with a competing blockchain that is longer than it?

For example to attack the current blockchain within the timespan of roughly a quarter of its current lifetime you would:

1. Work out the length of the current blockchain to be attacked.
2. Work out the maximum hashing power of the hardware you wish to use to generate the new blockchain.
3. Recursively divide the hashing power of the hardware by four for each difficulty adjustment the current blockchain has undergone. E.g. if you have a hashrate of 640 KHs and the blockchain has undergone 3 difficulty adjustments you would calculate 640KHs/4^3 = 10KHs.
4. Start generating the new blockchain from the genesis block, starting with the lowest calculated hashrate. For this example 10KHs.
5. Each time the blockchain’s mining difficulty is re-calculated the hardware then...

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First let’s discuss file sharing:
We cannot have a bloated blockchain for file sharing. Filesharing blocks have to expire or be reusable in some way. The filesharing blocks should simply be references that improve finding chunks of data. There was once a filesharing system OFFSystem, a brightnet. People send random strings that contain zero information until combined with other random strings to produce the data. There is no way to say who has any data until it is combined. No one knows what you have and no one can sue.

Seems like a good starting point.

To Tuck regarding exchanges:
I’d like to jump on this with a concept: FLUXchannel
We all know how difficulty works. Get a certain minimum of 0s and you get your reward. But this means 0s from the beginning of the binary representation. 000000blah works. blah000000blah does not. Pools reject hashes which have the same probability but happen to be shifted by a few bits. We should use these for other...

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