What are the best criticisms of blockchain technology?

[Geremia]

What are the best criticisms of blockchain technology? Specifically, what are the top flaws of the blockchain as it's currently implemented by Bitcoin?

A few I can think of:

• double SHA-256 proof-of-work isn't computationally useful for anything (GridCoin is still affected by this criticism to a certain extent);
• it's not as immune to centralization as it could be (control of blockchain is proportional to computing power; it should be proportional to number of human users).

(cf. related Bitcoin StackExchange question)

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[amaclin]

What are the best criticisms of blockchain technology?

Blockchain technology costs much more resources (energy) per transaction compared with centralized systems (if we are comparing systems with equal reliability)

Blockchain technology has less reliability compared with centralized systems (if we are comparing systems which take same energy)

[amaclin]

The very nature of a centralized system is unreliable because there is someone, somewhere, who holds the reigns.

Are you talking about Gavin? 

How so? I've never had a Bitcoin transaction reversed.

You will see doublespendings when difficulty drop down.
You can doublespend right now - just take one of shit-coins.

[tsoPANos]

And what about the HUGE blockchain size?
As time passes, it becomes more and more difficult to handle the blockchain.
Bitcoin have been up and running since 2009.
That is more than five years!
It is currently 34.5 gb, and it was 10 gb less 6 months ago!
This is a 25-30% increase in six months!

[amaclin]

And what about the HUGE blockchain size?

I've said above about the cost of resources. This means all resources and total costs. Traffic, hosting relays, disk storage, mining hardware - these things are resources.
The product of Bitcoin network is transactions.
Bitcoin network (as a bank/payment system) converts resources to transactions (transferring rights).

[medUSA]

What are the best criticisms of blockchain technology? Specifically, what are the top flaws of the blockchain as it's currently implemented by Bitcoin?

Depends on what's in fashion. This year is blockchain size so far, last year was PoW and 51% attack. I project in the few years, it will be weakness of SHA256.

[JeromeL]

• double SHA-256 proof-of-work isn't computationally useful for anything (GridCoin is still affected by this criticism to a certain extent);

If the computation was useful, it would be easier to attack the network : it is "useless computation" for security reasons.

[HCLivess]

- It is an app, not a protocol
- Development is slow
- Development is centralized
- Community is extremely conservative
- Inflation is high
- Transactions are slow
- Transactions are irreversible (fixed by multisig, which is too complicated)
- Mining is complicated and annoying
etc.

[Clint]

Personally using blockchain wallet. It's a good btc wallet for us to use. But I've experienced shut downs so many times, it ruined my transactions. So it's not a perfect wallet for us btc users. They definitely should improve 

[fbueller]

@Clint: Think he meant the technology, not the company named Blockchain.

[virtualx]

And what about the HUGE blockchain size?
As time passes, it becomes more and more difficult to handle the blockchain.
Bitcoin have been up and running since 2009.
That is more than five years!
It is currently 34.5 gb, and it was 10 gb less 6 months ago!
This is a 25-30% increase in six months!

Disks space has been increasing ever since that time.  Satoshi had the same question in 2009 and he wrote that disk space will increase over the next decades.
I do agree that a system which would not require this amount of disk space would be beneficial, but how would you implement that?

[Muhammed Zakir]

And what about the HUGE blockchain size?
As time passes, it becomes more and more difficult to handle the blockchain.
Bitcoin have been up and running since 2009.
That is more than five years!
It is currently 34.5 gb, and it was 10 gb less 6 months ago!
This is a 25-30% increase in six months!

Disks space has been increasing ever since that time.  Satoshi had the same question in 2009 and he wrote that disk space will increase over the next decades.
I do agree that a system which would not require this amount of disk space would be beneficial, but how would you implement that?

You can use pruning mode to save disk space.

[cr1776]

And what about the HUGE blockchain size?
As time passes, it becomes more and more difficult to handle the blockchain.
Bitcoin have been up and running since 2009.
That is more than five years!
It is currently 34.5 gb, and it was 10 gb less 6 months ago!
This is a 25-30% increase in six months!

Not sure where your statistics are coming from, but this is nowhere near true.  6 months ago it was around 27 GB. ( see eg. https://blockchain.info/charts/blocks-size?timespan=all&showDataPoints=false&daysAverageString=1&show_header=true&scale=0&address=  )

The blockchain size is not unmanageable and hard disk space is cheap.

p.s.  Plus pruning.

[Geremia]

You can use pruning mode to save disk space.

What's pruning mode? Is there a flag to turn it on?

[Muhammed Zakir]

You can use pruning mode to save disk space.

What's pruning mode? Is there a flag to turn it on?

See 'Block file pruning' in https://github.com/bitcoin/bitcoin/blob/v0.11.0rc1/doc/release-notes.md and also http://bitcoin.stackexchange.com/a/19928.

[Geremia]

You can use pruning mode to save disk space.

What's pruning mode? Is there a flag to turn it on?

See 'Block file pruning' in https://github.com/bitcoin/bitcoin/blob/v0.11.0rc1/doc/release-notes.md and also http://bitcoin.stackexchange.com/a/19928.

Oh, that's bleeding-edge then.

[Trouble821]

You can use pruning mode to save disk space.

What's pruning mode? Is there a flag to turn it on?

See 'Block file pruning' in https://github.com/bitcoin/bitcoin/blob/v0.11.0rc1/doc/release-notes.md and also http://bitcoin.stackexchange.com/a/19928.

Oh, that's bleeding-edge then.

It's a step in the right direction but it's not perfect.

Note also that any problem that would cause a user to reindex (e.g., disk corruption) will cause a pruned node to redownload the entire blockchain.

I have found myself using reindex quite often and would hate redownloading the blockchain each time it was necessary.

Nevertheless work's started on dealing with the huge blockchain and that's good.

[dogie]

1) Irreversibility, ie if someone sends to an incorrect / dead address / loses keys then its gone. Or people injection malicious stuff into the blockchain leaving it there forever.

2) Theoretical anonymity. While we all like privacy, there is a problem when something goes from 99.99% untraceable to 100% untraceable (TOR based tumbling). There ARE cases were its important that criminals are traceable even with great efforts, else it makes Bitcoin users a target. Imagine how attractive users are when the goods they take are untraceable, unmarked 'bills' with no risk of ever getting caught. I don't like it.

3) Vulnerable to attacks. With no central body that can react quickly, things like transaction floods can temporarily damage the network. Because it takes a community effort or dev census to nullify the attack, its much slower than someone who can implement needed changes instantaneously. Ie Theymos pulling the plug on the servers when he noticed the intrusion.

[funkenstein]

   double SHA-256 proof-of-work isn't computationally useful for anything

You don't find bitcoin useful?  I disagree. 

  control of blockchain is proportional to computing power; it should be proportional to number of human users.

It looks like you are saying, it should be vulnerable to Sybil attacks.  I disagree.     

[Geremia]

  double SHA-256 proof-of-work isn't computationally useful for anything

You don't find bitcoin useful?  I disagree.

Well, computationally un-useful for things besides Bitcoin; that's what I meant.