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Anonymity - good enough to protect criminals, not good enough to protect citizens against a state If you really want anonymity, bitcoin isn't the only blockcha

Anonymity - good enough to protect criminals, not good enough to protect citizens against a state If you really want anonymity, bitcoin isn't the only blockchain technology you have. I know you were focusing on bitcoin in your answer, but I feel the need to expand here because blockchain != bitcoin. Trustless consensus - 51% attack makes this unreliable, esp. with semi-anonymous actors 51% attack is overblown. The bitcoin miners self-police and are switching pools as they get close to 50%. And the worst thing that could happen with a 51% is a double-spend. Big whoop. Trustless transactions - POW as in bitcoin makes this impractical due to energy use and delays I don't follow you here. Sometimes the block size limit delays a transaction for a bit, but you still get trustless transactions. The bitcoin community is working to address this problem and I am confident this problem will be solved.

grey-area 10y ago
Anonymity - most people don't need or want it, and those who do need real anonymity, not traceable pseudo-anonymity. 51% attack - consider other uses like a shared ledger between 5 big banks, all of a sudden you just need 3 colluding and your blockchain is broken. Or bitcoin, most of the miners are in China, the state intervenes one day and secretly requires collusion. POW - 7 transactions a second, minutes to confirm and massive costs for those keeping full copies of the chain are big stumbling blocks to any blockchain based on POW as in the example or bitcoin. I think it has some fascinating ideas around shared trust, but Blockchains based on POW are fundamentally unsuited to the sort of large networks of transactions they are being proposed for and centralised solutions involving signing or hashing have the same advantages but solve all these problems and others like trust.
- Natanael_L 10y ago
  Things like Lightning Network helps Bitcoin scale by creating a network of payment channels, where you work with "transaction drafts" shared between various nodes that are updated for every transaction made by the involved parties, and which is frequently "settled" on the blockchain by being published to it in its latest version (followed by creating a new "draft"). This means that only a fraction of all transactions actually need to be visible on the blockchain since LN is a secure way to "keep tabs" on the current coin ownership. Using multisignature mechanisms and timelocks, this is very secure and abuse resistant.
SkyMarshal 10y ago
>And the worst thing that could happen with a 51% is a double-spend. Big whoop. That was the #1 problem that Bitcoin/blockchain solved. If it fails at that it calls into question the whole endeavor moreso than any other possible problem could.
- c0achmcguirk 10y ago
  And yet it hasn't failed to solve that. It's only a problem in theory. It requires hand-waving and speculation and then, in practice, it could be a problem. If you're worried about a double-spend, wait for 6 confirmations. Or wait for 10 if you really want to be vigilant. The 51% is one of the most successful FUD campaigns I've seen since Microsoft called the GPL a virus.
  - falcolas 10y ago
    All it would take is a state actor to decide to break that 51% mark, and bitcoin would crash. I wouldn't be terribly surprised if the US (specifically, the FBI or CIA) isn't poised to do just that if they feel it necessary. An "accepted" blockchain where all of the funds are diverted to their own wallet even for a day would be enough for all of the speculation that provides bitcoins with value to fall apart. Who would want to invest in a product when can demonstrably be devalued?
    - kordless 10y ago
      Actually, it would take an irrational state actor to attempt this and even then they might only be able to forge a few transactions before a fork was called. A hard fork is not assured to "crash" Bitcoin, so please don't present this as a forgone conclusion.
      - SkyMarshal 10y ago
        Or a state actor that is rational given certain externalities. Just because Bitcoin is expensive to attack does not mean it's irrational under all possible circumstances to attack it. War is expensive too, but it happens. This is the fundamental problem when ledger security depends in part on economic incentives.
ajnin 10y ago
> And the worst thing that could happen with a 51% is a double-spend. Maybe I misunderstood something, but couldn't someone with 51% of the power rewrite a block at any point in time in the past, and change history ? Or even write bogus transactions to the blockchain ? This would seem much more serious than double-spend, which in itself is already unacceptable for a monetary transaction system, and not to be brushed off so casually.
- c0achmcguirk 10y ago
  but couldn't someone with 51% of the power rewrite a block at any point in time in the past, and change history. In order to change history your miners would need to solve blocks much faster than the rest of the network consistently for multiple blocks. Then all the nodes on the bitcoin network would accept the false fork because it was longer. Or even write bogus transactions to the blockchain ? This would seem much more serious than double-spend You can't write a transaction without knowing the private key of the address you're transferring from. This is true whether there's a 51% attack or not. So you can't just write any old transaction to the blockchain. The rest of the network would reject the block with bad transactions in it. The big problem is buying something with bitcoin and receiving the purchased good--this transaction goes in Fork A. Then the attacker would start the 51% attack and create another fork--Fork B--which competes with Fork A. In Fork B the attack writes another transaction in which she sends the coins back to a wallet she controls. Then the attacker must continue to solve blocks at a faster rate than the rest of the network is solving it....AND before the rest of the bitcoin network notices what is going on. This is no small feat. and not to be brushed off so casually It's not brushed off casually. The 51% attack is brought up a lot in the cryptocurrency community. But it really isn't feasible on closer examination. In bitcoin it hasn't been a big deal because everyone is aware of the potential and self-polices.
- sunshinerag 10y ago
  A much more precise list of what can or cannot be done by a 51% attack https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_power https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_...

grey-area 10y ago

Anonymity - most people don't need or want it, and those who do need real anonymity, not traceable pseudo-anonymity. 51% attack - consider other uses like a shared ledger between 5 big banks, all of a sudden you just need 3 colluding and your blockchain is broken. Or bitcoin, most of the miners are in China, the state intervenes one day and secretly requires collusion. POW - 7 transactions a second, minutes to confirm and massive costs for those keeping full copies of the chain are big stumbling blocks to any blockchain based on POW as in the example or bitcoin. I think it has some fascinating ideas around shared trust, but Blockchains based on POW are fundamentally unsuited to the sort of large networks of transactions they are being proposed for and centralised solutions involving signing or hashing have the same advantages but solve all these problems and others like trust.

Natanael_L 10y ago
Things like Lightning Network helps Bitcoin scale by creating a network of payment channels, where you work with "transaction drafts" shared between various nodes that are updated for every transaction made by the involved parties, and which is frequently "settled" on the blockchain by being published to it in its latest version (followed by creating a new "draft"). This means that only a fraction of all transactions actually need to be visible on the blockchain since LN is a secure way to "keep tabs" on the current coin ownership. Using multisignature mechanisms and timelocks, this is very secure and abuse resistant.

SkyMarshal 10y ago

>And the worst thing that could happen with a 51% is a double-spend. Big whoop. That was the #1 problem that Bitcoin/blockchain solved. If it fails at that it calls into question the whole endeavor moreso than any other possible problem could.

c0achmcguirk 10y ago
And yet it hasn't failed to solve that. It's only a problem in theory. It requires hand-waving and speculation and then, in practice, it could be a problem. If you're worried about a double-spend, wait for 6 confirmations. Or wait for 10 if you really want to be vigilant. The 51% is one of the most successful FUD campaigns I've seen since Microsoft called the GPL a virus.
- falcolas 10y ago
  All it would take is a state actor to decide to break that 51% mark, and bitcoin would crash. I wouldn't be terribly surprised if the US (specifically, the FBI or CIA) isn't poised to do just that if they feel it necessary. An "accepted" blockchain where all of the funds are diverted to their own wallet even for a day would be enough for all of the speculation that provides bitcoins with value to fall apart. Who would want to invest in a product when can demonstrably be devalued?
  - kordless 10y ago
    Actually, it would take an irrational state actor to attempt this and even then they might only be able to forge a few transactions before a fork was called. A hard fork is not assured to "crash" Bitcoin, so please don't present this as a forgone conclusion.
    - SkyMarshal 10y ago
      Or a state actor that is rational given certain externalities. Just because Bitcoin is expensive to attack does not mean it's irrational under all possible circumstances to attack it. War is expensive too, but it happens. This is the fundamental problem when ledger security depends in part on economic incentives.

ajnin 10y ago

> And the worst thing that could happen with a 51% is a double-spend. Maybe I misunderstood something, but couldn't someone with 51% of the power rewrite a block at any point in time in the past, and change history ? Or even write bogus transactions to the blockchain ? This would seem much more serious than double-spend, which in itself is already unacceptable for a monetary transaction system, and not to be brushed off so casually.

c0achmcguirk 10y ago
but couldn't someone with 51% of the power rewrite a block at any point in time in the past, and change history. In order to change history your miners would need to solve blocks much faster than the rest of the network consistently for multiple blocks. Then all the nodes on the bitcoin network would accept the false fork because it was longer. Or even write bogus transactions to the blockchain ? This would seem much more serious than double-spend You can't write a transaction without knowing the private key of the address you're transferring from. This is true whether there's a 51% attack or not. So you can't just write any old transaction to the blockchain. The rest of the network would reject the block with bad transactions in it. The big problem is buying something with bitcoin and receiving the purchased good--this transaction goes in Fork A. Then the attacker would start the 51% attack and create another fork--Fork B--which competes with Fork A. In Fork B the attack writes another transaction in which she sends the coins back to a wallet she controls. Then the attacker must continue to solve blocks at a faster rate than the rest of the network is solving it....AND before the rest of the bitcoin network notices what is going on. This is no small feat. and not to be brushed off so casually It's not brushed off casually. The 51% attack is brought up a lot in the cryptocurrency community. But it really isn't feasible on closer examination. In bitcoin it hasn't been a big deal because everyone is aware of the potential and self-polices.
sunshinerag 10y ago
A much more precise list of what can or cannot be done by a 51% attack https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_computing_power https://en.bitcoin.it/wiki/Weaknesses#Attacker_has_a_lot_of_...