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This is very interesting: Bitcoin has a scripting language which enables more than a “send money from X to Y” transaction. A Bitcoin transaction can require M

This is very interesting: Bitcoin has a scripting language which enables more than a “send money from X to Y” transaction. A Bitcoin transaction can require M of N parties to approve a transaction. Imagine Wills that automatically unlock when most of the heirs agree that their parent has passed, no lawyer required. Or business accounts that require two of any three trusted signatures to approve an expenditure. Or wire escrows that go through when any arbiter agrees that the supplier sent the goods to the buyer. Or wallets that are socially secured by your friends and family. Or an allowance account accessible by the child and either of two parents. Or a crowdfunding of a Kickstarter project that pays out on milestones, based on the majority of the backers approving the next payment. The escrow in each case can be locked so that the arbiters can’t take the money themselves – only approve or deny the transaction. The scripting language can also unlock transactions based on other parameters. Unlocking them over time can enable automatic mortgage, trust, and allowance payouts. Unlocking them on guessable numbers creates a lottery auditable by third parties. One can even design smart property – for example, a car’s electronic key so that when and only when a payment is made by the car buyer to the seller, the seller’s car key stops working and the buyer’s car key (or mobile phone) starts the car. Imagine your self-driving car negotiating traffic, paying fractional bitcoin to neighboring cars in exchange for priority. I've been following Bitcoin since the beginning and had no idea it supported "transaction approved only when M of N participants agree." How do you feel about those scenarios? Also, does anyone know of other little-known Bitcoin functionality?

rms 13y ago
An important caveat is that Bitcoin Script isn't enabled in the current implementation of Bitcoin, for obvious security reasons. The immense possibility of Script is yet another reason I am long on Bitcoin.
- tlrobinson 13y ago
  Only parts of it aren't enabled. You can already do a lot with Script: "This is a list of all Script words (commands/functions). Some of the more complicated opcodes are disabled out of concern that the client might have a bug in their implementation; if a transaction using such an opcode were to be included in the chain any fix would risk forking the chain." https://en.bitcoin.it/wiki/Script https://en.bitcoin.it/wiki/Script
- maaku 13y ago
  What are you talking about? Every single transaction uses the bitcoin scripting language, and has since the genesis block. There are certain rules about which transactions are relayed based on the scripts they contain, but scripting certainly is an integral part of bitcoin as it exists today.
  - tedunangst 13y ago
    Custom scripts aren't run. At this point, scripts are just exceptionally long identifiers for predetermined actions.
    - maaku 13y ago
      Simply wrong. I suggest you actually look at the source code to bitcoind (start with script.cpp, and the validation methods in main.cpp/core.cpp which call it).
      - tedunangst 13y ago
        My mistake. I was under the impression the whitelist was quite restrictive, but maybe not.
    - nullc 13y ago
      Thats not correct. They're executed, and fancy scripts are sometimes used on the network. Common wallet software just uses templates to create and decide which scripts are relevant to them— but the network itself absolutely does validate them.
gojomo 13y ago
The scripting language vision has been there from the beginning, but parts of it have been 'off' (in the reference client) because of incomplete implementation, or concern that the implications and potential bugs aren't sufficiently understood. I wonder if a future Bitcoin offshoot might even use a more general standard language for in-ledger transactions. Javascript? LLVM?
- ssadler 13y ago
  They couldn't, because Javascript etc are turing complete, so you can't predict if they're going to end (halting problem). With bitcoin you know that the script will end and that the running time will correlate loosely with the size of the script, so you can't really use it to mess up network nodes. Butcoin scripts have no loops or goto.
  - gst 13y ago
    Actually you could. Just limit the max. number of instructions that are allowed to be executed in order for a script to be valid.
    - nullc 13y ago
      Indeed, you can, but then you have a very exact requirement on exactly how the interpreter is implemented which can never be optimized, and any disagreement between implementations can cause a world ending consensus failure. By not having looping or recursion script naturally gets an operation limit by virtue of having a size limit, and this is _relatively_ easy to get right between implementations. (Though, so far several of the alt implementations have gotten it wrong).
  - topynate 13y ago
    You could require all scripting to be done in a language supporting total functional programming, like Epigram. That would be fairly hilarious (also counterproductive, because the increased script size would cause blockchain bloat).
  - gojomo 13y ago
NhanH 13y ago
Bitcoin use a scripting language for the transactions, as described in here[0][1]. Interestingly, I believe that this is one of the case where "lazy programmers make best programmers": instead of implementing the transaction system, Satoshi decides that he couldn't be bothered and just put in a scripting system instead (I have no citation for this, and can't claim for certain that this is the case, it was just something I read a while ago). However, due to security concerns, I think that most of the scripting ability is currently disabled. [0]:https://en.bitcoin.it/wiki/Script https://en.bitcoin.it/wiki/Script [1]:https://en.bitcoin.it/wiki/Contracts https://en.bitcoin.it/wiki/Contracts
tlrobinson 13y ago
Yes, this is the most exciting part of Bitcoin, IMHO. It's quite amazing what sort of problems you can solve. I highly recommend watching this talk by Mike Hearn, as well as reading the links in NhanH's comment: https://www.youtube.com/watch?v=mD4L7xDNCmA https://www.youtube.com/watch?v=mD4L7xDNCmA
topynate 13y ago
Provably Prune-able Outputs! See https://bitcoinfoundation.org/blog/?p=290 https://bitcoinfoundation.org/blog/?p=290. The idea is to support adding a little bit (80 bytes) of extra data to a transaction, while signalling to people who don't need to know about it (i.e. almost everyone) that they can happily ignore any such data and thus avoid downloading it.
- taariqlewis 13y ago
  This has the potential to allow new protocols to be built ontop of bitcoin. Mastercoin is one new protocol that uses the pruneable, provable outputs functionality. Learn more about Mastercoin here: https://github.com/mastercoin-MSC/ https://github.com/mastercoin-MSC/
  - nwh 13y ago
    For those uninformed, "MasterCoin" is an impossible attempt at pegging Bitcoin to the USD (among other things). It of course doesn't work because there's a limited supply, which means that the prices are raised and you're no longer pegged. The whole setup is essentially designed by the creator to make him and his "donators" rich (buy some now and get 10% more! was the original post). Due to the ponzi-like setup, the people who paid 4 million dollars for "MasterCoin" are very, very vocal when it comes to promoting it. https://blockchain.info/address/1EXoDusjGwvnjZUyKkxZ4UHEf77z6A5S4P https://blockchain.info/address/1EXoDusjGwvnjZUyKkxZ4UHEf77z...
    - cdash 13y ago
      Kind of sounds like bitcoin.
      - jerguismi 13y ago
        Just another altcoin, with a twist.
nullc 13y ago
Here is an exceptionally fun example of Script use: https://bitcointalk.org/index.php?topic=293382.0 https://bitcointalk.org/index.php?topic=293382.0 Beyond script there isn't a whole lot— nlocktime lets you make transactions which cannot be mined until a specified time in the future. This lets you build protocols that have "refunds", so that they don't cause funds to get stuck if a participant walks away. But even just using a few features of script and nlocktime is exceptionally powerful: Securely and privately trading Bitcoins for other cryptocoins (including Bitcoins): https://bitcointalk.org/index.php?topic=321228.0 https://bitcointalk.org/index.php?topic=321228.0 or Buying computationally verifiable information in an environment of mutual distrust: https://en.bitcoin.it/wiki/User:Gmaxwell/why_hash_locked https://en.bitcoin.it/wiki/User:Gmaxwell/why_hash_locked One of the most important things script does is allows you to produce transactions which are bound into more complex protocols occurring outside of Bitcoin in a secure way. This allows you to extend Bitcoin's trustless decentralization into things which aren't part of Bitcoin proper.
skriticos2 13y ago
I have an issue with that particular scenario. What if your three hairs secretly hate you and just agree to declare you dead? But I can see it working with some adjustments: make your contractually obliged lawyer part of the transaction and include his fees. This way he can't grab all the money for himself and your usurpers can't get to your money that easy. I know, I'm pessimistic.
- GotAnyMegadeth 13y ago
  If that's the case, give your money to a Cat charity rather than your hateful heirs

rms 13y ago

An important caveat is that Bitcoin Script isn't enabled in the current implementation of Bitcoin, for obvious security reasons. The immense possibility of Script is yet another reason I am long on Bitcoin.

tlrobinson 13y ago
Only parts of it aren't enabled. You can already do a lot with Script: "This is a list of all Script words (commands/functions). Some of the more complicated opcodes are disabled out of concern that the client might have a bug in their implementation; if a transaction using such an opcode were to be included in the chain any fix would risk forking the chain." https://en.bitcoin.it/wiki/Script https://en.bitcoin.it/wiki/Script
maaku 13y ago
What are you talking about? Every single transaction uses the bitcoin scripting language, and has since the genesis block. There are certain rules about which transactions are relayed based on the scripts they contain, but scripting certainly is an integral part of bitcoin as it exists today.
- tedunangst 13y ago
  Custom scripts aren't run. At this point, scripts are just exceptionally long identifiers for predetermined actions.
  - maaku 13y ago
    Simply wrong. I suggest you actually look at the source code to bitcoind (start with script.cpp, and the validation methods in main.cpp/core.cpp which call it).
    - tedunangst 13y ago
      My mistake. I was under the impression the whitelist was quite restrictive, but maybe not.
  - nullc 13y ago
    Thats not correct. They're executed, and fancy scripts are sometimes used on the network. Common wallet software just uses templates to create and decide which scripts are relevant to them— but the network itself absolutely does validate them.

gojomo 13y ago

The scripting language vision has been there from the beginning, but parts of it have been 'off' (in the reference client) because of incomplete implementation, or concern that the implications and potential bugs aren't sufficiently understood. I wonder if a future Bitcoin offshoot might even use a more general standard language for in-ledger transactions. Javascript? LLVM?

ssadler 13y ago
They couldn't, because Javascript etc are turing complete, so you can't predict if they're going to end (halting problem). With bitcoin you know that the script will end and that the running time will correlate loosely with the size of the script, so you can't really use it to mess up network nodes. Butcoin scripts have no loops or goto.
- gst 13y ago
  Actually you could. Just limit the max. number of instructions that are allowed to be executed in order for a script to be valid.
  - nullc 13y ago
    Indeed, you can, but then you have a very exact requirement on exactly how the interpreter is implemented which can never be optimized, and any disagreement between implementations can cause a world ending consensus failure. By not having looping or recursion script naturally gets an operation limit by virtue of having a size limit, and this is _relatively_ easy to get right between implementations. (Though, so far several of the alt implementations have gotten it wrong).
- topynate 13y ago
  You could require all scripting to be done in a language supporting total functional programming, like Epigram. That would be fairly hilarious (also counterproductive, because the increased script size would cause blockchain bloat).
- gojomo 13y ago

NhanH 13y ago

Bitcoin use a scripting language for the transactions, as described in here[0][1]. Interestingly, I believe that this is one of the case where "lazy programmers make best programmers": instead of implementing the transaction system, Satoshi decides that he couldn't be bothered and just put in a scripting system instead (I have no citation for this, and can't claim for certain that this is the case, it was just something I read a while ago). However, due to security concerns, I think that most of the scripting ability is currently disabled. [0]:https://en.bitcoin.it/wiki/Script https://en.bitcoin.it/wiki/Script [1]:https://en.bitcoin.it/wiki/Contracts https://en.bitcoin.it/wiki/Contracts

tlrobinson 13y ago

Yes, this is the most exciting part of Bitcoin, IMHO. It's quite amazing what sort of problems you can solve. I highly recommend watching this talk by Mike Hearn, as well as reading the links in NhanH's comment: https://www.youtube.com/watch?v=mD4L7xDNCmA https://www.youtube.com/watch?v=mD4L7xDNCmA

topynate 13y ago

Provably Prune-able Outputs! See https://bitcoinfoundation.org/blog/?p=290 https://bitcoinfoundation.org/blog/?p=290. The idea is to support adding a little bit (80 bytes) of extra data to a transaction, while signalling to people who don't need to know about it (i.e. almost everyone) that they can happily ignore any such data and thus avoid downloading it.

taariqlewis 13y ago
This has the potential to allow new protocols to be built ontop of bitcoin. Mastercoin is one new protocol that uses the pruneable, provable outputs functionality. Learn more about Mastercoin here: https://github.com/mastercoin-MSC/ https://github.com/mastercoin-MSC/
- nwh 13y ago
  For those uninformed, "MasterCoin" is an impossible attempt at pegging Bitcoin to the USD (among other things). It of course doesn't work because there's a limited supply, which means that the prices are raised and you're no longer pegged. The whole setup is essentially designed by the creator to make him and his "donators" rich (buy some now and get 10% more! was the original post). Due to the ponzi-like setup, the people who paid 4 million dollars for "MasterCoin" are very, very vocal when it comes to promoting it. https://blockchain.info/address/1EXoDusjGwvnjZUyKkxZ4UHEf77z6A5S4P https://blockchain.info/address/1EXoDusjGwvnjZUyKkxZ4UHEf77z...
  - cdash 13y ago
    Kind of sounds like bitcoin.
    - jerguismi 13y ago
      Just another altcoin, with a twist.

nullc 13y ago

Here is an exceptionally fun example of Script use: https://bitcointalk.org/index.php?topic=293382.0 https://bitcointalk.org/index.php?topic=293382.0 Beyond script there isn't a whole lot— nlocktime lets you make transactions which cannot be mined until a specified time in the future. This lets you build protocols that have "refunds", so that they don't cause funds to get stuck if a participant walks away. But even just using a few features of script and nlocktime is exceptionally powerful: Securely and privately trading Bitcoins for other cryptocoins (including Bitcoins): https://bitcointalk.org/index.php?topic=321228.0 https://bitcointalk.org/index.php?topic=321228.0 or Buying computationally verifiable information in an environment of mutual distrust: https://en.bitcoin.it/wiki/User:Gmaxwell/why_hash_locked https://en.bitcoin.it/wiki/User:Gmaxwell/why_hash_locked One of the most important things script does is allows you to produce transactions which are bound into more complex protocols occurring outside of Bitcoin in a secure way. This allows you to extend Bitcoin's trustless decentralization into things which aren't part of Bitcoin proper.

skriticos2 13y ago

I have an issue with that particular scenario. What if your three hairs secretly hate you and just agree to declare you dead? But I can see it working with some adjustments: make your contractually obliged lawyer part of the transaction and include his fees. This way he can't grab all the money for himself and your usurpers can't get to your money that easy. I know, I'm pessimistic.

GotAnyMegadeth 13y ago
If that's the case, give your money to a Cat charity rather than your hateful heirs