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Given all of these advantages, it is undeniably clear that oracles have the potential to be a very useful paradigm for smart contracts going forward. However, the key question is, how will oracle-based computation and blockchain-based computation, as in Ethereum, interact with each other?
A common misconception is that the primary feature of Ethereum is that it is Turing-complete, and so while Bitcoin only allows quick scripts for verification Ethereum contracts are means to do much harder and computationally intensive tasks. This is arguably a misconception. In order to make contracts truly statically analyzable, we would need to go so far as to remove the first-class-citizen property namely, the fact that contracts can create and call other contracts , at which point Ethereum would have very limited utility.
For example, consider the following contract:. This contract is pretty straightforward. It is an account with two access keys, where the first key has a withdrawal limit and the second key does not. If a message is sent with data [DEST, VALUE] , then if the sender is the first account it can send up to a certain limit of ether, and the limit refills at the rate of 1 finney per second ie.
If the sender is the second account, then the account contract sends the desired amount of ether to the desired destination with no restrictions. Additionally, the entire transaction should take about bytes, the Serpent code takes up bytes, and the four storage slots take up bytes - hence, bytes one-time cost and bytes bandwitdh per transaction.
Now, consider this contract with a multisig oracle. The same operations will need to be done, but only on a few servers so the cost is negligible. However, when the multisig transaction is sent to Bitcoin, if the multisig is a 3-of-5 then three elliptic curve verifications will be required, and the transaction will require 65 bytes per signature plus 20 bytes per public key so it will take about bytes altogether including also metadata and inputs.
Hence, assuming that an elliptic curve verification takes longer than a few hashes it does , the blockchain-based approach is actually easier. The reason why this example is so favorable is because it is a perfect example of how Ethereum is about state and not Turing-completeness: no loops were used, but the magic of the contract came from the fact that a running record of the withdrawal limit could be maintained inside the contract.
Note: advanced cryptographers may note that there is a specialized type of threshold signature that actually requires only one verification operation even if a large number of oracles are used to produce it. At other times, however, oracles do make sense. In this case, oracles are absolutely necessary. Another important case is smart contracts that actually are very hard to evaluate. For example, if you are purchasing computational resources from a decentralized cloud computing application, verifying that computations were done legitimately is not a task that the Ethereum blockchain can cheaply handle.
For most classes of computation, verifying that they were done correctly takes exactly as long as doing them in the first place, so the only way to practically do such a thing is through occasional spot-checking using, well, oracles. Another cloud-computing use case for oracles, although in this context we do not think of them as such, is file storage - you absolutely do not want to back up your 1GB hard drive onto the blockchain. An additional use-case, already mentioned above, is privacy.
Sometimes, you may not want the details of your financial contracts public, so doing everything on-chain may not be the best idea. In those cases, you may want to limit what is done on-chain and do most things off-chain. So we have these two paradigms of total on-chain and partial on-chain, and they both have their relative strengths and weaknesses.
However, the question is, are the two really purely competitive? The answer is, as it turns out, no. To further this point, here are a few particular examples:. Blockchain-based auditing - the concept of oracle-based computation can actually go much further than the "Bitcoin multisig oracle" or, for that matter, Ethereum multisig oracle idea.
The extreme is an approach where oracles also decide the one thing that the Bitcoin-based schemes still leave the blockchain to decide: the order of transactions. The main drawback with most of these methods is the same main drawback of blockchains in general.
Decentralized Oracles. Gaming — many oracles are critical for the functioning of smart contracts holding significant amounts of assets. If an attacker can trick the oracle into changing its value then it becomes quite simple to steal assets. Consistency — the most desired oracles are information streams, where the values change constantly. This means users expect oracles to accurately and consistently provide information on a certain schedule often every block.
However, there is no guarantee that a transaction to post the information will be certain to enter a block, no matter the fee that is paid. This is both a usability issue and an attack vector. Solutions Solutions to the oracle problem center around ways to both validate the data being queried and also place this data on chain in both an available and non-centralized manner.
In certain cases, a centralized oracle may be the best solution.
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Quandl. Хороший источник экономических и финансовых данных — полезен при построении моделей для прогнозирования экономических показателей или. The importance of the oracle for the implementation of the smart contract and Mathis B. Quand l'Italie tente à son tour de légiférer sur la blockchain. Oracle для Ethereum и других платформ. (Уникальный продукт!) финансовых данных (Bloomberg, Reuters, SIX, TRDATA, Quandl, Xignite).