Ethereum oracle services
Original materials copyright with database high. At FileHorse check version and have should work: ssh also want x11vnc is uploaded to. You may have a bit of files hosted on and documentation in.
SPORTS BETTING ONLINE MALAYSIA YELLOW
Computational oracles also rely on off-chain nodes to perform intensive computational tasks, which would be impractical to execute on-chain, given gas costs and block size limits. For example, the oracle node may be tasked with generating a verifiably random figure e. Oracle design patterns Oracles come in different types, including immediate-read, publish-subscribe, and request-response, with the latter two being the most popular among Ethereum smart contracts.
Request-response oracles A request-response setup allows the client contract to request arbitrary data other than that provided by a publish-subscribe oracle. The oracle will have an on-chain component that receives a data request and passes it to an off-chain node for processing. Users initiating data queries must cover the cost of retrieving information from the off-chain source.
The client contract must also provide funds to cover gas costs incurred by the oracle contract in returning the response via the callback function specified in the request. Types of oracles Centralized oracles As the name suggests, a centralized oracle is one controlled by a single entity responsible for aggregating off-chain information and updating the oracle contract's data as requested.
Centralized oracles are efficient since they rely on a single source of truth. However, using a centralized oracle comes with various problems: Low correctness guarantees With centralized oracles, there's no way to confirm if the information provided is correct or not.
The oracle provider may be "reputable", but that doesn't eliminate the possibility of someone going rogue or a hacker tampering with the system. If the oracle becomes corrupt, smart contracts will execute based on bad data. Poor availability Centralized oracles aren't guaranteed to always make off-chain data available to other smart contracts. If the provider decides to turn off the service or a hacker hijacks the oracle's off-chain component, your smart contract is at risk of a denial of service DoS attack.
Paying the oracle for their services may encourage honest behavior, but this may not be enough. With smart contracts controlling enormous amounts of value, the payoff from manipulating oracle data is greater than ever. Decentralized oracles Decentralized oracles are designed to overcome the limitations of centralized oracles by eliminating single points of failure.
A decentralized oracle service comprises multiple participants in a peer-to-peer network that form consensus on off-chain data before sending it to a smart contract. A decentralized oracle should ideally be permissionless, trustless, and free from administration by a central party; in reality, decentralization among oracles is a spectrum.
Fully decentralized oracle networks also exist: these usually run as standalone blockchains and have defined consensus mechanisms for coordinating nodes and punishing misbehavior. Using decentralized oracles comes with the following benefits: High correctness guarantees Decentralized oracles attempt to achieve correctness of data using different approaches.
This includes using proofs attesting to the authenticity and integrity of the returned information and requiring multiple entities to collectively agree on the validity of off-chain data. Authenticity proofs Authenticity proofs are cryptographic mechanisms that enable independent verification of information retrieved from external sources.
These proofs can validate the source of the information and detect possible alterations to the data after retrieval. Some decentralized oracles use authenticity proofs to verify TLS sessions i. Trusted Execution Environment TEE attestations: A trusted execution environment TEE is a sandboxed computational environment that is isolated from the operational processes of its host system.
Users can also generate an attestation to prove an application instance is running within the trusted execution environment. Certain classes of decentralized oracles require oracle node operators to provide TEE attestations. This confirms to a user that the node operator is running an instance of oracle client in a trusted execution environment. Consensus-based validation of information Centralized oracles rely on a single source of truth when providing data to smart contracts, which introduces the possibility of publishing inaccurate information.
Decentralized oracles solve this problem by relying on multiple oracle nodes to query off-chain information. By comparing data from multiple sources, decentralized oracles reduce the risk of passing invalid information to on-chain contracts. 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.
Sure, you can use standard-form contracts, and people won't know that it's you who is making a contract for difference between ETH and USD at leverage, but the information leakage is still high. In those cases, you may want to limit what is done on-chain and do most things off-chain. So How Can They Work Together 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: SchellingCoin - incentivized decentralized oracles. The SchellingCoin protocol is a proof-of-concept that shows how we can create a decentralized oracle protocol that is incentive-compatible: have a two-step commitment protocol so that oracles do not initially know what each other's answers are, and then at the end have an Ethereum contract reward those oracles that are closest to the median.
This incentivizes everyone to respond with the truth, since it is very difficult to coordinate on a lie. An independently conceived alternative, TruthCoin , does a similar thing for prediction markets with binary outcomes eg. The idea is as follows. By default, we have M of N oracles running the code and providing their votes on the answers.
However, when an oracle is perceived to vote incorrectly, that oracles can be "challenged". At that point, the oracle must provide the code to the blockchain, the blockchain checks the code against a pre-provided hash and runs the code itself, and sees if the result matches. If the result does not match, or if the oracle never replies to the challenge, then it loses its security deposit. The game-theoretic equilibrium here is for there to be no cheating at all, since any attempt at cheating necessarily harms some other party and so that party has the incentive to perform a check.
Signature batching - one of the problems that I pointed out with the multisig oracle approach above is signature bloat: if you have three oracles signing everything, then that's extra bytes in the blockchain and three expensive verification operations per transaction.
However, with Ethereum we can be somewhat more clever - we can come up with a specialized "oracle contract", to which oracles can submit a single transaction with a single signature with a large number of votes batched together: [addr1, vote1, addr2, vote The oracle contract then processes the entire list of votes and updates all of the multisig voting pools contained inside it simultaneously.
Thus, one signature could be used to back an arbitrarily large number of votes, reducing the scalability concerns substantially. 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. If we abandon this requirement, then it is possible to achieve much higher degrees of efficiency by having an oracle maintain a centralized database of transactions and state as they come, providing a signed record of each new balance sheet as a transaction is applied, allowing for applications like microtransactions and high-frequency trading.
However, this has obvious trust-problems; particularly, what if the oracle double-spends? Fortunately, we can set up an Ethereum contract to solve the problem. Much like the verifiable computation example above, the idea is that by default everything would run entirely on the oracle, but if the oracle chooses to sign two different balance sheets that are the result of incompatible transactions then those two signatures can be imported into Ethereum, and the contract will verify that those two signatures are valid, and if they are the contract will take away the oracle's security deposit.
More complicated schemes to deal with other attack vectors are also possible. Verifiable secure multiparty computation - in the case where you are using oracles specifically for the purpose of maintaining private data, you can set up a protocol where the oracles securely choose a new secret key using multiparty random number generation every 24 hours, sign a message with the old key to prove to the world that the new key has authority, and then have to submit all of the computations that they made using the old key to the Ethereum blockchain for verification.
The old key would be revealed, but it would be useless since a message transferring ownership rights to the new key is already in the blockchain several blocks before. Any malfeasance or nonfeasance revealed in the audit would lead to the loss of a security deposit.
Ethereum oracle services crypto comparison
(time lapse) Ethereum Price Oracle Demo using Atra dTablesCRYPTO COIN VALUE IN INDIA
The oracles would run the code, and if the code execution leads to a withdrawal from the contract to some particular address then the oracles circulate a transaction sending the funds and sign it. The approach is still low-trust, as no single oracle has the ability to unilaterally withdraw the funds, but it has a number of particular advantages: Not every node in the blockchain needs to perform the computation - only a small number of oracles do It theoretically does not require as a platform anything more complicated than Bitcoin or Ripple as they currently stand Contracts have a somewhat higher degree of privacy - although exit transactions are still all visible, internal computations may not be.
The scheme can also be augmented with secure multiparty computation protocols so the contract can even contain private information something that would take efficient and secure obfuscation to work directly on Ethereum Contracts can rely on external information eg.
In fact, they can even rely on data from proprietary APIs, if the oracles subscribe to the APIs and pass along the costs to the contract users. 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. The primary feature of Ethereum is not Turing-completeness; in fact, we have a section in our whitepaper which makes the argument that even if we explicitly removed the ability of Ethereum contracts to be Turing-complete it would actually change very little and there would still be a need for "gas".
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: init: contract. 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. The storage database reads can be made efficient with caching, although the writes will require a few hashes each to rewrite the Patricia tree so they are not as easy; that's why SLOAD has a gas cost of 20 but SSTORE has a cost of up to 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. However, if we use a currency with such a feature built-in, then we are already abandoning Bitcoin's existing infrastructure and network effect; in that case, why not just use the Ethereum contract?
But Sometimes They Are At other times, however, oracles do make sense. The most common case that will appear in reality is the case of external data; sometimes, you want a financial contract that uses the price of the US dollar, and you can't cryptographically determine that just by doing a few hashes and measuring ratios.
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. Sure, you can use standard-form contracts, and people won't know that it's you who is making a contract for difference between ETH and USD at leverage, but the information leakage is still high.
The client contract must also provide funds to cover gas costs incurred by the oracle contract in returning the response via the callback function specified in the request. Types of oracles Centralized oracles As the name suggests, a centralized oracle is one controlled by a single entity responsible for aggregating off-chain information and updating the oracle contract's data as requested.
Centralized oracles are efficient since they rely on a single source of truth. However, using a centralized oracle comes with various problems: Low correctness guarantees With centralized oracles, there's no way to confirm if the information provided is correct or not.
The oracle provider may be "reputable", but that doesn't eliminate the possibility of someone going rogue or a hacker tampering with the system. If the oracle becomes corrupt, smart contracts will execute based on bad data. Poor availability Centralized oracles aren't guaranteed to always make off-chain data available to other smart contracts.
If the provider decides to turn off the service or a hacker hijacks the oracle's off-chain component, your smart contract is at risk of a denial of service DoS attack. Paying the oracle for their services may encourage honest behavior, but this may not be enough. With smart contracts controlling enormous amounts of value, the payoff from manipulating oracle data is greater than ever. Decentralized oracles Decentralized oracles are designed to overcome the limitations of centralized oracles by eliminating single points of failure.
A decentralized oracle service comprises multiple participants in a peer-to-peer network that form consensus on off-chain data before sending it to a smart contract. A decentralized oracle should ideally be permissionless, trustless, and free from administration by a central party; in reality, decentralization among oracles is a spectrum. Fully decentralized oracle networks also exist: these usually run as standalone blockchains and have defined consensus mechanisms for coordinating nodes and punishing misbehavior.
Using decentralized oracles comes with the following benefits: High correctness guarantees Decentralized oracles attempt to achieve correctness of data using different approaches. This includes using proofs attesting to the authenticity and integrity of the returned information and requiring multiple entities to collectively agree on the validity of off-chain data. Authenticity proofs Authenticity proofs are cryptographic mechanisms that enable independent verification of information retrieved from external sources.
These proofs can validate the source of the information and detect possible alterations to the data after retrieval. Some decentralized oracles use authenticity proofs to verify TLS sessions i. Trusted Execution Environment TEE attestations: A trusted execution environment TEE is a sandboxed computational environment that is isolated from the operational processes of its host system.
Users can also generate an attestation to prove an application instance is running within the trusted execution environment. Certain classes of decentralized oracles require oracle node operators to provide TEE attestations. This confirms to a user that the node operator is running an instance of oracle client in a trusted execution environment.
Consensus-based validation of information Centralized oracles rely on a single source of truth when providing data to smart contracts, which introduces the possibility of publishing inaccurate information. Decentralized oracles solve this problem by relying on multiple oracle nodes to query off-chain information. By comparing data from multiple sources, decentralized oracles reduce the risk of passing invalid information to on-chain contracts. Decentralized oracles, however, must deal with discrepancies in information retrieved from multiple off-chain sources.
An aggregation protocol then aggregates the votes and stakes and takes the answer supported by the majority as the valid one. Nodes whose answers deviate from the majority answer are penalized by having their tokens distributed to others who provide more correct values.
Forcing nodes to provide a bond before providing data incentivizes honest responses since they are assumed to be rational economic actors intent on maximizing returns. Schelling point mechanisms Schelling point is a game-theory concept that assumes multiple entities will always default to a common solution to a problem in absence of any communication. Schelling-point mechanisms are often used in decentralized oracle networks to enable nodes reach consensus on answers to data requests.