I am actually new to Hyperldeger fabric framework. I am working on research project where I want to select specific Endorsers from my end. Can we really do that ?
As far as I know, the Endorsement policy will be always in the syntax of "AND(Org1MSP.peer,Org2MSP.peer)". But I want to select the individual peers of the organization and currently it seems impossible. Is there any other workaround ?
Please put some light on this.
From your client, you can choose to select whatever endorser peers you prefer for each transaction through Transaction.setEndorserPeers(peers). But it is a client decision, not a network restriction. Another client could choose any other endorser selection strategy (as long as it fulfills the endorsement policies of the chaincode). At endorsement policy level, you cannot require specific peers.
Related
How to accomplish a transaction level consensus/endorsement between two organizations?
Let's say if OrgA sends Rs.5 to OrgB, OrgB should validate it and approve/decline based on some predefined agreement.
If OrgB expects Rs.15 and not Rs.10 for this transaction, it should raise a concern.
Where do we specify these details? I could see that the chaincode instantiate can specify policy but that is very generic as to how many endorsers should be there but not at a deeper level.
To achieve that, you will need a mechanism to set separate policies for individual keys, rather than the general chaincode-level policy for all the keys in the chaincode. This feature is part of Fabric 1.3, which will have a release candidate version (rc1) out within next few days.
More details here:
https://jira.hyperledger.org/browse/FAB-8812
what is Application's own signature in this context, and how can someone using hyperledger fabric node SDK can set the application's signature?
the application that you are talking about is simply a client app which talks to the ledger. The issue here is not the client app, the issue here is that you need a proper endorsement policy which establishes how anything goes onto the ledger.
Imagine this scenario ...
you have 2 orgs, Org1 and Org2, both owning one peer, P1 belongs to Org1, P2 belongs to Org2 and both peers joined on a channel, let's call it defaultchannel.
you deploy and instantiate your chaincode and set a basic endorsement policy which is 1-Of.
Each org has a client application, running against their own peer. When Org1 submits a transaction to the ledger, its validity is endorsed by itself, but not by the second org, because your policy requires only one to accomplish this. Basically in any network where you have more than one org, you really want a proper endorsement policy. 2-Of would work in the case of our example as any transaction would need to be validated by both orgs and that gives the ledger much better integrity.
Bottom line, your fabric network needs to be properly built and protected, especially in a production environment and this allows it to be protected by any client apps which have rights to interact with it. Your network being protected means that it doesn't matter how a client app is built and what it tries to do, it won't be able to bypass mechanisms such as the endorsement mechanisms.
Can someone explain how the immutability is implemented in Hyperledger Fabric? If we have private channel with little amount of peers, how it can be guaranteed, that one side hasn't changed data in it's ledger?
In order to guarantee that no party in the channel has tampered data in its own favor you need to present sophisticated endorsement policy to include all required parties and make sure they adequately represented within endorsement policy. Hence making it obligatory for client which issues new transaction to get endorsement from all interested parties, hence ensuring that all have same consistent state. For example if you have two organizations Org1 and Org2 and they do not trust each other, you would like to create endorsement policy:
AND(Org1.memmber, Org2.member)
Therefore client will have to collect endorsements from peers of both organization to consider the transaction valid those endorsement have to sign same bytes, which won't be the case if data was forged. You can read more about endorsements in official documentation. There is also a recent publication of Fabric architecture which explains it in more details.
NB: I am seeking to understand how endorsements works in general. This will help me determine how to design applications when using Hyperledger Composer.
When I read the links here and here, I came across this statement: "Transactions have to be “endorsed” and only endorsed transactions may be committed and have an effect on the state". The statement is clear. However, let's consider the composer developer tutorial here. We have a commodity that is currently owned by an owner(Trader1) who could sell it to somebody else(Trader 2). Currently, how many endorsements are needed for the transaction to be put on the blockchain? Because, when running the application, I only submit a transaction Trade and I get results. I only deal with one function, and I get results. The following things are transparent to me as a programmer:
Creation of a transaction proposal,
When the transaction proposal is endorsed and by whom,
Whether an endorsement is performed explicitly by a human on the other end or it's programmatically done by code
That there is a proposal response from the endorser and how many they are,
When the application verifies the endorsing peer signatures
When the application creates a transaction message from the transaction proposal and response
etc.
All I do is submit one transaction and get a result.
So it becomes hard for me to assess the value of endorsement policies besides the theory in the text. And thus, the difficulty in designing a program to utilize the same. For example, consider two scenarios which we could use to handle a Trade:
We need 2 endorsements from the seller and the buyer before a transaction is commited. This would effectively be one transaction (This is what is transparent to me)
We need 2 authorizations from seller and the buyer before a transaction is commited. These authorizations could update states in the commodity such that we capture the approval from both the seller and the buyer. This could be 2 transactions i.e. sellerTradeRequest, buyerTradeApproval. The sellerTradeRequest could update commodity.sellerApproval=true while the buyerTradeApproval could update commodity.buyerApproval=true. Then, a final trade transaction that checks that the states on the commodity are OK i.e. commodity.sellerApproval=true and commodity.buyerApproval=true before commiting the transaction.
If I get a clear distinction between 1 and 2, especially how composer enables 1 above. Then maybe I will start understanding how to use endorsements.
Could anyone help?
The endorsement process is described in the docs. That said, in simple terms, the process of endorsement involves an endorsing peer signing the read/write set of a transaction proposal with its certificate. This basically says: the peer identified by the signing certificate asserts that these are the read/write sets of the proposed transaction simulation.
A client that invokes a proposed transaction will need knowledge of the endorsement policy for that channel/chaincode so that it can transmit the proposed transaction to each of the endorsing peers (or to a sufficient subset of endorsing peers to satisfy the policy). When it has received the responses from each endorsing peer, it will check that the transaction is valid and then broadcast the endorsed transaction to the ordering service, which will add it to a block and broadcast to the validating peers for that channel.
Validating peers will then validate the endorsement policy of the channel/chaincode against the transactions in a block to ensure that:
all endorsements are valid (i.e. they are valid signatures from valid certificates over the expected message)
there are an appropriate number of endorsements
endorsements come from the expected source(s)
If the endorsement policy is satisfied, then the transaction is committed and the world state updated with the read/write set.
At present, Composer cannot manage the endorsement policy, but this is definitely on the development roadmap.
The endorsement policy enables you the chance to add an extra verification layer to your Blockchain. You define it when you create the channel.
When a (Initial) Peer sends a proposal, firts of all the proposal is send to all of the Peers that you have defined in your Endorsement policy.
Then, each Endorser Peer executes the proposal against its ledger. The Endorser Peer will send the result signed to the Initial Peer.
The Initial Peer will receive more than one respone. Then, the Initial Peer will verify all the signatures and will compare the result of each response. The result sent by each Endorse Peer have to be the same.
In that case, the Initial Peer will send the transaction to the Orderers. That transaction will wraper all the responses all of the Endorses Peers.
So, you should define your Endorsement policy according to your requirements
I am curious how does Fabric choose among one of selected Organizations in an "OR"-type Endorsement Policy. Is it a random choice or does it follow a predetermined logic?
For instance, let's say that I have a following policy :
OR('Org1.member', 'Org2.member', 'Org3.member')
Now, let's say that the Endorsing Peer which is supposed to process an incoming transaction proposal belongs to Org1.
Because of uncertainty about network connectivity and availability of other organizations, Org1 would be a preferred entity elected for endorsement (because it happens locally on that very same peer).
However, is this the case in Hyperledger Fabric?
Any help understanding the above will be greatly appreciated.
Fabric clients should be aware of the endorsement policies and it's up to them to decide on endorsing peers. So in your example with:
OR('Org1.member', 'Org2.member', 'Org3.member')
client should know that in order to get valid transaction it has to be endorsed by either someone from org1 or org2 or org3. So client could send transaction proposal to some peer into org1 and wait until get response. An alternative strategy would be to send transaction proposal to 3 peers one from each organization.
Once client collects enough endorsement it will submit transaction to the ordering service and prior to commit peer will ensure that endorsement policy being satisfied. Now please note that endorsement policy doesn't specifies exact endorsement peers, but just saying that it has to be someone from that org with certificate approved by org root CA.
So right now client has to know endorsement policies and being aware of the membership to being able sent transaction proposals, however there work in progress FAB-5451, to provide service discovery based capabilities so client will be able to dynamically learn policies and will be able to query for set of endorsing peers.
wouldn't it be better to step back from talking directly to peers and orderers? use channel instead. always speaking only to specific elements is SO fragile.