Smart contract limitations in Ethereum and Hyperledger Fabric

Question

I am trying to make a smart contract to achieve the following automatically. But I stuck in the implementation. How can I run the (2) Tx without having B to sign the Tx, ie: I want it to run automatically once (1) is activated and condition (2) is ready.

Pseudocode:

A send 50 to B        (1)
if (B > 50)           (2)
    B send 10 to C    (3)

The code above involves multiple owners, ie. A, B and C. Firstly, A actives the contract by running/signing Tx (1). Then the contract checks condition (2). Now but how can run(3) automatically without having to force B to sign?

Ultimately, is the contract able to sign (or proxy sign) on behave of B?

Answer 1

No, the contract cannot sign on behave of B.

A starts the transactions by sending necessary funds to the contract, and then the contract disperses funds according to the rules. So, A -> contract, contract -> B and possibly, contract -> C.

Although it's outside the question raised, it will possibly help you avoid refactoring later to observe the best practice of separating the two sends if B and/or C are untrusted contracts. You would just do the accounting in the deposit step, and then use a withdrawal pattern as B & C claim their entitlements (separate transactions).

Hope it helps.