zkApps composability, pt 3: witness Party #294
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MartinMinkov
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ymekuria
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bkase
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| @@ -404,14 +430,9 @@ class Int64 extends CircuitValue implements BalanceChange { | |||
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| // --- circuit-compatible operations below --- | |||
| // the assumption here is that all Int64 values that appear in a circuit are already checked as valid | |||
| // this is because Circuit.witness calls .check | |||
| // this is because Circuit.witness calls .check, which calls .check on each prop, i.e. UInt64 and Sign | |||
| // so we only have to do additional checks if an operation on valid inputs can have an invalid outcome (example: overflow) | |||
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The comment? No. I did mean to remove the custom check method, because now the check method on the base class does what we need
| return fields.pop()!; | ||
| }, | ||
| Bool(fields: Field[]) { | ||
| return Bool.Unsafe.ofField(fields.pop()!); |
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this is only invoked on generated code we control from the json layout right?
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Yes! So it's safe because we know the field we're reading out was a Bool originally
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This adds the capability to "witness a Party" -- i.e., doing something like
Circuit.witness(() => party). (Which isn't possible withCircuit.witnessdirectly).Motivation: This was the main hurdle to take for implementing zkApp composability. When calling another zkApp, we actually don't want to run its computation inside the caller's circuit. Instead, we want the callee to be its own party, with its own proof. In the caller's circuit we just want to pull the result of the call out of our hat (= witness it). That result is the callee's party, plus the input and output arguments of the call. We connect it to the actual computation & its proof by having the callee's party's hash as part of the public input in the caller circuit.
To create a party witness we want to leverage the auto-generated party structure from OCaml -- to avoid hard-coding the party structure again. So, this PR
Party implements Types.Party. I.e., the Party class exactly conforms to the TS type that is generated. The changes needed wereSignthat's part ofInt64, so that in the party we can have theBalancebe aUint64+Signinstead of anInt64directlyauthorizationfield which has to be compatible with the OCaml typeThe PR also significantly changes the generated
js-layout, by changing the js deriver (see Mina companion), but this is actually an orthogonal change, only a small part of it was really needed here.