80 lines
2.7 KiB
Markdown
80 lines
2.7 KiB
Markdown
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order: 11
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# Object-Capability Model
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## Intro
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When thinking about security, it is good to start with a specific threat model. Our threat model is the following:
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> We assume that a thriving ecosystem of Cosmos-SDK modules that are easy to compose into a blockchain application will contain faulty or malicious modules.
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The Cosmos SDK is designed to address this threat by being the
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foundation of an object capability system.
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> The structural properties of object capability systems favor
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> modularity in code design and ensure reliable encapsulation in
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> code implementation.
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>
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> These structural properties facilitate the analysis of some
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> security properties of an object-capability program or operating
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> system. Some of these — in particular, information flow properties
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> — can be analyzed at the level of object references and
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> connectivity, independent of any knowledge or analysis of the code
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> that determines the behavior of the objects.
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>
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> As a consequence, these security properties can be established
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> and maintained in the presence of new objects that contain unknown
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> and possibly malicious code.
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>
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> These structural properties stem from the two rules governing
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> access to existing objects:
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>
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> 1. An object A can send a message to B only if object A holds a
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> reference to B.
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> 2. An object A can obtain a reference to C only
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> if object A receives a message containing a reference to C. As a
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> consequence of these two rules, an object can obtain a reference
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> to another object only through a preexisting chain of references.
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> In short, "Only connectivity begets connectivity."
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For an introduction to object-capabilities, see this [Wikipedia article](https://en.wikipedia.org/wiki/Object-capability_model).
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## Ocaps in practice
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The idea is to only reveal what is necessary to get the work done.
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For example, the following code snippet violates the object capabilities
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principle:
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```go
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type AppAccount struct {...}
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account := &AppAccount{
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Address: pub.Address(),
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Coins: sdk.Coins{sdk.NewInt64Coin("ATM", 100)},
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}
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sumValue := externalModule.ComputeSumValue(account)
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```
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The method `ComputeSumValue` implies a pure function, yet the implied
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capability of accepting a pointer value is the capability to modify that
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value. The preferred method signature should take a copy instead.
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```go
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sumValue := externalModule.ComputeSumValue(*account)
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```
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In the Cosmos SDK, you can see the application of this principle in the
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gaia app.
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+++ https://github.com/cosmos/cosmos-sdk/blob/v0.41.4/simapp/app.go#L249-L273
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The following diagram shows the current dependencies between keepers.
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## Next {hide}
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Learn about the [`runTx` middleware](./runtx_middleware.md) {hide}
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