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Aptos Move Prover

February 22, 2023
Yoonsoo Jang
Software Engineer, DSRV

Introduction​

Move Prover is a tool for verifying your move smart contract. If you describe specifications with MSL(Move Specification Language) for a function, move prover checks if the specifications are satisfied for all inputs of the function. Unlike unit test, verification of MSL is exhaustive and holds for all possible inputs and global states of a Move module or transaction scripts.

info

Please refer to here to get started.

Create Template​

Create a simple example contract code written in Move. You can create a sample contract hello_prover by selecting the template option and clicking the Create Template button.

template-code-aptos

Source Code To Prove​

Note that plus1 function is intentionally implemented wrongly to see if move prover really works.

prove.move
module 0x42::prove {
    fun plus1(x: u64): u64 {
        // x+1
        x+2 // error intended
    }
    
    spec plus1 {
        ensures result == x+1;
    }
    
    fun abortsIf0(x: u64) {
        if (x == 0) {
            abort(0)
        };
    }

    spec abortsIf0 {
        aborts_if x == 0;
    }
}

Project To Prove​

Select the project you want to verify using move prover. For now, let's choose aptos/hello_prover

new-project-aptos

Prove​

Click the Prove button. This button trigger aptos cli command aptos move prove for your project.

new-project-aptos

Check Out The Result​

Move prover results in an error message because it found the error case which the result is not equal to x plus 1.

new-project-aptos

Correct The Source Code And Prove Again​

Comment out x+2 and uncomment x+1 and click Prove button again.

prove.move
module 0x42::prove {
    fun plus1(x: u64): u64 {
        x+1
        // x+2 // error intended
    }
    
    spec plus1 {
        ensures result == x+1;
    }
    
    fun abortsIf0(x: u64) {
        if (x == 0) {
            abort(0)
        };
    }

    spec abortsIf0 {
        aborts_if x == 0;
    }
}

You will see the verification success message like below.

new-project-aptos

Reference​

https://osec.io/blog/tutorials/2022-09-16-move-prover

https://github.com/move-language/move/blob/main/language/move-prover/doc/user/prover-guide.md