Signing a message and veryfying signer's address in ethereum

About

This repo contains 3 different ways of signing a message off-chain and verifying signer's address on-chain using solidity ecrecover

Requirements

• Truffle installed (you can install it as npm -i -g truffle)
• Ganache running on port 7545
• install dependencies (npm install)
• .env file containing private key for account[0] from Ganache

Usage

truffle test

Examples

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Use case 1

• Use web3.js for off-line signing
• Hash the message before signing
• Use unlocked account from ether client (i.e. ganache) for signing

Process flow chart

• Off line signature (test/testVerifier1.js)

flowchart LR;
    A(msg to sign)-->|web3.utils.sha3|B(hashed msg\n32 bytes)-->X-->C(signature)-->|slice signature|D(r,s,v);
    F(address) <--> G[(private key)]-->X((web3.eth.sign))
    style D fill:#f9f,stroke:#333,stroke-width:4px,color:#000
    style B fill:#fd5,stroke:#333,stroke-width:4px,color:#000
    style F fill:#0F0,stroke:#333,stroke-width:4px,color:#000

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• On chain verification (contracts/Verifier1.sol)

flowchart LR;
    A(hashed msg\n32 bytes)-->X((abi.encodePacked))-->B(concatenated\nstring)-->|keccak256|D(hashed string)-->C(ecrecover)-->G(address);
    E(eth \nspecific \nsignature prefix *)-->X;
    F(r,s,v)-->C;
    style F fill:#f9f,stroke:#333,stroke-width:4px,color:#000
    style A fill:#fd5,stroke:#333,stroke-width:4px,color:#000
    style C fill:#fff,stroke:#333,stroke-width:4px,color:#F00
    style G fill:#0F0,stroke:#333,stroke-width:4px,color:#000

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Use case 2

• Use web3.js for off-line signing
• Use unlocked account from ether client (i.e. ganache) for signing
• Append eth specific prefix off-line before passing data on-chain

Process flow chart

• Off line signature (test/testVerifier2.js)

flowchart LR;
    A(msg to sign)-->|to hex|B(hex\nencoded\nmsg)-->X-->C(signature)-->|slice signature|D(r,s,v);
    F(address) <--> G[(private key)]-->X((web3.eth.sign))
    E(eth \nspecific \nsignature prefix *)-->Y;
    A-->Y((concatenate))-->|web3.utils.sha3|Z(concatenated\nmsg\nhashed\n32bytes)
    style D fill:#f9f,stroke:#333,stroke-width:4px,color:#000
    style Z fill:#fd5,stroke:#333,stroke-width:4px,color:#000
    style F fill:#0F0,stroke:#333,stroke-width:4px,color:#000

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• On chain verification (contracts/Verifier2.sol)

flowchart LR;
   D(concatenated\nmsg\nhashed\n32bytes)-->C(ecrecover)-->G(address);
   
    F(r,s,v)-->C;
    style F fill:#f9f,stroke:#333,stroke-width:4px,color:#000
    style D fill:#fd5,stroke:#333,stroke-width:4px,color:#000
    style C fill:#fff,stroke:#333,stroke-width:4px,color:#F00
    style G fill:#0F0,stroke:#333,stroke-width:4px,color:#000

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Use case 3

• Use ethers.js
• Does not require unlocked account
• Sign message off line via wallet.signMessage
• Get signature components with ethers.utils.splitSignature
• Pass arbitrary length message to verifier contract (i.e. not fixed to 32 bytes)
• Use in-line assembly to deconstruct and reconstruct message to verify

Process flow chart:

• Off line signature (test/testVerifier3.js)

flowchart LR;
    A(msg)-->X;
    F(address) <--> G(key)-->|new ethers.Wallet|X[(wallet)]-->|wallet.signMessage|Y(signature)-->|ethers.utils.splitSignature|D(r,s,v)
    style D fill:#f9f,stroke:#333,stroke-width:4px,color:#000
    style F fill:#0F0,stroke:#333,stroke-width:4px,color:#000
    style A fill:#fd5,stroke:#333,stroke-width:4px,color:#000

Loading

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• On chain verification (contracts/Verifier3.sol)

flowchart LR;
    A(msg)-->X((abi.encodePacked))-->B(concatenated\nstring)-->|keccak256|D(hashed string)-->C(ecrecover)-->G(address);
    E(eth \nspecific \nsignature prefix *)-->Y[(construct\neth prefix\nvar length)]-->X;
    A-->Y
    F(r,s,v)-->C;
    style F fill:#f9f,stroke:#333,stroke-width:4px,color:#000
    style A fill:#fd5,stroke:#333,stroke-width:4px,color:#000
    style C fill:#fff,stroke:#333,stroke-width:4px,color:#F00
    style G fill:#0F0,stroke:#333,stroke-width:4px,color:#000

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* \x19Ethereum Signed Message:\n" + len(hashedMessage)