juanblanco/Nethereum.Signer.EIP712v5.8.0

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Nethereum signer library to sign and encode messages according to EIP-712

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Published

Jan 6, 2026

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$ dotnet add package Nethereum.Signer.EIP712

Readme

Nethereum.Signer.EIP712

EIP-712 typed structured data signing for secure off-chain message authentication compatible with MetaMask's eth_signTypedData_v4.

Overview

Nethereum.Signer.EIP712 implements EIP-712, the standard for hashing and signing typed structured data. This enables signing complex objects (not just strings) in a way that's human-readable in MetaMask and other wallets, preventing phishing attacks where users unknowingly sign malicious transactions.

Key Features:

Sign complex typed data structures (objects, arrays, nested types)
Compatible with MetaMask's eth_signTypedData_v4
Human-readable signature prompts in wallets (shows fields, not raw hex)
Domain separation prevents replay attacks across different dApps
Type-safe C# API with automatic schema generation
Signature recovery to verify signers

Use Cases:

Gasless meta-transactions (user signs intent, relayer pays gas)
Off-chain order books (DEX orders, NFT listings)
Permit functionality (ERC-20 approvals via signature)
DAO voting (off-chain vote aggregation)
Session keys and delegated permissions

Installation

dotnet add package Nethereum.Signer.EIP712

Or via Package Manager Console:

Install-Package Nethereum.Signer.EIP712

Dependencies

Nethereum:

Nethereum.ABI - EIP-712 encoding implementation
Nethereum.Signer - Core ECDSA signing
Nethereum.Util - Keccak hashing
Nethereum.Hex - Hex encoding

Key Concepts

EIP-712 vs Regular Message Signing

Aspect	Regular (EIP-191)	EIP-712
Data	Arbitrary bytes/string	Typed structured data
Wallet Display	Hex hash (unreadable)	Human-readable fields
Type Safety	None	Full type checking
Phishing Protection	Weak	Strong (user sees what they sign)
Use Cases	Simple messages	Complex objects, transactions

Domain Separator

The domain separator prevents signatures from being valid across different:

Name: Application name
Version: Schema version
ChainId: Network (prevents mainnet/testnet replay)
VerifyingContract: Contract address that will verify the signature

TypedData Structure

public class TypedData<TDomain>
{
    public TDomain Domain { get; set; }                           // Domain separator
    public Dictionary<string, MemberDescription[]> Types { get; set; }  // Type definitions
    public string PrimaryType { get; set; }                       // Main message type
    public object Message { get; set; }                           // Actual data
}

Quick Start

using Nethereum.Signer;
using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;

// 1. Define your message type
public class Mail
{
    public Person From { get; set; }
    public Person To { get; set; }
    public string Contents { get; set; }
}

public class Person
{
    public string Name { get; set; }
    public string Wallet { get; set; }
}

// 2. Create domain
var domain = new Domain
{
    Name = "Ether Mail",
    Version = "1",
    ChainId = 1,
    VerifyingContract = "0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC"
};

// 3. Create typed data
var mail = new Mail
{
    From = new Person { Name = "Alice", Wallet = "0x..." },
    To = new Person { Name = "Bob", Wallet = "0x..." },
    Contents = "Hello Bob!"
};

// 4. Sign
var signer = new Eip712TypedDataSigner();
var key = new EthECKey("YOUR_PRIVATE_KEY");
string signature = signer.SignTypedData(mail, domain, "Mail", key);

Usage Examples

Example 1: Simple Typed Message (Real Test Example)

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using Nethereum.Signer;
using System.Collections.Generic;

// Define domain
var domain = new Domain
{
    Name = "Ether Mail",
    Version = "1",
    ChainId = 1,
    VerifyingContract = "0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC"
};

// Define type schema
var typedData = new TypedData<Domain>
{
    Domain = domain,
    Types = new Dictionary<string, MemberDescription[]>
    {
        ["EIP712Domain"] = new[]
        {
            new MemberDescription { Name = "name", Type = "string" },
            new MemberDescription { Name = "version", Type = "string" },
            new MemberDescription { Name = "chainId", Type = "uint256" },
            new MemberDescription { Name = "verifyingContract", Type = "address" }
        },
        ["Mail"] = new[]
        {
            new MemberDescription { Name = "from", Type = "Person" },
            new MemberDescription { Name = "to", Type = "Person[]" },
            new MemberDescription { Name = "contents", Type = "string" }
        },
        ["Person"] = new[]
        {
            new MemberDescription { Name = "name", Type = "string" },
            new MemberDescription { Name = "wallets", Type = "address[]" }
        }
    },
    PrimaryType = "Mail",
    Message = new[]
    {
        new MemberValue
        {
            TypeName = "Person",
            Value = new[]
            {
                new MemberValue { TypeName = "string", Value = "Cow" },
                new MemberValue { TypeName = "address[]", Value = new List<string>
                {
                    "0xCD2a3d9F938E13CD947Ec05AbC7FE734Df8DD826",
                    "0xDeaDbeefdEAdbeefdEadbEEFdeadbeEFdEaDbeeF"
                }}
            }
        },
        new MemberValue
        {
            TypeName = "Person[]",
            Value = new List<MemberValue[]>
            {
                new[]
                {
                    new MemberValue { TypeName = "string", Value = "Bob" },
                    new MemberValue { TypeName = "address[]", Value = new List<string>
                    {
                        "0xbBbBBBBbbBBBbbbBbbBbbbbBBbBbbbbBbBbbBBbB"
                    }}
                }
            }
        },
        new MemberValue { TypeName = "string", Value = "Hello, Bob!" }
    }
};

// Sign
var signer = new Eip712TypedDataSigner();
var key = new EthECKey("94e001d6adf3a3275d5dd45971c2a5f6637d3e9c51f9693f2e678f649e164fa5");
string signature = signer.SignTypedDataV4(typedData, key);

Console.WriteLine($"Signature: {signature}");

// Verify
string recoveredAddress = signer.RecoverFromSignatureV4(typedData, signature);
Console.WriteLine($"Signer: {recoveredAddress}");
Console.WriteLine($"Match: {key.GetPublicAddress() == recoveredAddress}");

Example 2: ERC-2612 Permit (Gasless Approval)

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using Nethereum.Signer;
using System.Numerics;

// ERC-20 Permit allows approvals via signature (no gas cost)
public class Permit
{
    public string Owner { get; set; }
    public string Spender { get; set; }
    public BigInteger Value { get; set; }
    public BigInteger Nonce { get; set; }
    public BigInteger Deadline { get; set; }
}

var domain = new Domain
{
    Name = "USD Coin",
    Version = "2",
    ChainId = 1,
    VerifyingContract = "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48" // USDC
};

var permit = new Permit
{
    Owner = "0x5B38Da6a701c568545dCfcB03FcB875f56beddC4",
    Spender = "0xAb8483F64d9C6d1EcF9b849Ae677dD3315835cb2",
    Value = BigInteger.Parse("1000000000"), // 1000 USDC (6 decimals)
    Nonce = 0,
    Deadline = 1735689600 // Unix timestamp
};

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("YOUR_PRIVATE_KEY");

// This signature can be submitted by anyone to approve the spender
string signature = signer.SignTypedData(permit, domain, "Permit", key);

// The spender can now call: token.permit(owner, spender, value, deadline, v, r, s)
// No gas cost for the owner!

Example 3: Meta-Transaction (Gasless Transaction)

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using System.Numerics;

public class MetaTransaction
{
    public BigInteger Nonce { get; set; }
    public string From { get; set; }
    public string FunctionSignature { get; set; }
}

var domain = new Domain
{
    Name = "My dApp",
    Version = "1",
    ChainId = 137, // Polygon
    VerifyingContract = "0x..." // Your contract address
};

var metaTx = new MetaTransaction
{
    Nonce = 0,
    From = "0x...", // User address
    FunctionSignature = "0x..." // Encoded function call
};

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("USER_PRIVATE_KEY");
string signature = signer.SignTypedData(metaTx, domain, "MetaTransaction", key);

// Relayer submits this to: contract.executeMetaTransaction(from, functionSignature, signature)
// User doesn't pay gas - relayer does!

Example 4: DEX Order (0x Protocol Style)

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using System.Numerics;

public class Order
{
    public string MakerAddress { get; set; }
    public string TakerAddress { get; set; }
    public string MakerAssetAddress { get; set; }
    public string TakerAssetAddress { get; set; }
    public BigInteger MakerAssetAmount { get; set; }
    public BigInteger TakerAssetAmount { get; set; }
    public BigInteger ExpirationTimeSeconds { get; set; }
    public BigInteger Salt { get; set; }
}

var domain = new Domain
{
    Name = "0x Protocol",
    Version = "3.0.0",
    ChainId = 1,
    VerifyingContract = "0x..." // Exchange contract
};

var order = new Order
{
    MakerAddress = "0x...",
    TakerAddress = "0x0000000000000000000000000000000000000000", // Anyone can fill
    MakerAssetAddress = "0x...", // WETH
    TakerAssetAddress = "0x...", // DAI
    MakerAssetAmount = BigInteger.Parse("1000000000000000000"), // 1 WETH
    TakerAssetAmount = BigInteger.Parse("2000000000000000000000"), // 2000 DAI
    ExpirationTimeSeconds = 1735689600,
    Salt = BigInteger.Parse("12345")
};

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("MAKER_PRIVATE_KEY");
string signature = signer.SignTypedData(order, domain, "Order", key);

// Order is signed off-chain, submitted to relayer, filled on-chain

Example 5: DAO Vote (Snapshot Style)

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;

public class Vote
{
    public string From { get; set; }
    public string Space { get; set; }
    public long Timestamp { get; set; }
    public string Proposal { get; set; }
    public int Choice { get; set; } // 1 = For, 2 = Against, 3 = Abstain
}

var domain = new Domain
{
    Name = "snapshot",
    Version = "0.1.4"
};

var vote = new Vote
{
    From = "0x...", // Voter address
    Space = "aave.eth",
    Timestamp = 1735689600,
    Proposal = "0x...", // Proposal ID
    Choice = 1 // Vote "For"
};

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("VOTER_PRIVATE_KEY");
string signature = signer.SignTypedData(vote, domain, "Vote", key);

// Vote is aggregated off-chain, no gas cost for voters

Example 6: Sign from JSON (Real Test Example)

using Nethereum.Signer.EIP712;
using Nethereum.Signer;

// Sign typed data directly from JSON (useful for frontend integration)
var typedDataJson = @"{
    'domain': {
        'chainId': 1,
        'name': 'Ether Mail',
        'verifyingContract': '0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC',
        'version': '1'
    },
    'message': {
        'contents': 'Hello, Bob!',
        'from': {
            'name': 'Cow',
            'wallets': [
                '0xCD2a3d9F938E13CD947Ec05AbC7FE734Df8DD826',
                '0xDeaDbeefdEAdbeefdEadbEEFdeadbeEFdEaDbeeF'
            ]
        },
        'to': [{
            'name': 'Bob',
            'wallets': ['0xbBbBBBBbbBBBbbbBbbBbbbbBBbBbbbbBbBbbBBbB']
        }]
    },
    'primaryType': 'Mail',
    'types': {
        'EIP712Domain': [
            {'name': 'name', 'type': 'string'},
            {'name': 'version', 'type': 'string'},
            {'name': 'chainId', 'type': 'uint256'},
            {'name': 'verifyingContract', 'type': 'address'}
        ],
        'Mail': [
            {'name': 'from', 'type': 'Person'},
            {'name': 'to', 'type': 'Person[]'},
            {'name': 'contents', 'type': 'string'}
        ],
        'Person': [
            {'name': 'name', 'type': 'string'},
            {'name': 'wallets', 'type': 'address[]'}
        ]
    }
}";

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("94e001d6adf3a3275d5dd45971c2a5f6637d3e9c51f9693f2e678f649e164fa5");

// Sign JSON directly
string signature = signer.SignTypedDataV4(typedDataJson, key);

// Recover signer from JSON + signature
string recoveredAddress = signer.RecoverFromSignatureV4(typedDataJson, signature);
Console.WriteLine($"Signer: {recoveredAddress}");

Example 7: NFT Lazy Minting

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using System.Numerics;

public class LazyMint
{
    public BigInteger TokenId { get; set; }
    public string TokenURI { get; set; }
    public string Creator { get; set; }
    public BigInteger RoyaltyBps { get; set; } // Basis points (100 = 1%)
}

var domain = new Domain
{
    Name = "LazyNFT",
    Version = "1",
    ChainId = 1,
    VerifyingContract = "0x..." // NFT contract
};

var lazyMint = new LazyMint
{
    TokenId = 12345,
    TokenURI = "ipfs://QmYx...",
    Creator = "0x...", // Artist address
    RoyaltyBps = 1000 // 10% royalty
};

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("ARTIST_PRIVATE_KEY");
string signature = signer.SignTypedData(lazyMint, domain, "LazyMint", key);

// NFT is not minted until someone buys it
// Buyer pays gas to mint + purchase in one transaction
// contract.buyAndMint(tokenId, tokenURI, creator, royaltyBps, signature)

Example 8: Session Key Authorization

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using System.Numerics;

public class SessionKey
{
    public string SessionPublicKey { get; set; }
    public BigInteger ExpiresAt { get; set; }
    public string[] AllowedContracts { get; set; }
}

var domain = new Domain
{
    Name = "GameSession",
    Version = "1",
    ChainId = 137,
    VerifyingContract = "0x..." // Game contract
};

var sessionKey = new SessionKey
{
    SessionPublicKey = "0x...", // Temporary key for gaming session
    ExpiresAt = DateTimeOffset.UtcNow.AddHours(24).ToUnixTimeSeconds(),
    AllowedContracts = new[] { "0x...", "0x..." } // Game contracts
};

var signer = new Eip712TypedDataSigner();
var mainKey = new EthECKey("MAIN_WALLET_PRIVATE_KEY");
string signature = signer.SignTypedData(sessionKey, domain, "SessionKey", mainKey);

// Session key can now make transactions within constraints
// User doesn't need to approve each action - better UX for games

Example 9: Verify Signature Without Private Key

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using Nethereum.Util;

// You have a signature and need to verify who signed it
var typedData = new TypedData<Domain>
{
    Domain = new Domain { Name = "MyApp", Version = "1", ChainId = 1 },
    // ... rest of typed data
};

string receivedSignature = "0x...";
string expectedSigner = "0x...";

var signer = new Eip712TypedDataSigner();

// Recover the address that created the signature
string recoveredAddress = signer.RecoverFromSignatureV4(typedData, receivedSignature);

// Verify it matches expected signer
bool isValid = expectedSigner.IsTheSameAddress(recoveredAddress);

if (isValid)
{
    Console.WriteLine("Signature is valid!");
    // Process the signed message
}
else
{
    Console.WriteLine($"Invalid signature!");
    Console.WriteLine($"Expected: {expectedSigner}");
    Console.WriteLine($"Got: {recoveredAddress}");
}

API Reference

Eip712TypedDataSigner

Main class for EIP-712 signing operations.

public class Eip712TypedDataSigner
{
    // Sign typed data (generates schema automatically)
    public string SignTypedData<T, TDomain>(T data, TDomain domain, string primaryTypeName, EthECKey key);

    // Sign pre-defined typed data
    public string SignTypedData<TDomain>(TypedData<TDomain> typedData, EthECKey key);

    // Sign for eth_signTypedData_v4 compatibility
    public string SignTypedDataV4<TDomain>(TypedData<TDomain> typedData, EthECKey key);
    public string SignTypedDataV4(string json, EthECKey key);
    public string SignTypedDataV4<T, TDomain>(T message, TypedData<TDomain> typedData, EthECKey key);

    // Sign with external signer (hardware wallet, etc.)
    public Task<string> SignTypedDataV4<TDomain>(TypedData<TDomain> typedData, IEthExternalSigner signer);

    // Recover signer address from signature
    public string RecoverFromSignatureV4<TDomain>(TypedData<TDomain> typedData, string signature);
    public string RecoverFromSignatureV4(string json, string signature);
    public string RecoverFromSignatureV4(byte[] encodedData, string signature);

    // Encode typed data (for custom workflows)
    public byte[] EncodeTypedData<TDomain>(TypedData<TDomain> typedData);
    public byte[] EncodeTypedData(string json);

    // Singleton instance
    public static Eip712TypedDataSigner Current { get; }
}

Related Packages

Used By (Consumers)

Nethereum.Accounts - Account signing with EIP-712
Nethereum.Contracts.Standards - ERC-2612 Permit, EIP-3009
Nethereum.X402 - HTTP 402 payment authorization

Dependencies

Nethereum.ABI - EIP-712 encoding engine
Nethereum.Signer - ECDSA signing primitives
Nethereum.Util - Keccak hashing
Nethereum.Hex - Hex encoding

Important Notes

MetaMask Compatibility

Always use SignTypedDataV4 for MetaMask compatibility:

// CORRECT - Works with MetaMask
string signature = signer.SignTypedDataV4(typedData, key);

// WRONG - Old format, not recommended
string signature = signer.SignTypedData(typedData, key);

Domain Separator is Critical

Always include proper domain to prevent cross-app replay:

// CORRECT - Unique per app and chain
var domain = new Domain
{
    Name = "My dApp",
    Version = "1",
    ChainId = 1, // REQUIRED for replay protection
    VerifyingContract = "0x..." // REQUIRED
};

// WRONG - Missing chainId allows replay attacks
var domain = new Domain
{
    Name = "My dApp",
    Version = "1"
};

Type Order Matters

Member order in type definitions must match exactly:

// CORRECT - Consistent order
new MemberDescription { Name = "name", Type = "string" },
new MemberDescription { Name = "wallet", Type = "address" }

// WRONG - Different order produces different hash
new MemberDescription { Name = "wallet", Type = "address" },
new MemberDescription { Name = "name", Type = "string" }

Frontend Integration

JSON format matches JavaScript exactly:

// Frontend (JavaScript)
const signature = await ethereum.request({
  method: 'eth_signTypedData_v4',
  params: [account, JSON.stringify(typedData)]
});

// Backend (.NET) - Same JSON structure
string signature = signer.SignTypedDataV4(jsonString, key);

Additional Resources

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Nethereum.Signer.EIP712

EIP-712 typed structured data signing for secure off-chain message authentication compatible with MetaMask's eth_signTypedData_v4.

Overview

Key Features:

Sign complex typed data structures (objects, arrays, nested types)
Compatible with MetaMask's eth_signTypedData_v4
Human-readable signature prompts in wallets (shows fields, not raw hex)
Domain separation prevents replay attacks across different dApps
Type-safe C# API with automatic schema generation
Signature recovery to verify signers

Use Cases:

Gasless meta-transactions (user signs intent, relayer pays gas)
Off-chain order books (DEX orders, NFT listings)
Permit functionality (ERC-20 approvals via signature)
DAO voting (off-chain vote aggregation)
Session keys and delegated permissions

Installation

dotnet add package Nethereum.Signer.EIP712

Or via Package Manager Console:

Install-Package Nethereum.Signer.EIP712

Dependencies

Nethereum:

Nethereum.ABI - EIP-712 encoding implementation
Nethereum.Signer - Core ECDSA signing
Nethereum.Util - Keccak hashing
Nethereum.Hex - Hex encoding

Key Concepts

EIP-712 vs Regular Message Signing

Aspect	Regular (EIP-191)	EIP-712
Data	Arbitrary bytes/string	Typed structured data
Wallet Display	Hex hash (unreadable)	Human-readable fields
Type Safety	None	Full type checking
Phishing Protection	Weak	Strong (user sees what they sign)
Use Cases	Simple messages	Complex objects, transactions

Domain Separator

The domain separator prevents signatures from being valid across different:

Name: Application name
Version: Schema version
ChainId: Network (prevents mainnet/testnet replay)
VerifyingContract: Contract address that will verify the signature

TypedData Structure

public class TypedData<TDomain>
{
    public TDomain Domain { get; set; }                           // Domain separator
    public Dictionary<string, MemberDescription[]> Types { get; set; }  // Type definitions
    public string PrimaryType { get; set; }                       // Main message type
    public object Message { get; set; }                           // Actual data
}

Quick Start

using Nethereum.Signer;
using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;

// 1. Define your message type
public class Mail
{
    public Person From { get; set; }
    public Person To { get; set; }
    public string Contents { get; set; }
}

public class Person
{
    public string Name { get; set; }
    public string Wallet { get; set; }
}

// 2. Create domain
var domain = new Domain
{
    Name = "Ether Mail",
    Version = "1",
    ChainId = 1,
    VerifyingContract = "0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC"
};

// 3. Create typed data
var mail = new Mail
{
    From = new Person { Name = "Alice", Wallet = "0x..." },
    To = new Person { Name = "Bob", Wallet = "0x..." },
    Contents = "Hello Bob!"
};

// 4. Sign
var signer = new Eip712TypedDataSigner();
var key = new EthECKey("YOUR_PRIVATE_KEY");
string signature = signer.SignTypedData(mail, domain, "Mail", key);

Usage Examples

Example 1: Simple Typed Message (Real Test Example)

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using Nethereum.Signer;
using System.Collections.Generic;

// Define domain
var domain = new Domain
{
    Name = "Ether Mail",
    Version = "1",
    ChainId = 1,
    VerifyingContract = "0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC"
};

// Define type schema
var typedData = new TypedData<Domain>
{
    Domain = domain,
    Types = new Dictionary<string, MemberDescription[]>
    {
        ["EIP712Domain"] = new[]
        {
            new MemberDescription { Name = "name", Type = "string" },
            new MemberDescription { Name = "version", Type = "string" },
            new MemberDescription { Name = "chainId", Type = "uint256" },
            new MemberDescription { Name = "verifyingContract", Type = "address" }
        },
        ["Mail"] = new[]
        {
            new MemberDescription { Name = "from", Type = "Person" },
            new MemberDescription { Name = "to", Type = "Person[]" },
            new MemberDescription { Name = "contents", Type = "string" }
        },
        ["Person"] = new[]
        {
            new MemberDescription { Name = "name", Type = "string" },
            new MemberDescription { Name = "wallets", Type = "address[]" }
        }
    },
    PrimaryType = "Mail",
    Message = new[]
    {
        new MemberValue
        {
            TypeName = "Person",
            Value = new[]
            {
                new MemberValue { TypeName = "string", Value = "Cow" },
                new MemberValue { TypeName = "address[]", Value = new List<string>
                {
                    "0xCD2a3d9F938E13CD947Ec05AbC7FE734Df8DD826",
                    "0xDeaDbeefdEAdbeefdEadbEEFdeadbeEFdEaDbeeF"
                }}
            }
        },
        new MemberValue
        {
            TypeName = "Person[]",
            Value = new List<MemberValue[]>
            {
                new[]
                {
                    new MemberValue { TypeName = "string", Value = "Bob" },
                    new MemberValue { TypeName = "address[]", Value = new List<string>
                    {
                        "0xbBbBBBBbbBBBbbbBbbBbbbbBBbBbbbbBbBbbBBbB"
                    }}
                }
            }
        },
        new MemberValue { TypeName = "string", Value = "Hello, Bob!" }
    }
};

// Sign
var signer = new Eip712TypedDataSigner();
var key = new EthECKey("94e001d6adf3a3275d5dd45971c2a5f6637d3e9c51f9693f2e678f649e164fa5");
string signature = signer.SignTypedDataV4(typedData, key);

Console.WriteLine($"Signature: {signature}");

// Verify
string recoveredAddress = signer.RecoverFromSignatureV4(typedData, signature);
Console.WriteLine($"Signer: {recoveredAddress}");
Console.WriteLine($"Match: {key.GetPublicAddress() == recoveredAddress}");

Example 2: ERC-2612 Permit (Gasless Approval)

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using Nethereum.Signer;
using System.Numerics;

// ERC-20 Permit allows approvals via signature (no gas cost)
public class Permit
{
    public string Owner { get; set; }
    public string Spender { get; set; }
    public BigInteger Value { get; set; }
    public BigInteger Nonce { get; set; }
    public BigInteger Deadline { get; set; }
}

var domain = new Domain
{
    Name = "USD Coin",
    Version = "2",
    ChainId = 1,
    VerifyingContract = "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48" // USDC
};

var permit = new Permit
{
    Owner = "0x5B38Da6a701c568545dCfcB03FcB875f56beddC4",
    Spender = "0xAb8483F64d9C6d1EcF9b849Ae677dD3315835cb2",
    Value = BigInteger.Parse("1000000000"), // 1000 USDC (6 decimals)
    Nonce = 0,
    Deadline = 1735689600 // Unix timestamp
};

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("YOUR_PRIVATE_KEY");

// This signature can be submitted by anyone to approve the spender
string signature = signer.SignTypedData(permit, domain, "Permit", key);

// The spender can now call: token.permit(owner, spender, value, deadline, v, r, s)
// No gas cost for the owner!

Example 3: Meta-Transaction (Gasless Transaction)

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using System.Numerics;

public class MetaTransaction
{
    public BigInteger Nonce { get; set; }
    public string From { get; set; }
    public string FunctionSignature { get; set; }
}

var domain = new Domain
{
    Name = "My dApp",
    Version = "1",
    ChainId = 137, // Polygon
    VerifyingContract = "0x..." // Your contract address
};

var metaTx = new MetaTransaction
{
    Nonce = 0,
    From = "0x...", // User address
    FunctionSignature = "0x..." // Encoded function call
};

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("USER_PRIVATE_KEY");
string signature = signer.SignTypedData(metaTx, domain, "MetaTransaction", key);

// Relayer submits this to: contract.executeMetaTransaction(from, functionSignature, signature)
// User doesn't pay gas - relayer does!

Example 4: DEX Order (0x Protocol Style)

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using System.Numerics;

public class Order
{
    public string MakerAddress { get; set; }
    public string TakerAddress { get; set; }
    public string MakerAssetAddress { get; set; }
    public string TakerAssetAddress { get; set; }
    public BigInteger MakerAssetAmount { get; set; }
    public BigInteger TakerAssetAmount { get; set; }
    public BigInteger ExpirationTimeSeconds { get; set; }
    public BigInteger Salt { get; set; }
}

var domain = new Domain
{
    Name = "0x Protocol",
    Version = "3.0.0",
    ChainId = 1,
    VerifyingContract = "0x..." // Exchange contract
};

var order = new Order
{
    MakerAddress = "0x...",
    TakerAddress = "0x0000000000000000000000000000000000000000", // Anyone can fill
    MakerAssetAddress = "0x...", // WETH
    TakerAssetAddress = "0x...", // DAI
    MakerAssetAmount = BigInteger.Parse("1000000000000000000"), // 1 WETH
    TakerAssetAmount = BigInteger.Parse("2000000000000000000000"), // 2000 DAI
    ExpirationTimeSeconds = 1735689600,
    Salt = BigInteger.Parse("12345")
};

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("MAKER_PRIVATE_KEY");
string signature = signer.SignTypedData(order, domain, "Order", key);

// Order is signed off-chain, submitted to relayer, filled on-chain

Example 5: DAO Vote (Snapshot Style)

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;

public class Vote
{
    public string From { get; set; }
    public string Space { get; set; }
    public long Timestamp { get; set; }
    public string Proposal { get; set; }
    public int Choice { get; set; } // 1 = For, 2 = Against, 3 = Abstain
}

var domain = new Domain
{
    Name = "snapshot",
    Version = "0.1.4"
};

var vote = new Vote
{
    From = "0x...", // Voter address
    Space = "aave.eth",
    Timestamp = 1735689600,
    Proposal = "0x...", // Proposal ID
    Choice = 1 // Vote "For"
};

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("VOTER_PRIVATE_KEY");
string signature = signer.SignTypedData(vote, domain, "Vote", key);

// Vote is aggregated off-chain, no gas cost for voters

Example 6: Sign from JSON (Real Test Example)

using Nethereum.Signer.EIP712;
using Nethereum.Signer;

// Sign typed data directly from JSON (useful for frontend integration)
var typedDataJson = @"{
    'domain': {
        'chainId': 1,
        'name': 'Ether Mail',
        'verifyingContract': '0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC',
        'version': '1'
    },
    'message': {
        'contents': 'Hello, Bob!',
        'from': {
            'name': 'Cow',
            'wallets': [
                '0xCD2a3d9F938E13CD947Ec05AbC7FE734Df8DD826',
                '0xDeaDbeefdEAdbeefdEadbEEFdeadbeEFdEaDbeeF'
            ]
        },
        'to': [{
            'name': 'Bob',
            'wallets': ['0xbBbBBBBbbBBBbbbBbbBbbbbBBbBbbbbBbBbbBBbB']
        }]
    },
    'primaryType': 'Mail',
    'types': {
        'EIP712Domain': [
            {'name': 'name', 'type': 'string'},
            {'name': 'version', 'type': 'string'},
            {'name': 'chainId', 'type': 'uint256'},
            {'name': 'verifyingContract', 'type': 'address'}
        ],
        'Mail': [
            {'name': 'from', 'type': 'Person'},
            {'name': 'to', 'type': 'Person[]'},
            {'name': 'contents', 'type': 'string'}
        ],
        'Person': [
            {'name': 'name', 'type': 'string'},
            {'name': 'wallets', 'type': 'address[]'}
        ]
    }
}";

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("94e001d6adf3a3275d5dd45971c2a5f6637d3e9c51f9693f2e678f649e164fa5");

// Sign JSON directly
string signature = signer.SignTypedDataV4(typedDataJson, key);

// Recover signer from JSON + signature
string recoveredAddress = signer.RecoverFromSignatureV4(typedDataJson, signature);
Console.WriteLine($"Signer: {recoveredAddress}");

Example 7: NFT Lazy Minting

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using System.Numerics;

public class LazyMint
{
    public BigInteger TokenId { get; set; }
    public string TokenURI { get; set; }
    public string Creator { get; set; }
    public BigInteger RoyaltyBps { get; set; } // Basis points (100 = 1%)
}

var domain = new Domain
{
    Name = "LazyNFT",
    Version = "1",
    ChainId = 1,
    VerifyingContract = "0x..." // NFT contract
};

var lazyMint = new LazyMint
{
    TokenId = 12345,
    TokenURI = "ipfs://QmYx...",
    Creator = "0x...", // Artist address
    RoyaltyBps = 1000 // 10% royalty
};

var signer = new Eip712TypedDataSigner();
var key = new EthECKey("ARTIST_PRIVATE_KEY");
string signature = signer.SignTypedData(lazyMint, domain, "LazyMint", key);

// NFT is not minted until someone buys it
// Buyer pays gas to mint + purchase in one transaction
// contract.buyAndMint(tokenId, tokenURI, creator, royaltyBps, signature)

Example 8: Session Key Authorization

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using System.Numerics;

public class SessionKey
{
    public string SessionPublicKey { get; set; }
    public BigInteger ExpiresAt { get; set; }
    public string[] AllowedContracts { get; set; }
}

var domain = new Domain
{
    Name = "GameSession",
    Version = "1",
    ChainId = 137,
    VerifyingContract = "0x..." // Game contract
};

var sessionKey = new SessionKey
{
    SessionPublicKey = "0x...", // Temporary key for gaming session
    ExpiresAt = DateTimeOffset.UtcNow.AddHours(24).ToUnixTimeSeconds(),
    AllowedContracts = new[] { "0x...", "0x..." } // Game contracts
};

var signer = new Eip712TypedDataSigner();
var mainKey = new EthECKey("MAIN_WALLET_PRIVATE_KEY");
string signature = signer.SignTypedData(sessionKey, domain, "SessionKey", mainKey);

// Session key can now make transactions within constraints
// User doesn't need to approve each action - better UX for games

Example 9: Verify Signature Without Private Key

using Nethereum.Signer.EIP712;
using Nethereum.ABI.EIP712;
using Nethereum.Util;

// You have a signature and need to verify who signed it
var typedData = new TypedData<Domain>
{
    Domain = new Domain { Name = "MyApp", Version = "1", ChainId = 1 },
    // ... rest of typed data
};

string receivedSignature = "0x...";
string expectedSigner = "0x...";

var signer = new Eip712TypedDataSigner();

// Recover the address that created the signature
string recoveredAddress = signer.RecoverFromSignatureV4(typedData, receivedSignature);

// Verify it matches expected signer
bool isValid = expectedSigner.IsTheSameAddress(recoveredAddress);

if (isValid)
{
    Console.WriteLine("Signature is valid!");
    // Process the signed message
}
else
{
    Console.WriteLine($"Invalid signature!");
    Console.WriteLine($"Expected: {expectedSigner}");
    Console.WriteLine($"Got: {recoveredAddress}");
}

API Reference

Eip712TypedDataSigner

Main class for EIP-712 signing operations.

public class Eip712TypedDataSigner
{
    // Sign typed data (generates schema automatically)
    public string SignTypedData<T, TDomain>(T data, TDomain domain, string primaryTypeName, EthECKey key);

    // Sign pre-defined typed data
    public string SignTypedData<TDomain>(TypedData<TDomain> typedData, EthECKey key);

    // Sign for eth_signTypedData_v4 compatibility
    public string SignTypedDataV4<TDomain>(TypedData<TDomain> typedData, EthECKey key);
    public string SignTypedDataV4(string json, EthECKey key);
    public string SignTypedDataV4<T, TDomain>(T message, TypedData<TDomain> typedData, EthECKey key);

    // Sign with external signer (hardware wallet, etc.)
    public Task<string> SignTypedDataV4<TDomain>(TypedData<TDomain> typedData, IEthExternalSigner signer);

    // Recover signer address from signature
    public string RecoverFromSignatureV4<TDomain>(TypedData<TDomain> typedData, string signature);
    public string RecoverFromSignatureV4(string json, string signature);
    public string RecoverFromSignatureV4(byte[] encodedData, string signature);

    // Encode typed data (for custom workflows)
    public byte[] EncodeTypedData<TDomain>(TypedData<TDomain> typedData);
    public byte[] EncodeTypedData(string json);

    // Singleton instance
    public static Eip712TypedDataSigner Current { get; }
}

Related Packages

Used By (Consumers)

Nethereum.Accounts - Account signing with EIP-712
Nethereum.Contracts.Standards - ERC-2612 Permit, EIP-3009
Nethereum.X402 - HTTP 402 payment authorization

Dependencies

Nethereum.ABI - EIP-712 encoding engine
Nethereum.Signer - ECDSA signing primitives
Nethereum.Util - Keccak hashing
Nethereum.Hex - Hex encoding

Important Notes

MetaMask Compatibility

Always use SignTypedDataV4 for MetaMask compatibility:

// CORRECT - Works with MetaMask
string signature = signer.SignTypedDataV4(typedData, key);

// WRONG - Old format, not recommended
string signature = signer.SignTypedData(typedData, key);

Domain Separator is Critical

Always include proper domain to prevent cross-app replay:

// CORRECT - Unique per app and chain
var domain = new Domain
{
    Name = "My dApp",
    Version = "1",
    ChainId = 1, // REQUIRED for replay protection
    VerifyingContract = "0x..." // REQUIRED
};

// WRONG - Missing chainId allows replay attacks
var domain = new Domain
{
    Name = "My dApp",
    Version = "1"
};

Type Order Matters

Member order in type definitions must match exactly:

// CORRECT - Consistent order
new MemberDescription { Name = "name", Type = "string" },
new MemberDescription { Name = "wallet", Type = "address" }

// WRONG - Different order produces different hash
new MemberDescription { Name = "wallet", Type = "address" },
new MemberDescription { Name = "name", Type = "string" }

Frontend Integration

JSON format matches JavaScript exactly:

// Frontend (JavaScript)
const signature = await ethereum.request({
  method: 'eth_signTypedData_v4',
  params: [account, JSON.stringify(typedData)]
});

// Backend (.NET) - Same JSON structure
string signature = signer.SignTypedDataV4(jsonString, key);