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Overview

This reference documents all the methods available in the Flow.Net SDK, and explains in detail how these methods work.

The library client specifications can be found here:

Getting Started

Installing

Package Manager Console

Run following command in VS Package Manager Console:

Install-Package Flow.Net.Sdk

Command Line

Run following command in command line:

dotnet add package Flow.Net.Sdk

---

Connect

The library uses HTTP or gRPC APIs to communicate with the access nodes and it must be configured with correct access node API URL.

You can check more examples for creating clients in the examples:

Basic Example:

// HTTP client
var flowHttpClient = new FlowHttpClient(new HttpClient(), new FlowClientOptions { ServerUrl = Sdk.Client.Http.ServerUrl.EmulatorHost });

// gRPC client
var flowGrpcClient = new FlowGrpcClient(new FlowGrpcClientOptions { ServerUrl = Sdk.Client.Grpc.ServerUrl.EmulatorHost })

Querying the Flow Network

After you have established a connection with an access node, you can query the Flow network to retrieve data about blocks, accounts, events and transactions. We will explore how to retrieve each of these entities in the sections below.

Get Blocks

Query the network for block by id, height or get the latest block.

📖 Block ID is SHA3-256 hash of the entire block payload. This hash is stored as an ID field on any block response object (ie. response from GetLatestBlock).

📖 Block height expresses the height of the block on the chain. The latest block height increases by one for every valid block produced.

Examples

This example depicts ways to get the latest block as well as any other block by height or ID:

private async Task Demo()
{
    // get the latest sealed block
    var latestBlock = await FlowClient.GetLatestBlockAsync();
    PrintResult(latestBlock);

    // get the block by ID
    var blockByIdResult = await FlowClient.GetBlockByIdAsync(latestBlock.Header.Id);
    PrintResult(blockByIdResult);

    // get block by height
    var blockByHeightResult = await FlowClient.GetBlockByHeightAsync(latestBlock.Header.Height);
    PrintResult(blockByHeightResult);
}

private void PrintResult(FlowBlock flowBlock)
{
    Console.WriteLine($"ID: {flowBlock.Header.Id}");
    Console.WriteLine($"height: {flowBlock.Header.Height}");
    Console.WriteLine($"timestamp: {flowBlock.Header.Timestamp}\n");            
}

Example output:

ID: 7bc42fe85d32ca513769a74f97f7e1a7bad6c9407f0d934c2aa645ef9cf613c7
height: 0
timestamp: 19/12/2018 22:32:30 +00:00

ID: 7bc42fe85d32ca513769a74f97f7e1a7bad6c9407f0d934c2aa645ef9cf613c7
height: 0
timestamp: 19/12/2018 22:32:30 +00:00

ID: 7bc42fe85d32ca513769a74f97f7e1a7bad6c9407f0d934c2aa645ef9cf613c7
height: 0
timestamp: 19/12/2018 22:32:30 +00:00

Get Account

Retrieve any account from Flow network's latest block or from a specified block height.

📖 Account address is a unique account identifier. Be mindful about the 0x prefix, you should use the prefix as a default representation but be careful and safely handle user inputs without the prefix.

An account includes the following data:

• Address: the account address.
• Balance: balance of the account.
• Contracts: list of contracts deployed to the account.
• Keys: list of keys associated with the account.

Examples

Example depicts ways to get an account at the latest block and at a specific block height:

private async Task Demo()
{
    // get account from the latest block
    var address = new FlowAddress("f8d6e0586b0a20c7");
    var account = await FlowClient.GetAccountAtLatestBlockAsync(address.Address);
    PrintResult(account);

    // get account from the block by height 0
    account = await FlowClient.GetAccountAtBlockHeightAsync(address.Address, 0);
    PrintResult(account);
}

private void PrintResult(FlowAccount flowAccount)
{
    Console.WriteLine($"Address: {flowAccount.Address.Address}");
    Console.WriteLine($"Balance: {flowAccount.Balance}");
    Console.WriteLine($"Contracts: {flowAccount.Contracts.Count}");
    Console.WriteLine($"Keys: {flowAccount.Keys.Count}\n");
}

Example output:

Address: f8d6e0586b0a20c7
Balance: 999999999999700000
Contracts: 2
Keys: 1

Address: f8d6e0586b0a20c7
Balance: 999999999999700000
Contracts: 2
Keys: 1

Get Transactions

Retrieve transactions from the network by providing a transaction ID. After a transaction has been submitted, you can also get the transaction result to check the status.

📖 Transaction ID is a hash of the encoded transaction payload and can be calculated before submitting the transaction to the network.

⚠️ The transaction ID provided must be from the current spork.

📖 Transaction status represents the state of transaction in the blockchain. Status can change until is finalized.

Status	Final	Description
UNKNOWN	❌	The transaction has not yet been seen by the network
PENDING	❌	The transaction has not yet been included in a block
FINALIZED	❌	The transaction has been included in a block
EXECUTED	❌	The transaction has been executed but the result has not yet been sealed
SEALED	✅	The transaction has been executed and the result is sealed in a block
EXPIRED	✅	The transaction reference block is outdated before being executed

private async Task Demo(string transactionId)
{
    var tx = await FlowClient.GetTransactionAsync(transactionId);
    PrintTransaction(tx);

    var txr = await FlowClient.GetTransactionResultAsync(transactionId);
    PrintTransactionResult(txr);
}

private void PrintTransaction(FlowTransactionBase tx)
{
    Console.WriteLine($"ReferenceBlockId: {tx.ReferenceBlockId}");
    Console.WriteLine($"Payer: {tx.Payer.Address}");
    Console.WriteLine("Authorizers: [{0}]", string.Join(", ", tx.Authorizers.Select(s => s.Address).ToArray()));
    Console.WriteLine($"Proposer: {tx.ProposalKey.Address.Address}");
}

private void PrintTransactionResult(FlowTransactionResult txr)
{
    Console.WriteLine($"Status: {txr.Status}");
    Console.WriteLine($"Error: {txr.ErrorMessage}\n");
}

Example output:

ReferenceBlockId: a31c341a905dcfd16d8c0be0ebec389222572ff6dd2957bd944f55ee80c4dca9
Payer: f8d6e0586b0a20c7
Authorizers: []
Proposer: f8d6e0586b0a20c7
Status: Sealed
Error:

Get Events

Retrieve events by a given type in a specified block height range or through a list of block IDs.

📖 Event type is a string that follow a standard format:

A.{contract address}.{contract name}.{event name}

Please read more about events in the documentation. The exception to this standard are core events, and you should read more about them in this document.

📖 Block height range expresses the height of the start and end block in the chain.

Examples

Example depicts ways to get events within block range or by block IDs:

private async Task Demo(FlowAccount flowAccount, ByteString flowTransactionId)
{
    // Query for account creation events by type
    var eventsForHeightRange = await FlowClient.GetEventsForHeightRangeAsync("flow.AccountCreated", 0, 100);
    PrintEvents(eventsForHeightRange);

    // Query for our custom event by type
    var customType = $"A.{flowAccount.Address.HexValue}.EventDemo.Add";
    var customEventsForHeightRange = await FlowClient.GetEventsForHeightRangeAsync(customType, 0, 100);
    PrintEvents(customEventsForHeightRange);

    // Get events directly from transaction result
    var txResult = await FlowClient.GetTransactionResultAsync(flowTransactionId);
    PrintEvent(txResult.Events);
}

private void PrintEvents(IEnumerable<FlowBlockEvent> flowBlockEvents)
{
    foreach(var blockEvent in flowBlockEvents)
        PrintEvent(blockEvent.Events);
}

private void PrintEvent(IEnumerable<FlowEvent> flowEvents)
{
    foreach(var @event in flowEvents)
    {
        Console.WriteLine($"Type: {@event.Type}");
        Console.WriteLine($"Values: {@event.Payload.Encode()}");
        Console.WriteLine($"Transaction ID: {@event.TransactionId.FromByteStringToHex()} \n");
    }
}

Example output:

Type: flow.AccountCreated
Values: {"type":"Event","value":{"id":"flow.AccountCreated","fields":[{"name":"address","value":{"type":"Address","value":"0x01cf0e2f2f715450"}}]}}
Transaction ID: 6edf928c88717fdaefe0849e014d7d4f7931471cdb6ae9329f992d4751844099

Type: A.01cf0e2f2f715450.EventDemo.Add
Values: {"type":"Event","value":{"id":"A.01cf0e2f2f715450.EventDemo.Add","fields":[{"name":"x","value":{"type":"Int","value":"2"}},{"name":"y","value":{"type":"Int","value":"3"}},{"name":"sum","value":{"type":"Int","value":"5"}}]}}
Transaction ID: 72ae51dbfcda12fdda9b97cf3e8df54980111c4b4bb7f0f86f9113420f21bece

Type: A.01cf0e2f2f715450.EventDemo.Add
Values: {"type":"Event","value":{"id":"A.01cf0e2f2f715450.EventDemo.Add","fields":[{"name":"x","value":{"type":"Int","value":"2"}},{"name":"y","value":{"type":"Int","value":"3"}},{"name":"sum","value":{"type":"Int","value":"5"}}]}}
Transaction ID: 72ae51dbfcda12fdda9b97cf3e8df54980111c4b4bb7f0f86f9113420f21bece

Get Collections

Retrieve a batch of transactions that have been included in the same block, known as collections. Collections are used to improve consensus throughput by increasing the number of transactions per block and they act as a link between a block and a transaction.

📖 Collection ID is SHA3-256 hash of the collection payload.

private async Task Demo(FlowCollectionGuarantee flowCollectionGuarantee)
{
    // get collection by ID
    var collection = await FlowClient.GetCollectionByIdAsync(flowCollectionGuarantee.CollectionId);
    PrintCollection(collection);
}

private void PrintCollection(FlowCollectionResponse flowCollection)
{
    Console.WriteLine($"ID: {flowCollection.Id.FromByteStringToHex()}");
    Console.WriteLine("Transactions: [{0}]", string.Join(", ", flowCollection.TransactionIds.Select(s => s.FromByteStringToHex()).ToArray()));
}

Example output:

ID: 31a5c134b24fb556069575fa3acdfbdf6a0b4faf072df85c32ad476cba308468
Transactions: [6edf928c88717fdaefe0849e014d7d4f7931471cdb6ae9329f992d4751844099]

Execute Scripts

Scripts allow you to write arbitrary non-mutating Cadence code on the Flow blockchain and return data. You can learn more about Cadence and scripts here, but we are now only interested in executing the script code and getting back the data.

We can execute a script using the latest state of the Flow blockchain or we can choose to execute the script at a specific time in history defined by a block height or block ID.

📖 Block ID is SHA3-256 hash of the entire block payload, but you can get that value from the block response properties.

📖 Block height expresses the height of the block in the chain.

private async Task Demo()
{
    // simple script
    var script = @"
pub fun main(a: Int): Int {
    return a + 10
}";

    var arguments = new List<ICadence>
    {
        new CadenceNumber(CadenceNumberType.Int, "5")
    };

    var response = await FlowClient.ExecuteScriptAtLatestBlockAsync(
        new FlowScript
        {
            Script = script,
            Arguments = arguments
        });
    Console.WriteLine($"Value: {response.As<CadenceNumber>().Value}");

    // complex script
    var complexScript = @"
pub struct User {
    pub var balance: UFix64
    pub var address: Address
    pub var name: String

    init(name: String, address: Address, balance: UFix64) {
        self.name = name
        self.address = address
        self.balance = balance
    }
}
    pub fun main(name: String): User {
    return User(
        name: name,
        address: 0x1,
        balance: 10.0
    )
}";

    var complexArguments = new List<ICadence>
    {
        new CadenceString("Dete")
    };
    var complexResponse = await FlowClient.ExecuteScriptAtLatestBlockAsync(
        new FlowScript
        {
            Script = complexScript,
            Arguments = complexArguments
        });
    PrintComplexScript(complexResponse);
}

public class User
{
    public decimal Balance { get; set; }
    public string Address { get; set; }
    public string Name { get; set; }
}

private void PrintComplexScript(ICadence cadenceResponse)
{
    var user = new User
    {
        Name = cadenceResponse.As<CadenceComposite>().CompositeFieldAs<CadenceString>("name").Value,
        Address = cadenceResponse.As<CadenceComposite>().CompositeFieldAs<CadenceAddress>("address").Value,
        Balance = decimal.Parse(cadenceResponse.As<CadenceComposite>().CompositeFieldAs<CadenceNumber>("balance").Value)
    };

    Console.WriteLine($"Name: {user.Name}");
    Console.WriteLine($"Address: {user.Address}");
    Console.WriteLine($"Balance: {user.Balance}");
}

Example output:

Value: 15
Name: Dete
Address: 0000000000000001
Balance: 10.00000000

Mutate Flow Network

Flow, like most blockchains, allows anybody to submit a transaction that mutates the shared global chain state. A transaction is an object that holds a payload, which describes the state mutation, and one or more authorizations that permit the transaction to mutate the state owned by specific accounts.

Transaction data is composed and signed with help of the SDK. The signed payload of transaction then gets submitted to the access node API. If a transaction is invalid or the correct number of authorizing signatures are not provided, it gets rejected.

Executing a transaction requires couple of steps:

• Building a transaction.
• Signing a transaction.
• Sending a transaction.

Transactions

A transaction is nothing more than a signed set of data that includes script code which are instructions on how to mutate the network state and properties that define and limit it's execution. All these properties are explained bellow.

📖 Script field is the portion of the transaction that describes the state mutation logic. On Flow, transaction logic is written in Cadence. Here is an example transaction script:

transaction(greeting: String) {
  execute {
    log(greeting.concat(", World!"))
  }
}

📖 Arguments. A transaction can accept zero or more arguments that are passed into the Cadence script. The arguments on the transaction must match the number and order declared in the Cadence script. Sample script from above accepts a single String argument.

📖 Proposal key must be provided to act as a sequence number and prevent reply and other potential attacks.

Each account key maintains a separate transaction sequence counter; the key that lends its sequence number to a transaction is called the proposal key.

A proposal key contains three fields:

• Account address
• Key index
• Sequence number

A transaction is only valid if its declared sequence number matches the current on-chain sequence number for that key. The sequence number increments by one after the transaction is executed.

📖 Payer is the account that pays the fees for the transaction. A transaction must specify exactly one payer. The payer is only responsible for paying the network and gas fees; the transaction is not authorized to access resources or code stored in the payer account.

📖 Authorizers are accounts that authorize a transaction to read and mutate their resources. A transaction can specify zero or more authorizers, depending on how many accounts the transaction needs to access.

The number of authorizers on the transaction must match the number of AuthAccount parameters declared in the prepare statement of the Cadence script.

Example transaction with multiple authorizers:

transaction {
  prepare(authorizer1: AuthAccount, authorizer2: AuthAccount) { }
}

📖 Gas limit is the limit on the amount of computation a transaction requires, and it will abort if it exceeds its gas limit. Cadence uses metering to measure the number of operations per transaction. You can read more about it in the Cadence documentation.

The gas limit depends on the complexity of the transaction script. Until dedicated gas estimation tooling exists, it's best to use the emulator to test complex transactions and determine a safe limit.

📖 Reference block specifies an expiration window (measured in blocks) during which a transaction is considered valid by the network. A transaction will be rejected if it is submitted past its expiry block. Flow calculates transaction expiry using the reference block field on a transaction. A transaction expires after 600 blocks are committed on top of the reference block, which takes about 10 minutes at average Mainnet block rates.

Build Transactions

Building a transaction involves setting the required properties explained above and producing a transaction object.

Here we define a simple transaction script that will be used to execute on the network and serve as a good learning example.

transaction(greeting: String) {

  let guest: Address

  prepare(authorizer: AuthAccount) {
    self.guest = authorizer.address
  }

  execute {
    log(greeting.concat(",").concat(guest.toString()))
  }
}

private async Task Demo()
{
    // reading script from folder
    var script = Utilities.ReadCadenceScript("greeting");

    var proposerAddress = new FlowAddress("9a0766d93b6608b7");
    uint proposerKeyIndex = 3;

    var payerAddress = new FlowAddress("631e88ae7f1d7c20");
    var authorizerAddress = new FlowAddress("7aad92e5a0715d21");

    // Establish a connection with an access node
    var accessAPIHost = "";
    var flowClient = new FlowHttpClient(new HttpClient(), accessAPIHost);

    // Get the latest sealed block to use as a reference block
    var latestBlock = await flowClient.GetLatestBlockHeaderAsync();

    // Get the latest account info for this address
    var proposerAccount = await flowClient.GetAccountAtLatestBlockAsync(proposerAddress.Address);

    // Get the latest sequence number for this key
    var proposerKey = proposerAccount.Keys.FirstOrDefault(w => w.Index == proposerKeyIndex);
    var sequenceNumber = proposerKey.SequenceNumber;

    var tx = new FlowTransaction
    {
        Script = script,
        GasLimit = 100,
        ProposalKey = new FlowProposalKey
        {
            Address = proposerAddress,
            KeyId = proposerKeyIndex,
            SequenceNumber = sequenceNumber
        },
        Payer = payerAddress,
        ReferenceBlockId = latestBlock.Id
    };

    // Add authorizer
    tx.Authorizers.Add(authorizerAddress);

    // Add argument            
    tx.Arguments.Add(new CadenceString("Hello"));
}

After you have successfully built a transaction the next step in the process is to sign it.

Sign Transactions

Flow introduces new concepts that allow for more flexibility when creating and signing transactions. Before trying the examples below, we recommend that you read through the transaction signature documentation.

After you have successfully built a transaction the next step in the process is to sign it. Flow transactions have envelope and payload signatures, and you should learn about each in the signature documentation.

Quick example of building a transaction:

var proposerAccount = new FlowAccount();
var proposerKey = proposerAccount.Keys.FirstOrDefault(w => w.Index == 1);

var tx = new FlowTransaction
{
    Script = "transaction { execute { log(\"Hello, World!\") } }",
    GasLimit = 100,
    ProposalKey = new FlowProposalKey
    {
        Address = proposerAccount.Address,
        KeyId = proposerKey.Index,
        SequenceNumber = proposerKey.SequenceNumber
    },
    Payer = proposerAccount.Address
};

Signatures can be generated more securely using keys stored in a hardware device such as an HSM. The ISigner interface is intended to be flexible enough to support a variety of signer implementations and is not limited to in-memory implementations.

Simple signature example:

// construct a signer from your private key and configured signature/hash algorithms
var signer = Sdk.Core.Crypto.Ecdsa.Utilities.CreateSigner("privateKey", SignatureAlgo.ECDSA_P256, HashAlgo.SHA3_256);

FlowTransaction.AddEnvelopeSignature(tx, proposerAccount.Address, proposerKey.Index, signer);

Flow supports great flexibility when it comes to transaction signing, we can define multiple authorizers (multi-sig transactions) and have different payer account than proposer. We will explore advanced signing scenarios bellow.

Single party, single signature

• Proposer, payer and authorizer are the same account (0x01).
• Only the envelope must be signed.
• Proposal key must have full signing weight.

Account	Key ID	Weight
0x01	1	1.0

// generate key
var flowAccountKey = FlowAccountKey.GenerateRandomEcdsaKey(SignatureAlgo.ECDSA_P256, HashAlgo.SHA3_256);
// create account with key
var account1 = await CreateAccountAsync(new List<FlowAccountKey> { flowAccountKey });
// select key
var account1Key = account1.Keys.FirstOrDefault();

// get the latest sealed block to use as a reference block
var latestBlock = await FlowClient.GetLatestBlockAsync();

var tx = new FlowTransaction
{
    Script = "transaction {prepare(signer: AuthAccount) { log(signer.address) }}",
    GasLimit = 100,
    Payer = account1.Address,
    ProposalKey = new FlowProposalKey
    {
        Address = account1.Address,
        KeyId = account1Key.Index,
        SequenceNumber = account1Key.SequenceNumber
    },
    ReferenceBlockId = latestBlock.Header.Id,
};

// authorizers
tx.Authorizers.Add(account1.Address);

// account 1 signs the envelope with key 1
tx = FlowTransaction.AddEnvelopeSignature(tx, account1.Address, account1Key.Index, account1Key.Signer);

// send transaction
var txResponse = await FlowClient.SendTransactionAsync(tx);

Single party, multiple signatures

• Proposer, payer and authorizer are the same account (0x01).
• Only the envelope must be signed.
• Each key has weight 0.5, so two signatures are required.

Account	Key ID	Weight
0x01	1	0.5
0x01	2	0.5

// generate key 1 for account1
var flowAccountKey1 = FlowAccountKey.GenerateRandomEcdsaKey(SignatureAlgo.ECDSA_P256, HashAlgo.SHA3_256, 500);
// generate key 2 for account1
var flowAccountKey2 = FlowAccountKey.GenerateRandomEcdsaKey(SignatureAlgo.ECDSA_P256, HashAlgo.SHA3_256, 500);

// create account with keys
var account1 = await CreateAccountAsync(new List<FlowAccountKey> { flowAccountKey1, flowAccountKey2 });

// select keys
var account1Key1 = account1.Keys[0];
var account1Key2 = account1.Keys[1];

// get the latest sealed block to use as a reference block
var latestBlock = await FlowClient.GetLatestBlockAsync();

var tx = new FlowTransaction
{
    Script = "transaction {prepare(signer: AuthAccount) { log(signer.address) }}",
    GasLimit = 9999,
    Payer = account1.Address,
    ProposalKey = new FlowProposalKey
    {
        Address = account1.Address,
        KeyId = account1Key1.Index,
        SequenceNumber = account1Key1.SequenceNumber
    },
    ReferenceBlockId = latestBlock.Header.Id
};

// authorizers
tx.Authorizers.Add(account1.Address);

// account 1 signs the envelope with key 1
tx = FlowTransaction.AddEnvelopeSignature(tx, account1.Address, account1Key1.Index, account1Key1.Signer);

// account 1 signs the envelope with key 2
tx = FlowTransaction.AddEnvelopeSignature(tx, account1.Address, account1Key2.Index, account1Key2.Signer);

// send transaction
var txResponse = await FlowClient.SendTransactionAsync(tx);

Multiple parties

• Proposer and authorizer are the same account (0x01).
• Payer is a separate account (0x02).
• Account 0x01 signs the payload.
• Account 0x02 signs the envelope.
  • Account 0x02 must sign last since it is the payer.

Account	Key ID	Weight
0x01	1	1.0
0x02	3	1.0

// generate key for account1
var flowAccountKey1 = FlowAccountKey.GenerateRandomEcdsaKey(SignatureAlgo.ECDSA_P256, HashAlgo.SHA3_256);
// create account1
var account1 = await CreateAccountAsync(new List<FlowAccountKey> { flowAccountKey1 });
// select account1 key
var account1Key = account1.Keys.FirstOrDefault();

// generate key for account2
var flowAccountKey2 = FlowAccountKey.GenerateRandomEcdsaKey(SignatureAlgo.ECDSA_P256, HashAlgo.SHA3_256);
// create account2
var account2 = await CreateAccountAsync(new List<FlowAccountKey> { flowAccountKey2 });
// select account2 key
var account2Key = account2.Keys.FirstOrDefault();

// get the latest sealed block to use as a reference block
var latestBlock = await FlowClient.GetLatestBlockAsync();

var tx = new FlowTransaction
{
    Script = "transaction {prepare(signer: AuthAccount) { log(signer.address) }}",
    GasLimit = 9999,
    Payer = account2.Address,
    ProposalKey = new FlowProposalKey
    {
        Address = account1.Address,
        KeyId = account1Key.Index,
        SequenceNumber = account1Key.SequenceNumber
    },
    ReferenceBlockId = latestBlock.Header.Id,
};

// authorizers
tx.Authorizers.Add(account1.Address);

// account 1 signs the payload with key 1
tx = FlowTransaction.AddPayloadSignature(tx, account1.Address, account1Key.Index, account1Key.Signer);

// account 2 signs the envelope
tx = FlowTransaction.AddEnvelopeSignature(tx, account2.Address, account2Key.Index, account2Key.Signer);

// send transaction
var txResponse = await FlowClient.SendTransactionAsync(tx);

Multiple parties, two authorizers

• Proposer and authorizer are the same account (0x01).
• Payer is a separate account (0x02).
• Account 0x01 signs the payload.
• Account 0x02 signs the envelope.
  • Account 0x02 must sign last since it is the payer.
• Account 0x02 is also an authorizer to show how to include two AuthAccounts into an transaction

Account	Key ID	Weight
0x01	1	1.0
0x02	3	1.0

// generate key for account1
var flowAccountKey1 = FlowAccountKey.GenerateRandomEcdsaKey(SignatureAlgo.ECDSA_P256, HashAlgo.SHA3_256);
// create account1
var account1 = await CreateAccountAsync(new List<FlowAccountKey> { flowAccountKey1 });
// select account1 key
var account1Key = account1.Keys.FirstOrDefault();

// generate key for account2
var flowAccountKey2 = FlowAccountKey.GenerateRandomEcdsaKey(SignatureAlgo.ECDSA_P256, HashAlgo.SHA3_256);
// create account2
var account2 = await CreateAccountAsync(new List<FlowAccountKey> { flowAccountKey2 });
// select account2 key
var account2Key = account2.Keys.FirstOrDefault();

// get the latest sealed block to use as a reference block
var latestBlock = await FlowClient.GetLatestBlockAsync();

var tx = new FlowTransaction
{
    Script = @"
transaction { 
    prepare(signer1: AuthAccount, signer2: AuthAccount) { 
        log(signer1.address) 
        log(signer2.address)
    }
}",
    GasLimit = 9999,
    Payer = account2.Address,
    ProposalKey = new FlowProposalKey
    {
        Address = account1.Address,
        KeyId = account1Key.Index,
        SequenceNumber = account1Key.SequenceNumber
    },
    ReferenceBlockId = latestBlock.Header.Id
};

// authorizers
tx.Authorizers.Add(account1.Address);
tx.Authorizers.Add(account2.Address);

// account 1 signs the payload with key 1
tx = FlowTransaction.AddPayloadSignature(tx, account1.Address, account1Key.Index, account1Key.Signer);

// account 2 signs the envelope
tx = FlowTransaction.AddEnvelopeSignature(tx, account2.Address, account2Key.Index, account2Key.Signer);

// send transaction
var txResponse = await FlowClient.SendTransactionAsync(tx);

Multiple parties, multiple signatures

• Proposer and authorizer are the same account (0x01).
• Payer is a separate account (0x02).
• Account 0x01 signs the payload.
• Account 0x02 signs the envelope.
  • Account 0x02 must sign last since it is the payer.
• Both accounts must sign twice (once with each of their keys).

Account	Key ID	Weight
0x01	1	0.5
0x01	2	0.5
0x02	3	0.5
0x02	4	0.5

// generate key 1 for account1
var flowAccount1Key1 = FlowAccountKey.GenerateRandomEcdsaKey(SignatureAlgo.ECDSA_P256, HashAlgo.SHA2_256, 500);
// generate key 2 for account1
var flowAccount1Key2 = FlowAccountKey.GenerateRandomEcdsaKey(SignatureAlgo.ECDSA_P256, HashAlgo.SHA2_256, 500);
// create account1
var account1 = await CreateAccountAsync(new List<FlowAccountKey> { flowAccount1Key1, flowAccount1Key2 });

// generate key 1 for account2
var flowAccount2Key3 = FlowAccountKey.GenerateRandomEcdsaKey(SignatureAlgo.ECDSA_P256, HashAlgo.SHA3_256, 500);
// generate key 2 for account2
var flowAccount2Key4 = FlowAccountKey.GenerateRandomEcdsaKey(SignatureAlgo.ECDSA_P256, HashAlgo.SHA3_256, 500);
// create account2
var account2 = await CreateAccountAsync(new List<FlowAccountKey> { flowAccount2Key3, flowAccount2Key4 });

// get the latest sealed block to use as a reference block
var latestBlock = await FlowClient.GetLatestBlockAsync();

var tx = new FlowTransaction
{
    Script = "transaction {prepare(signer: AuthAccount) { log(signer.address) }}",
    GasLimit = 9999,
    Payer = account2.Address,
    ProposalKey = new FlowProposalKey
    {
        Address = account1.Address,
        KeyId = account1.Keys[0].Index,
        SequenceNumber = account1.Keys[0].SequenceNumber
    },
    ReferenceBlockId = latestBlock.Header.Id
};

// authorizers
tx.Authorizers.Add(account1.Address);

// account 1 signs the payload with key 1
tx = FlowTransaction.AddPayloadSignature(tx, account1.Address, account1.Keys[0].Index, account1.Keys[0].Signer);

// account 1 signs the payload with key 2
tx = FlowTransaction.AddPayloadSignature(tx, account1.Address, account1.Keys[1].Index, account1.Keys[1].Signer);

// account 2 signs the envelope with key 3
tx = FlowTransaction.AddEnvelopeSignature(tx, account2.Address, account2.Keys[0].Index, account2.Keys[0].Signer);

// account 2 signs the envelope with key 3
tx = FlowTransaction.AddEnvelopeSignature(tx, account2.Address, account2.Keys[1].Index, account2.Keys[1].Signer);

// send transaction
var txResponse = await FlowClient.SendTransactionAsync(tx);

Send Transactions

After a transaction has been built and signed, it can be sent to the Flow blockchain where it will be executed. If sending was successful you can then retrieve the transaction result.

// send transaction
var txResponse = await FlowClient.SendTransactionAsync(tx);

Create Accounts

On Flow, account creation happens inside a transaction. Because the network allows for a many-to-many relationship between public keys and accounts, it's not possible to derive a new account address from a public key offline.

The Flow VM uses a deterministic address generation algorithm to assigen account addresses on chain. You can find more details about address generation in the accounts & keys documentation.

Public Key

Flow uses ECDSA key pairs to control access to user accounts. Each key pair can be used in combination with the SHA2-256 or SHA3-256 hashing algorithms.

⚠️ You'll need to authorize at least one public key to control your new account.

Flow represents ECDSA public keys in raw form without additional metadata. Each key is a single byte slice containing a concatenation of its X and Y components in big-endian byte form.

A Flow account can contain zero (not possible to control) or more public keys, referred to as account keys. Read more about accounts in the documentation.

An account key contains the following data:

• Raw public key (described above)
• Signature algorithm
• Hash algorithm
• Weight (integer between 0-1000)

Account creation happens inside a transaction, which means that somebody must pay to submit that transaction to the network. We'll call this person the account creator. Make sure you have read sending a transaction section first.

// read flow.json
var config = Utilities.ReadConfig();
// get account from config
var accountConfig = config.Accounts["emulator-account"];
// get service account at latest block
var serviceAccount = await FlowClient.GetAccountAtLatestBlockAsync(accountConfig.Address);
// add a Signer with the serviceAccount and the accountConfig
serviceAccount = Utilities.AddSignerFromConfigAccount(accountConfig, serviceAccount);

// creator key to use
var serviceAccountKey = serviceAccount.Keys.FirstOrDefault();

// use template to create a transaction
var tx = AccountTemplates.CreateAccount(newFlowAccountKeys, serviceAccount.Address);

// set the transaction payer and proposal key
tx.Payer = serviceAccount.Address;
tx.ProposalKey = new FlowProposalKey
{
    Address = serviceAccount.Address,
    KeyId = serviceAccountKey.Index,
    SequenceNumber = serviceAccountKey.SequenceNumber
};

// get the latest sealed block to use as a reference block
var latestBlock = await FlowClient.GetLatestBlockAsync();
tx.ReferenceBlockId = latestBlock.Header.Id;

// sign and submit the transaction
tx = FlowTransaction.AddEnvelopeSignature(tx, serviceAccount.Address, serviceAccountKey.Index, serviceAccountKey.Signer);

var response = await FlowClient.SendTransactionAsync(tx);

After the account creation transaction has been submitted you can retrieve the new account address by getting the transaction result.

The new account address will be emitted in a system-level flow.AccountCreated event.

 var result = await GetTransactionResultAsync(transactionResponse.Id);

if (result.Status == TransactionStatus.Sealed)
{
    var newAccountAddress = sealedResponse.Events.AccountCreatedAddress();

    // get new account details
    var newAccount = await FlowClient.GetAccountAtLatestBlockAsync(newAccountAddress);
    newAccount.Keys = FlowAccountKey.UpdateFlowAccountKeys(newFlowAccountKeys, newAccount.Keys);
    return newAccount;
}

Generate Keys

Flow uses ECDSA signatures to control access to user accounts. Each key pair can be used in combination with the SHA2-256 or SHA3-256 hashing algorithms.

Here's how to generate an ECDSA private key for the P-256 (secp256r1) curve.

var newKeys = Sdk.Core.Crypto.Ecdsa.Utilities.GenerateKeyPair(SignatureAlgo.ECDSA_P256);
var publicKey = Sdk.Core.Crypto.Ecdsa.Utilities.DecodePublicKeyToHex(newKeys);
var privateKey = Sdk.Core.Crypto.Ecdsa.Utilities.DecodePrivateKeyToHex(newKeys);

The example above uses an ECDSA key pair on the P-256 (secp256r1) elliptic curve. Flow also supports the secp256k1 curve used by Bitcoin and Ethereum. Read more about supported algorithms here.