Multi-signature wallet concept in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Multi-signature wallet concept

Create Wallet with M-of-N Signatures

↓

Transaction Proposal Created

↓

Signers Review Transaction

↓

Signer 1

↓

Collect Signatures

↓

Check if Signatures >= M

↓

Execute Transaction

↓

Complete

The wallet requires multiple signatures (M out of N) to approve a transaction before it executes.

Execution Sample

Blockchain / Solidity

// Pseudocode for M-of-N multisig wallet
wallet = createWallet(signers=[A,B,C], required=2)
transaction = wallet.proposeTransaction(to='Bob', amount=10)
transaction.sign(A)
transaction.sign(B)
if transaction.signaturesCount() >= wallet.required:
    transaction.execute()

This code shows creating a wallet needing 2 of 3 signatures, proposing a transaction, collecting signatures, and executing if enough signatures are collected.

Execution Table

Step	Action	Signatures Collected	Condition (signatures >= required)	Result
1	Create wallet with 3 signers, 2 required	0	0 >= 2? No	Wallet ready
2	Propose transaction to Bob	0	0 >= 2? No	Transaction created
3	Signer A signs	1	1 >= 2? No	Waiting for more signatures
4	Signer B signs	2	2 >= 2? Yes	Transaction executed
5	Transaction complete	2	2 >= 2? Yes	Funds sent to Bob

💡 Transaction executes when collected signatures reach required threshold (2).

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
signatures_collected	0	1	2	2
transaction_status	pending	pending	executed	executed

Key Moments - 3 Insights

Why doesn't the transaction execute after the first signature?

Because the wallet requires 2 signatures (M=2), and after step 3 only 1 signature is collected, so the condition signatures >= required is false (see execution_table row 3).

What happens if a signer tries to sign twice?

The wallet counts unique signatures only, so signing twice doesn't increase signatures_collected beyond the unique count, preventing premature execution.

Can the transaction execute if fewer than required signatures are collected?

No, the condition signatures >= required must be true to execute (see execution_table step 4). Otherwise, the transaction waits.

Visual Quiz - 3 Questions

Look at the execution table, how many signatures are collected after step 3?

A 1

B 2

C 0

D 3

💡 Hint

Check the 'Signatures Collected' column at step 3 in the execution_table.

At which step does the transaction execute?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look for the first step where 'Result' is 'Transaction executed' in the execution_table.

If the required signatures changed to 3, what would happen at step 4?

A Transaction is canceled

B Transaction executes

C Transaction waits for more signatures

D Transaction executes partially

💡 Hint

Compare the 'Condition' column in execution_table for signatures >= required with required=3.

Concept Snapshot

Multi-signature wallet requires M of N signatures to approve.
Create wallet with signers and required count.
Propose transaction, collect signatures.
Execute only if signatures >= required.
Prevents single signer control.
Enhances security by shared approval.

Full Transcript

A multi-signature wallet is a special wallet that needs multiple people to agree before sending money. We create the wallet with a list of signers and how many must approve (M of N). When someone wants to send money, they create a transaction proposal. Each signer reviews and signs it. The wallet counts how many signatures it has. If the number of signatures is at least the required number, the transaction runs and sends the money. Otherwise, it waits for more signatures. This way, no single person can spend money alone, making it safer.

Practice

1. What is the main purpose of a multi-signature wallet in blockchain?

easy

A. To require multiple approvals before spending funds

B. To speed up transaction processing

C. To store private keys on a single device

D. To allow unlimited spending by one user

Solution

1. Step 1: Understand the multi-signature wallet concept

   A multi-signature wallet requires more than one person to approve a transaction before it can be executed.

2. Step 2: Identify the main purpose

   This setup protects funds by preventing a single user from spending money alone, increasing security.

3. Final Answer:

   To require multiple approvals before spending funds -> Option A

4. Quick Check:

   Multi-signature = multiple approvals [OK]

Hint: Multi-signature means multiple people must approve [OK]

Common Mistakes:

• Thinking it speeds up transactions
• Believing one user controls all funds
• Confusing it with single-key wallets

2. Which of the following is the correct way to define a multi-signature wallet threshold in Solidity?

easy

A. bool threshold = true;

B. uint8 threshold = '2';

C. string threshold = 2;

D. uint8 threshold = 1;

Solution

1. Step 1: Identify correct data type for threshold

   The threshold is a number representing how many signatures are needed, so an unsigned integer like uint8 is appropriate.

2. Step 2: Check syntax correctness

   Assigning a number directly to uint8 is correct. Using quotes or wrong types causes errors.

3. Final Answer:

   uint8 threshold = 1; -> Option D

4. Quick Check:

   Threshold is a number, use uint8 [OK]

Hint: Threshold is a number, use uint type without quotes [OK]

Common Mistakes:

• Using quotes around numbers
• Assigning string type to threshold
• Using boolean type for threshold

3. Given this Solidity snippet for a multi-signature wallet, what will be the value of isApproved after calling approveTransaction(1, msg.sender) if the threshold is 2 and only one approval is made?

mapping(uint => mapping(address => bool)) approvals;
uint8 threshold = 2;

function approveTransaction(uint txId, address approver) public {
  approvals[txId][approver] = true;
}

function isApproved(uint txId) public view returns (bool) {
  uint count = 0;
  for (uint i = 0; i < owners.length; i++) {
    if (approvals[txId][owners[i]]) {
      count++;
    }
  }
  return count >= threshold;
}

medium

A. true

B. false

C. Compilation error

D. Undefined behavior

Solution

1. Step 1: Understand approval counting logic

   The function counts how many owners approved the transaction and compares it to the threshold.

2. Step 2: Analyze given scenario

   Only one approval is made but threshold is 2, so count is 1 which is less than 2.

3. Final Answer:

   false -> Option B

4. Quick Check:

   Approvals < threshold = false [OK]

Hint: Approval count must meet threshold to be true [OK]

Common Mistakes:

• Assuming one approval is enough
• Ignoring threshold comparison
• Confusing approval mapping structure

4. Identify the bug in this Solidity function for approving transactions in a multi-signature wallet:

function approveTransaction(uint txId) public {
  approvals[txId][msg.sender] = true;
  if (isApproved(txId)) {
    executeTransaction(txId);
  }
}

function isApproved(uint txId) public view returns (bool) {
  uint count = 0;
  for (uint i = 0; i <= owners.length; i++) {
    if (approvals[txId][owners[i]]) {
      count++;
    }
  }
  return count >= threshold;
}

medium

A. Missing event emission after approval

B. approveTransaction should be external, not public

C. Loop condition should be < instead of <=

D. executeTransaction should not be called inside approveTransaction

Solution

1. Step 1: Check the for loop boundary

   The loop uses i <= owners.length, which causes out-of-bounds access because array indices go from 0 to length-1.

2. Step 2: Correct the loop condition

   Changing to i < owners.length prevents accessing invalid index and runtime errors.

3. Final Answer:

   Loop condition should be < instead of <= -> Option C

4. Quick Check:

   Array index out of bounds fixed by < [OK]

Hint: Array loops use < length, not <= length [OK]

Common Mistakes:

• Using <= in loops causing errors
• Ignoring array index limits
• Thinking event emission fixes logic bugs

5. You want to create a multi-signature wallet that requires 3 out of 5 owners to approve a transaction. Which approach correctly enforces this rule in Solidity?

mapping(uint => mapping(address => bool)) approvals;
address[5] owners;
uint8 threshold = 3;

function executeTransaction(uint txId) public {
  uint count = 0;
  for (uint i = 0; i < owners.length; i++) {
    if (approvals[txId][owners[i]]) {
      count++;
    }
  }
  if (count >= threshold) {
    // execute the transaction
  } else {
    revert("Not enough approvals");
  }
}

hard

A. This code correctly enforces the 3-of-5 approval rule

B. The threshold should be set to 5 to require all owners

C. The loop should iterate over approvals, not owners

D. Revert should be replaced with a simple return statement

Solution

1. Step 1: Analyze the approval counting logic

   The code counts how many owners approved the transaction by checking the approvals mapping for each owner.

2. Step 2: Check threshold enforcement

   If the count is at least the threshold (3), the transaction executes; otherwise, it reverts with an error.

3. Final Answer:

   This code correctly enforces the 3-of-5 approval rule -> Option A

4. Quick Check:

   Count approvals >= threshold = enforce rule [OK]

Hint: Count approvals, compare with threshold, revert if not met [OK]

Common Mistakes:

• Setting threshold incorrectly
• Looping over wrong data structure
• Using return instead of revert for errors