Sending transactions in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a transaction in blockchain?

A transaction is a record of value transfer between two parties on the blockchain. It usually involves sending cryptocurrency or data from one address to another.

beginner

What information is typically required to send a transaction?

You need the sender's address, recipient's address, amount to send, and a digital signature to prove ownership of the sender's funds.

intermediate

Why do transactions require a digital signature?

A digital signature proves that the sender owns the funds and authorizes the transaction. It prevents others from spending your cryptocurrency without permission.

intermediate

What is a nonce in a blockchain transaction?

A nonce is a number used once to keep transactions unique and prevent replay attacks. It usually counts how many transactions the sender has made.

beginner

What happens after you send a transaction to the blockchain network?

The transaction is broadcast to nodes, verified, and then included in a block by miners or validators. Once confirmed, the transaction is permanent and visible on the blockchain.

What is the main purpose of a digital signature in a blockchain transaction?

A To hide the sender's address

B To encrypt the transaction data

C To speed up the transaction

D To prove ownership and authorize the transaction

A digital signature proves that the sender owns the funds and authorizes the transaction.

Which of the following is NOT typically part of a blockchain transaction?

A Sender's address

B Sender's private key

C Amount to send

D Recipient's address

The sender's private key is used to create the digital signature but is never included in the transaction itself.

What does the nonce in a transaction help prevent?

A Replay attacks

B Network congestion

C Transaction fees

D Double spending

The nonce keeps transactions unique and prevents replay attacks.

After sending a transaction, what is the next step before it is confirmed?

A It is automatically confirmed

B It is deleted from the sender's wallet

C It is broadcast to the network nodes

D It is encrypted

The transaction is broadcast to nodes for verification and inclusion in a block.

What does it mean when a transaction is confirmed on the blockchain?

A It is permanently recorded and visible on the blockchain

B It is waiting to be signed

C It is still in the sender's wallet

D It has been canceled

Confirmation means the transaction is included in a block and permanently recorded.

Explain the steps involved in sending a transaction on a blockchain network.

Think about what happens from making the transaction to it being recorded.

Why is a nonce important in blockchain transactions and how does it work?

Consider how the blockchain avoids duplicate or repeated transactions.

Practice

1.

What is the main purpose of sending a transaction on a blockchain?

easy

A. To create a new blockchain network

B. To mine new blocks

C. To move value or data from one account to another

D. To delete data from the blockchain

Solution

1. Step 1: Understand what a transaction does

   A transaction moves value or data between accounts on the blockchain.

2. Step 2: Compare options to the definition

   Only To move value or data from one account to another correctly describes sending a transaction.

3. Final Answer:

   To move value or data from one account to another -> Option C

4. Quick Check:

   Transaction purpose = move value/data [OK]

Hint: Transactions move value or data, not create or delete [OK]

Common Mistakes:

• Confusing transactions with mining
• Thinking transactions create blockchains
• Believing transactions delete blockchain data

2.

Which of the following is the correct way to sign a transaction before sending it?

transaction.sign(____)

easy

A. sender's public key

B. sender's private key

C. receiver's private key

D. network's public key

Solution

1. Step 1: Identify the key needed for signing

   Transactions must be signed with the sender's private key to prove ownership.

2. Step 2: Match the correct key to the method

   Only the sender's private key can sign the transaction securely.

3. Final Answer:

   sender's private key -> Option B

4. Quick Check:

   Sign with private key = sender's private key [OK]

Hint: Sign with sender's private key, never public key [OK]

Common Mistakes:

• Using public key to sign
• Using receiver's key instead of sender's
• Confusing private and public keys

3.

Consider this code snippet sending a transaction:

tx = {
  'to': '0xabc123',
  'value': 10,
  'nonce': 5,
  'gas': 21000
}
signed_tx = sign_transaction(tx, private_key)
result = send_transaction(signed_tx)
print(result)

What will print(result) most likely output if the nonce is incorrect?

medium

A. 'Nonce too low or too high error'

B. 'Transaction successful'

C. 'Gas limit exceeded error'

D. 'Invalid signature error'

Solution

1. Step 1: Understand nonce role in transactions

   Nonce must be correct and sequential to avoid replay or duplication errors.

2. Step 2: Identify error caused by wrong nonce

   An incorrect nonce causes a 'Nonce too low or too high' error during sending.

3. Final Answer:

   'Nonce too low or too high error' -> Option A

4. Quick Check:

   Wrong nonce = nonce error [OK]

Hint: Wrong nonce causes nonce error, not gas or signature errors [OK]

Common Mistakes:

• Confusing nonce error with gas error
• Assuming signature error for nonce issues
• Expecting success despite wrong nonce

4.

Given this code snippet, what is the main error preventing the transaction from sending?

tx = {
  'to': '0xdef456',
  'value': 5,
  'nonce': 3
}
signed_tx = sign_transaction(tx, private_key)
result = send_transaction(signed_tx)
print(result)

Options:

medium

A. Receiver address is invalid

B. Incorrect private key used for signing

C. Nonce value is too high

D. Missing gas field in the transaction

Solution

1. Step 1: Check required transaction fields

   Gas is required to pay for transaction processing; missing gas causes failure.

2. Step 2: Verify other fields and keys

   Nonce and receiver address look valid; no info about wrong private key.

3. Final Answer:

   Missing gas field in the transaction -> Option D

4. Quick Check:

   Missing gas = transaction fails [OK]

Hint: Always include gas field to avoid transaction failure [OK]

Common Mistakes:

• Ignoring gas field requirement
• Assuming nonce or address is wrong without evidence
• Not checking transaction structure

5.

You want to send multiple transactions quickly from the same account. Which approach ensures all transactions are accepted without nonce conflicts?

1. Use the same nonce for all transactions
2. Increment nonce by 1 for each transaction
3. Use random nonce values
4. Skip nonce and rely on network

hard

A. Increment nonce by 1 for each transaction

B. Skip nonce and rely on network

C. Use random nonce values

D. Use the same nonce for all transactions

Solution

1. Step 1: Understand nonce role in multiple transactions

   Nonce must be unique and sequential per account to avoid conflicts.

2. Step 2: Identify correct nonce handling method

   Incrementing nonce by 1 for each transaction ensures proper ordering and acceptance.

3. Final Answer:

   Increment nonce by 1 for each transaction -> Option A

4. Quick Check:

   Sequential nonce = no conflicts [OK]

Hint: Always increment nonce by 1 for each new transaction [OK]

Common Mistakes:

• Reusing same nonce causing rejection
• Using random nonce causing errors
• Assuming network assigns nonce automatically