Why security prevents financial loss in Blockchain / Solidity - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a transaction is valid before processing.

Blockchain / Solidity

if transaction.[1]():
    process(transaction)

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Asign

Bis_valid

Csend

Dexecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using methods that perform actions instead of checking validity.

The is_valid() method checks if the transaction meets all security rules before processing.

2fill in blank

medium

Complete the code to verify the digital signature of a transaction.

Blockchain / Solidity

if verify_signature(transaction.[1], public_key):
    approve(transaction)

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Ahash

Bamount

Ctimestamp

Dsignature

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to verify the hash or amount instead of the signature.

The signature is used to verify that the transaction was authorized by the owner.

3fill in blank

hard

Fix the error in the code that prevents unauthorized spending.

Blockchain / Solidity

if balance >= transaction.[1]:
    deduct(balance, transaction.amount)

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Aamount

Bfee

Csignature

Dtimestamp

Attempts:

3 left

💡 Hint

Common Mistakes

Checking fee or signature instead of the amount.

The code must check if the balance is enough for the amount to prevent overspending.

4fill in blank

hard

Fill both blanks to create a secure transaction record with hash and timestamp.

Blockchain / Solidity

transaction_record = {
    'hash': [1],
    'timestamp': [2]
}

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Acompute_hash(transaction)

Bget_time()

Ccurrent_time()

Dtransaction_data

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong functions for hash or timestamp.

The compute_hash(transaction) creates a unique fingerprint, and current_time() records when it happened.

5fill in blank

hard

Fill all three blanks to filter and store only secure transactions.

Blockchain / Solidity

secure_transactions = {
    [1]: [2] for [3] in transactions
    if verify_signature([3], public_key)
}

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Atx_id

Btx_data

Ctx

Dtransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing variable names or using wrong keys and values.

We use tx_id as the key, tx_data as the value, and loop over each tx in transactions.