Blockchain Replay Attack Detection: Learn

Term DefinitionBlockchainA decentralized distributed ledger technology used to record transaction data. Replay AttackA network attack in which an attacker intercepts and repeatedly sends valid data packets in an attempt to trick the recipient into repeating an action. TimestampAn electronic mark that records the time when an event occurred, used to prove the order in which events occurred. Validation RangeA preset time window that limits the validity of a transaction timestamp to prevent replay of old transactions. Transaction IDA string used to uniquely identify a transaction, such as a hash of transaction information. ID DatabaseA database that stores verified transaction IDs, used to detect duplicate transactions. Consensus ValidationThe process of reaching agreement between nodes in a blockchain network to confirm the validity of transactions. Genesis BlockThe first block in a blockchain that contains basic information and rules about the blockchain. Account/Balance ModelA blockchain transaction model that tracks the balance of each account and executes transactions based on the account balance. Account NonceA mechanism used in the account/balance model to prevent replay attacks, where each account has a unique nonce that identifies the order of transactions.

Short Answer Questions

What is a replay attack and how does it affect blockchain?

A replay attack is when an attacker intercepts and repeatedly sends valid data packets in an attempt to trick the recipient into repeating an operation. In a blockchain, an attacker can replay previous transaction information, such as a transfer transaction, in an attempt to withdraw funds multiple times.

How does the traditional account/balance model try to prevent replay attacks? What are its limitations?

The traditional account/balance model uses an account random number mechanism to prevent replay attacks, and each transaction is attached with an increasing random number. However, this mechanism requires the user terminal to communicate with the blockchain node to obtain the random number, which increases the communication burden. In addition, if the transaction order is disrupted, the account random number mechanism may fail, causing the transaction to fail.

How does the replay attack detection method described in the learning guide work?

The method combines timestamp verification and transaction identification verification to detect replay attacks. First, a timestamp is attached to each transaction. The blockchain node checks the validity of the timestamp based on a preset verification range. Then, the blockchain node generates a hash value of the transaction information as a transaction identification and compares it with the record in the identification database to determine whether the transaction is repeated.

What is the verification range and what role does it play in replay attack detection?

The verification range is a preset time window that limits the validity of transaction timestamps, such as within two hours from the latest block timestamp. By limiting the time range, blockchain nodes do not need to search the entire blockchain to detect replay attacks, which improves detection efficiency and reduces storage requirements.

Describe two different methods for adding timestamps to transactions.

The transaction initiator (e.g., a user terminal) can add a timestamp when submitting a transaction.

The blockchain node that receives an unconfirmed transaction can add a timestamp when receiving the transaction.

Why is using an identity database more efficient than searching the entire blockchain?

Searching the entire blockchain requires reading a large amount of data from the hard disk, which is inefficient and costly. The identity database only stores transaction identities within a recent period of time, which can be quickly queried from the cache, improving detection efficiency.

When verifying transactions, what is the order of timestamp verification and transaction identity verification?

Timestamp verification and transaction identity verification can be performed in any order without affecting the results.

Describe the key differences between method 400 and method 450.

After verifying the transaction timestamp, method 400 checks whether the transaction identity exists in the identity database. Method 450 directly checks whether the transaction identifier exists in the identifier database included in the verification range.

In addition to the Ethereum system, what other blockchain systems can the replay attack detection method be applied to?

The method can be applied to various blockchain systems, such as PBFT system, HoneyBadger system and Hashgraph system.

What are the advantages of the replay attack detection method compared with the traditional account random number mechanism?

Reduce the communication cost between the user terminal and the blockchain node.

Allow valid transactions from the same account to be executed in any order without causing transaction failure.

Support multiple transactions from the same account to be executed concurrently in a short period of time.

Reduce the burden of consensus verification and improve transaction processing efficiency.

No need to synchronize the time between the user terminal and the blockchain node.