Replay attack bitcoin

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We may be compensated when you click, sign up for, deposit, or spend on a given platform. Learn more. When a coin does a hard fork, two identical blockchains exist until changes to one of the chains is made. To avoid transaction replays transactions made on one chain being broadcast on the other , at least one chain must implement replay protection developers of one chain must change the format of transactions to make them unique.

After-all, the only difference between the two chains if nothing is changed by developers is that there are two copies of the chain and miners are committing transactions to each chain separately.

Addresses are the same, keys are the same, the format of transactions are the same, etcпїЅ and this leaves an opening for exploits. Replay attacks can result in lost funds due to both the original coin and the forked coin being sent to the same address.

Learn more about Teams. Ask Question. Asked 2 years, 4 months ago. Modified 2 years, 4 months ago. Viewed times. I have 30 BTC. So after transferring, I should have Ethereum solves it by having nonce field in each account.

Question 1 How does bitcoin solve this case without SegWit? Question 2 how does bitcoin solve this case with SegWit? Improve this question. Nika Kurashvili Nika Kurashvili 2 2 silver badges 6 6 bronze badges. Add a comment. Sorted by: Reset to default. Highest score default Date modified newest first Date created oldest first. Transactions destroy coins and create new coins. A new transaction attempting to spend a coin that has been destroyed is simply invalid. Improve this answer.

You could even create 2 TXs that double spend and send them to different peers. Different nodes would have conflicting TXs but only one would be mined. When nodes with the "wrong" TX see the block that confirms the "right" TX they evict the "wrong" TX from their mempools. This is a deeper implementation detail that I'm not entirely sure about.

I think the UTXO set is technically what is confirmed in blocks. Coins that are spent in the mempool only unconfirmed are tracked in memory in a different data structure, but either way the node considers a coin destroyed as part of the mempool-insertion process.

Well confirmed TXs don't go to the mempool because confirmed means it is in a block so if anything it is removed from the mempool. But absolutely only valid transactions are inserted into the mempool.

Like I said, the node assumes that every TX in the mempool can be confirmed in the next block this includes rules about relative locktime etc пїЅ pinhead. The on-disk UTXO set only contains the effect of confirmed transactions.

The result is that always, all mempoll transactions are consistent with the blockchain and eachother. Transaction validity does not depend on any state other than the UTXO set, so once validated they are known to be forever valid unless double spent.

I don't know the details about Ethereum, but I believe it has much weaker guarantees about mempool tx validity. Ethereum is off-topic for this forum and I can't help you. Show 14 more comments.

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According to the agreement above, SegWit implementation was to be followed up with a Bitcoin hard fork in November. This fork, called SegWit2x or Bitcoin2x, was supposed to take all the good stuff from the SegWit-improved Bitcoin blockchain and upgrade on it by increasing the block size to 2Mb. Replay attacks have been a regular occurrence, not just in crypto world, but in all sorts of internet-related communications for quite a while; now is as good a time as any to explain what those attacks are and how you can protect yourself from them.

In order to understand replay attacks, we first have to understand how bitcoin transactions work. They are similar to banking transactions. Bitcoin can be compared to a ledger, except its digital, decentralized and global; Bitcoin transactions are its bank checks. This ledger is stored online and anyone who wants to audit it can do so by downloading an entire copy of the blockchain. Individual transactions are visible to everyone and anyone can observe and verify them.

This ledger can be upgraded hard forked. A hard fork creates a new ledger while keeping all the legacy ledger data intact. Once a hard fork is created, the legacy network users have two options: to stay on the old ledger or move onto the new one. If everyone moves, the new ledger becomes global as the old one is pushed aside. If only a portion of users move, we get two ledgers, the legacy ledger and the forked ledger.

After the fork happens, new blocks will be found for each blockchain and the chains will start differing from one another. A replay attack occurs when a malicious player copies a stream of messages between two parties and replays the stream to one or more of the parties.

This problem is a common occurrence in blockchain transactions. You will now, post-split, own the same amount of resources on both ledgers, meaning that your balance in legacy coin stays the same while your balance in the new coin will be equal to your legacy holdings. This can potentially be a problem; if you send a transaction order through one ledger, a malicious player can theoretically intercept your hash function and use it to copy the transaction order and present it on the other ledger.

The person who duplicates your order presents the copy of your check on the other ledger is replaying the transaction, making you the victim of a replay attack. For example, if a user wants to spend two Bitcoin on the legacy ledger, a replay attack could cause an equal transaction of two Bitcoin on the forked ledger as well.

While replay attacks have happened in the past on the Bitcoin network, they were small scale and never really had any major effects.

Similar issues happened on the Ethereum network after it split into two separate ledgers, Ethereum and Ethereum Classic. As an individual user you need to be aware that your funds are vulnerable and that you need to take proper precautions to ensure they are protected. Many individual, user side based concepts have been put out in the ether and they can be used to protect your funds from a replay attack:.

Choosing a wallet that operates on both networks ensures that users can operate with the full value and capability of their currency.

Therefore, the best choice is to use a wallet that provides an easy-to-use platform and operates on both sides of the network. However, while these factors are important, the most important component of a digital wallet is its security standards пїЅ specifically regarding the replay attacks that often accompany hard forks like SegWit2x.

Services like BTC. Coinbase transactions that are created after the fork are different on each chain. Coinbase transactions are therefore not replayable on any other ledger. If you create a transaction that mixes with a non-replayable transaction, the new transaction will be non-replayable as well. Thus, mixing your transactions with Coinbase transactions makes them non-replayable and has an added bonus of making the transactions that mix with these already mixed transactions non-replayable as well.

If one of the blockchains has significantly more frequent blocks than the other, one can create two transactions: One with a nLocktime for the next block on the faster chain, and another that spends at least one of the inputs from the first transaction with a very high fee. First, you broadcast the transaction with the nLocktime which will hopefully get included in the next block on the fast chain. Once it is confirmed, the doublespend is broadcast with a very high fee to the slower chain, hoping that it will get confirmed before the height of the nLocktime of the first transaction is reached.

After waiting some more confirmations for safety, the outputs of these two transactions can now be used to create transactions specific to only one chain. Create a pair of transactions with different recipient addresses that you own that spend the same funds.

Broadcast both at the same time and hope that one gets confirmed on one chain at the same time that the other gets confirmed on the second.

If unsuccessful, repeat. It is possible that miners on the ledger blockchain are mining transactions with different fees than on the fork, so you can broadcast a low-fee version of your transaction on the low-fee chain, wait for it to confirm, and then broadcast a higher-fee version on the high-fee chain. A good blockchain that hopes to achieve commercial adoption needs to have its own built-in mechanisms which will protect the network from replay attacks.

Replay protection is fairly easy to implement but it requires a hard fork of the original blockchain. Therefore, a quality fork needs to implement a form of replay protection, and there are a couple of those out there as well.

One of the best techniques to avert replay attacks is to use strong digital signatures with timestamps. Another technique that could be used is to create random session keys which are time bound and process bound.

A one-time password for each request also helps in preventing replay attacks and is frequently used in banking operations. Other techniques used against replay attacks include sequencing of messages and non-acceptance of duplicated messages.

Thus, any node now auditing Bitcoin will automatically reject a Bitcoin Cash check since the check has that special mark. Anyone auditing Bitcoin Cash will reject a Bitcoin check since the check is missing the special mark.

This special mark is called replay protection since it prevents replay attacks. The developers behind Segwit2x are refusing to add replay protection. Unfortunately, most replay protection schemes are hard forks.

Because hard forks are not backwards compatible and not everyone will upgrade, this will cause two different ledgers. So, if Bitcoin Core added replay protection in the short time span for the Segwit2x hard fork 3 months , this would most likely create three different ledgers: Segwit2x, Bitcoin with Replay and Bitcoin Legacy.

And that is not even counting Bitcoin Cash. This refusal by Bitcoin Core is consistent with the refusal to hard fork to Segwit2x. If Bitcoin Core developers were comfortable with a hard fork in the 3-month timeline, making a hard fork similar to Segwit2x would have made more sense.

Instead, since many Bitcoin Core developers feel that 3 months is too short to prepare for a hard fork, replay protection on Bitcoin Core is a non-starter. If you are a Bitcoin user and you want to protect yourself from replay attacks after the 2x hard fork, you will want to disentangle your accounts on the two different ledgers: Bitcoin Core and Segwit2x.

One way users can clearly separate their accounts is by mixing coins. You may think that no such transactions exist, but there is at least one category of transactions that are not replayable. Coinbase transactions, or the reward that miners get, that are created after the fork will certainly be different on both chains. Coinbase transactions are therefore not replayable on the other ledger. If you create a transaction that mixes with any non-replayable transaction, the result is another non-replayable transaction.

Thus, any transactions mixing with Coinbase transactions will themselves be non-replayable and the transactions that mix with the Coinbase-mixed transactions are also non-replayable. Mixing in this way, many transactions will be non-replayable and will propagate throughout the system.

Exchanges and merchants may want to set up a mixing service to make transacting on both chains easier. Though this may seem scary, but given the experiences with Bitcoin Cash, this may not be so terrible after all. Want to get curated Technical Bitcoin News? Sign up for the Bitcoin Tech Talk newsletter!

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