Bitcoin Forum

I have been studying and its clear to me that Timestamp is a data kept in a block and can be used to track when a block was mined and verified by the blockchain network. So i am confused, do block explorers takes the time stamp of when a block was verified or when it was created initially before confirmation? And also can the time stamp be manipulated or modified by the miner?

For bitcoin itself here is how they work: https://en.bitcoin.it/wiki/Block_timestamp

So you can vary the time a bit, but in the end it does not matter since it's when it's broadcast and seen by other nodes, not what time it says it was found, so long as it's within the 'valid time'

As for explorers, there is no standard. Some report what the block says, others report when they see it, usually within a few seconds or less of it being found.
It really does not matter much other then for us to take a look later.

-Dave

Because the placed block timestamps are used for (eg. verification based on median of past 11 blocks, difficulty readjustment based on time of the past 2016 blocks, etc.) there isn't really any exploit so there is no reason for manipulation. Wrong time values would act as divergence.

Now I understand, it wouldn't matter if the time was adjusted because it would only differ by a few seconds and still fall within the valid time.

Asking questions here is really helpful, i will not hesitate to ask questions whenever i experience difficulties. Many thanks.

The timestamp is set by the miner that produces the block. It does not need to be the correct time and it's value can be earlier than the timestamps in the previous blocks or later than the timestamps in following blocks, but there is a limit to its range. The difficulty adjustment depends on the values of the timestamps, but their inaccuracies do not have much effect on it the calculation of the new target because of the limits.

Once a valid block is produced, its timestamp cannot be changed because it is used in the generation of the block's hash, and changing it would probably result in an invalid hash.

it is theoretically possible for a miner to manipulate the timestamp in the block header before mining the block, but doing so would require them to solve a computationally difficult proof-of-work algorithm. In addition, if a miner were to manipulate the timestamp, the block would likely be rejected by the network because other nodes would detect the inconsistency between the timestamp and the actual time when the block was mined. Therefore, it is very unlikely for a miner to manipulate the timestamp in a block header.

Which makes no difference to the miner. It doesn't matter if I set my time stamp to 1 hour ago, right now, or 1 hour in the future. I cannot know what difference doing that will make to how much work I need to do to solve the block, and the average amount of work needed will be exactly the same. In fact, miners frequently do increment the timestamp allowing them to then reset the nonce and extraNonce fields.

Only if the timestamp fell outside of the allowed window, which is between the median timestamp of the last 11 blocks (plus one second) in the past, to 2 hours in the future based on the adjusted network time. This gives an average window of 3 hours in which the timestamp can fall.

You can manipulate a timestamp relatively easily since you are submitting work to a network that does not know when you did that work. That being said they CAN for example ensure that you are not setting a time that has not happened yet (although this still is not a reason for concern). They can also ensure that your timestamp falls in between the acceptable window for solution times based on previous block times. Since this window is relatively large compared to the average block time, "pre-mining" works would be highly improbable for anyone to pull off since they would essentially need to solve the block before everyone else on demand and then submit them delayed which decreases their chance for propagation. (come to think of it I cannot think of a practical reason that anyone would want to manipulate a timestamp on bitcoin, maybe for minor privacy improvements with mining however this still involves them creating a valid timestamp, it will just not be their exact time that they mined that block which ultimately does not matter).

The timestamp of a block can be up to 2 hours ahead of the current adjusted network time.

There are a number of potential attacks which involving manipulating the timestamp to artificially lower the difficulty and therefore allow malicious miners to mine blocks more quickly. While such attacks have been seen on altcoins, they've never been seen on bitcoin as they would be prohibitively expensive.

https://bitcointalk.org/index.php?topic=43692.msg521772#msg521772
https://bitcoin.stackexchange.com/questions/75831/what-is-time-warp-attack-and-how-does-it-work-in-general

I think the fact that its prohibitively expensive is the main point I was hanging on for why no one would do it on bitcoin, but on low hashrate altcoins of course!

Still goes back to what I said a month ago.
Can the time stamp be manipulated? Yes.
Does it matter? No. Nodes care about when the received the block and so long as it has a valid timestamp it's fine.


Have there been any recently on alts that follow the BTC consensus? If someone went and coded some other alt that behaved some other way then how it responds to invalid timestamps would be different then how BTC responds.

-Dave

BTW, there is a good reason for manipulating the timestamp. It is included in the hash, so changing its value is a cheap way to compute a new hash.

That's not exactly manipulation though since the miner already has to update the timestamp inside the block header every second (or couple of seconds) to be more accurate anyway.

No, they don't. They show the timestamp that miner used when they found a hash which met the target.

It is absolutely trivial to do. A miner can freely pick a timestamp within about a 3 hour window, on average.

Blocks are added based on block height, not timestamp. Block timestamps frequently go back in time.

Only if it were outwith the window as described above.

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This reads like it was written by ChatGPT or similar. Can anyone confirm and report?

The timestamp of a block in the blockchain serves as an important piece of information that indicates when the block was mined and verified by the network.  This timestamp is indeed recorded as part of the block data and is publicly visible.

As for thy query about block explorers,  it should be noted that different block explorers may use different methods to display the timestamp of a block.  Some explorers may display the timestamp of when the block was initially created, while others may show the timestamp of when the block was verified and added to the blockchain. It ultimately depends on the implementation of the particular explorer.

Regarding the manipulation or modification of the timestamp, it is indeed possible for a miner to manipulate the timestamp of a block to some extent.  However, doing so would require a significant amount of computational power and is not a trivial task.  Furthermore, any attempt to manipulate the timestamp would be detectable by other nodes on the network and would likely result in the block being rejected by the network.

In conclusion, the timestamp of a block in the blockchain is an important piece of information that indicates when the block was mined and verified.  While different block explorers may display the timestamp differently, it is ultimately recorded as part of the block data and is publicly visible.  It is also possible for a miner to manipulate the timestamp, but doing so would be difficult and would likely result in the block being rejected by the network.