<p>Yes, Bitcoin can act as a time-stamping authority. However, depending on your application the accuracy of the Bitcoin blocks may not be sufficient.</p>

<p>Nodes only reject blocks that are greater than 2 hours into the future, and blocks created earlier than the median time of the past 11 blocks. Therefore, timestamps may be off by several hours.</p>

<p>also see: <a href="https://bitcoin.stackexchange.com/q/20479/5406">How accurate is Bitcoin network time?</a></p>

CC BY-SA 3.0
2016-01-02T11:59:26.887Z
2016-01-02T11:59:26.887Z
2017-04-13T12:47:33.660Z
Murch
<p>I don't think decentralized time-stamping authority does Bitcoin full justice, but yes blocks are timestamped and yes there is consensus on actual time. Albeit within a few hours margin. That even means that sometimes the timestamp on a newer block is further in the past than the timestamp of an older block.</p>

CC BY-SA 3.0
2015-12-30T15:55:31.353Z
"_Albeit within a few hours margin._" So, using the blockchain for priority disputes (putting a hash in a block with, e.g., [Proof of Existence](https://proofofexistence.com/)) could still occur if they get into the same block. "_sometimes the timestamp on a newer block is further in the past than the timestamp of an older block._" When has that happened?
Geremia
CC BY-SA 3.0
2015-12-30T16:52:34.900Z
In the same block yes. I guess that's a reason why the blockchain makes more sense as a money application: a Bitcoin can only be spent once whether it's in the same block or not. Such a Proof of Existence hash is not limited like that.  Time warps happen all the time: http://bitcoin.stackexchange.com/questions/3743/how-can-an-earlier-block-have-a-later-timestamp
Jannes
CC BY-SA 3.0
2015-12-30T23:11:13.143Z
@Geremia - it happens a ton! I was just looking at the last several weeks of block header data, there are a couple hundred blocks where timestamps are out of order - but only by a couple minutes, usually.
David Manheim
CC BY-SA 3.0
2015-12-31T01:12:33.707Z
@DavidManheim If that's true, then what's the point of timestamping blocks (besides it acting as another sort of nonce)?
Geremia
CC BY-SA 3.0
2015-12-31T05:33:02.467Z
@geremia just friends on how accurate your timestamps need to be. Watches are often not accurate to the second either, does that make them completely useless? Besides often you're only interested in the ordering, not the exact timestamp. Bitcoin itself only depends on the timestamps when doing the 2-weekly difficulty readjustment: it needs to correlate actual time with the number of blocks. At that scale the timestamps are accurate enough.
Jannes
CC BY-SA 3.0
2015-12-30T09:28:32.677Z
2015-12-30T09:28:32.677Z
Jannes
<p>Can Bitcoin/blockchain be thought of as a decentralized <a href="https://en.wikipedia.org/wiki/Trusted_timestamping" rel="noreferrer">time-stamping authority (TSA)</a>? Is there true consensus in the Bitcoin network on a mined block's time, or just that the block was mined?</p>

<network><timestamp><decentralization><consensus>
Is Bitcoin a decentralized time-stamping authority?
Geremia
# Is Bitcoin a decentralized time-stamping authority?

(Asked by: username_0 on 2015-12-30)

Can Bitcoin/blockchain be thought of as a decentralized [time-stamping authority (TSA)](https://en.wikipedia.org/wiki/Trusted_timestamping)? Is there true consensus in the Bitcoin network on a mined block's time, or just that the block was mined?

**Tags:** network, timestamp, decentralization, consensus


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## 2 answers

### Answer by username_1 on 2016-01-02. Score: 3 | Accepted answer

Yes, Bitcoin can act as a time-stamping authority. However, depending on your application the accuracy of the Bitcoin blocks may not be sufficient.

Nodes only reject blocks that are greater than 2 hours into the future, and blocks created earlier than the median time of the past 11 blocks. Therefore, timestamps may be off by several hours.

also see: [How accurate is Bitcoin network time?](https://bitcoin.stackexchange.com/q/20479/5406)


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### Answer by username_2 on 2015-12-30. Score: 1

I don't think decentralized time-stamping authority does Bitcoin full justice, but yes blocks are timestamped and yes there is consensus on actual time. Albeit within a few hours margin. That even means that sometimes the timestamp on a newer block is further in the past than the timestamp of an older block.

> **Comments:**
> **username_0**: "_Albeit within a few hours margin._" So, using the blockchain for priority disputes (putting a hash in a block with, e.g., [Proof of Existence](https://proofofexistence.com/)) could still occur if they get into the same block. "_sometimes the timestamp on a newer block is further in the past than the timestamp of an older block._" When has that happened?  
> **username_2**: In the same block yes. I guess that's a reason why the blockchain makes more sense as a money application: a Bitcoin can only be spent once whether it's in the same block or not. Such a Proof of Existence hash is not limited like that.  Time warps happen all the time: http://bitcoin.stackexchange.com/questions/3743/how-can-an-earlier-block-have-a-later-timestamp  
> **username_3**: @username_0 - it happens a ton! I was just looking at the last several weeks of block header data, there are a couple hundred blocks where timestamps are out of order - but only by a couple minutes, usually.  
> **username_0**: @username_3 If that's true, then what's the point of timestamping blocks (besides it acting as another sort of nonce)?  
> **username_2**: @username_0 just friends on how accurate your timestamps need to be. Watches are often not accurate to the second either, does that make them completely useless? Besides often you're only interested in the ordering, not the exact timestamp. Bitcoin itself only depends on the timestamps when doing the 2-weekly difficulty readjustment: it needs to correlate actual time with the number of blocks. At that scale the timestamps are accurate enough.  

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