ブロックチェーンと時間の問題

ブロックチェーンでの時間はどの位正確なのか?という質問をよくされる。
そして、実際の要件で時間が問題になることが多いので、簡単にまとめる。

概要

• 各ノードは時間に嘘をつける
• ビットコインなどのパブリックの実装では、ある程度の幅の範囲の時間でないといけない実装になっている

ざっくりしかまとめる時間がないので、そのまま公開

Bitcoin wiki

• Block timestamp – Bitcoin Wiki

A timestamp is accepted as valid if it is greater than the median timestamp of previous 11 blocks, and less than the network-adjusted time + 2 hours. “Network-adjusted time” is the median of the timestamps returned by all nodes connected to you.

QA: StackExchange

• Which is the reliability of a transaction timestamp? – Bitcoin Stack Exchange

• timestamp – How accurate is Bitcoin network time? – Bitcoin Stack Exchange

• The median time advertised by peers (if between ±70 minutes from system time)
• System time

So block timestamps are:

• < 2 hours from “network time”.
• > median of last 11 blocks.

• timestamp – How does Bitcoin figure out what time it is? – Bitcoin Stack Exchange

Reddit

• Satoshi did NOT introduce a transaction timestamp in bitcoin software : Bitcoin

• We need a standard for Bitcoin blockchain timestamps! Proposal Inside! Feedback please! : Bitcoin

Blog

• culubas: Timejacking & Bitcoin

Bitcoin Blockchain Timestamping Overview

List of timestamping services by using Bitcoin blockchain

https://docs.google.com/spreadsheets/d/1rTxK5sVsktBYkwFZH6TLWKN7FTBXDuN2G1ePED6Rscg/edit#gid=0

timejaking attack

• security – Was a timejacking attack ever performed? – Bitcoin Stack Exchange