It looked at first to me like the normative unwrapping approach Greg mentioned would be the best solution, but would that still be breaking timelocked transactions? A change to how timestamp values map to real time across the 2106 boundary, for transactions spanning the transition? Henry On Mon, Dec 15, 2025, 14:30 Josh Doman wrote: > > your idea is to have the header nTime used for difficulty adjustment > enforced in the coinbase tx. > > Correct. As written, BIP54 makes that soft fork impossible, leaving a hard > fork as the only option to resolve nTime overflow. > > > I was about to write this email myself, but then I realized that since > BIP 113, timelocks are based on MTP time, and any soft-fork mechanism that > messes with MTP time will destroy existing transaction's timelock semantics. > > Yes, it's unfortunate. There is certainly a tradeoff. On the one hand, > there is a risk of coin confiscation, if the soft fork isn't signaled early > enough (a few decades in advance is probably sufficient). On the other > hand, there are material benefits to avoiding a hard fork (i.e. you get a > smooth and secure upgrade path, developers can write immutable programs > that verify the chain, etc). > > I think it's presumptive to assume which option a future generation would > prefer, in the year 2070, 2080, 2090, 2100, etc, given the tradeoffs > involved. I'm not suggesting we decide today, but I am suggesting that > BIP54 may be unnecessarily restrictive. > > The following modification to BIP54 would resolve the timewarp attack > while leaving open the possibility of an nTime soft fork: > 1) Add a u64 timestamp to the coinbase and enforce BIP54 there (in > addition to other timestamp rules) > 2) Given a block of height N, where N % 2016 = 2015, the difference > between the nTime and the nTime at height (N - 2015) must be the same as in > the coinbase. > > On Monday, December 15, 2025 at 11:36:31 AM UTC-5 Russell O'Connor wrote: > > I was about to write this email myself, but then I realized that since BIP > 113, timelocks are based on MTP time, and any soft-fork mechanism that > messes with MTP time will destroy existing transaction's timelock > semantics. Now I think the best is to have a hardfork. > > On Sun, Dec 14, 2025 at 3:33 PM Josh Doman wrote: > > *TLDR:* The "timewarp attack" could enable a future soft fork that fixes > the timestamp overflow bug. > > I saw there is a discussion about a hard fork to handle the timestamp > overflow bug, by migrating from u32 to u64 timestamps.[1] I considered > making this post in that thread, but as it has more to do with the Great > Consensus Cleanup [2], I thought it better to make this its own post. > > My question is: *does BIP54 inadvertently preclude the possibility of a > soft fork to handle timestamp overflow?* > > Conceptually, I think you could implement a soft fork that resolves the > timestamp overflow bug, by using the "timewarp attack" [3] to intentionally > minimize the timestamp and reduce the legacy difficulty, while > simultaneously using a u64 timestamp in the coinbase transaction to enforce > the real difficulty target. > > In short, the "timewarp attack" makes it possible to increment the u32 > timestamp by 1 second each block, ensuring the chain will practically never > halt (provided the soft fork is adopted sufficiently in advance). > > Formally, given a block of height N and a timestamp T at activation height > H: > - if N % 2016 < 2015: miners set the legacy timestamp to T + (N - H). > - if N % 2016 = 2015, miners set the legacy timestamp to min(2^32 - 1, > timestamp in the coinbase transaction). > - nodes require that the block hash meets the difficulty target determined > in the coinbase (in addition to the artificially low legacy difficulty > target). > > This solution, of course, doesn't work if the Great Consensus Cleanup is > adopted and the "timewarp attack" gets fixed. Also, it will make header and > SPV validation more complex, as nodes will need the coinbase transaction > and a merkle proof in order to validate the header chain. Perhaps worst of > all, it could confiscate coins that are locked to a timestamp, rather than > a block height. > > The upside is that this is a soft fork, rather than a hard fork, which has > its own advantages. Meanwhile, confiscation concerns could potentially be > mitigated by signaling activation several decades in advance. > > Is the possibility of a soft fork worth forgoing the timewarp fix? I'm not > sure. A compromise could be to expire the timewarp fix after a certain > block height, but that introduces a new set of tradeoffs. > > Josh > > [1] https://groups.google.com/g/bitcoindev/c/PHZEIRb04RY > [2] https://github.com/bitcoin/bips/blob/master/bip-0054.md > [3] > https://bitcoin.stackexchange.com/questions/75831/what-is-time-warp-attack-and-how-does-it-work-in-general/75834#75834 > > -- > > You received this message because you are subscribed to the Google Groups > "Bitcoin Development Mailing List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to bitcoindev+...@googlegroups.com. > To view this discussion visit > https://groups.google.com/d/msgid/bitcoindev/2ac708f3-8e73-4cd5-ba62-be64a2acea04n%40googlegroups.com > > . > > -- > You received this message because you are subscribed to the Google Groups > "Bitcoin Development Mailing List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to bitcoindev+unsubscribe@googlegroups.com. > To view this discussion visit > https://groups.google.com/d/msgid/bitcoindev/e7a70843-a304-4d04-9365-08b8b4259caen%40googlegroups.com > > . > -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. 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