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Specify a retrospective soft fork implemented in zcashd v2.1.1-1 that limits the nTime field 

of a block relative to its median-time-past.
Correct the definition of median-time-past for the first PoWMedianBlockSpan blocks in a chain.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>
This commit is contained in:
Daira Hopwood 2020-02-06 22:40:00 +00:00
parent ed6baf0fef
commit 0d582758dd
1 changed files with 20 additions and 3 deletions
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23
protocol/protocol.tex
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@ -873,6 +873,7 @@ electronic commerce and payment, financial privacy, proof of work, zero knowledg
\newcommand{\activationHeight}{\term{activation block height}} \newcommand{\activationHeight}{\term{activation block height}}
\newcommand{\activationHeights}{\terms{activation block height}} \newcommand{\activationHeights}{\terms{activation block height}}
\newcommand{\genesisBlock}{\term{genesis block}} \newcommand{\genesisBlock}{\term{genesis block}}
\newcommand{\medianTimePast}{\term{median-time-past}}
\newcommand{\transaction}{\term{transaction}} \newcommand{\transaction}{\term{transaction}}
\newcommand{\transactions}{\terms{transaction}} \newcommand{\transactions}{\terms{transaction}}
\newcommand{\Transaction}{\titleterm{Transaction}} \newcommand{\Transaction}{\titleterm{Transaction}}
@ -9032,6 +9033,11 @@ the consensus protocol.
Let $\ThresholdBits$ be as defined in \crossref{diffadjustment}, and let $\PoWMedianBlockSpan$ Let $\ThresholdBits$ be as defined in \crossref{diffadjustment}, and let $\PoWMedianBlockSpan$
be the constant defined in \crossref{constants}. be the constant defined in \crossref{constants}.
\defining{Define the \medianTimePast of a \block to be the median (as defined in \crossref{diffadjustment})
of the $\nTimeField$ fields of the \emph{preceding} $\PoWMedianBlockSpan$ \blocks (or all
preceding \blocks if there are fewer than $\PoWMedianBlockSpan$). The \medianTimePast of a
\genesisBlock is not defined.}
\vspace{2ex} \vspace{2ex}
\begin{consensusrules} \begin{consensusrules}
\item The \blockVersionNumber{} \MUST be greater than or equal to $4$. \item The \blockVersionNumber{} \MUST be greater than or equal to $4$.
@ -9039,8 +9045,11 @@ be the constant defined in \crossref{constants}.
$\ThresholdBits(\BlockHeight)$. $\ThresholdBits(\BlockHeight)$.
\item The \block{} \MUST pass the difficulty filter defined in \crossref{difficulty}. \item The \block{} \MUST pass the difficulty filter defined in \crossref{difficulty}.
\item $\solution$ \MUST represent a \validEquihashSolution as defined in \crossref{equihash}. \item $\solution$ \MUST represent a \validEquihashSolution as defined in \crossref{equihash}.
\item $\nTimeField$ \MUST be strictly greater than the median time of the previous \item For each \block other than the \genesisBlock, $\nTimeField$ \MUST be strictly greater
$\PoWMedianBlockSpan$ \blocks. than the \medianTimePast of that \block.
\item For each \block at \blockHeight $2$ or greater on the production network, or \blockHeight
$653606$ or greater on the test network, $\nTimeField$ \MUST be less than or equal to
the \medianTimePast of that \block plus $90 \mult 60$ seconds.
\item The size of a \block{} \MUST be less than or equal to $2000000$ bytes. \item The size of a \block{} \MUST be less than or equal to $2000000$ bytes.
\saplingonwarditem{$\hashFinalSaplingRoot$ \MUST be $\LEBStoOSPOf{256}{\rt}$ where \saplingonwarditem{$\hashFinalSaplingRoot$ \MUST be $\LEBStoOSPOf{256}{\rt}$ where
$\rt$ is the \merkleRoot of the \Sapling{} \noteCommitmentTree for the final $\rt$ is the \merkleRoot of the \Sapling{} \noteCommitmentTree for the final
@ -9078,6 +9087,10 @@ rejected by this rule at a given point in time may later be accepted.
the median of the timestamps of the past $\PoWMedianBlockSpan$ \blocks. The the median of the timestamps of the past $\PoWMedianBlockSpan$ \blocks. The
Bitcoin Developer Reference \cite{Bitcoin-Block} was previously in error on this point, Bitcoin Developer Reference \cite{Bitcoin-Block} was previously in error on this point,
but has now been corrected. but has now been corrected.
\item The rule limiting $\nTimeField$ to be no later than $90 \mult 60$ seconds after the
\medianTimePast is a retrospective consensus change, applied as a soft fork in
\zcashd v2.1.1-1. It had not been violated by any \block from the given \blockHeights
in the consensus \blockchains of either the production or test networks.
\overwinter{ \overwinter{
\item There are no changes to the \blockVersionNumber or format for \Overwinter. \item There are no changes to the \blockVersionNumber or format for \Overwinter.
} }
@ -10251,6 +10264,10 @@ Peter Newell's illustration of the Jubjub bird, from \cite{Carroll1902}.
\historyentry{2020.1.0}{2020-02-06} \historyentry{2020.1.0}{2020-02-06}
\begin{itemize} \begin{itemize}
\item Specify a retrospective soft fork implemented in \zcashd v2.1.1-1 that
limits the $\nTimeField$ field of a \block relative to its \medianTimePast.
\item Correct the definition of \medianTimePast for the first $\PoWMedianBlockSpan$
\blocks in a \blockchain.
\item Add acknowledgements to Henry de Valence, Deirdre Connolly, Chelsea Komlo, \item Add acknowledgements to Henry de Valence, Deirdre Connolly, Chelsea Komlo,
and Zancas Wilcox. and Zancas Wilcox.
\item Add an acknowledgement to Trail of Bits for their security audit. \item Add an acknowledgement to Trail of Bits for their security audit.
@ -13165,7 +13182,7 @@ the cost of batched verification is therefore
\listtheorems{theorem,lemma} \listtheorems{theorem,lemma}
} }
\needspace{30ex}
\phantompart{Index}{index} \phantompart{Index}{index}
\begin{flushleft} \begin{flushleft}