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Restructured from flat .tex/.pdf files into per-paper subdirectories. Added Antje Worring as co-author on all papers. Synced PDFs to pdfs/ for download site.
80 lines
3.0 KiB
TeX
80 lines
3.0 KiB
TeX
\section{Architecture}
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\label{sec:architecture}
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\subsection{Anchor Lifecycle}
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\begin{enumerate}[nosep]
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\item \textbf{Compute}: Application computes SHA-256 Merkle root of
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serialized CRDT \texttt{DocumentSnapshot} every $N$ operations or
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$T$ seconds (configurable; default $N=1000$, $T=300$s).
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\item \textbf{Submit}: Application calls
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\texttt{anchor.Submit(appID, height, root)} which encodes a
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72-byte payload and sends an EVM transaction to the anchor
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precompile.
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\item \textbf{Finalize}: Transaction is included in a block and
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finalized by Quasar certificate (Q-Chain) or Snow consensus
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(C-Chain). The anchor is now immutable.
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\item \textbf{Verify}: Any party calls \texttt{anchor.Get(appID, height)}
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via \texttt{eth\_call}, recomputes the local Merkle root from their
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CRDT state, and compares.
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\end{enumerate}
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\subsection{Precompile Design}
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The anchor precompile is a stateful EVM precompile registered at address
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\texttt{0x0700\ldots10} (Privacy/Encryption page, C-Chain slot, item 0x10
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in the LP addressing scheme). It exposes four functions via ABI selector:
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\begin{center}
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\begin{tabular}{llr}
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\toprule
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\textbf{Function} & \textbf{Selector} & \textbf{Gas} \\
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\midrule
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\texttt{submit(bytes32,uint64,bytes32)} & \texttt{0x3c21e8a1} & 25,400 \\
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\texttt{get(bytes32,uint64)} & \texttt{0x8eaa6ac0} & 2,600 \\
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\texttt{getLatest(bytes32)} & \texttt{0xba41d847} & 2,600 \\
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\texttt{list(bytes32,uint64,uint64)} & \texttt{0x70fa9a4d} & 2,600 + 200/entry \\
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\bottomrule
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\end{tabular}
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\end{center}
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\subsubsection{Storage Layout}
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Each anchor occupies two EVM storage slots:
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\begin{itemize}[nosep]
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\item Slot $\texttt{keccak256}(\mathit{appID} \| h)$: the 32-byte root.
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\item Slot $\texttt{keccak256}(\mathit{appID} \| \texttt{``latest''})$:
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the highest submitted height for this appID (8 bytes, right-padded).
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\end{itemize}
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\noindent
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This gives $O(1)$ lookup per anchor and $O(1)$ latest-height query. The
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\texttt{list} function iterates heights $[h_{\text{from}}, h_{\text{to}})$,
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issuing one \texttt{SLOAD} per height.
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\subsubsection{Gas Cost Derivation}
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\begin{align*}
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\text{submit gas} &= G_{\text{base}} + 2 \times G_{\text{sstore\_new}} + G_{\text{keccak}} \\
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&= 400 + 2 \times 12{,}000 + 600 + 400 \\
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&= 25{,}400
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\end{align*}
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\noindent
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where $G_{\text{sstore\_new}} = 12{,}000$ for writing a new storage slot
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(after EIP-2929 warm access), $G_{\text{keccak}} = 600$ for the two hash
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computations, and $G_{\text{base}} = 400$ for ABI decoding and validation.
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A \texttt{get} call costs 2,600 (one warm \texttt{SLOAD}).
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\subsection{Height Monotonicity Invariant}
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The precompile enforces $h > h_{\text{latest}}$ for a given appID. Attempts
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to submit a height $\leq$ the current latest revert with
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\texttt{AnchorHeightNotMonotonic}. This prevents retroactive anchor
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forgery: once height 100 is anchored, no one can insert a different root
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at height 100 or below.
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% ============================================================================
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