Certora: verify ERC4626 round-trip properties - #465
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Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01CfzVWCYX7Nrnu4P6h4EuP9
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Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01CfzVWCYX7Nrnu4P6h4EuP9
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Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01CfzVWCYX7Nrnu4P6h4EuP9
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01CfzVWCYX7Nrnu4P6h4EuP9
The intermediate lemma proving OZ's real Math.mulDiv matches the basic floor/ceil cvlMulDiv summary does not discharge. The prover returns fast counterexamples (not timeouts) for every rounding mode, in both an exact mathint-division form and a tight two-sided multiplicative-bounds form. Witness (floor, assert (res+1)*d > x*y): x=0xb6db..6dc (~8.27e76), y=7, d=6, returned res=0 on a non-reverting path -- true floor is ~9.65e76. Witness (ceil, assert res*d >= x*y): x=2^255+2, y=4, d=3, returned res=1 -- true ceil is ~7.7e76. The returned values are unrelated to floor/ceil(x*y/d): the prover over-approximates Math.mulDiv's 512-bit mulmod + Newton-Raphson modular-inverse bytecode and admits arbitrary small results. With mulDiv un-summarized there is no ghost to constrain, so no lemma fixes this. Reverting to keep PR green; the Math.mulDiv => cvlMulDiv summary in ERC4626.spec remains an assumption. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01CfzVWCYX7Nrnu4P6h4EuP9
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Looks good to me.
The mulDiv summary is ignoring reverts and uses require_uint256. This is only sound because we don't check for reverts in the rules.
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Requested by Mathis GD · Slack thread
Adds a Certora spec covering the last unchecked item in the formal verification wish list: the ERC4626 round-trip properties (the a16z
erc4626-testsERC4626.prop.solL244-318) hold — no deposit→redeem, mint→withdraw, or reverse round trip lets a user extract more than they put in.certora/specs/ERC4626.specproves the eight a16z round-trip inequalities (each rule named for its counterpart) plus two conversion lemmas. It proves them at fixed vault totals via thepreview/convertpath: the Morpho-Blue-dependenttotalAssetsfee accrual is summarized to arbitrary-but-fixed totals (a sound over-approximation) so the proof isolates exactly the rounding-direction correctness these properties test, without the supply-accounting cost that timed out #419.Math.mulDivis summarized to exact mathint floor/ceil semantics for SMT tractability. A matchingcertora/confs/ERC4626.confand the CI matrix entry are included.Generated by Claude Code