feat: hash `AssetVaultKey` before insertion into asset vault SMT by partylikeits1983 · Pull Request #2912 · 0xMiden/protocol

partylikeits1983 · 2026-05-12T21:43:43Z

Summary

Closes #2518.

Two non-fungible assets issued by the same faucet share the third element of their raw AssetVaultKey (the faucet ID suffix), which the SMT uses to determine leaf membership. Without hashing, they always landed in the same leaf, risking the per-leaf cap and degrading tree balance.

This PR mirrors the existing raw-key/hashed-key pattern already used by StorageMap in this crate:

AssetVaultKey::to_smt_key() returns the Poseidon2 hash of the raw key. to_leaf_index is rerouted through it.
AssetVault and PartialVault now store the SMT keyed by hashed keys, plus a BTreeMap<AssetVaultKey, Word> of raw keys for iteration and proof reconstruction.
AssetWitness carries both the SmtProof and the raw key(s) it covers; new validates each (key, value) pair against the proof.
The MASM kernel adds a private hash_asset_key helper (exec.poseidon2::hash) and injects it before every smt::set / smt::get / smt::peek in asset_vault.masm (same pattern as hash_map_key in account.masm).
Host-side read_vault_asset / read_vault_asset_witnesses updated for the new layout.

A regression test (two_non_fungible_assets_from_same_faucet_use_different_leaves) covers the original bug end-to-end.

Targets mmagician-claude-setup to keep the diff clean. Will be retargeted to next and rebased once that branch lands.

bobbinth · 2026-05-13T01:53:53Z

This is something we need to do but it'll also complicate asset retrieval from the AccountStateForest in the node (same issues as we've faced with storage map values). cc @kkovaacs.

PhilippGackstatter

I looked at parts of the asset vault related changes and left some comments.

Two non-fungible assets issued by the same faucet share the third element of their raw AssetVaultKey (the faucet ID suffix), which the SMT uses to determine leaf membership. Without hashing, they always landed in the same leaf, risking the per-leaf cap and harming tree balance. Mirrors the existing raw-key/hashed-key pattern used by StorageMap: - AssetVaultKey::to_smt_key() returns Poseidon2 hash of the raw key. - AssetVault and PartialVault store the SMT keyed by hashed keys, plus a BTreeMap<AssetVaultKey, Word> of raw keys for iteration and proofs. - AssetWitness carries both the SmtProof and the raw key(s) it covers. - The MASM kernel injects exec.poseidon2::hash before every smt::set, smt::get, smt::peek in asset_vault.masm (same as hash_map_key in account.masm). Closes #2518.

- Make `PartialVault::add` atomic: extend `entries` only after SMT proof insertion succeeds, preserving the entries-subset-of-SMT invariant on error. - Filter zero-amount fungible assets out of `AssetVault::new`'s `entries` map so the map and the underlying SMT stay in sync (the SMT treats empty values as no-ops). - Correct the suffix/prefix wording: `LeafIndex<Word>` uses `value[3]`, which is the faucet ID prefix, not the suffix. Fixed in `vault_key.rs`, `vault/mod.rs` doc + test, and `docs/src/asset.md`. - Tighten `AssetWitness::new_unchecked`: document the proof-vs-pair precondition explicitly and `debug_assert!` it. - Add `PartialVault::with_witnesses` and `PartialVault::add` tests: happy-path (with round-trip serialization for `with_witnesses`) and root-mismatch failure paths (the `add` failure doubles as a regression test for the atomicity fix above).

- Rename `AssetVaultKey::to_smt_key` to `hash` and have it return a new `AssetVaultKeyHash` newtype (mirrors `StorageMapKey::hash` -> `StorageMapKeyHash`). Updates all call sites and the MASM `hash_asset_key` doc to point at `AssetVaultKey::hash`. - Restrict `AssetWitness::entries` to `pub(super)`; it is an internal helper used by `PartialVault` and not part of the public surface. - Rework `Deserializable for PartialVault` to use `read_many_iter` for `num_entries` (protects against unbounded length prefixes) and route through a new private `from_partial_smt_and_keys` constructor that performs the per-entry validation. Repurposes the previously-dead `PartialAssetVaultError::InvalidAssetInSmt` variant as `InvalidAssetForKey { key, value, source }`.

…masm Co-authored-by: Philipp Gackstatter <PhilippGackstatter@users.noreply.github.com>

…-vault-key-smt # Conflicts: # crates/miden-protocol/src/asset/vault/mod.rs # crates/miden-protocol/src/asset/vault/vault_key.rs # crates/miden-protocol/src/errors/mod.rs

Hashing the AssetVaultKey before the asset vault SMT set adds a fixed cost to the fee-removal smt::set in the epilogue, pushing the measured post-compute-fee cycle count (863) past the old estimate (858). Add a dedicated VAULT_KEY_HASH_CYCLES=50 constant (in epilogue.masm and the mirrored test) rather than inflating SMT_SET_ADDITIONAL_CYCLES, whose documented meaning is smt::set's worst-minus-best spread. The fee estimate stays a safe upper bound (608+250+50=908 > 863).

Fumuran

Looks good! For now I only (yet) reviewed the masm code, and left a few comments and questions

Fumuran · 2026-05-22T16:08:29Z

+# ASSET KEY HASHING
+#! Hashes the raw asset vault key into the key used by the asset vault SMT.
+#!
+#! See [`AssetVaultKey::to_smt_key`] in Rust for the rationale.
+#!
+#! Inputs:  [ASSET_KEY]
+#! Outputs: [HASHED_ASSET_KEY]
+proc hash_asset_key
+    exec.poseidon2::hash
+    # => [HASHED_ASSET_KEY]
+end
+


nit: I would move it to the bottom of the file, since it is kind of helper procedure

Fumuran · 2026-05-22T16:19:30Z

+    # hash the asset key before using it as the SMT key
+    swapw exec.hash_asset_key swapw
+    # => [MERGED_ASSET_VALUE, HASHED_ASSET_KEY, VAULT_ROOT, CUR_VAULT_VALUE, MERGED_ASSET_VALUE]
+


question: I wonder whether should we create a set_asset procedure to accompany the get_asset one, which would hash the provided key internally. It is fine as is, I just thought that it will be a bit more consistent and will save a bit of code: we are setting an asset at least four times in this module.

Fumuran · 2026-05-22T16:27:31Z

+# fee is undercharged. The most recently observed worst case is 863 cycles, leaving 45 cycles of
+# margin against this 908-cycle budget; the margin is empirical, so re-measure when the epilogue or
+# smt::set changes. The fee-removal smt::set cost cannot be inflated by an adversary: vault keys are
+# hashed before insertion (see AssetVaultKey::hash), so leaf indices are uniformly distributed and
+# entries cannot be concentrated into the fee asset's leaf without breaking the hash's collision
+# resistance. The multi-leaf smt::set worst case is not yet exercised (see test_fee.rs TODO).
+const ESTIMATED_AFTER_COMPUTE_FEE_CYCLES=NUM_POST_COMPUTE_FEE_CYCLES+SMT_SET_ADDITIONAL_CYCLES+VAULT_KEY_HASH_CYCLES


nit: probably we can slightly shorten this description?

yeah good catch :)

claude likes extremely long descriptions (they don't always make sense)

partylikeits1983 added a commit that referenced this pull request May 12, 2026

chore: add CHANGELOG entry for #2912

cbb11d4

partylikeits1983 changed the title ~~feat: hash AssetVaultKey before insertion into asset vault SMT~~ feat: hash AssetVaultKey before insertion into asset vault SMT May 12, 2026

partylikeits1983 mentioned this pull request May 12, 2026

chore: Claude-first setup #2783

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partylikeits1983 marked this pull request as ready for review May 13, 2026 03:39

Base automatically changed from mmagician-claude-setup to next May 13, 2026 05:43

PhilippGackstatter reviewed May 13, 2026

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partylikeits1983 requested review from Fumuran and mmagician May 13, 2026 14:50

partylikeits1983 added 2 commits May 13, 2026 11:10

chore: add CHANGELOG entry for #2912

b1486c8

partylikeits1983 added the pr-from-maintainers PRs that come from internal contributors or integration partners. They should be given priority label May 13, 2026

partylikeits1983 force-pushed the ajl-claude-hash-asset-vault-key-smt branch from cbb11d4 to 59521ea Compare May 13, 2026 18:43

claude and others added 3 commits May 13, 2026 14:56

Update crates/miden-protocol/asm/kernels/transaction/lib/asset_vault.…

10256cd

…masm Co-authored-by: Philipp Gackstatter <PhilippGackstatter@users.noreply.github.com>

Merge branch 'next' into ajl-claude-hash-asset-vault-key-smt

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partylikeits1983 self-assigned this May 21, 2026

claude and others added 3 commits May 21, 2026 16:18

Merge remote-tracking branch 'origin/next' into ajl-claude-hash-asset…

5b142c6

…-vault-key-smt # Conflicts: # crates/miden-protocol/src/asset/vault/mod.rs # crates/miden-protocol/src/asset/vault/vault_key.rs # crates/miden-protocol/src/errors/mod.rs

Merge branch 'next' into ajl-claude-hash-asset-vault-key-smt

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Fumuran reviewed May 22, 2026

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feat: hash `AssetVaultKey` before insertion into asset vault SMT#2912

feat: hash `AssetVaultKey` before insertion into asset vault SMT#2912
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partylikeits1983 commented May 12, 2026 •

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