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feat(spv): anchor header trust to hardcoded mainnet checkpoints

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ChainProfiles.Mainnet.Checkpoints was an empty array with a "populate
before release" TODO, and even BlockHeaderInfo.MatchesCheckpoint()/
IsValidChild() — the methods meant to enforce it — were never called
anywhere in WalletSynchronizer. So on this LWMA chain, where PoW can't
be recomputed client-side (SkipPowValidation), a malicious or
eclipsing server could hand back any internally-consistent 80-byte
header for a Merkle proof: nothing tied it to the real Palladium
chain.

Populated Mainnet.Checkpoints with 24 real [height, hash, bits]
checkpoints (every 20,000 blocks + one near tip), pulled via RPC from
a fully-synced palladiumd. Testnet/Regtest are left empty (no node
available to verify against, and WalletSynchronizer already treats a
missing checkpoint as a no-op, so this is safe, just unanchored).

Added WalletSynchronizer.AnchorToCheckpointAsync: for every header
used in a Merkle proof, downloads the intervening headers back to the
nearest checkpoint at or below that height and verifies an unbroken
prev-hash chain terminating in the checkpoint's exact hash, finally
wiring up the previously-dead MatchesCheckpoint/IsValidChild. Verified
ranges are memoized in-memory per sync session to avoid re-walking.

Updated SECURITY.md and USERGUIDE.md to describe what is actually
enforced now (previously the guide deliberately avoided promising
checkpoint anchoring, since the array was empty).
This commit is contained in:
Davide Grilli
2026-07-07 15:12:09 +02:00
parent 69be42aba0
commit e349a80ddc
5 changed files with 206 additions and 11 deletions
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SECURITY.md
+1 -1
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@@ -21,7 +21,7 @@ It does **not** protect against:
This wallet is an SPV client, not a full node. It validates:
- Block headers (proof of work checked up to the last checkpoint; `SkipPowValidation` is enabled because LWMA difficulty cannot be recomputed client-side — trust is anchored to hardcoded checkpoints in `Core/Chain/ChainProfiles.cs`)
- Block headers: `SkipPowValidation` is enabled because LWMA difficulty cannot be recomputed client-side, so proof of work is never checked. Instead, every header used for a Merkle proof is hash-chain-linked (prev-hash) back to the nearest hardcoded checkpoint at or below its height, and that checkpoint's hash must match exactly (`Core/Chain/ChainProfiles.cs`, enforced in `Core/Spv/WalletSynchronizer.AnchorToCheckpointAsync`). Currently populated for mainnet only (every 20,000 blocks); testnet/regtest have no checkpoints yet, so headers there are trusted at face value
- Transaction inclusion in a confirmed block (Merkle branch proof, mandatory for every confirmed transaction — see `Core/Spv/MerkleProof.cs`)
It does **not** validate: