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feat: add MPF exclusion proofs with Aiken parity #150

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Merged
paolino merged 2 commits into from
Apr 23, 2026
Merged

feat: add MPF exclusion proofs with Aiken parity #150

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7c4f7cd
feat: add MPF exclusion proofs with property parity
paolino Apr 23, 2026
bd05ee6
fix: match upstream Aiken fork-prefix encoding
paolino Apr 23, 2026
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2 changes: 2 additions & 0 deletions lib/mpf-write/MPF.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ module MPF

-- * Re-exports from Proof
, module MPF.Proof.Insertion
, module MPF.Proof.Exclusion

-- * Re-exports from Backend
, module MPF.Backend.Standalone
Expand All @@ -32,4 +33,5 @@ import MPF.Hashes.Aiken
import MPF.Hashes.CBOR
import MPF.Insertion
import MPF.Interface
import MPF.Proof.Exclusion
import MPF.Proof.Insertion
29 changes: 23 additions & 6 deletions lib/mpf-write/MPF/Hashes/Aiken.hs
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Expand Up @@ -125,7 +125,8 @@ encodeBranch branchJump (HexDigit pos) siblingHashes =
-- | Encode a Fork step.
--
-- @skip@ = length of the fork's branch jump prefix.
-- Inner Neighbor: nibble (int), prefix (packed nibbles), root (32 bytes).
-- Inner Neighbor: nibble (int), prefix (one byte per nibble),
-- root (32 bytes).
encodeFork
:: HexKey -> HexDigit -> HexKey -> MPFHash -> Builder.Builder
encodeFork branchJump (HexDigit nibble) neighborPrefix neighborRoot =
Expand All @@ -135,11 +136,20 @@ encodeFork branchJump (HexDigit nibble) neighborPrefix neighborRoot =
<> cborTag 121
<> listBegin
<> cborUInt (fromIntegral nibble)
<> cborBytes (packHexKey neighborPrefix)
<> cborBytes (encodeNibblePrefix neighborPrefix)
<> cborBytes (renderMPFHash neighborRoot)
<> cborBreak
<> cborBreak

-- | Encode a fork prefix as one byte per nibble.
--
-- This matches the upstream JS/Aiken codec, where a prefix
-- like @[1,2]@ becomes bytes @01 02@ rather than a single
-- packed byte @12@.
encodeNibblePrefix :: HexKey -> ByteString
encodeNibblePrefix =
B.pack . map (\(HexDigit d) -> d)

-- | Encode a Leaf step.
--
-- @skip@ = length of the leaf's branch jump prefix.
Expand Down Expand Up @@ -305,9 +315,15 @@ unpackFullKeyPath = concatMap byteToNibbles . B.unpack
, HexDigit (b `mod` 16)
]

-- | Unpack nibble-packed prefix to HexKey
unpackNibblePrefix :: ByteString -> HexKey
unpackNibblePrefix = unpackFullKeyPath
-- | Unpack a fork prefix encoded as one byte per nibble.
unpackNibblePrefix :: ByteString -> Maybe HexKey
unpackNibblePrefix =
mapM toNibble . B.unpack
where
toNibble :: Word8 -> Maybe HexDigit
toNibble w
| w < 16 = Just (HexDigit w)
| otherwise = Nothing

-- | Parse a Branch step (after tag 121 and list begin)
parseBranchStep :: Parser (MPFProofStep MPFHash)
Expand Down Expand Up @@ -357,12 +373,13 @@ parseForkStep bs = do
(rootBS, bs6) <- parseCBORBytes bs5
((), bs7) <- parseBreak bs6
((), bs8) <- parseBreak bs7
neighborPrefix <- unpackNibblePrefix prefixBS
let branchJump = replicate skip (HexDigit 0)
Just
( ProofStepFork
{ psfBranchJump = branchJump
, psfOurPosition = HexDigit 0
, psfNeighborPrefix = unpackNibblePrefix prefixBS
, psfNeighborPrefix = neighborPrefix
, psfNeighborIndex = HexDigit (fromIntegral nibble)
, psfMerkleRoot = MPFHash rootBS
}
Expand Down
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