;; @contract stateless contract to verify bitcoin transaction
;; @version 5
;; version 5 adds support for txid generation and improves security
;; Error codes
(define-constant ERR-OUT-OF-BOUNDS u1)
(define-constant ERR-TOO-MANY-TXINS u2)
(define-constant ERR-TOO-MANY-TXOUTS u3)
(define-constant ERR-VARSLICE-TOO-LONG u4)
(define-constant ERR-BAD-HEADER u5)
(define-constant ERR-HEADER-HEIGHT-MISMATCH u6)
(define-constant ERR-INVALID-MERKLE-PROOF u7)
(define-constant ERR-PROOF-TOO-SHORT u8)
(define-constant ERR-TOO-MANY-WITNESSES u9)
(define-constant ERR-INVALID-COMMITMENT u10)
(define-constant ERR-WITNESS-TX-NOT-IN-COMMITMENT u11)
(define-constant ERR-NOT-SEGWIT-TRANSACTION u12)
(define-constant ERR-LEFTOVER-DATA u13)
;;
;; Helper functions to parse bitcoin transactions
;;
;; Create a list with n elments `true`. n must be smaller than 9.
(define-private (bool-list-of-len (n uint))
(unwrap-panic (slice? (list true true true true true true true true) u0 n)))
;; Reads the next two bytes from txbuff as a little-endian 16-bit integer, and updates the index.
;; Returns (ok { uint16: uint, ctx: { txbuff: (buff 4096), index: uint } }) on success.
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff
(define-read-only (read-uint8 (ctx { txbuff: (buff 4096), index: uint}))
(let ((data (get txbuff ctx))
(base (get index ctx)))
(ok {uint8: (buff-to-uint-le (unwrap-panic (as-max-len? (unwrap! (slice? data base (+ base u1)) (err ERR-OUT-OF-BOUNDS)) u1))),
ctx: { txbuff: data, index: (+ u1 base)}})))
;; Reads the next two bytes from txbuff as a little-endian 16-bit integer, and updates the index.
;; Returns (ok { uint16: uint, ctx: { txbuff: (buff 4096), index: uint } }) on success.
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff
(define-read-only (read-uint16 (ctx { txbuff: (buff 4096), index: uint}))
(let ((data (get txbuff ctx))
(base (get index ctx)))
(ok {uint16: (buff-to-uint-le (unwrap-panic (as-max-len? (unwrap! (slice? data base (+ base u2)) (err ERR-OUT-OF-BOUNDS)) u2))),
ctx: { txbuff: data, index: (+ u2 base)}})))
;; Reads the next four bytes from txbuff as a little-endian 32-bit integer, and updates the index.
;; Returns (ok { uint32: uint, ctx: { txbuff: (buff 4096), index: uint } }) on success.
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff
(define-read-only (read-uint32 (ctx { txbuff: (buff 4096), index: uint}))
(let ((data (get txbuff ctx))
(base (get index ctx)))
(ok {uint32: (buff-to-uint-le (unwrap-panic (as-max-len? (unwrap! (slice? data base (+ base u4)) (err ERR-OUT-OF-BOUNDS)) u4))),
ctx: { txbuff: data, index: (+ u4 base)}})))
;; Reads the next eight bytes from txbuff as a little-endian 64-bit integer, and updates the index.
;; Returns (ok { uint64: uint, ctx: { txbuff: (buff 4096), index: uint } }) on success.
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff
(define-read-only (read-uint64 (ctx { txbuff: (buff 4096), index: uint}))
(let ((data (get txbuff ctx))
(base (get index ctx)))
(ok {uint64: (buff-to-uint-le (unwrap-panic (as-max-len? (unwrap! (slice? data base (+ base u8)) (err ERR-OUT-OF-BOUNDS)) u8))),
ctx: { txbuff: data, index: (+ u8 base)}})))
;; Reads the next varint from txbuff, and updates the index.
;; Returns (ok { varint: uint, ctx: { txbuff: (buff 4096), index: uint } }) on success
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff.
(define-read-only (read-varint (ctx { txbuff: (buff 4096), index: uint}))
(let ((ptr (get index ctx))
(tx (get txbuff ctx))
(byte (buff-to-uint-le (unwrap! (element-at tx ptr)
(err ERR-OUT-OF-BOUNDS)))))
(if (<= byte u252)
;; given byte is the varint
(ok { varint: byte, ctx: { txbuff: tx, index: (+ u1 ptr)}})
(if (is-eq byte u253)
(let (
;; next two bytes is the varint
(parsed-u16 (try! (read-uint16 { txbuff: tx, index: (+ u1 ptr)}))))
(ok { varint: (get uint16 parsed-u16), ctx: (get ctx parsed-u16)}))
(if (is-eq byte u254)
(let (
;; next four bytes is the varint
(parsed-u32 (try! (read-uint32 { txbuff: tx, index: (+ u1 ptr)}))))
(ok { varint: (get uint32 parsed-u32), ctx: (get ctx parsed-u32)}))
(let (
;; next eight bytes is the varint
(parsed-u64 (try! (read-uint64 { txbuff: tx, index: (+ u1 ptr)}))))
(ok { varint: (get uint64 parsed-u64), ctx: (get ctx parsed-u64)})))))))
;; Reads a varint-prefixed byte slice from txbuff, and updates the index to point to the byte after the varint and slice.
;; Returns (ok { varslice: (buff 4096), ctx: { txbuff: (buff 4096), index: uint } }) on success, where varslice has the length of the varint prefix.
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff.
(define-read-only (read-varslice (old-ctx { txbuff: (buff 4096), index: uint}))
(let ((parsed (try! (read-varint old-ctx)))
(ctx (get ctx parsed))
(slice-start (get index ctx))
(target-index (+ slice-start (get varint parsed)))
(txbuff (get txbuff ctx)))
(ok {varslice: (unwrap! (slice? txbuff slice-start target-index) (err ERR-OUT-OF-BOUNDS)),
ctx: { txbuff: txbuff, index: target-index}})))
(define-private (reverse-buff16 (input (buff 16)))
(unwrap-panic (slice? (unwrap-panic (to-consensus-buff? (buff-to-uint-le input))) u1 u17)))
(define-read-only (reverse-buff32 (input (buff 32)))
(unwrap-panic (as-max-len? (concat
(reverse-buff16 (unwrap-panic (as-max-len? (unwrap-panic (slice? input u16 u32)) u16)))
(reverse-buff16 (unwrap-panic (as-max-len? (unwrap-panic (slice? input u0 u16)) u16)))) u32)))
;; Reads a little-endian hash -- consume the next 32 bytes, and reverse them.
;; Returns (ok { hashslice: (buff 32), ctx: { txbuff: (buff 4096), index: uint } }) on success, and updates the index.
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff.
(define-read-only (read-hashslice (old-ctx { txbuff: (buff 4096), index: uint}))
(let ((slice-start (get index old-ctx))
(target-index (+ u32 slice-start))
(txbuff (get txbuff old-ctx))
(hash-le (unwrap-panic
(as-max-len? (unwrap!
(slice? txbuff slice-start target-index) (err ERR-OUT-OF-BOUNDS)) u32))))
(ok {hashslice: (reverse-buff32 hash-le),
ctx: { txbuff: txbuff, index: target-index}})))
;; Inner fold method to read the next tx input from txbuff.
;; The index in ctx will be updated to point to the next tx input if all goes well (or to the start of the outputs)
;; Returns (ok { ... }) on success.
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff.
;; Returns (err ERR-VARSLICE-TOO-LONG) if we find a scriptSig that's too long to parse.
;; Returns (err ERR-TOO-MANY-TXINS) if there are more than eight inputs to read.
(define-read-only (read-next-txin (ignored bool)
(result (response {ctx: { txbuff: (buff 4096), index: uint },
remaining: uint,
txins: (list 8 {outpoint: {
hash: (buff 32),
index: uint},
scriptSig: (buff 256), ;; just big enough to hold a 2-of-3 multisig script
sequence: uint})}
uint)))
(let ((state (unwrap! result result)))
(let ((remaining (get remaining state))
(ctx (get ctx state))
(parsed-hash (try! (read-hashslice ctx)))
(parsed-index (try! (read-uint32 (get ctx parsed-hash))))
(parsed-scriptSig (try! (read-varslice (get ctx parsed-index))))
(parsed-sequence (try! (read-uint32 (get ctx parsed-scriptSig))))
(new-ctx (get ctx parsed-sequence)))
(ok {ctx: new-ctx,
remaining: (- remaining u1),
txins: (unwrap!
(as-max-len?
(append (get txins state) { outpoint: {
hash: (get hashslice parsed-hash),
index: (get uint32 parsed-index) },
scriptSig: (unwrap! (as-max-len? (get varslice parsed-scriptSig) u256) (err ERR-VARSLICE-TOO-LONG)),
sequence: (get uint32 parsed-sequence)}) u8)
(err ERR-TOO-MANY-TXINS))}))
))
;; Read a transaction's inputs.
;; Returns (ok { txins: (list { ... }), remaining: uint, ctx: { txbuff: (buff 4096), index: uint } }) on success, and updates the index in ctx to point to the start of the tx outputs.
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff.
;; Returns (err ERR-VARSLICE-TOO-LONG) if we find a scriptSig that's too long to parse.
;; Returns (err ERR-TOO-MANY-TXINS) if there are more than eight inputs to read.
(define-read-only (read-txins (ctx { txbuff: (buff 4096), index: uint}))
(let ((parsed-num-txins (try! (read-varint ctx)))
(num-txins (get varint parsed-num-txins))
(new-ctx (get ctx parsed-num-txins)))
(if (> num-txins u8)
(err ERR-TOO-MANY-TXINS)
(fold read-next-txin (bool-list-of-len num-txins) (ok { ctx: new-ctx, remaining: num-txins, txins: (list)})))))
;; Read the next transaction output, and update the index in ctx to point to the next output.
;; Returns (ok { ... }) on success
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff.
;; Returns (err ERR-VARSLICE-TOO-LONG) if we find a scriptPubKey that's too long to parse.
;; Returns (err ERR-TOO-MANY-TXOUTS) if there are more than eight outputs to read.
(define-read-only (read-next-txout (ignored bool)
(result (response {ctx: { txbuff: (buff 4096), index: uint },
txouts: (list 8 {value: uint,
scriptPubKey: (buff 128)})}
uint)))
(let ((state (unwrap! result result))
(parsed-value (try! (read-uint64 (get ctx state))))
(parsed-script (try! (read-varslice (get ctx parsed-value))))
(new-ctx (get ctx parsed-script)))
(ok {ctx: new-ctx,
txouts: (unwrap!
(as-max-len?
(append (get txouts state)
{ value: (get uint64 parsed-value),
scriptPubKey: (unwrap! (as-max-len? (get varslice parsed-script) u128) (err ERR-VARSLICE-TOO-LONG))}) u8)
(err ERR-TOO-MANY-TXOUTS))})))
;; Read all transaction outputs in a transaction. Update the index to point to the first byte after the outputs, if all goes well.
;; Returns (ok { txouts: (list { ... }), remaining: uint, ctx: { txbuff: (buff 4096), index: uint } }) on success, and updates the index in ctx to point to the start of the tx outputs.
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff.
;; Returns (err ERR-VARSLICE-TOO-LONG) if we find a scriptPubKey that's too long to parse.
;; Returns (err ERR-TOO-MANY-TXOUTS) if there are more than eight outputs to read.
(define-read-only (read-txouts (ctx { txbuff: (buff 4096), index: uint}))
(let ((parsed-num-txouts (try! (read-varint ctx)))
(num-txouts (get varint parsed-num-txouts))
(new-ctx (get ctx parsed-num-txouts)))
(if (> num-txouts u8)
(err ERR-TOO-MANY-TXOUTS)
(fold read-next-txout (bool-list-of-len num-txouts) (ok { ctx: new-ctx, txouts: (list)})))))
;; Read the stack item of the witness field, and update the index in ctx to point to the next item.
(define-read-only (read-next-item (ignored bool)
(result (response {ctx: { txbuff: (buff 4096), index: uint },
items: (list 8 (buff 128))}
uint)))
(let ((state (unwrap! result result))
(parsed-item (try! (read-varslice (get ctx state))))
(new-ctx (get ctx parsed-item)))
(ok {ctx: new-ctx,
items: (unwrap!
(as-max-len?
(append (get items state) (unwrap! (as-max-len? (get varslice parsed-item) u128) (err ERR-VARSLICE-TOO-LONG))) u8)
(err ERR-TOO-MANY-WITNESSES))})))
;; Read the next witness data, and update the index in ctx to point to the next witness.
(define-read-only (read-next-witness (ignored bool)
(result (response
{ ctx: {txbuff: (buff 4096), index: uint}, witnesses: (list 8 (list 8 (buff 128))) } uint)))
(let ((state (unwrap! result result))
(parsed-num-items (try! (read-varint (get ctx state))))
(ctx (get ctx parsed-num-items))
(varint (get varint parsed-num-items)))
(if (> varint u0)
;; read all stack items for current txin and add to witnesses.
(let ((parsed-items (try! (fold read-next-item (bool-list-of-len varint) (ok { ctx: ctx, items: (list)})))))
(ok {
witnesses: (unwrap-panic (as-max-len? (append (get witnesses state) (get items parsed-items)) u8)),
ctx: (get ctx parsed-items)
}))
;; txin has not witness data, add empty list to witnesses.
(ok {
witnesses: (unwrap-panic (as-max-len? (append (get witnesses state) (list)) u8)),
ctx: ctx
}))))
;; Read all witness data in a transaction. Update the index to point to the end of the tx, if all goes well.
;; Returns (ok {witnesses: (list 8 (list 8 (buff 128))), ctx: { txbuff: (buff 4096), index: uint } }) on success, and updates the index in ctx to point after the end of the tx.
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff.
;; Returns (err ERR-VARSLICE-TOO-LONG) if we find a scriptPubKey that's too long to parse.
;; Returns (err ERR-TOO-MANY-WITNESSES) if there are more than eight witness data or stack items to read.
(define-read-only (read-witnesses (ctx { txbuff: (buff 4096), index: uint }) (num-txins uint))
(fold read-next-witness (bool-list-of-len num-txins) (ok { ctx: ctx, witnesses: (list) })))
;;
;; Parses a Bitcoin transaction, with up to 8 inputs and 8 outputs, with scriptSigs of up to 256 bytes each, and with scriptPubKeys up to 128 bytes.
;; It will also calculate and return the TXID if calculate-txid is set to true.
;; Returns a tuple structured as follows on success:
;; (ok {
;; version: uint, ;; tx version
;; segwit-marker: uint,
;; segwit-version: uint,
;; txid: (optional (buff 32))
;; ins: (list 8
;; {
;; outpoint: { ;; pointer to the utxo this input consumes
;; hash: (buff 32),
;; index: uint
;; },
;; scriptSig: (buff 256), ;; spending condition script
;; sequence: uint
;; }),
;; outs: (list 8
;; {
;; value: uint, ;; satoshis sent
;; scriptPubKey: (buff 128) ;; parse this to get an address
;; }),
;; witnesses: (list 8 (list 8 (buff 128))),
;; locktime: uint
;; })
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff.
;; Returns (err ERR-VARSLICE-TOO-LONG) if we find a scriptPubKey or scriptSig that's too long to parse.
;; Returns (err ERR-TOO-MANY-TXOUTS) if there are more than eight inputs to read.
;; Returns (err ERR-TOO-MANY-TXINS) if there are more than eight outputs to read.
;; Returns (err ERR-NOT-SEGWIT-TRANSACTION) if tx is not a segwit transaction.
;; Returns (err ERR-LEFTOVER-DATA) if the tx buffer contains leftover data at the end.
(define-read-only (parse-wtx (tx (buff 4096)) (calculate-txid bool))
(let ((ctx { txbuff: tx, index: u0})
(parsed-version (try! (read-uint32 ctx)))
(parsed-segwit-marker (try! (read-uint8 (get ctx parsed-version))))
(parsed-segwit-version (try! (read-uint8 (get ctx parsed-segwit-marker))))
(parsed-txins (try! (read-txins (get ctx parsed-segwit-version))))
(parsed-txouts (try! (read-txouts (get ctx parsed-txins))))
(parsed-witnesses (try! (read-witnesses (get ctx parsed-txouts) (len (get txins parsed-txins)))))
(parsed-locktime (try! (read-uint32 (get ctx parsed-witnesses))))
)
(asserts! (and (is-eq (get uint8 parsed-segwit-marker) u0) (is-eq (get uint8 parsed-segwit-version) u1)) (err ERR-NOT-SEGWIT-TRANSACTION))
(asserts! (is-eq (len tx) (get index (get ctx parsed-locktime))) (err ERR-LEFTOVER-DATA))
(ok {version: (get uint32 parsed-version),
segwit-marker: (get uint8 parsed-segwit-marker),
segwit-version: (get uint8 parsed-segwit-version),
ins: (get txins parsed-txins),
outs: (get txouts parsed-txouts),
txid: (if calculate-txid
(some (reverse-buff32 (sha256 (sha256
(concat
(unwrap-panic (slice? tx u0 u4))
(concat
(unwrap-panic (slice? tx (get index (get ctx parsed-segwit-version)) (get index (get ctx parsed-txouts))))
(unwrap-panic (slice? tx (get index (get ctx parsed-witnesses)) (len tx)))))))))
none),
witnesses: (get witnesses parsed-witnesses),
locktime: (get uint32 parsed-locktime)
})))
;;
;; Parses a Bitcoin transaction, with up to 8 inputs and 8 outputs, with scriptSigs of up to 256 bytes each, and with scriptPubKeys up to 128 bytes.
;; Returns a tuple structured as follows on success:
;; (ok {
;; version: uint, ;; tx version
;; ins: (list 8
;; {
;; outpoint: { ;; pointer to the utxo this input consumes
;; hash: (buff 32),
;; index: uint
;; },
;; scriptSig: (buff 256), ;; spending condition script
;; sequence: uint
;; }),
;; outs: (list 8
;; {
;; value: uint, ;; satoshis sent
;; scriptPubKey: (buff 128) ;; parse this to get an address
;; }),
;; locktime: uint
;; })
;; Returns (err ERR-OUT-OF-BOUNDS) if we read past the end of txbuff.
;; Returns (err ERR-VARSLICE-TOO-LONG) if we find a scriptPubKey or scriptSig that's too long to parse.
;; Returns (err ERR-TOO-MANY-TXOUTS) if there are more than eight inputs to read.
;; Returns (err ERR-TOO-MANY-TXINS) if there are more than eight outputs to read.
;; Returns (err ERR-LEFTOVER-DATA) if the tx buffer contains leftover data at the end.
(define-read-only (parse-tx (tx (buff 4096)))
(let ((ctx { txbuff: tx, index: u0})
(parsed-version (try! (read-uint32 ctx)))
(parsed-txins (try! (read-txins (get ctx parsed-version))))
(parsed-txouts (try! (read-txouts (get ctx parsed-txins))))
(parsed-locktime (try! (read-uint32 (get ctx parsed-txouts)))))
;; check if it is a non-segwit transaction?
;; at least check what happens
(asserts! (is-eq (len tx) (get index (get ctx parsed-locktime))) (err ERR-LEFTOVER-DATA))
(ok {version: (get uint32 parsed-version),
ins: (get txins parsed-txins),
outs: (get txouts parsed-txouts),
locktime: (get uint32 parsed-locktime)})))
;; Parse a Bitcoin block header.
;; Returns a tuple structured as folowed on success:
;; (ok {
;; version: uint, ;; block version,
;; parent: (buff 32), ;; parent block hash,
;; merkle-root: (buff 32), ;; merkle root for all this block's transactions
;; timestamp: uint, ;; UNIX epoch timestamp of this block, in seconds
;; nbits: uint, ;; compact block difficulty representation
;; nonce: uint ;; PoW solution
;; })
(define-read-only (parse-block-header (headerbuff (buff 80)))
(let ((ctx { txbuff: headerbuff, index: u0})
(parsed-version (try! (read-uint32 ctx)))
(parsed-parent-hash (try! (read-hashslice (get ctx parsed-version))))
(parsed-merkle-root (try! (read-hashslice (get ctx parsed-parent-hash))))
(parsed-timestamp (try! (read-uint32 (get ctx parsed-merkle-root))))
(parsed-nbits (try! (read-uint32 (get ctx parsed-timestamp))))
(parsed-nonce (try! (read-uint32 (get ctx parsed-nbits)))))
(ok {version: (get uint32 parsed-version),
parent: (get hashslice parsed-parent-hash),
merkle-root: (get hashslice parsed-merkle-root),
timestamp: (get uint32 parsed-timestamp),
nbits: (get uint32 parsed-nbits),
nonce: (get uint32 parsed-nonce)})))
(define-read-only (get-bc-h-hash (bh uint))
(get-burn-block-info? header-hash bh))
;; Verify that a block header hashes to a burnchain header hash at a given height.
;; Returns true if so; false if not.
(define-read-only (verify-block-header (headerbuff (buff 80)) (expected-block-height uint))
(match (get-bc-h-hash expected-block-height)
bhh (is-eq bhh (reverse-buff32 (sha256 (sha256 headerbuff))))
false))
;; Get the txid of a transaction, but little-endian.
;; This is the reverse of what you see on block explorers.
(define-read-only (get-reversed-txid (tx (buff 4096)))
(sha256 (sha256 tx)))
;; Get the txid of a transaction.
;; This is what you see on block explorers.
(define-read-only (get-txid (tx (buff 4096)))
(reverse-buff32 (sha256 (sha256 tx))))
;; Determine if the ith bit in a uint is set to 1
(define-read-only (is-bit-set (val uint) (bit uint))
(> (bit-and val (bit-shift-left u1 bit)) u0))
;; Verify the next step of a Merkle proof.
;; This hashes cur-hash against the ctr-th hash in proof-hashes, and uses that as the next cur-hash.
;; The path is a bitfield describing the walk from the txid up to the merkle root:
;; * if the ith bit is 0, then cur-hash is hashed before the next proof-hash (cur-hash is "left").
;; * if the ith bit is 1, then the next proof-hash is hashed before cur-hash (cur-hash is "right").
;; The proof verifies if cur-hash is equal to root-hash, and we're out of proof-hashes to check.
;; Note, ctr is expected to be < (len proof-hashes), verified can be true only if ctr + 1 == (len proof-hashes).
(define-private (inner-merkle-proof-verify (ctr uint) (state { path: uint, root-hash: (buff 32), proof-hashes: (list 14 (buff 32)), tree-depth: uint, cur-hash: (buff 32), verified: bool}))
(let ((path (get path state))
(is-left (is-bit-set path ctr))
(proof-hashes (get proof-hashes state))
(cur-hash (get cur-hash state))
(root-hash (get root-hash state))
(h1 (if is-left (unwrap-panic (element-at proof-hashes ctr)) cur-hash))
(h2 (if is-left cur-hash (unwrap-panic (element-at proof-hashes ctr))))
(next-hash (sha256 (sha256 (concat h1 h2))))
(is-verified (and (is-eq (+ u1 ctr) (len proof-hashes)) (is-eq next-hash root-hash))))
(merge state { cur-hash: next-hash, verified: is-verified})))
;; Verify a Merkle proof, given the _reversed_ txid of a transaction, the merkle root of its block, and a proof consisting of:
;; * The index in the block where the transaction can be found (starting from 0),
;; * The list of hashes that link the txid to the merkle root,
;; * The depth of the block's merkle tree (required because Bitcoin does not identify merkle tree nodes as being leaves or intermediates).
;; The _reversed_ txid is required because that's the order (little-endian) processes them in.
;; The tx-index is required because it tells us the left/right traversals we'd make if we were walking down the tree from root to transaction,
;; and is thus used to deduce the order in which to hash the intermediate hashes with one another to link the txid to the merkle root.
;; Returns (ok true) if the proof is valid.
;; Returns (ok false) if the proof is invalid.
;; Returns (err ERR-PROOF-TOO-SHORT) if the proof's hashes aren't long enough to link the txid to the merkle root.
(define-read-only (verify-merkle-proof (reversed-txid (buff 32)) (merkle-root (buff 32)) (proof { tx-index: uint, hashes: (list 14 (buff 32)), tree-depth: uint}))
(if (> (get tree-depth proof) (len (get hashes proof)))
(err ERR-PROOF-TOO-SHORT)
(ok
(get verified
(fold inner-merkle-proof-verify
(unwrap-panic (slice? (list u0 u1 u2 u3 u4 u5 u6 u7 u8 u9 u10 u11 u12 u13) u0 (get tree-depth proof)))
{ path: (+ (pow u2 (get tree-depth proof)) (get tx-index proof)), root-hash: merkle-root, proof-hashes: (get hashes proof), cur-hash: reversed-txid, tree-depth: (get tree-depth proof), verified: false})))))
;; Helper for wtxid commitments
;; Gets the scriptPubKey in the last output that follows the 0x6a24aa21a9ed pattern regardless of its content
;; as per BIP-0141 (https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki#commitment-structure)
(define-read-only (get-commitment-scriptPubKey (outs (list 8 { value: uint, scriptPubKey: (buff 128) })))
(fold inner-get-commitment-scriptPubKey outs 0x))
(define-read-only (inner-get-commitment-scriptPubKey (out { value: uint, scriptPubKey: (buff 128) }) (result (buff 128)))
(let ((commitment (get scriptPubKey out)))
(if (is-commitment-pattern commitment) commitment result)))
;; Returns false, if scriptPubKey does not have the commitment prefix.
(define-read-only (is-commitment-pattern (scriptPubKey (buff 128)))
(asserts! (is-eq (unwrap! (slice? scriptPubKey u0 u6) false) 0x6a24aa21a9ed) false))
;;
;; Top-level verification functions
;;
;; Determine whether or not a Bitcoin transaction without witnesses
;; was mined in a prior Bitcoin block.
;; It takes the block height, the transaction, the block header and a merkle proof, and determines that:
;; * the block header corresponds to the block that was mined at the given Bitcoin height
;; * the transaction's merkle proof links it to the block header's merkle root.
;; To verify that the merkle root is part of the block header there are two options:
;; a) read the merkle root from the header buffer
;; b) build the header buffer from its parts including the merkle root
;;
;; The merkle proof is a list of sibling merkle tree nodes that allow us to calculate the parent node from two children nodes in each merkle tree level,
;; the depth of the block's merkle tree, and the index in the block in which the given transaction can be found (starting from 0).
;; The first element in hashes must be the given transaction's sibling transaction's ID. This and the given transaction's txid are hashed to
;; calculate the parent hash in the merkle tree, which is then hashed with the *next* hash in the proof, and so on and so forth, until the final
;; hash can be compared against the block header's merkle root field. The tx-index tells us in which order to hash each pair of siblings.
;; Note that the proof hashes -- including the sibling txid -- must be _little-endian_ hashes, because this is how Bitcoin generates them.
;; This is the reverse of what you'd see in a block explorer!
;;
;; Returns (ok true) if the proof checks out.
;; Returns (ok false) if not.
;; Returns (err ERR-PROOF-TOO-SHORT) if the proof doesn't contain enough intermediate hash nodes in the merkle tree.
(define-read-only (was-tx-mined-compact (height uint) (tx (buff 4096))
(header (buff 80))
(proof { tx-index: uint, hashes: (list 14 (buff 32)), tree-depth: uint}))
(let ((block (unwrap! (parse-block-header header) (err ERR-BAD-HEADER))))
(was-tx-mined-internal height tx header (get merkle-root block) proof)))
;; Private function to verify block header and merkle proof.
;; This function must only be called with the merkle root of the provided header.
;; Use was-tx-mined-compact with header as a buffer or
;; was-tx-mined with header as a tuple.
;; Returns txid if tx was mined else err u1 if the header is invalid or err u2 if the proof is invalid.
(define-private (was-tx-mined-internal (height uint) (tx (buff 4096)) (header (buff 80)) (merkle-root (buff 32)) (proof { tx-index: uint, hashes: (list 14 (buff 32)), tree-depth: uint}))
(if (verify-block-header header height)
(let ((reversed-txid (get-reversed-txid tx))
(txid (reverse-buff32 reversed-txid)))
;; verify merkle proof
(asserts!
(or
(is-eq merkle-root txid) ;; true, if the transaction is the only transaction
(try! (verify-merkle-proof reversed-txid (reverse-buff32 merkle-root) proof)))
(err ERR-INVALID-MERKLE-PROOF))
(ok txid))
(err ERR-HEADER-HEIGHT-MISMATCH)))
;; Determine whether or not a Bitcoin transaction
;; with witnesses was mined in a prior Bitcoin block.
;; It takes
;; a) the bitcoin block height, the transaction "tx" with witness data,
;; the bitcoin block header, the tx index in the block and
;; b) the depth of merkle proof of the block and
;; c) the merkle proof of the wtxid "wproof", its root "witness-merkle-proof",
;; the witness reserved value and
;; d) the coinbase transaction "ctx" without witnesses (non-segwit) and its merkle proof "cproof".
;;
;; It determines that:
;; * the block header corresponds to the block that was mined at the given Bitcoin height
;; * the coinbase tx was mined and it contains the commitment to the wtxids
;; * the wtxid of the tx is part of the commitment.
;;
;; The tree depth for wproof and cproof are the same.
;; The coinbase tx index is always 0.
;;
;; It returns (ok wtxid), if it was mined.
(define-read-only (was-segwit-tx-mined-compact
(height uint)
(wtx (buff 4096))
(header (buff 80))
(tx-index uint)
(tree-depth uint)
(wproof (list 14 (buff 32)))
(witness-merkle-root (buff 32))
(witness-reserved-value (buff 32))
(ctx (buff 1024))
(cproof (list 14 (buff 32))))
(begin
;; verify that the coinbase tx is correct
(try! (was-tx-mined-compact height ctx header { tx-index: u0, hashes: cproof, tree-depth: tree-depth }))
(let (
(witness-out (get-commitment-scriptPubKey (get outs (try! (parse-tx ctx)))))
(final-hash (sha256 (sha256 (concat witness-merkle-root witness-reserved-value))))
(reversed-wtxid (get-reversed-txid wtx))
(wtxid (reverse-buff32 reversed-wtxid))
)
;; verify wtxid commitment
(asserts! (is-eq witness-out (concat 0x6a24aa21a9ed final-hash)) (err ERR-INVALID-COMMITMENT))
;; verify witness merkle tree
(asserts! (try! (verify-merkle-proof reversed-wtxid witness-merkle-root
{ tx-index: tx-index, hashes: wproof, tree-depth: tree-depth })) (err ERR-WITNESS-TX-NOT-IN-COMMITMENT))
(ok wtxid))))