Skip to content
Permalink
Branch: master
Find file Copy path
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
861 lines (759 sloc) 28.5 KB
// Copyright (c) 2013-2017 The btcsuite developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package txscript
import (
"bytes"
"encoding/binary"
"fmt"
"time"
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/btcsuite/btcd/wire"
)
// Bip16Activation is the timestamp where BIP0016 is valid to use in the
// blockchain. To be used to determine if BIP0016 should be called for or not.
// This timestamp corresponds to Sun Apr 1 00:00:00 UTC 2012.
var Bip16Activation = time.Unix(1333238400, 0)
// SigHashType represents hash type bits at the end of a signature.
type SigHashType uint32
// Hash type bits from the end of a signature.
const (
SigHashOld SigHashType = 0x0
SigHashAll SigHashType = 0x1
SigHashNone SigHashType = 0x2
SigHashSingle SigHashType = 0x3
SigHashAnyOneCanPay SigHashType = 0x80
// sigHashMask defines the number of bits of the hash type which is used
// to identify which outputs are signed.
sigHashMask = 0x1f
)
// These are the constants specified for maximums in individual scripts.
const (
MaxOpsPerScript = 201 // Max number of non-push operations.
MaxPubKeysPerMultiSig = 20 // Multisig can't have more sigs than this.
MaxScriptElementSize = 520 // Max bytes pushable to the stack.
)
// isSmallInt returns whether or not the opcode is considered a small integer,
// which is an OP_0, or OP_1 through OP_16.
func isSmallInt(op *opcode) bool {
if op.value == OP_0 || (op.value >= OP_1 && op.value <= OP_16) {
return true
}
return false
}
// isScriptHash returns true if the script passed is a pay-to-script-hash
// transaction, false otherwise.
func isScriptHash(pops []parsedOpcode) bool {
return len(pops) == 3 &&
pops[0].opcode.value == OP_HASH160 &&
pops[1].opcode.value == OP_DATA_20 &&
pops[2].opcode.value == OP_EQUAL
}
// IsPayToScriptHash returns true if the script is in the standard
// pay-to-script-hash (P2SH) format, false otherwise.
func IsPayToScriptHash(script []byte) bool {
pops, err := parseScript(script)
if err != nil {
return false
}
return isScriptHash(pops)
}
// isWitnessScriptHash returns true if the passed script is a
// pay-to-witness-script-hash transaction, false otherwise.
func isWitnessScriptHash(pops []parsedOpcode) bool {
return len(pops) == 2 &&
pops[0].opcode.value == OP_0 &&
pops[1].opcode.value == OP_DATA_32
}
// IsPayToWitnessScriptHash returns true if the is in the standard
// pay-to-witness-script-hash (P2WSH) format, false otherwise.
func IsPayToWitnessScriptHash(script []byte) bool {
pops, err := parseScript(script)
if err != nil {
return false
}
return isWitnessScriptHash(pops)
}
// IsPayToWitnessPubKeyHash returns true if the is in the standard
// pay-to-witness-pubkey-hash (P2WKH) format, false otherwise.
func IsPayToWitnessPubKeyHash(script []byte) bool {
pops, err := parseScript(script)
if err != nil {
return false
}
return isWitnessPubKeyHash(pops)
}
// isWitnessPubKeyHash returns true if the passed script is a
// pay-to-witness-pubkey-hash, and false otherwise.
func isWitnessPubKeyHash(pops []parsedOpcode) bool {
return len(pops) == 2 &&
pops[0].opcode.value == OP_0 &&
pops[1].opcode.value == OP_DATA_20
}
// IsWitnessProgram returns true if the passed script is a valid witness
// program which is encoded according to the passed witness program version. A
// witness program must be a small integer (from 0-16), followed by 2-40 bytes
// of pushed data.
func IsWitnessProgram(script []byte) bool {
// The length of the script must be between 4 and 42 bytes. The
// smallest program is the witness version, followed by a data push of
// 2 bytes. The largest allowed witness program has a data push of
// 40-bytes.
if len(script) < 4 || len(script) > 42 {
return false
}
pops, err := parseScript(script)
if err != nil {
return false
}
return isWitnessProgram(pops)
}
// isWitnessProgram returns true if the passed script is a witness program, and
// false otherwise. A witness program MUST adhere to the following constraints:
// there must be exactly two pops (program version and the program itself), the
// first opcode MUST be a small integer (0-16), the push data MUST be
// canonical, and finally the size of the push data must be between 2 and 40
// bytes.
func isWitnessProgram(pops []parsedOpcode) bool {
return len(pops) == 2 &&
isSmallInt(pops[0].opcode) &&
canonicalPush(pops[1]) &&
(len(pops[1].data) >= 2 && len(pops[1].data) <= 40)
}
// ExtractWitnessProgramInfo attempts to extract the witness program version,
// as well as the witness program itself from the passed script.
func ExtractWitnessProgramInfo(script []byte) (int, []byte, error) {
pops, err := parseScript(script)
if err != nil {
return 0, nil, err
}
// If at this point, the scripts doesn't resemble a witness program,
// then we'll exit early as there isn't a valid version or program to
// extract.
if !isWitnessProgram(pops) {
return 0, nil, fmt.Errorf("script is not a witness program, " +
"unable to extract version or witness program")
}
witnessVersion := asSmallInt(pops[0].opcode)
witnessProgram := pops[1].data
return witnessVersion, witnessProgram, nil
}
// isPushOnly returns true if the script only pushes data, false otherwise.
func isPushOnly(pops []parsedOpcode) bool {
// NOTE: This function does NOT verify opcodes directly since it is
// internal and is only called with parsed opcodes for scripts that did
// not have any parse errors. Thus, consensus is properly maintained.
for _, pop := range pops {
// All opcodes up to OP_16 are data push instructions.
// NOTE: This does consider OP_RESERVED to be a data push
// instruction, but execution of OP_RESERVED will fail anyways
// and matches the behavior required by consensus.
if pop.opcode.value > OP_16 {
return false
}
}
return true
}
// IsPushOnlyScript returns whether or not the passed script only pushes data.
//
// False will be returned when the script does not parse.
func IsPushOnlyScript(script []byte) bool {
pops, err := parseScript(script)
if err != nil {
return false
}
return isPushOnly(pops)
}
// parseScriptTemplate is the same as parseScript but allows the passing of the
// template list for testing purposes. When there are parse errors, it returns
// the list of parsed opcodes up to the point of failure along with the error.
func parseScriptTemplate(script []byte, opcodes *[256]opcode) ([]parsedOpcode, error) {
retScript := make([]parsedOpcode, 0, len(script))
for i := 0; i < len(script); {
instr := script[i]
op := &opcodes[instr]
pop := parsedOpcode{opcode: op}
// Parse data out of instruction.
switch {
// No additional data. Note that some of the opcodes, notably
// OP_1NEGATE, OP_0, and OP_[1-16] represent the data
// themselves.
case op.length == 1:
i++
// Data pushes of specific lengths -- OP_DATA_[1-75].
case op.length > 1:
if len(script[i:]) < op.length {
str := fmt.Sprintf("opcode %s requires %d "+
"bytes, but script only has %d remaining",
op.name, op.length, len(script[i:]))
return retScript, scriptError(ErrMalformedPush,
str)
}
// Slice out the data.
pop.data = script[i+1 : i+op.length]
i += op.length
// Data pushes with parsed lengths -- OP_PUSHDATAP{1,2,4}.
case op.length < 0:
var l uint
off := i + 1
if len(script[off:]) < -op.length {
str := fmt.Sprintf("opcode %s requires %d "+
"bytes, but script only has %d remaining",
op.name, -op.length, len(script[off:]))
return retScript, scriptError(ErrMalformedPush,
str)
}
// Next -length bytes are little endian length of data.
switch op.length {
case -1:
l = uint(script[off])
case -2:
l = ((uint(script[off+1]) << 8) |
uint(script[off]))
case -4:
l = ((uint(script[off+3]) << 24) |
(uint(script[off+2]) << 16) |
(uint(script[off+1]) << 8) |
uint(script[off]))
default:
str := fmt.Sprintf("invalid opcode length %d",
op.length)
return retScript, scriptError(ErrMalformedPush,
str)
}
// Move offset to beginning of the data.
off += -op.length
// Disallow entries that do not fit script or were
// sign extended.
if int(l) > len(script[off:]) || int(l) < 0 {
str := fmt.Sprintf("opcode %s pushes %d bytes, "+
"but script only has %d remaining",
op.name, int(l), len(script[off:]))
return retScript, scriptError(ErrMalformedPush,
str)
}
pop.data = script[off : off+int(l)]
i += 1 - op.length + int(l)
}
retScript = append(retScript, pop)
}
return retScript, nil
}
// parseScript preparses the script in bytes into a list of parsedOpcodes while
// applying a number of sanity checks.
func parseScript(script []byte) ([]parsedOpcode, error) {
return parseScriptTemplate(script, &opcodeArray)
}
// unparseScript reversed the action of parseScript and returns the
// parsedOpcodes as a list of bytes
func unparseScript(pops []parsedOpcode) ([]byte, error) {
script := make([]byte, 0, len(pops))
for _, pop := range pops {
b, err := pop.bytes()
if err != nil {
return nil, err
}
script = append(script, b...)
}
return script, nil
}
// DisasmString formats a disassembled script for one line printing. When the
// script fails to parse, the returned string will contain the disassembled
// script up to the point the failure occurred along with the string '[error]'
// appended. In addition, the reason the script failed to parse is returned
// if the caller wants more information about the failure.
func DisasmString(buf []byte) (string, error) {
var disbuf bytes.Buffer
opcodes, err := parseScript(buf)
for _, pop := range opcodes {
disbuf.WriteString(pop.print(true))
disbuf.WriteByte(' ')
}
if disbuf.Len() > 0 {
disbuf.Truncate(disbuf.Len() - 1)
}
if err != nil {
disbuf.WriteString("[error]")
}
return disbuf.String(), err
}
// removeOpcode will remove any opcode matching ``opcode'' from the opcode
// stream in pkscript
func removeOpcode(pkscript []parsedOpcode, opcode byte) []parsedOpcode {
retScript := make([]parsedOpcode, 0, len(pkscript))
for _, pop := range pkscript {
if pop.opcode.value != opcode {
retScript = append(retScript, pop)
}
}
return retScript
}
// canonicalPush returns true if the object is either not a push instruction
// or the push instruction contained wherein is matches the canonical form
// or using the smallest instruction to do the job. False otherwise.
func canonicalPush(pop parsedOpcode) bool {
opcode := pop.opcode.value
data := pop.data
dataLen := len(pop.data)
if opcode > OP_16 {
return true
}
if opcode < OP_PUSHDATA1 && opcode > OP_0 && (dataLen == 1 && data[0] <= 16) {
return false
}
if opcode == OP_PUSHDATA1 && dataLen < OP_PUSHDATA1 {
return false
}
if opcode == OP_PUSHDATA2 && dataLen <= 0xff {
return false
}
if opcode == OP_PUSHDATA4 && dataLen <= 0xffff {
return false
}
return true
}
// removeOpcodeByData will return the script minus any opcodes that would push
// the passed data to the stack.
func removeOpcodeByData(pkscript []parsedOpcode, data []byte) []parsedOpcode {
retScript := make([]parsedOpcode, 0, len(pkscript))
for _, pop := range pkscript {
if !canonicalPush(pop) || !bytes.Contains(pop.data, data) {
retScript = append(retScript, pop)
}
}
return retScript
}
// calcHashPrevOuts calculates a single hash of all the previous outputs
// (txid:index) referenced within the passed transaction. This calculated hash
// can be re-used when validating all inputs spending segwit outputs, with a
// signature hash type of SigHashAll. This allows validation to re-use previous
// hashing computation, reducing the complexity of validating SigHashAll inputs
// from O(N^2) to O(N).
func calcHashPrevOuts(tx *wire.MsgTx) chainhash.Hash {
var b bytes.Buffer
for _, in := range tx.TxIn {
// First write out the 32-byte transaction ID one of whose
// outputs are being referenced by this input.
b.Write(in.PreviousOutPoint.Hash[:])
// Next, we'll encode the index of the referenced output as a
// little endian integer.
var buf [4]byte
binary.LittleEndian.PutUint32(buf[:], in.PreviousOutPoint.Index)
b.Write(buf[:])
}
return chainhash.DoubleHashH(b.Bytes())
}
// calcHashSequence computes an aggregated hash of each of the sequence numbers
// within the inputs of the passed transaction. This single hash can be re-used
// when validating all inputs spending segwit outputs, which include signatures
// using the SigHashAll sighash type. This allows validation to re-use previous
// hashing computation, reducing the complexity of validating SigHashAll inputs
// from O(N^2) to O(N).
func calcHashSequence(tx *wire.MsgTx) chainhash.Hash {
var b bytes.Buffer
for _, in := range tx.TxIn {
var buf [4]byte
binary.LittleEndian.PutUint32(buf[:], in.Sequence)
b.Write(buf[:])
}
return chainhash.DoubleHashH(b.Bytes())
}
// calcHashOutputs computes a hash digest of all outputs created by the
// transaction encoded using the wire format. This single hash can be re-used
// when validating all inputs spending witness programs, which include
// signatures using the SigHashAll sighash type. This allows computation to be
// cached, reducing the total hashing complexity from O(N^2) to O(N).
func calcHashOutputs(tx *wire.MsgTx) chainhash.Hash {
var b bytes.Buffer
for _, out := range tx.TxOut {
wire.WriteTxOut(&b, 0, 0, out)
}
return chainhash.DoubleHashH(b.Bytes())
}
// calcWitnessSignatureHash computes the sighash digest of a transaction's
// segwit input using the new, optimized digest calculation algorithm defined
// in BIP0143: https://github.com/bitcoin/bips/blob/master/bip-0143.mediawiki.
// This function makes use of pre-calculated sighash fragments stored within
// the passed HashCache to eliminate duplicate hashing computations when
// calculating the final digest, reducing the complexity from O(N^2) to O(N).
// Additionally, signatures now cover the input value of the referenced unspent
// output. This allows offline, or hardware wallets to compute the exact amount
// being spent, in addition to the final transaction fee. In the case the
// wallet if fed an invalid input amount, the real sighash will differ causing
// the produced signature to be invalid.
func calcWitnessSignatureHash(subScript []parsedOpcode, sigHashes *TxSigHashes,
hashType SigHashType, tx *wire.MsgTx, idx int, amt int64) ([]byte, error) {
// As a sanity check, ensure the passed input index for the transaction
// is valid.
if idx > len(tx.TxIn)-1 {
return nil, fmt.Errorf("idx %d but %d txins", idx, len(tx.TxIn))
}
// We'll utilize this buffer throughout to incrementally calculate
// the signature hash for this transaction.
var sigHash bytes.Buffer
// First write out, then encode the transaction's version number.
var bVersion [4]byte
binary.LittleEndian.PutUint32(bVersion[:], uint32(tx.Version))
sigHash.Write(bVersion[:])
// Next write out the possibly pre-calculated hashes for the sequence
// numbers of all inputs, and the hashes of the previous outs for all
// outputs.
var zeroHash chainhash.Hash
// If anyone can pay isn't active, then we can use the cached
// hashPrevOuts, otherwise we just write zeroes for the prev outs.
if hashType&SigHashAnyOneCanPay == 0 {
sigHash.Write(sigHashes.HashPrevOuts[:])
} else {
sigHash.Write(zeroHash[:])
}
// If the sighash isn't anyone can pay, single, or none, the use the
// cached hash sequences, otherwise write all zeroes for the
// hashSequence.
if hashType&SigHashAnyOneCanPay == 0 &&
hashType&sigHashMask != SigHashSingle &&
hashType&sigHashMask != SigHashNone {
sigHash.Write(sigHashes.HashSequence[:])
} else {
sigHash.Write(zeroHash[:])
}
txIn := tx.TxIn[idx]
// Next, write the outpoint being spent.
sigHash.Write(txIn.PreviousOutPoint.Hash[:])
var bIndex [4]byte
binary.LittleEndian.PutUint32(bIndex[:], txIn.PreviousOutPoint.Index)
sigHash.Write(bIndex[:])
if isWitnessPubKeyHash(subScript) {
// The script code for a p2wkh is a length prefix varint for
// the next 25 bytes, followed by a re-creation of the original
// p2pkh pk script.
sigHash.Write([]byte{0x19})
sigHash.Write([]byte{OP_DUP})
sigHash.Write([]byte{OP_HASH160})
sigHash.Write([]byte{OP_DATA_20})
sigHash.Write(subScript[1].data)
sigHash.Write([]byte{OP_EQUALVERIFY})
sigHash.Write([]byte{OP_CHECKSIG})
} else {
// For p2wsh outputs, and future outputs, the script code is
// the original script, with all code separators removed,
// serialized with a var int length prefix.
rawScript, _ := unparseScript(subScript)
wire.WriteVarBytes(&sigHash, 0, rawScript)
}
// Next, add the input amount, and sequence number of the input being
// signed.
var bAmount [8]byte
binary.LittleEndian.PutUint64(bAmount[:], uint64(amt))
sigHash.Write(bAmount[:])
var bSequence [4]byte
binary.LittleEndian.PutUint32(bSequence[:], txIn.Sequence)
sigHash.Write(bSequence[:])
// If the current signature mode isn't single, or none, then we can
// re-use the pre-generated hashoutputs sighash fragment. Otherwise,
// we'll serialize and add only the target output index to the signature
// pre-image.
if hashType&SigHashSingle != SigHashSingle &&
hashType&SigHashNone != SigHashNone {
sigHash.Write(sigHashes.HashOutputs[:])
} else if hashType&sigHashMask == SigHashSingle && idx < len(tx.TxOut) {
var b bytes.Buffer
wire.WriteTxOut(&b, 0, 0, tx.TxOut[idx])
sigHash.Write(chainhash.DoubleHashB(b.Bytes()))
} else {
sigHash.Write(zeroHash[:])
}
// Finally, write out the transaction's locktime, and the sig hash
// type.
var bLockTime [4]byte
binary.LittleEndian.PutUint32(bLockTime[:], tx.LockTime)
sigHash.Write(bLockTime[:])
var bHashType [4]byte
binary.LittleEndian.PutUint32(bHashType[:], uint32(hashType))
sigHash.Write(bHashType[:])
return chainhash.DoubleHashB(sigHash.Bytes()), nil
}
// CalcWitnessSigHash computes the sighash digest for the specified input of
// the target transaction observing the desired sig hash type.
func CalcWitnessSigHash(script []byte, sigHashes *TxSigHashes, hType SigHashType,
tx *wire.MsgTx, idx int, amt int64) ([]byte, error) {
parsedScript, err := parseScript(script)
if err != nil {
return nil, fmt.Errorf("cannot parse output script: %v", err)
}
return calcWitnessSignatureHash(parsedScript, sigHashes, hType, tx, idx,
amt)
}
// shallowCopyTx creates a shallow copy of the transaction for use when
// calculating the signature hash. It is used over the Copy method on the
// transaction itself since that is a deep copy and therefore does more work and
// allocates much more space than needed.
func shallowCopyTx(tx *wire.MsgTx) wire.MsgTx {
// As an additional memory optimization, use contiguous backing arrays
// for the copied inputs and outputs and point the final slice of
// pointers into the contiguous arrays. This avoids a lot of small
// allocations.
txCopy := wire.MsgTx{
Version: tx.Version,
TxIn: make([]*wire.TxIn, len(tx.TxIn)),
TxOut: make([]*wire.TxOut, len(tx.TxOut)),
LockTime: tx.LockTime,
}
txIns := make([]wire.TxIn, len(tx.TxIn))
for i, oldTxIn := range tx.TxIn {
txIns[i] = *oldTxIn
txCopy.TxIn[i] = &txIns[i]
}
txOuts := make([]wire.TxOut, len(tx.TxOut))
for i, oldTxOut := range tx.TxOut {
txOuts[i] = *oldTxOut
txCopy.TxOut[i] = &txOuts[i]
}
return txCopy
}
// CalcSignatureHash will, given a script and hash type for the current script
// engine instance, calculate the signature hash to be used for signing and
// verification.
func CalcSignatureHash(script []byte, hashType SigHashType, tx *wire.MsgTx, idx int) ([]byte, error) {
parsedScript, err := parseScript(script)
if err != nil {
return nil, fmt.Errorf("cannot parse output script: %v", err)
}
return calcSignatureHash(parsedScript, hashType, tx, idx), nil
}
// calcSignatureHash will, given a script and hash type for the current script
// engine instance, calculate the signature hash to be used for signing and
// verification.
func calcSignatureHash(script []parsedOpcode, hashType SigHashType, tx *wire.MsgTx, idx int) []byte {
// The SigHashSingle signature type signs only the corresponding input
// and output (the output with the same index number as the input).
//
// Since transactions can have more inputs than outputs, this means it
// is improper to use SigHashSingle on input indices that don't have a
// corresponding output.
//
// A bug in the original Satoshi client implementation means specifying
// an index that is out of range results in a signature hash of 1 (as a
// uint256 little endian). The original intent appeared to be to
// indicate failure, but unfortunately, it was never checked and thus is
// treated as the actual signature hash. This buggy behavior is now
// part of the consensus and a hard fork would be required to fix it.
//
// Due to this, care must be taken by software that creates transactions
// which make use of SigHashSingle because it can lead to an extremely
// dangerous situation where the invalid inputs will end up signing a
// hash of 1. This in turn presents an opportunity for attackers to
// cleverly construct transactions which can steal those coins provided
// they can reuse signatures.
if hashType&sigHashMask == SigHashSingle && idx >= len(tx.TxOut) {
var hash chainhash.Hash
hash[0] = 0x01
return hash[:]
}
// Remove all instances of OP_CODESEPARATOR from the script.
script = removeOpcode(script, OP_CODESEPARATOR)
// Make a shallow copy of the transaction, zeroing out the script for
// all inputs that are not currently being processed.
txCopy := shallowCopyTx(tx)
for i := range txCopy.TxIn {
if i == idx {
// UnparseScript cannot fail here because removeOpcode
// above only returns a valid script.
sigScript, _ := unparseScript(script)
txCopy.TxIn[idx].SignatureScript = sigScript
} else {
txCopy.TxIn[i].SignatureScript = nil
}
}
switch hashType & sigHashMask {
case SigHashNone:
txCopy.TxOut = txCopy.TxOut[0:0] // Empty slice.
for i := range txCopy.TxIn {
if i != idx {
txCopy.TxIn[i].Sequence = 0
}
}
case SigHashSingle:
// Resize output array to up to and including requested index.
txCopy.TxOut = txCopy.TxOut[:idx+1]
// All but current output get zeroed out.
for i := 0; i < idx; i++ {
txCopy.TxOut[i].Value = -1
txCopy.TxOut[i].PkScript = nil
}
// Sequence on all other inputs is 0, too.
for i := range txCopy.TxIn {
if i != idx {
txCopy.TxIn[i].Sequence = 0
}
}
default:
// Consensus treats undefined hashtypes like normal SigHashAll
// for purposes of hash generation.
fallthrough
case SigHashOld:
fallthrough
case SigHashAll:
// Nothing special here.
}
if hashType&SigHashAnyOneCanPay != 0 {
txCopy.TxIn = txCopy.TxIn[idx : idx+1]
}
// The final hash is the double sha256 of both the serialized modified
// transaction and the hash type (encoded as a 4-byte little-endian
// value) appended.
wbuf := bytes.NewBuffer(make([]byte, 0, txCopy.SerializeSizeStripped()+4))
txCopy.SerializeNoWitness(wbuf)
binary.Write(wbuf, binary.LittleEndian, hashType)
return chainhash.DoubleHashB(wbuf.Bytes())
}
// asSmallInt returns the passed opcode, which must be true according to
// isSmallInt(), as an integer.
func asSmallInt(op *opcode) int {
if op.value == OP_0 {
return 0
}
return int(op.value - (OP_1 - 1))
}
// getSigOpCount is the implementation function for counting the number of
// signature operations in the script provided by pops. If precise mode is
// requested then we attempt to count the number of operations for a multisig
// op. Otherwise we use the maximum.
func getSigOpCount(pops []parsedOpcode, precise bool) int {
nSigs := 0
for i, pop := range pops {
switch pop.opcode.value {
case OP_CHECKSIG:
fallthrough
case OP_CHECKSIGVERIFY:
nSigs++
case OP_CHECKMULTISIG:
fallthrough
case OP_CHECKMULTISIGVERIFY:
// If we are being precise then look for familiar
// patterns for multisig, for now all we recognize is
// OP_1 - OP_16 to signify the number of pubkeys.
// Otherwise, we use the max of 20.
if precise && i > 0 &&
pops[i-1].opcode.value >= OP_1 &&
pops[i-1].opcode.value <= OP_16 {
nSigs += asSmallInt(pops[i-1].opcode)
} else {
nSigs += MaxPubKeysPerMultiSig
}
default:
// Not a sigop.
}
}
return nSigs
}
// GetSigOpCount provides a quick count of the number of signature operations
// in a script. a CHECKSIG operations counts for 1, and a CHECK_MULTISIG for 20.
// If the script fails to parse, then the count up to the point of failure is
// returned.
func GetSigOpCount(script []byte) int {
// Don't check error since parseScript returns the parsed-up-to-error
// list of pops.
pops, _ := parseScript(script)
return getSigOpCount(pops, false)
}
// GetPreciseSigOpCount returns the number of signature operations in
// scriptPubKey. If bip16 is true then scriptSig may be searched for the
// Pay-To-Script-Hash script in order to find the precise number of signature
// operations in the transaction. If the script fails to parse, then the count
// up to the point of failure is returned.
func GetPreciseSigOpCount(scriptSig, scriptPubKey []byte, bip16 bool) int {
// Don't check error since parseScript returns the parsed-up-to-error
// list of pops.
pops, _ := parseScript(scriptPubKey)
// Treat non P2SH transactions as normal.
if !(bip16 && isScriptHash(pops)) {
return getSigOpCount(pops, true)
}
// The public key script is a pay-to-script-hash, so parse the signature
// script to get the final item. Scripts that fail to fully parse count
// as 0 signature operations.
sigPops, err := parseScript(scriptSig)
if err != nil {
return 0
}
// The signature script must only push data to the stack for P2SH to be
// a valid pair, so the signature operation count is 0 when that is not
// the case.
if !isPushOnly(sigPops) || len(sigPops) == 0 {
return 0
}
// The P2SH script is the last item the signature script pushes to the
// stack. When the script is empty, there are no signature operations.
shScript := sigPops[len(sigPops)-1].data
if len(shScript) == 0 {
return 0
}
// Parse the P2SH script and don't check the error since parseScript
// returns the parsed-up-to-error list of pops and the consensus rules
// dictate signature operations are counted up to the first parse
// failure.
shPops, _ := parseScript(shScript)
return getSigOpCount(shPops, true)
}
// GetWitnessSigOpCount returns the number of signature operations generated by
// spending the passed pkScript with the specified witness, or sigScript.
// Unlike GetPreciseSigOpCount, this function is able to accurately count the
// number of signature operations generated by spending witness programs, and
// nested p2sh witness programs. If the script fails to parse, then the count
// up to the point of failure is returned.
func GetWitnessSigOpCount(sigScript, pkScript []byte, witness wire.TxWitness) int {
// If this is a regular witness program, then we can proceed directly
// to counting its signature operations without any further processing.
if IsWitnessProgram(pkScript) {
return getWitnessSigOps(pkScript, witness)
}
// Next, we'll check the sigScript to see if this is a nested p2sh
// witness program. This is a case wherein the sigScript is actually a
// datapush of a p2wsh witness program.
sigPops, err := parseScript(sigScript)
if err != nil {
return 0
}
if IsPayToScriptHash(pkScript) && isPushOnly(sigPops) &&
IsWitnessProgram(sigScript[1:]) {
return getWitnessSigOps(sigScript[1:], witness)
}
return 0
}
// getWitnessSigOps returns the number of signature operations generated by
// spending the passed witness program wit the passed witness. The exact
// signature counting heuristic is modified by the version of the passed
// witness program. If the version of the witness program is unable to be
// extracted, then 0 is returned for the sig op count.
func getWitnessSigOps(pkScript []byte, witness wire.TxWitness) int {
// Attempt to extract the witness program version.
witnessVersion, witnessProgram, err := ExtractWitnessProgramInfo(
pkScript,
)
if err != nil {
return 0
}
switch witnessVersion {
case 0:
switch {
case len(witnessProgram) == payToWitnessPubKeyHashDataSize:
return 1
case len(witnessProgram) == payToWitnessScriptHashDataSize &&
len(witness) > 0:
witnessScript := witness[len(witness)-1]
pops, _ := parseScript(witnessScript)
return getSigOpCount(pops, true)
}
}
return 0
}
// IsUnspendable returns whether the passed public key script is unspendable, or
// guaranteed to fail at execution. This allows inputs to be pruned instantly
// when entering the UTXO set.
func IsUnspendable(pkScript []byte) bool {
pops, err := parseScript(pkScript)
if err != nil {
return true
}
return len(pops) > 0 && pops[0].opcode.value == OP_RETURN
}
You can’t perform that action at this time.