txscript: Implement CheckLockTimeVerify (BIP0065)

See https://github.com/bitcoin/bips/blob/master/bip-0065.mediawiki for
more information.

This commit mimics Bitcoin Core commit bc60b2b4b401f0adff5b8b9678903ff8feb5867b
and includes additional tests from Bitcoin Core commit
cb54d17355864fa08826d6511a0d7692b21ef2c9

txscript/data/tx_invalid.json

@@ -114,6 +114,78 @@
 [[["a955032f4d6b0c9bfe8cad8f00a8933790b9c1dc28c82e0f48e75b35da0e4944", 0, "IF CODESEPARATOR ENDIF 0x21 0x0378d430274f8c5ec1321338151e9f27f4c676a008bdf8638d07c0b6be9ab35c71 CHECKSIGVERIFY CODESEPARATOR 1"]],
 "010000000144490eda355be7480f2ec828dcc1b9903793a8008fad8cfe9b0c6b4d2f0355a9000000004a483045022100fa4a74ba9fd59c59f46c3960cf90cbe0d2b743c471d24a3d5d6db6002af5eebb02204d70ec490fd0f7055a7c45f86514336e3a7f03503dacecabb247fc23f15c83510100ffffffff010000000000000000016a00000000", "P2SH"],
 
+["CHECKLOCKTIMEVERIFY tests"],
+
+["By-height locks, with argument just beyond tx nLockTime"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "1 NOP2 1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "499999999 NOP2 1"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000fe64cd1d", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["By-time locks, with argument just beyond tx nLockTime (but within numerical boundaries)"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "500000001 NOP2 1"]],
+"01000000010001000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000065cd1d", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4294967295 NOP2 1"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000feffffff", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Argument missing"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "NOP2 1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000001b1010000000100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Argument negative with by-blockheight nLockTime=0"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "-1 NOP2 1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Argument negative with by-blocktime nLockTime=500,000,000"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "-1 NOP2 1"]],
+"01000000010001000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000065cd1d", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000004005194b1010000000100000000000000000002000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Input locked"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0 NOP2 1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffffff0100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0"]],
+"01000000010001000000000000000000000000000000000000000000000000000000000000000000000251b1ffffffff0100000000000000000002000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Another input being unlocked isn't sufficient; the CHECKLOCKTIMEVERIFY-using input must be unlocked"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0 NOP2 1"] ,
+  ["0000000000000000000000000000000000000000000000000000000000000200", 1, "1"]],
+"010000000200010000000000000000000000000000000000000000000000000000000000000000000000ffffffff00020000000000000000000000000000000000000000000000000000000000000100000000000000000100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Argument/tx height/time mismatch, both versions"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0 NOP2 1"]],
+"01000000010001000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000065cd1d", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0"]],
+"01000000010001000000000000000000000000000000000000000000000000000000000000000000000251b100000000010000000000000000000065cd1d", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "499999999 NOP2 1"]],
+"01000000010001000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000065cd1d", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "500000000 NOP2 1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "500000000 NOP2 1"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000ff64cd1d", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Argument 2^32 with nLockTime=2^32-1"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4294967296 NOP2 1"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000ffffffff", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Same, but with nLockTime=2^31-1"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "2147483648 NOP2 1"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000ffffff7f", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["6 byte non-minimally-encoded arguments are invalid even if their contents are valid"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0x06 0x000000000000 NOP2 1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Failure due to failing CHECKLOCKTIMEVERIFY in scriptSig"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "1"]],
+"01000000010001000000000000000000000000000000000000000000000000000000000000000000000251b1000000000100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Failure due to failing CHECKLOCKTIMEVERIFY in redeemScript"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "HASH160 0x14 0xc5b93064159b3b2d6ab506a41b1f50463771b988 EQUAL"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000030251b1000000000100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
 
 ["Make diffs cleaner by leaving a comment here without comma at the end"]
 ]

txscript/data/tx_valid.json

@@ -187,5 +187,47 @@
 "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", "P2SH"],
 
 
+["CHECKLOCKTIMEVERIFY tests"],
+
+["By-height locks, with argument == 0 and == tx nLockTime"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0 NOP2 1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "499999999 NOP2 1"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000ff64cd1d", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0 NOP2 1"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000ff64cd1d", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["By-time locks, with argument just beyond tx nLockTime (but within numerical boundaries)"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "500000000 NOP2 1"]],
+"01000000010001000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000065cd1d", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4294967295 NOP2 1"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000ffffffff", "P2SH,CHECKLOCKTIMEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "500000000 NOP2 1"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000ffffffff", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Any non-maxint nSequence is fine"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0 NOP2 1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000000feffffff0100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["The argument can be calculated rather than created directly by a PUSHDATA"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "499999999 1ADD NOP2 1"]],
+"01000000010001000000000000000000000000000000000000000000000000000000000000000000000000000000010000000000000000000065cd1d", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Perhaps even by an ADD producing a 5-byte result that is out of bounds for other opcodes"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "2147483647 2147483647 ADD NOP2 1"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000feffffff", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["5 byte non-minimally-encoded arguments are valid"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0x05 0x0000000000 NOP2 1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Valid CHECKLOCKTIMEVERIFY in scriptSig"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "1"]],
+"01000000010001000000000000000000000000000000000000000000000000000000000000000000000251b1000000000100000000000000000001000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+
+["Valid CHECKLOCKTIMEVERIFY in redeemScript"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "HASH160 0x14 0xc5b93064159b3b2d6ab506a41b1f50463771b988 EQUAL"]],
+"0100000001000100000000000000000000000000000000000000000000000000000000000000000000030251b1000000000100000000000000000001000000", "P2SH,CHECKLOCKTIMEVERIFY"],
+
 ["Make diffs cleaner by leaving a comment here without comma at the end"]
 ]

txscript/engine.go

@@ -33,6 +33,11 @@ const (
 	// executed.
 	ScriptDiscourageUpgradableNops
 
+	// ScriptVerifyCheckLockTimeVerify defines whether to verify that
+	// a transaction output is spendable based on the locktime.
+	// This is BIP0065.
+	ScriptVerifyCheckLockTimeVerify
+
 	// ScriptVerifyCleanStack defines that the stack must contain only
 	// one stack element after evaluation and that the element must be
 	// true if interpreted as a boolean.  This is rule 6 of BIP0062.

txscript/opcode.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"crypto/sha1"
 	"encoding/binary"
+	"errors"
 	"fmt"
 	"hash"
 
@@ -212,6 +213,7 @@ const (
 	OP_CHECKMULTISIGVERIFY = 0xaf // 175
 	OP_NOP1                = 0xb0 // 176
 	OP_NOP2                = 0xb1 // 177
+	OP_CHECKLOCKTIMEVERIFY = 0xb1 // 177 - AKA OP_NOP2
 	OP_NOP3                = 0xb2 // 178
 	OP_NOP4                = 0xb3 // 179
 	OP_NOP5                = 0xb4 // 180
@@ -413,6 +415,7 @@ var opcodeArray = [256]opcode{
 	OP_ENDIF:               {OP_ENDIF, "OP_ENDIF", 1, opcodeEndif},
 	OP_VERIFY:              {OP_VERIFY, "OP_VERIFY", 1, opcodeVerify},
 	OP_RETURN:              {OP_RETURN, "OP_RETURN", 1, opcodeReturn},
+	OP_CHECKLOCKTIMEVERIFY: {OP_CHECKLOCKTIMEVERIFY, "OP_CHECKLOCKTIMEVERIFY", 1, opcodeCheckLockTimeVerify},
 
 	// Stack opcodes.
 	OP_TOALTSTACK:   {OP_TOALTSTACK, "OP_TOALTSTACK", 1, opcodeToAltStack},
@@ -495,7 +498,6 @@ var opcodeArray = [256]opcode{
 
 	// Reserved opcodes.
 	OP_NOP1:  {OP_NOP1, "OP_NOP1", 1, opcodeNop},
-	OP_NOP2:  {OP_NOP2, "OP_NOP2", 1, opcodeNop},
 	OP_NOP3:  {OP_NOP3, "OP_NOP3", 1, opcodeNop},
 	OP_NOP4:  {OP_NOP4, "OP_NOP4", 1, opcodeNop},
 	OP_NOP5:  {OP_NOP5, "OP_NOP5", 1, opcodeNop},
@@ -873,7 +875,7 @@ func opcodeN(op *parsedOpcode, vm *Engine) error {
 // the flag to discourage use of NOPs is set for select opcodes.
 func opcodeNop(op *parsedOpcode, vm *Engine) error {
 	switch op.opcode.value {
-	case OP_NOP1, OP_NOP2, OP_NOP3, OP_NOP4, OP_NOP5,
+	case OP_NOP1, OP_NOP3, OP_NOP4, OP_NOP5,
 		OP_NOP6, OP_NOP7, OP_NOP8, OP_NOP9, OP_NOP10:
 		if vm.hasFlag(ScriptDiscourageUpgradableNops) {
 			return fmt.Errorf("OP_NOP%d reserved for soft-fork "+
@@ -1006,6 +1008,86 @@ func opcodeReturn(op *parsedOpcode, vm *Engine) error {
 	return ErrStackEarlyReturn
 }
 
+// opcodeCheckLockTimeVerify compares the top item on the data stack to the
+// LockTime field of the transaction containing the script signature
+// validating if the transaction outputs are spendable yet.  If flag
+// ScriptVerifyCheckLockTimeVerify is not set, the code continues as if OP_NOP2
+// were executed.
+func opcodeCheckLockTimeVerify(op *parsedOpcode, vm *Engine) error {
+	// If the ScriptVerifyCheckLockTimeVerify script flag is not set, treat
+	// opcode as OP_NOP2 instead.
+	if !vm.hasFlag(ScriptVerifyCheckLockTimeVerify) {
+		if vm.hasFlag(ScriptDiscourageUpgradableNops) {
+			return errors.New("OP_NOP2 reserved for soft-fork " +
+				"upgrades")
+		}
+		return nil
+	}
+
+	// The current transaction locktime is a uint32 resulting in a maximum
+	// locktime of 2^32-1 (the year 2106).  However, scriptNums are signed
+	// and therefore a standard 4-byte scriptNum would only support up to a
+	// maximum of 2^31-1 (the year 2038).  Thus, a 5-byte scriptNum is used
+	// here since it will support up to 2^39-1 which allows dates beyond the
+	// current locktime limit.
+	//
+	// PeekByteArray is used here instead of PeekInt because we do not want
+	// to be limited to a 4-byte integer for reasons specified above.
+	so, err := vm.dstack.PeekByteArray(0)
+	if err != nil {
+		return err
+	}
+	lockTime, err := makeScriptNum(so, vm.dstack.verifyMinimalData, 5)
+	if err != nil {
+		return err
+	}
+
+	// In the rare event that the argument may be < 0 due to some arithmetic
+	// being done first, you can always use 0 OP_MAX OP_CHECKLOCKTIMEVERIFY.
+	if lockTime < 0 {
+		return fmt.Errorf("negative locktime: %d", lockTime)
+	}
+
+	// The lock time field of a transaction is either a block height at
+	// which the transaction is finalized or a timestamp depending on if the
+	// value is before the txscript.LockTimeThreshold.  When it is under the
+	// threshold it is a block height.
+	//
+	// The lockTimes in both the script and transaction must be of the same
+	// type.
+	if !((vm.tx.LockTime < LockTimeThreshold && int64(lockTime) < int64(LockTimeThreshold)) ||
+		(vm.tx.LockTime >= LockTimeThreshold && int64(lockTime) >= int64(LockTimeThreshold))) {
+		return fmt.Errorf("mismatched locktime types -- tx locktime %d, stack "+
+			"locktime %d", vm.tx.LockTime, lockTime)
+	}
+
+	if int64(lockTime) > int64(vm.tx.LockTime) {
+		str := "locktime requirement not satisfied -- locktime is " +
+			"greater than the transaction locktime: %d > %d"
+		return fmt.Errorf(str, lockTime, vm.tx.LockTime)
+	}
+
+	// The lock time feature can also be disabled, thereby bypassing
+	// OP_CHECKLOCKTIMEVERIFY, if every transaction input has been finalized by
+	// setting its sequence to the maximum value (wire.MaxTxInSequenceNum).  This
+	// condition would result in the transaction being allowed into the blockchain
+	// making the opcode ineffective.
+	//
+	// This condition is prevented by enforcing that the input being used by
+	// the opcode is unlocked (its sequence number is less than the max
+	// value).  This is sufficient to prove correctness without having to
+	// check every input.
+	//
+	// NOTE: This implies that even if the transaction is not finalized due to
+	// another input being unlocked, the opcode execution will still fail when the
+	// input being used by the opcode is locked.
+	if vm.tx.TxIn[vm.txIdx].Sequence == wire.MaxTxInSequenceNum {
+		return errors.New("transaction input is finalized")
+	}
+
+	return nil
+}
+
 // opcodeToAltStack removes the top item from the main data stack and pushes it
 // onto the alternate data stack.
 //
@@ -2109,11 +2191,13 @@ var OpcodeByName = make(map[string]byte)
 
 func init() {
 	// Initialize the opcode name to value map using the contents of the
-	// opcode array.  Also add entries for "OP_FALSE" and "OP_TRUE" since
+	// opcode array.  Also add entries for "OP_FALSE", "OP_TRUE", and
-	// they are aliases for "OP_0" and "OP_1", respectively.
+	// "OP_NOP2" since they are aliases for "OP_0", "OP_1",
+	// and "OP_CHECKLOCKTIMEVERIFY" respectively.
 	for _, op := range opcodeArray {
 		OpcodeByName[op.name] = op.value
 	}
 	OpcodeByName["OP_FALSE"] = OP_FALSE
 	OpcodeByName["OP_TRUE"] = OP_TRUE
+	OpcodeByName["OP_NOP2"] = OP_CHECKLOCKTIMEVERIFY
 }

txscript/opcode_test.go

@@ -109,8 +109,13 @@ func TestOpcodeDisasm(t *testing.T) {
 
 		// OP_NOP1 through OP_NOP10.
 		case opcodeVal >= 0xb0 && opcodeVal <= 0xb9:
+			// OP_NOP2 is an alias of OP_CHECKLOCKTIMEVERIFY
+			if opcodeVal == 0xb1 {
+				expectedStr = "OP_CHECKLOCKTIMEVERIFY"
+			} else {
 				val := byte(opcodeVal - (0xb0 - 1))
 				expectedStr = "OP_NOP" + strconv.Itoa(int(val))
+			}
 
 		// OP_UNKNOWN#.
 		case opcodeVal >= 0xba && opcodeVal <= 0xf8 || opcodeVal == 0xfc:
@@ -166,8 +171,13 @@ func TestOpcodeDisasm(t *testing.T) {
 
 		// OP_NOP1 through OP_NOP10.
 		case opcodeVal >= 0xb0 && opcodeVal <= 0xb9:
+			// OP_NOP2 is an alias of OP_CHECKLOCKTIMEVERIFY
+			if opcodeVal == 0xb1 {
+				expectedStr = "OP_CHECKLOCKTIMEVERIFY"
+			} else {
 				val := byte(opcodeVal - (0xb0 - 1))
 				expectedStr = "OP_NOP" + strconv.Itoa(int(val))
+			}
 
 		// OP_UNKNOWN#.
 		case opcodeVal >= 0xba && opcodeVal <= 0xf8 || opcodeVal == 0xfc:

txscript/reference_test.go

@@ -124,6 +124,8 @@ func parseScriptFlags(flagStr string) (ScriptFlags, error) {
 		switch flag {
 		case "":
 			// Nothing.
+		case "CHECKLOCKTIMEVERIFY":
+			flags |= ScriptVerifyCheckLockTimeVerify
 		case "CLEANSTACK":
 			flags |= ScriptVerifyCleanStack
 		case "DERSIG":

txscript/standard.go

@@ -31,6 +31,7 @@ const (
 		ScriptStrictMultiSig |
 		ScriptDiscourageUpgradableNops |
 		ScriptVerifyCleanStack |
+		ScriptVerifyCheckLockTimeVerify |
 		ScriptVerifyLowS
 )