txscript: Implement CheckSequenceVerify (BIP0112)

txscript/consensus.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2015 The btcsuite developers
+// Copyright (c) 2015-2016 The btcsuite developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -8,7 +8,6 @@ const (
 	// LockTimeThreshold is the number below which a lock time is
 	// interpreted to be a block number.  Since an average of one block
 	// is generated per 10 minutes, this allows blocks for about 9,512
-	// years.  However, if the field is interpreted as a timestamp, given
+	// years.
-	// the lock time is a uint32, the max is sometime around 2106.
+	LockTimeThreshold = 5e8 // Tue Nov 5 00:53:20 1985 UTC
-	LockTimeThreshold uint32 = 5e8 // Tue Nov 5 00:53:20 1985 UTC
 )

txscript/data/tx_invalid.json

@@ -191,5 +191,59 @@
 [[["b1dbc81696c8a9c0fccd0693ab66d7c368dbc38c0def4e800685560ddd1b2132", 0, "DUP HASH160 0x14 0x4b3bd7eba3bc0284fd3007be7f3be275e94f5826 EQUALVERIFY CHECKSIG"]],
 "010000000132211bdd0d568506804eef0d8cc3db68c3d766ab9306cdfcc0a9c89616c8dbb1000000006c493045022100c7bb0faea0522e74ff220c20c022d2cb6033f8d167fb89e75a50e237a35fd6d202203064713491b1f8ad5f79e623d0219ad32510bfaa1009ab30cbee77b59317d6e30001210237af13eb2d84e4545af287b919c2282019c9691cc509e78e196a9d8274ed1be0ffffffff0100000000000000001976a914f1b3ed2eda9a2ebe5a9374f692877cdf87c0f95b88ac00000000", "P2SH,DERSIG"],
 
+["CHECKSEQUENCEVERIFY tests"],
+
+["By-height locks, with argument just beyond txin.nSequence"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "1 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4259839 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000feff40000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["By-time locks, with argument just beyond txin.nSequence (but within numerical boundries)"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4194305 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000040000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4259839 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000feff40000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Argument missing"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Argument negative with by-blockheight txin.nSequence=0"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "-1 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Argument negative with by-blocktime txin.nSequence=CTxIn::SEQUENCE_UNITS_THRESHOD"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "-1 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000040000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Argument/tx height/time mismatch, both versions"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000040000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "65535 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000040000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4194304 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4259839 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["6 byte non-minimally-encoded arguments are invalid even if their contents are valid"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0x06 0x000000000000 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffff00000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Failure due to failing CHECKSEQUENCEVERIFY in scriptSig"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "1"]],
+"02000000010001000000000000000000000000000000000000000000000000000000000000000000000251b2000000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Failure due to failing CHECKSEQUENCEVERIFY in redeemScript"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "HASH160 0x14 0x7c17aff532f22beb54069942f9bf567a66133eaf EQUAL"]],
+"0200000001000100000000000000000000000000000000000000000000000000000000000000000000030251b2000000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Failure due to insufficient tx.nVersion (<2)"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0 NOP3 1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4194304 NOP3 1"]],
+"010000000100010000000000000000000000000000000000000000000000000000000000000000000000000040000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
 ["Make diffs cleaner by leaving a comment here without comma at the end"]
 ]

txscript/data/tx_valid.json

@@ -233,5 +233,89 @@
 [[["b1dbc81696c8a9c0fccd0693ab66d7c368dbc38c0def4e800685560ddd1b2132", 0, "DUP HASH160 0x14 0x4b3bd7eba3bc0284fd3007be7f3be275e94f5826 EQUALVERIFY CHECKSIG"]],
 "010000000132211bdd0d568506804eef0d8cc3db68c3d766ab9306cdfcc0a9c89616c8dbb1000000006c493045022100c7bb0faea0522e74ff220c20c022d2cb6033f8d167fb89e75a50e237a35fd6d202203064713491b1f8ad5f79e623d0219ad32510bfaa1009ab30cbee77b59317d6e30001210237af13eb2d84e4545af287b919c2282019c9691cc509e78e196a9d8274ed1be0ffffffff0100000000000000001976a914f1b3ed2eda9a2ebe5a9374f692877cdf87c0f95b88ac00000000", "P2SH"],
 
+["CHECKSEQUENCEVERIFY tests"],
+
+["By-height locks, with argument == 0 and == txin.nSequence"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "65535 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffff00000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "65535 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffbf7f0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffbf7f0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["By-time locks, with argument == 0 and == txin.nSequence"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4194304 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000040000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4259839 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffff40000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4259839 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffff7f0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4194304 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffff7f0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Upper sequence with upper sequence is fine"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "2147483648 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000000800100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4294967295 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000000800100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "2147483648 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000feffffff0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4294967295 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000feffffff0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "2147483648 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffffff0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4294967295 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffffff0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Argument 2^31 with various nSequence"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "2147483648 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffbf7f0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "2147483648 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffff7f0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "2147483648 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffffff0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Argument 2^32-1 with various nSequence"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4294967295 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffbf7f0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4294967295 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffff7f0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4294967295 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffffff0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Argument 3<<31 with various nSequence"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "6442450944 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffbf7f0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "6442450944 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffff7f0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "6442450944 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffffffff0100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["5 byte non-minimally-encoded operandss are valid"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "0x05 0x0000000000 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["The argument can be calculated rather than created directly by a PUSHDATA"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4194303 1ADD NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000040000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "4194304 1SUB NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000ffff00000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["An ADD producing a 5-byte result that sets CTxIn::SEQUENCE_LOCKTIME_DISABLED_FLAG"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "2147483647 65536 NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "2147483647 4259840 ADD NOP3 1"]],
+"020000000100010000000000000000000000000000000000000000000000000000000000000000000000000040000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Valid CHECKSEQUENCEVERIFY in scriptSig"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "1"]],
+"02000000010001000000000000000000000000000000000000000000000000000000000000000000000251b2010000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
+["Valid CHECKSEQUENCEVERIFY in redeemScript"],
+[[["0000000000000000000000000000000000000000000000000000000000000100", 0, "HASH160 0x14 0x7c17aff532f22beb54069942f9bf567a66133eaf EQUAL"]],
+"0200000001000100000000000000000000000000000000000000000000000000000000000000000000030251b2010000000100000000000000000000000000", "P2SH,CHECKSEQUENCEVERIFY"],
+
 ["Make diffs cleaner by leaving a comment here without comma at the end"]
 ]

txscript/engine.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2013-2015 The btcsuite developers
+// Copyright (c) 2013-2016 The btcsuite developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -38,6 +38,11 @@ const (
 	// This is BIP0065.
 	ScriptVerifyCheckLockTimeVerify
 
+	// ScriptVerifyCheckSequenceVerify defines whether to allow execution
+	// pathways of a script to be restricted based on the age of the output
+	// being spent.  This is BIP0112.
+	ScriptVerifyCheckSequenceVerify
+
 	// 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

@@ -216,6 +216,7 @@ const (
 	OP_NOP2                = 0xb1 // 177
 	OP_CHECKLOCKTIMEVERIFY = 0xb1 // 177 - AKA OP_NOP2
 	OP_NOP3                = 0xb2 // 178
+	OP_CHECKSEQUENCEVERIFY = 0xb2 // 178 - AKA OP_NOP3
 	OP_NOP4                = 0xb3 // 179
 	OP_NOP5                = 0xb4 // 180
 	OP_NOP6                = 0xb5 // 181
@@ -417,6 +418,7 @@ var opcodeArray = [256]opcode{
 	OP_VERIFY:              {OP_VERIFY, "OP_VERIFY", 1, opcodeVerify},
 	OP_RETURN:              {OP_RETURN, "OP_RETURN", 1, opcodeReturn},
 	OP_CHECKLOCKTIMEVERIFY: {OP_CHECKLOCKTIMEVERIFY, "OP_CHECKLOCKTIMEVERIFY", 1, opcodeCheckLockTimeVerify},
+	OP_CHECKSEQUENCEVERIFY: {OP_CHECKSEQUENCEVERIFY, "OP_CHECKSEQUENCEVERIFY", 1, opcodeCheckSequenceVerify},
 
 	// Stack opcodes.
 	OP_TOALTSTACK:   {OP_TOALTSTACK, "OP_TOALTSTACK", 1, opcodeToAltStack},
@@ -499,7 +501,6 @@ var opcodeArray = [256]opcode{
 
 	// Reserved opcodes.
 	OP_NOP1:  {OP_NOP1, "OP_NOP1", 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},
 	OP_NOP6:  {OP_NOP6, "OP_NOP6", 1, opcodeNop},
@@ -876,7 +877,7 @@ 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_NOP3, OP_NOP4, OP_NOP5,
+	case OP_NOP1, 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 "+
@@ -1009,6 +1010,25 @@ func opcodeReturn(op *parsedOpcode, vm *Engine) error {
 	return ErrStackEarlyReturn
 }
 
+// verifyLockTime is a helper function used to validate locktimes.
+func verifyLockTime(txLockTime, threshold, lockTime int64) error {
+	// The lockTimes in both the script and transaction must be of the same
+	// type.
+	if !((txLockTime < threshold && lockTime < threshold) ||
+		(txLockTime >= threshold && lockTime >= threshold)) {
+		return fmt.Errorf("mismatched locktime types -- tx locktime %d, stack "+
+			"locktime %d", txLockTime, lockTime)
+	}
+
+	if lockTime > txLockTime {
+		str := "locktime requirement not satisfied -- locktime is " +
+			"greater than the transaction locktime: %d > %d"
+		return fmt.Errorf(str, lockTime, txLockTime)
+	}
+
+	return nil
+}
+
 // 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
@@ -1043,8 +1063,9 @@ func opcodeCheckLockTimeVerify(op *parsedOpcode, vm *Engine) error {
 		return err
 	}
 
-	// In the rare event that the argument may be < 0 due to some arithmetic
+	// In the rare event that the argument needs to be < 0 due to some
-	// being done first, you can always use 0 OP_MAX OP_CHECKLOCKTIMEVERIFY.
+	// arithmetic being done first, you can always use
+	// 0 OP_MAX OP_CHECKLOCKTIMEVERIFY.
 	if lockTime < 0 {
 		return fmt.Errorf("negative locktime: %d", lockTime)
 	}
@@ -1053,19 +1074,10 @@ func opcodeCheckLockTimeVerify(op *parsedOpcode, vm *Engine) error {
 	// 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.
-	//
+	err = verifyLockTime(int64(vm.tx.LockTime), LockTimeThreshold,
-	// The lockTimes in both the script and transaction must be of the same
+		int64(lockTime))
-	// type.
+	if err != nil {
-	if !((vm.tx.LockTime < LockTimeThreshold && int64(lockTime) < int64(LockTimeThreshold)) ||
+		return err
-		(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
@@ -1089,6 +1101,84 @@ func opcodeCheckLockTimeVerify(op *parsedOpcode, vm *Engine) error {
 	return nil
 }
 
+// opcodeCheckSequenceVerify 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
+// ScriptVerifyCheckSequenceVerify is not set, the code continues as if OP_NOP3
+// were executed.
+func opcodeCheckSequenceVerify(op *parsedOpcode, vm *Engine) error {
+	// If the ScriptVerifyCheckSequenceVerify script flag is not set, treat
+	// opcode as OP_NOP3 instead.
+	if !vm.hasFlag(ScriptVerifyCheckSequenceVerify) {
+		if vm.hasFlag(ScriptDiscourageUpgradableNops) {
+			return errors.New("OP_NOP3 reserved for soft-fork " +
+				"upgrades")
+		}
+		return nil
+	}
+
+	if vm.tx.Version < 2 {
+		return fmt.Errorf("invalid transaction version: %d",
+			vm.tx.Version)
+	}
+
+	// The current transaction sequence is a uint32 resulting in a maximum
+	// sequence of 2^32-1.  However, scriptNums are signed and therefore a
+	// standard 4-byte scriptNum would only support up to a maximum of
+	// 2^31-1.  Thus, a 5-byte scriptNum is used here since it will support
+	// up to 2^39-1 which allows sequences beyond the current sequence
+	// 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
+	}
+	stackSequence, err := makeScriptNum(so, vm.dstack.verifyMinimalData, 5)
+	if err != nil {
+		return err
+	}
+
+	// In the rare event that the argument needs to be < 0 due to some
+	// arithmetic being done first, you can always use
+	// 0 OP_MAX OP_CHECKSEQUENCEVERIFY.
+	if stackSequence < 0 {
+		return fmt.Errorf("negative sequence: %d", stackSequence)
+	}
+
+	sequence := int64(stackSequence)
+
+	// To provide for future soft-fork extensibility, if the
+	// operand has the disabled lock-time flag set,
+	// CHECKSEQUENCEVERIFY behaves as a NOP.
+	if sequence&int64(wire.SequenceLockTimeDisabled) != 0 {
+		return nil
+	}
+
+	// Sequence numbers with their most significant bit set are not
+	// consensus constrained. Testing that the transaction's sequence
+	// number does not have this bit set prevents using this property
+	// to get around a CHECKSEQUENCEVERIFY check.
+	txSequence := int64(vm.tx.TxIn[vm.txIdx].Sequence)
+	if txSequence&int64(wire.SequenceLockTimeDisabled) != 0 {
+		return fmt.Errorf("transaction sequence has sequence "+
+			"locktime disabled bit set: 0x%x", txSequence)
+	}
+
+	// Mask off non-consensus bits before doing comparisons.
+	lockTimeMask := int64(wire.SequenceLockTimeIsSeconds |
+		wire.SequenceLockTimeMask)
+	err = verifyLockTime(txSequence&lockTimeMask,
+		wire.SequenceLockTimeIsSeconds,
+		sequence&lockTimeMask)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
 // opcodeToAltStack removes the top item from the main data stack and pushes it
 // onto the alternate data stack.
 //
@@ -2201,4 +2291,5 @@ func init() {
 	OpcodeByName["OP_FALSE"] = OP_FALSE
 	OpcodeByName["OP_TRUE"] = OP_TRUE
 	OpcodeByName["OP_NOP2"] = OP_CHECKLOCKTIMEVERIFY
+	OpcodeByName["OP_NOP3"] = OP_CHECKSEQUENCEVERIFY
 }

txscript/opcode_test.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2013-2015 The btcsuite developers
+// Copyright (c) 2013-2016 The btcsuite developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -109,10 +109,14 @@ func TestOpcodeDisasm(t *testing.T) {
 
 		// OP_NOP1 through OP_NOP10.
 		case opcodeVal >= 0xb0 && opcodeVal <= 0xb9:
-			// OP_NOP2 is an alias of OP_CHECKLOCKTIMEVERIFY
+			switch opcodeVal {
-			if opcodeVal == 0xb1 {
+			case 0xb1:
+				// OP_NOP2 is an alias of OP_CHECKLOCKTIMEVERIFY
 				expectedStr = "OP_CHECKLOCKTIMEVERIFY"
-			} else {
+			case 0xb2:
+				// OP_NOP3 is an alias of OP_CHECKSEQUENCEVERIFY
+				expectedStr = "OP_CHECKSEQUENCEVERIFY"
+			default:
 				val := byte(opcodeVal - (0xb0 - 1))
 				expectedStr = "OP_NOP" + strconv.Itoa(int(val))
 			}
@@ -171,10 +175,14 @@ func TestOpcodeDisasm(t *testing.T) {
 
 		// OP_NOP1 through OP_NOP10.
 		case opcodeVal >= 0xb0 && opcodeVal <= 0xb9:
-			// OP_NOP2 is an alias of OP_CHECKLOCKTIMEVERIFY
+			switch opcodeVal {
-			if opcodeVal == 0xb1 {
+			case 0xb1:
+				// OP_NOP2 is an alias of OP_CHECKLOCKTIMEVERIFY
 				expectedStr = "OP_CHECKLOCKTIMEVERIFY"
-			} else {
+			case 0xb2:
+				// OP_NOP3 is an alias of OP_CHECKSEQUENCEVERIFY
+				expectedStr = "OP_CHECKSEQUENCEVERIFY"
+			default:
 				val := byte(opcodeVal - (0xb0 - 1))
 				expectedStr = "OP_NOP" + strconv.Itoa(int(val))
 			}

txscript/reference_test.go

@@ -128,6 +128,8 @@ func parseScriptFlags(flagStr string) (ScriptFlags, error) {
 			// Nothing.
 		case "CHECKLOCKTIMEVERIFY":
 			flags |= ScriptVerifyCheckLockTimeVerify
+		case "CHECKSEQUENCEVERIFY":
+			flags |= ScriptVerifyCheckSequenceVerify
 		case "CLEANSTACK":
 			flags |= ScriptVerifyCleanStack
 		case "DERSIG":

txscript/standard.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2013-2015 The btcsuite developers
+// Copyright (c) 2013-2016 The btcsuite developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -32,6 +32,7 @@ const (
 		ScriptDiscourageUpgradableNops |
 		ScriptVerifyCleanStack |
 		ScriptVerifyCheckLockTimeVerify |
+		ScriptVerifyCheckSequenceVerify |
 		ScriptVerifyLowS
 )
 

wire/msgtx.go

@@ -24,14 +24,26 @@ const (
 	// MaxPrevOutIndex is the maximum index the index field of a previous
 	// outpoint can be.
 	MaxPrevOutIndex uint32 = 0xffffffff
-)
 
-const (
+	// SequenceLockTimeDisabled is a flag that if set on a transaction
-	// defaultTxInOutAlloc is the default size used for the backing array
+	// input's sequence number, the sequence number will not be interpreted
-	// for transaction inputs and outputs.  The array will dynamically grow
+	// as a relative locktime.
-	// as needed, but this figure is intended to provide enough space for
+	SequenceLockTimeDisabled = 1 << 31
-	// the number of inputs and outputs in a typical transaction without
+
-	// needing to grow the backing array multiple times.
+	// SequenceLockTimeIsSeconds is a flag that if set on a transaction
+	// input's sequence number, the relative locktime has units of 512
+	// seconds.
+	SequenceLockTimeIsSeconds = 1 << 22
+
+	// SequenceLockTimeMask is a mask that extracts the relative locktime
+	// when masked against the transaction input sequence number.
+	SequenceLockTimeMask = 0x0000ffff
+
+	// defaultTxInOutAlloc is the default size used for the backing array for
+	// transaction inputs and outputs.  The array will dynamically grow as needed,
+	// but this figure is intended to provide enough space for the number of
+	// inputs and outputs in a typical transaction without needing to grow the
+	// backing array multiple times.
 	defaultTxInOutAlloc = 15
 
 	// minTxInPayload is the minimum payload size for a transaction input.