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txscript: Add new flag ScriptVerifyMinimalData
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The ScriptVerifyMinimalData enforces that all push operations use the
minimal data push required.  This is part of BIP0062.

This commit mimics Bitcoin Core commit
698c6abb25c1fbbc7fa4ba46b60e9f17d97332ef
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@dajohi
dajohi committed Feb 24, 2015
1 parent 63c1172 commit 5a4312d
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Showing 6 changed files with 242 additions and 2 deletions.
96 changes: 96 additions & 0 deletions txscript/data/script_invalid.json
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Original file line number Diff line number Diff line change
Expand Up @@ -403,6 +403,102 @@
["0 0x01 VER", "HASH160 0x14 0x0f4d7845db968f2a81b530b6f3c1d6246d4c7e01 EQUAL", "P2SH,STRICTENC", "OP_VER in P2SH should fail"],

["0x00", "'00' EQUAL", "P2SH,STRICTENC", "Basic OP_0 execution"],

["MINIMALDATA enforcement for PUSHDATAs"],

["0x4c 0x00", "DROP 1", "MINIMALDATA", "Empty vector minimally represented by OP_0"],
["0x01 0x81", "DROP 1", "MINIMALDATA", "-1 minimally represented by OP_1NEGATE"],
["0x01 0x01", "DROP 1", "MINIMALDATA", "1 to 16 minimally represented by OP_1 to OP_16"],
["0x01 0x02", "DROP 1", "MINIMALDATA"],
["0x01 0x03", "DROP 1", "MINIMALDATA"],
["0x01 0x04", "DROP 1", "MINIMALDATA"],
["0x01 0x05", "DROP 1", "MINIMALDATA"],
["0x01 0x06", "DROP 1", "MINIMALDATA"],
["0x01 0x07", "DROP 1", "MINIMALDATA"],
["0x01 0x08", "DROP 1", "MINIMALDATA"],
["0x01 0x09", "DROP 1", "MINIMALDATA"],
["0x01 0x0a", "DROP 1", "MINIMALDATA"],
["0x01 0x0b", "DROP 1", "MINIMALDATA"],
["0x01 0x0c", "DROP 1", "MINIMALDATA"],
["0x01 0x0d", "DROP 1", "MINIMALDATA"],
["0x01 0x0e", "DROP 1", "MINIMALDATA"],
["0x01 0x0f", "DROP 1", "MINIMALDATA"],
["0x01 0x10", "DROP 1", "MINIMALDATA"],

["0x4c 0x48 0x111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111", "DROP 1", "MINIMALDATA",
"PUSHDATA1 of 72 bytes minimally represented by direct push"],

["0x4d 0xFF00 0x111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111", "DROP 1", "MINIMALDATA",
"PUSHDATA2 of 255 bytes minimally represented by PUSHDATA1"],

["0x4f 0x00100000 0x11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111", "DROP 1", "MINIMALDATA",
"PUSHDATA4 of 256 bytes minimally represented by PUSHDATA2"],


["MINIMALDATA enforcement for numeric arguments"],

["0x01 0x00", "NOT DROP 1", "MINIMALDATA", "numequals 0"],
["0x02 0x0000", "NOT DROP 1", "MINIMALDATA", "numequals 0"],
["0x01 0x80", "NOT DROP 1", "MINIMALDATA", "0x80 (negative zero) numequals 0"],
["0x02 0x0080", "NOT DROP 1", "MINIMALDATA", "numequals 0"],
["0x02 0x0500", "NOT DROP 1", "MINIMALDATA", "numequals 5"],
["0x03 0x050000", "NOT DROP 1", "MINIMALDATA", "numequals 5"],
["0x02 0x0580", "NOT DROP 1", "MINIMALDATA", "numequals -5"],
["0x03 0x050080", "NOT DROP 1", "MINIMALDATA", "numequals -5"],
["0x03 0xff7f80", "NOT DROP 1", "MINIMALDATA", "Minimal encoding is 0xffff"],
["0x03 0xff7f00", "NOT DROP 1", "MINIMALDATA", "Minimal encoding is 0xff7f"],
["0x04 0xffff7f80", "NOT DROP 1", "MINIMALDATA", "Minimal encoding is 0xffffff"],
["0x04 0xffff7f00", "NOT DROP 1", "MINIMALDATA", "Minimal encoding is 0xffff7f"],

["Test every numeric-accepting opcode for correct handling of the numeric minimal encoding rule"],

["1 0x02 0x0000", "PICK DROP", "MINIMALDATA"],
["1 0x02 0x0000", "ROLL DROP 1", "MINIMALDATA"],
["0x02 0x0000", "1ADD DROP 1", "MINIMALDATA"],
["0x02 0x0000", "1SUB DROP 1", "MINIMALDATA"],
["0x02 0x0000", "NEGATE DROP 1", "MINIMALDATA"],
["0x02 0x0000", "ABS DROP 1", "MINIMALDATA"],
["0x02 0x0000", "NOT DROP 1", "MINIMALDATA"],
["0x02 0x0000", "0NOTEQUAL DROP 1", "MINIMALDATA"],

["0 0x02 0x0000", "ADD DROP 1", "MINIMALDATA"],
["0x02 0x0000 0", "ADD DROP 1", "MINIMALDATA"],
["0 0x02 0x0000", "SUB DROP 1", "MINIMALDATA"],
["0x02 0x0000 0", "SUB DROP 1", "MINIMALDATA"],
["0 0x02 0x0000", "BOOLAND DROP 1", "MINIMALDATA"],
["0x02 0x0000 0", "BOOLAND DROP 1", "MINIMALDATA"],
["0 0x02 0x0000", "BOOLOR DROP 1", "MINIMALDATA"],
["0x02 0x0000 0", "BOOLOR DROP 1", "MINIMALDATA"],
["0 0x02 0x0000", "NUMEQUAL DROP 1", "MINIMALDATA"],
["0x02 0x0000 1", "NUMEQUAL DROP 1", "MINIMALDATA"],
["0 0x02 0x0000", "NUMEQUALVERIFY 1", "MINIMALDATA"],
["0x02 0x0000 0", "NUMEQUALVERIFY 1", "MINIMALDATA"],
["0 0x02 0x0000", "NUMNOTEQUAL DROP 1", "MINIMALDATA"],
["0x02 0x0000 0", "NUMNOTEQUAL DROP 1", "MINIMALDATA"],
["0 0x02 0x0000", "LESSTHAN DROP 1", "MINIMALDATA"],
["0x02 0x0000 0", "LESSTHAN DROP 1", "MINIMALDATA"],
["0 0x02 0x0000", "GREATERTHAN DROP 1", "MINIMALDATA"],
["0x02 0x0000 0", "GREATERTHAN DROP 1", "MINIMALDATA"],
["0 0x02 0x0000", "LESSTHANOREQUAL DROP 1", "MINIMALDATA"],
["0x02 0x0000 0", "LESSTHANOREQUAL DROP 1", "MINIMALDATA"],
["0 0x02 0x0000", "GREATERTHANOREQUAL DROP 1", "MINIMALDATA"],
["0x02 0x0000 0", "GREATERTHANOREQUAL DROP 1", "MINIMALDATA"],
["0 0x02 0x0000", "MIN DROP 1", "MINIMALDATA"],
["0x02 0x0000 0", "MIN DROP 1", "MINIMALDATA"],
["0 0x02 0x0000", "MAX DROP 1", "MINIMALDATA"],
["0x02 0x0000 0", "MAX DROP 1", "MINIMALDATA"],

["0x02 0x0000 0 0", "WITHIN DROP 1", "MINIMALDATA"],
["0 0x02 0x0000 0", "WITHIN DROP 1", "MINIMALDATA"],
["0 0 0x02 0x0000", "WITHIN DROP 1", "MINIMALDATA"],

["0 0 0x02 0x0000", "CHECKMULTISIG DROP 1", "MINIMALDATA"],
["0 0x02 0x0000 0", "CHECKMULTISIG DROP 1", "MINIMALDATA"],
["0 0x02 0x0000 0 1", "CHECKMULTISIG DROP 1", "MINIMALDATA"],
["0 0 0x02 0x0000", "CHECKMULTISIGVERIFY 1", "MINIMALDATA"],
["0 0x02 0x0000 0", "CHECKMULTISIGVERIFY 1", "MINIMALDATA"],


["Order of CHECKMULTISIG evaluation tests, inverted by swapping the order of"],
["pubkeys/signatures so they fail due to the STRICTENC rules on validly encoded"],
["signatures and pubkeys."],
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45 changes: 45 additions & 0 deletions txscript/data/script_valid.json
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Expand Up @@ -569,6 +569,51 @@
["0x04 0xffff7f80", "0x03 0xffffff NUMEQUAL", "", ""],
["0x04 0xffff7f00", "0x03 0xffff7f NUMEQUAL", "", ""],

["Unevaluated non-minimal pushes are ignored"],

["0 IF 0x4c 0x00 ENDIF 1", "", "MINIMALDATA", "non-minimal PUSHDATA1 ignored"],
["0 IF 0x4d 0x0000 ENDIF 1", "", "MINIMALDATA", "non-minimal PUSHDATA2 ignored"],
["0 IF 0x4c 0x00000000 ENDIF 1", "", "MINIMALDATA", "non-minimal PUSHDATA4 ignored"],
["0 IF 0x01 0x81 ENDIF 1", "", "MINIMALDATA", "1NEGATE equiv"],
["0 IF 0x01 0x01 ENDIF 1", "", "MINIMALDATA", "OP_1 equiv"],
["0 IF 0x01 0x02 ENDIF 1", "", "MINIMALDATA", "OP_2 equiv"],
["0 IF 0x01 0x03 ENDIF 1", "", "MINIMALDATA", "OP_3 equiv"],
["0 IF 0x01 0x04 ENDIF 1", "", "MINIMALDATA", "OP_4 equiv"],
["0 IF 0x01 0x05 ENDIF 1", "", "MINIMALDATA", "OP_5 equiv"],
["0 IF 0x01 0x06 ENDIF 1", "", "MINIMALDATA", "OP_6 equiv"],
["0 IF 0x01 0x07 ENDIF 1", "", "MINIMALDATA", "OP_7 equiv"],
["0 IF 0x01 0x08 ENDIF 1", "", "MINIMALDATA", "OP_8 equiv"],
["0 IF 0x01 0x09 ENDIF 1", "", "MINIMALDATA", "OP_9 equiv"],
["0 IF 0x01 0x0a ENDIF 1", "", "MINIMALDATA", "OP_10 equiv"],
["0 IF 0x01 0x0b ENDIF 1", "", "MINIMALDATA", "OP_11 equiv"],
["0 IF 0x01 0x0c ENDIF 1", "", "MINIMALDATA", "OP_12 equiv"],
["0 IF 0x01 0x0d ENDIF 1", "", "MINIMALDATA", "OP_13 equiv"],
["0 IF 0x01 0x0e ENDIF 1", "", "MINIMALDATA", "OP_14 equiv"],
["0 IF 0x01 0x0f ENDIF 1", "", "MINIMALDATA", "OP_15 equiv"],
["0 IF 0x01 0x10 ENDIF 1", "", "MINIMALDATA", "OP_16 equiv"],

["Numeric minimaldata rules are only applied when a stack item is numerically evaluated; the push itself is allowed"],

["0x01 0x00", "1", "MINIMALDATA"],
["0x01 0x80", "1", "MINIMALDATA"],
["0x02 0x0180", "1", "MINIMALDATA"],
["0x02 0x0100", "1", "MINIMALDATA"],
["0x02 0x0200", "1", "MINIMALDATA"],
["0x02 0x0300", "1", "MINIMALDATA"],
["0x02 0x0400", "1", "MINIMALDATA"],
["0x02 0x0500", "1", "MINIMALDATA"],
["0x02 0x0600", "1", "MINIMALDATA"],
["0x02 0x0700", "1", "MINIMALDATA"],
["0x02 0x0800", "1", "MINIMALDATA"],
["0x02 0x0900", "1", "MINIMALDATA"],
["0x02 0x0a00", "1", "MINIMALDATA"],
["0x02 0x0b00", "1", "MINIMALDATA"],
["0x02 0x0c00", "1", "MINIMALDATA"],
["0x02 0x0d00", "1", "MINIMALDATA"],
["0x02 0x0e00", "1", "MINIMALDATA"],
["0x02 0x0f00", "1", "MINIMALDATA"],
["0x02 0x1000", "1", "MINIMALDATA"],

["Valid version of the 'Test every numeric-accepting opcode for correct handling of the numeric minimal encoding rule' script_invalid test"],

["1 0x02 0x0000", "PICK DROP", ""],
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6 changes: 5 additions & 1 deletion txscript/internal_test.go
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Expand Up @@ -4563,11 +4563,15 @@ func parseScriptFlags(flagStr string) (ScriptFlags, error) {
sFlags := strings.Split(flagStr, ",")
for _, flag := range sFlags {
switch flag {
case "":
// Nothing.
case "DERSIG":
flags |= ScriptVerifyDERSignatures
case "DISCOURAGE_UPGRADABLE_NOPS":
flags |= ScriptDiscourageUpgradableNops
case "", "NONE":
case "MINIMALDATA":
flags |= ScriptVerifyMinimalData
case "NONE":
// Nothing.
case "NULLDUMMY":
flags |= ScriptStrictMultiSig
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45 changes: 45 additions & 0 deletions txscript/opcode.go
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Original file line number Diff line number Diff line change
Expand Up @@ -933,6 +933,41 @@ func (pop *parsedOpcode) conditional() bool {
}
}

// checkMinimalDataPush returns whether or not the current data
// push uses the correct opcode.
func (pop *parsedOpcode) checkMinimalDataPush() error {
data := pop.data
dataLen := len(data)
opcode := pop.opcode.value

if dataLen == 0 && opcode != OP_0 {
return ErrStackMinimalData
} else if dataLen == 1 && data[0] >= 1 && data[0] <= 16 {
if opcode != OP_1+data[0]-1 {
// Should have used OP_1 .. OP_16
return ErrStackMinimalData
}
} else if dataLen == 1 && data[0] == 0x81 {
if opcode != OP_1NEGATE {
return ErrStackMinimalData
}
} else if dataLen <= 75 {
if int(opcode) != dataLen {
// Should have used a direct push
return ErrStackMinimalData
}
} else if dataLen <= 255 {
if opcode != OP_PUSHDATA1 {
return ErrStackMinimalData
}
} else if dataLen <= 65535 {
if opcode != OP_PUSHDATA2 {
return ErrStackMinimalData
}
}
return nil
}

// exec peforms execution on the opcode. It takes into account whether or not
// it is hidden by conditionals, but some rules still must be tested in this
// case.
Expand Down Expand Up @@ -963,6 +998,16 @@ func (pop *parsedOpcode) exec(s *Script) error {
if s.condStack[0] != OpCondTrue && !pop.conditional() {
return nil
}

// Ensure all executed data push opcodes use the minimal encoding when
// the minimal data verification is set.
if s.dstack.verifyMinimalData && s.condStack[0] == OpCondTrue &&
pop.opcode.value >= 0 && pop.opcode.value <= OP_PUSHDATA4 {
if err := pop.checkMinimalDataPush(); err != nil {
return err
}
}

return pop.opcode.opfunc(pop, s)
}

Expand Down
13 changes: 13 additions & 0 deletions txscript/script.go
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Original file line number Diff line number Diff line change
Expand Up @@ -126,6 +126,11 @@ var (
// ErrStackInvalidPubKey is returned when the ScriptVerifyScriptEncoding
// flag is set and the script contains invalid pubkeys.
ErrStackInvalidPubKey = errors.New("invalid strict pubkey")

// ErrStackMinimalData is returned when the ScriptVerifyMinimalData flag
// is set and the script contains push operations that do not use
// the minimal opcode required.
ErrStackMinimalData = errors.New("non-minimally encoded script number")
)

const (
Expand Down Expand Up @@ -638,6 +643,10 @@ const (
// to compily with the DER format.
ScriptVerifyDERSignatures

// ScriptVerifyMinimalData defines that signatures must use the smallest
// push operator. This is both rules 3 and 4 of BIP0062.
ScriptVerifyMinimalData

// ScriptVerifySigPushOnly defines that signature scripts must contain
// only pushed data. This is rule 2 of BIP0062.
ScriptVerifySigPushOnly
Expand Down Expand Up @@ -700,6 +709,10 @@ func NewScript(scriptSig []byte, scriptPubKey []byte, txidx int, tx *wire.MsgTx,
if flags&ScriptVerifyDERSignatures == ScriptVerifyDERSignatures {
m.verifyDERSignatures = true
}
if flags&ScriptVerifyMinimalData == ScriptVerifyMinimalData {
m.dstack.verifyMinimalData = true
m.astack.verifyMinimalData = true
}

m.tx = *tx
m.txidx = txidx
Expand Down
39 changes: 38 additions & 1 deletion txscript/stack.go
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Original file line number Diff line number Diff line change
Expand Up @@ -100,7 +100,34 @@ func fromBool(v bool) []byte {
// Objects may be shared, therefore in usage if a value is to be changed it
// *must* be deep-copied first to avoid changing other values on the stack.
type Stack struct {
stk [][]byte
stk [][]byte
verifyMinimalData bool
}

// checkMinimalData returns whether or not the passed byte array adheres to
// the minimal encoding requirements, if enabled.
func (s *Stack) checkMinimalData(so []byte) error {
if !s.verifyMinimalData || len(so) == 0 {
return nil
}

// Check that the number is encoded with the minimum possible
// number of bytes.
//
// If the most-significant-byte - excluding the sign bit - is zero
// then we're not minimal. Note how this test also rejects the
// negative-zero encoding, 0x80.
if so[len(so)-1]&0x7f == 0 {
// One exception: if there's more than one byte and the most
// significant bit of the second-most-significant-byte is set
// it would conflict with the sign bit. An example of this case
// is +-255, which encode to 0xff00 and 0xff80 respectively.
// (big-endian).
if len(so) == 1 || so[len(so)-2]&0x80 == 0 {
return ErrStackMinimalData
}
}
return nil
}

// PushByteArray adds the given back array to the top of the stack.
Expand Down Expand Up @@ -132,6 +159,11 @@ func (s *Stack) PopInt() (*big.Int, error) {
if err != nil {
return nil, err
}

if err := s.checkMinimalData(so); err != nil {
return nil, err
}

return asInt(so)
}

Expand Down Expand Up @@ -160,6 +192,11 @@ func (s *Stack) PeekInt(idx int) (i *big.Int, err error) {
if err != nil {
return nil, err
}

if err := s.checkMinimalData(so); err != nil {
return nil, err
}

return asInt(so)
}

Expand Down

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