Is this transaction spendable? | Bitcointalksearch.org

Muhammed Zakir

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Quote from: rollingMyCar on November 15, 2014, 07:20:09 AM

Quote from: amaclin on November 13, 2014, 04:49:37 PM

Quote from: rollingMyCar on November 13, 2014, 04:35:47 PM

what is altstack? Huh

do you have some tutorials?

thanks

it is alternative/secondary stack
it is not used now for standard scripts
but the operations are valid

Where i can get more info a bout altstack?
Do you Have some docs or links?
Thanks!

See https://bitcoin.org/en/developer-guide#p2pkh-script-validation

~~MZ~~

rollingMyCar

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Quote from: amaclin on November 13, 2014, 04:49:37 PM

Quote from: rollingMyCar on November 13, 2014, 04:35:47 PM

what is altstack? Huh

do you have some tutorials?

thanks

it is alternative/secondary stack
it is not used now for standard scripts
but the operations are valid

Where i can get more info a bout altstack?
Do you Have some docs or links?
Thanks!

amaclin

legendary

Activity: 1260

Merit: 1019

Quote from: rollingMyCar on November 13, 2014, 04:35:47 PM

what is altstack? Huh

do you have some tutorials?

thanks

it is alternative/secondary stack
it is not used now for standard scripts
but the operations are valid

rollingMyCar

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Activity: 112

Merit: 10

what is altstack? Huh

do you have some tutorials?

thanks

TimS

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Merit: 253

Quote from: Yoghurt114 on July 30, 2014, 10:32:22 AM

I'm curious though.

Can anyone think of a script that uses the altstack and can do something no other script can?

I'm pretty sure that theoretically, there's nothing you can do with altstack that you can't without (given enough space). However, it can make some things simpler/shorter, and since there is a limit on the script size, that can make it quite useful.

amaclin

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Quote

Can anyone think of a script that uses the altstack and can do something no other script can?

Some algorithms will be much more shorter using the altStack.
For example this script is only 10 bytes long

Code:

OP_TOALTSTACK
OP_TOALTSTACK
OP_TOALTSTACK
OP_HASH160
OP_FROMALTSTACK
OP_HASH160
OP_FROMALTSTACK
OP_HASH160
OP_FROMALTSTACK
OP_HASH160

and (I can be wrong, please correct me) replaces 4 values on the top of the stack with their hashes, leaving the original order.
Try to do the same without altStack in less than 10 bytes.

Update1: OK, may be it is possible to do with OP_2DUP and OP_2SWAP opcodes. You can try to find out your own examples for using altStack

Update2: Note, that bitcoin script language is not Turing-complete. Not all things are even possible with current opcode set

DeathAndTaxes

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Gerald Davis

Quote from: Yoghurt114 on July 30, 2014, 10:32:22 AM

I'm curious though.

Can anyone think of a script that uses the altstack and can do something no other script can?

An m of n PubKeyHash (as opposed to PubKey) multisig. I haven't exhaustively tested it so there may be some clever solution I just didn't see but anything not involving altstack ends up being much longer and more complex.

Yoghurt114

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I'm curious though.

Can anyone think of a script that uses the altstack and can do something no other script can?

poutine310

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I created this transaction and it is in fact unspendable due to the fact the alt stack does not persist from the scriptSig to the scriptPubKey. I'm glad it sparked some discussion though.

rapport

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Quote from: poisenrang on July 25, 2014, 04:12:57 PM

maybe its about the fees?

amaclin has answered above

poisenrang

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maybe its about the fees?

rapport

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Merit: 100

Good explanation, thanks!
PS I think your English is good and better than what you probably think

amaclin

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Quote

Hmm do you mean OP_TOALTSTACK is broken and shouldn't be used?

It is not broken. It can be used in scriptSig and scriptPubKey for storing local values during evaluation.
But after evaluating scriptSig the contents of altstack are cleared.
The only way to pass values from scriptSig to scriptPubKey is stack not altstack.

I do not see any reason to change or even think about changing this behavior.
And I do not see any reason to use altstack right now.

rapport

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Hmm do you mean OP_TOALTSTACK is broken and shouldn't be used?

amaclin

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Code:

bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, const CTransaction& txTo, unsigned int nIn,
   unsigned int flags, int nHashType)
{
   vector > stack, stackCopy;
   if (!EvalScript(stack, scriptSig, txTo, nIn, flags, nHashType))
   return false;
   if (flags & SCRIPT_VERIFY_P2SH)
   stackCopy = stack;
   if (!EvalScript(stack, scriptPubKey, txTo, nIn, flags, nHashType))
   return false;

Evaluating scriptSig and scriptPubKey deal with the same stack (of course, the first one is pushing, second is checking)
But they use local altStack for calculations!!!
So, it is impossible to push value with scriptSig to altStack and pop it later when processing scriptPubKey.

This output is unspendable. Coins lost.

TimS

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Activity: 250

Merit: 253

Quote from: Taras on July 22, 2014, 06:38:03 PM

The transaction has the following metadata:

Interesting...

Yep, that site (which appears safe to me) explains itself:

Quote

Since the blockchain is for transaction data, the above string [script tag] should do nothing. If this text is inserted into a page without escaping, then there is potentially a XSS issue. Since some sites that allow you to view the blockchain ALSO are wallets, the security ramifications of a hole like this could be very great.

Taras

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Please do not PM me loan requests!

The transaction has the following metadata:

Interesting...

Yoghurt114

newbie

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In the code linked in the previous post, I found this (https://gitorious.org/bitcoin/luke-jr-bitcoin/source/5f8e7180c4b34d5f46c61a6dd2242f4249b5f79a:src/script.cpp#L453):

Code:

case OP_FROMALTSTACK:
   {
   if (altstack.size() < 1)
   return false;
   stack.push_back(altstacktop(-1));
   popstack(altstack);
   }
   break;

~~//Edit: Wrong~~

amaclin

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Quote

I took a closer look at the transaction and I can't find any reason why it is being rejected by Eligius. Unfortunately bitcoind lacks good tools for validating transactions. Optimally decoderawtransaction & decodescript would return IsStandard and IsValid parameters but they don't. You may want to reach out to Eligius pool directly.

There is no direct connection to Eligius from Internet. We can reach only the gate node.
68.168.105.168:8333 (I think that it is gate node) also ignores redeem tx.

It is possible to download, compile and debug Luke's version of bitcoin
https://gitorious.org/bitcoin/luke-jr-bitcoin/source/5f8e7180c4b34d5f46c61a6dd2242f4249b5f79a:

DeathAndTaxes

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Gerald Davis

TimS,

I took a closer look at the transaction and I can't find any reason why it is being rejected by Eligius. Unfortunately bitcoind lacks good tools for validating transactions. Optimally decoderawtransaction & decodescript would return IsStandard and IsValid parameters but they don't. You may want to reach out to Eligius pool directly.

Topic: Is this transaction spendable? (Read 5123 times)