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Title: 2 extra bytes before ScriptSig Post by: jackjack on August 10, 2011, 05:48:04 PM Hi,
I'm currently reading a transaction: http://blockexplorer.com/rawtx/947656865df51aaa6ea3d7535263f0e3358fa700e7ff4769645741e9d7b473b8 The hex data of txin #1 is: Quote 4f539888478f3bfcd6ea1c52a3f3bcb5abf645ee5dccfb5e34aa30ac7579eeff 03000000 8c49 304602210090e58c2e9c3686557553f085958bf2a17c89044858c457921a55a781f04147ac02210 0eec9749891436ac36e937412d1e9bde7adda176bafe3c839d938c6159cb0e50201 41 042e6c25cb2712f6f997004d675432d480540851db63fccfea9f45ec968a76ffeda1b41c85cf3d4 6176a86d8b6cfe33993cd01246e3a08bbcee05b2fde0bba5653 ffffffff We have: prevout_hash, prevout_n, 8c49, scriptsig41pubkey, seq So, what is 8c49 ? Title: Re: 2 extra bytes before ScriptSig Post by: theymos on August 10, 2011, 06:15:27 PM Code: 4f539888478f3bfcd6ea1c52a3f3bcb5abf645ee5dccfb5e34aa30ac7579eeff prev_out Title: Re: 2 extra bytes before ScriptSig Post by: jackjack on August 10, 2011, 06:40:23 PM Thanks!
Title: Re: 2 extra bytes before ScriptSig Post by: etotheipi on August 10, 2011, 09:15:37 PM This is a very complete breakdown of the bytemap of a transaction, all the way down to the signature pieces and the DER encoding:
http://dl.dropbox.com/u/1139081/BitcoinImg/TxBinaryMap.png This is from my thread here (http://"https://bitcointalk.org/index.php?topic=29416.0") where I created quite a few visualizations to help clarify questions like this. P.S. - In case it's too small to read: The 0x8c is the var_int describing the length of the entire script. Following that, you're going to see inside the signature: Byte 0: length of signature (73 bytes in your case) Byte 1: 0x30 (DER code) Byte 2: length of DER encoded (r,s) pair with extra DER encoding bytes (yes, seems redundant) Byte 3: 0x02 (DER code) Byte 4: length of signature r-value Byte 4+x: r-value (approx 31-34 bytes) Byte 4+x+1: 0x02 (DER code) Byte 4+x+2: length of s-value (approx 31-34 bytes) Byte [end]: 0x01 (end of sig) That describes the first piece of the script--the signature part--the second part is the public key, for reference: Byte 0: length of public key (this will always be 65) Byte 1: 0x04 +32 Bytes: x-value of EC public key point +32 Bytes: y-value of EC public key point Title: Re: 2 extra bytes before ScriptSig Post by: ctoon6 on August 10, 2011, 09:38:14 PM This is from my thread here (http://"https://bitcointalk.org/index.php?topic=29416.0") where I created quite a few visualizations to help clarify questions like this. here (https://bitcointalk.org/index.php?topic=29416) the link is not right, do not put quotes in Code: [url=https://www.example.com/]example[/url] Title: Re: 2 extra bytes before ScriptSig Post by: jackjack on August 11, 2011, 12:53:32 AM Thanks for the graph, etotheipi
I love the bitcoin address graph too ;) Title: Re: 2 extra bytes before ScriptSig Post by: jackjack on August 11, 2011, 04:00:27 AM Last question: I know how to sign something with a privkey, but what is the message signed in <sig>?
I found that on the wiki: Quote The other component is an ECDSA signature over a hash of a simplified version of the transaction. It, combined with the public key, proves the transaction was created by the real owner of the address in question. Various flags define how the transaction is simplified and can be used to create different types of payment. which doesn't really help me, I still don't know what "simplified version" it isI found the table here too: https://en.bitcoin.it/wiki/Script#Scripts I understand it but OP_CHECKSIG verifies <sig> is from <pubKey>, I don't see the message signed I couldn't find help in the OP_CHECKSIG page neither: https://en.bitcoin.it/wiki/OP_CHECKSIG I also tried with this etotheipi's image: http://dl.dropbox.com/u/1139081/BitcoinImg/OpCheckSigDiagram.png Still doesn't work, I tried with Hash256 as sha256 and sha256^2 but none worked Title: Re: 2 extra bytes before ScriptSig Post by: Mike Hearn on August 11, 2011, 12:15:06 PM Look at the SignatureHash() function in the source code. The description on OP_CHECKSIG should also be complete enough for you to implement. The signature comes with flags that describe how the transactions is simplified - it mostly means deleting or clearing parts of the structure depending on the sighash flags. Eg SIGHASH_ANYONECANPAY means only that input exists in the simplified form.
Title: Re: 2 extra bytes before ScriptSig Post by: jackjack on August 11, 2011, 02:17:19 PM Thanks, it still doesn't work, but that helped me
I chose SIGHASH_ALL and nvin=0, so SignatureHash becomes: Quote CTransaction txTmp(txTo); The only thing I'm not sure is the blue linescriptCode.FindAndDelete(CScript(OP_CODESEPARATOR)); //no codeseparator, scriptPubkey was just OPDUP UPHASH HASH VERIFY CHECKSIG // Blank out other inputs' signatures for (int i = 0; i < txTmp.vin.size(); i++) txTmp.vin.scriptSig = CScript(); txTmp.vin[0].scriptSig = scriptCode; // Serialize and hash CDataStream ss(SER_GETHASH); ss.reserve(10000); ss << txTmp << nHashType; return Hash(ss.begin(), ss.end()); I think it initializes ss with "04 00 00 00 00 00 00 00" ( 1 << 2 as an int64) I tested "04 00 00 00" and "" also But none works Also, is that ss? (I took a transaction with only 1 input and 1 output this time: http://blockexplorer.com/rawtx/a467d767729385c191d3e463ceb8a436a1c0dda9d362955909c64196db86e573 ) Code: 04000000 or 0400000000000000 or nothing Title: Re: 2 extra bytes before ScriptSig Post by: jackjack on August 12, 2011, 03:49:04 AM Solved here: https://bitcointalk.org/index.php?topic=36464 (fr)
Title: Re: 2 extra bytes before ScriptSig Post by: etotheipi on August 14, 2011, 04:01:07 AM Jackjack,
Since I don't know French, I can't tell what the "solution" was that you linked to. What problem did you have with my diagram (http://dl.dropbox.com/u/1139081/BitcoinImg/OpCheckSigDiagram.png)? I'd like to update it to clarify whatever difficulties you had. If I had to guess, I'd bet there was some endian-ness issues. That's always the problem. Scripts and key-data are usually big-endian, just about everything is little-endian. Except for those times that it isn't... Title: Re: 2 extra bytes before ScriptSig Post by: jackjack on August 14, 2011, 12:32:40 PM Jackjack, I didn't translate because actually I was the problem. I didn't fully understand your diagram, I forgot to use binary instead of hex strings(that's always my problem ;) ), I was disappoint because the only official example is actually an old example which isn't used anymore, I hashed the message twice (once in the sig function, once before calling it), and yes, a little endianness problemSince I don't know French, I can't tell what the "solution" was that you linked to. What problem did you have with my diagram (http://dl.dropbox.com/u/1139081/BitcoinImg/OpCheckSigDiagram.png)? I'd like to update it to clarify whatever difficulties you had. If I had to guess, I'd bet there was some endian-ness issues. That's always the problem. Scripts and key-data are usually big-endian, just about everything is little-endian. Except for those times that it isn't... I think one thing should be changed though: you should write Hash (as in the client source) or sha^2 instead of hash256 Title: Re: 2 extra bytes before ScriptSig Post by: etotheipi on August 14, 2011, 12:55:45 PM Thanks Jackjack. The diagram has been updated!
At least, once you finally get it, you know your library is awesome because executing a single OP_CHECKSIG requires just about everything else to be right. So, congrats :) |