5

I'm attempting to validate a p2sh transaction from the live bitcoin blockchain, however it is failing the checksig. I am using pybitcointools for the checksig and I have successfully validated lots of other txhash/pubkey/signature sets so I don't think the problem lies in the ECDSA library.

I think I must be evaluating p2sh incorrectly. Please could someone tell me where I am going wrong:

tx hash 7edb32d4ffd7a385b763c7a8e56b6358bcd729e747290624e18acdbe6209fc45 spends txout with index 0 from tx hash 40eee3ae1760e3a8532263678cdf64569e6ad06abc133af64f735e52562bccc8.

First I evaluate the scriptsig:

OP_FALSE
OP_PUSHDATA0(72)
3045022100ad0851c69dd756b45190b5a8e97cb4ac3c2b0fa2f2aae23aed6ca97ab33bf88302200b248593abc1259512793e7dea61036c601775ebb23640a0120b0dba2c34b79001
OP_PUSHDATA0(69)
5141042f90074d7a5bf30c72cf3a8dfd1381bdbd30407010e878f3a11269d5f74a58788505cdca22ea6eab7cfb40dc0e07aba200424ab0d79122a653ad0c7ec9896bdf51ae

This leaves the stack like so:

0 - 00
1 - 3045022100ad0851c69dd756b45190b5a8e97cb4ac3c2b0fa2f2aae23aed6ca97ab33bf88302200b248593abc1259512793e7dea61036c601775ebb23640a0120b0dba2c34b79001
2 - 5141042f90074d7a5bf30c72cf3a8dfd1381bdbd30407010e878f3a11269d5f74a58788505cdca22ea6eab7cfb40dc0e07aba200424ab0d79122a653ad0c7ec9896bdf51ae    

I back this up as stack_copy.

Then I evaluate the scriptpubkey:

OP_HASH160
OP_PUSHDATA0(20)
e9c3dd0c07aac76179ebc76a6c78d4d67c6c160a
OP_EQUAL

This passes fine.

Finally I evaluate the p2sh - I restore stack_copy and pop the last item (2) off the stack. I deserialize it to get the following script:

OP_TRUE
OP_PUSHDATA0(65)
042f90074d7a5bf30c72cf3a8dfd1381bdbd30407010e878f3a11269d5f74a58788505cdca22ea6eab7cfb40dc0e07aba200424ab0d79122a653ad0c7ec9896bdf
OP_TRUE
OP_CHECKMULTISIG

And then evaluate this using stack_copy (without element 2 which has just been popped). The data for the checksig evaluation is:

serial tx: 0100000001c8cc2b56525e734ff63a13bc6ad06a9e5664df8c67632253a8e36017aee3ee4000000000455141042f90074d7a5bf30c72cf3a8dfd1381bdbd30407010e878f3a11269d5f74a58788505cdca22ea6eab7cfb40dc0e07aba200424ab0d79122a653ad0c7ec9896bdf51aefeffffff0120f40e00000000001976a9141d30342095961d951d306845ef98ac08474b36a088ac0000000001000000
txhash: 8fcf56ee75816930fb141fdc19b2aa1bc721b124d2a76d5f0c1be17bcd21ccdc
pubkey: 042f90074d7a5bf30c72cf3a8dfd1381bdbd30407010e878f3a11269d5f74a58788505cdca22ea6eab7cfb40dc0e07aba200424ab0d79122a653ad0c7ec9896bdf
signature: 3045022100ad0851c69dd756b45190b5a8e97cb4ac3c2b0fa2f2aae23aed6ca97ab33bf88302200b248593abc1259512793e7dea61036c601775ebb23640a0120b0dba2c34b790

However this is failing! Let me know if you need more information and I can provide it.

  • my bad. the serialized tx is wrong. will add full details in a second once i have verified... – mulllhausen Nov 11 '15 at 12:06
1

i had the locktime field of the spending transaction accidentally set to 0 when in fact it is 272295 for this transaction.

{
    "hash": "7edb32d4ffd7a385b763c7a8e56b6358bcd729e747290624e18acdbe6209fc45",
    "num_inputs": 1,
    "input": {
        "0": {
            "funds": 990000,
            "hash": "40eee3ae1760e3a8532263678cdf64569e6ad06abc133af64f735e52562bccc8",
            "index": 0,
            "parsed_script": "OP_FALSE OP_PUSHDATA0(72) 3045022100ad0851c69dd756b45190b5a8e97cb4ac3c2b0fa2f2aae23aed6ca97ab33bf88302200b248593abc1259512793e7dea61036c601775ebb23640a0120b0dba2c34b79001 OP_PUSHDATA0(69) 5141042f90074d7a5bf30c72cf3a8dfd1381bdbd30407010e878f3a11269d5f74a58788505cdca22ea6eab7cfb40dc0e07aba200424ab0d79122a653ad0c7ec9896bdf51ae",  
            "script_length": 144,
            "sequence_num": 4294967294
        }
    },
    "lock_time": 272295,
    "num_outputs": 1,
    "output": {
        "0": {
            "addresses": [
                "13fLLox43yXYvfoZadXpGbkTUXkW8bhqut"
            ],
            "funds": 980000,
            "parsed_script": "OP_DUP OP_HASH160 OP_PUSHDATA0(20) 1d30342095961d951d306845ef98ac08474b36a0 OP_EQUALVERIFY OP_CHECKSIG",
            "script_length": 25
        }
    },
    "size": 229,
    "version": 1
}

and the serialized tx with the txin 0 script replaced with the following script:

OP_TRUE
OP_PUSHDATA0(65)
042f90074d7a5bf30c72cf3a8dfd1381bdbd30407010e878f3a11269d5f74a58788505cdca22ea6eab7cfb40dc0e07aba200424ab0d79122a653ad0c7ec9896bdf
OP_TRUE
OP_CHECKMULTISIG

should actually be:

0100000001c8cc2b56525e734ff63a13bc6ad06a9e5664df8c67632253a8e36017aee3ee4000000000455141042f90074d7a5bf30c72cf3a8dfd1381bdbd30407010e878f3a11269d5f74a58788505cdca22ea6eab7cfb40dc0e07aba200424ab0d79122a653ad0c7ec9896bdf51aefeffffff0120f40e00000000001976a9141d30342095961d951d306845ef98ac08474b36a088aca727040001000000

only the final 8 bytes that contain the locktime are different from before: a727040001000000

the new serial tx has hash:

607789be41392e6b12735a79bc9ea94573b4e39948badef18ca48e85ee15196d

and the signature and pubkey from before were already correct. these evaluate correctly in pybitcointools now, like so:

pybitcointools.ecdsa_raw_verify(tx_hash, pybitcointools.der_decode_sig(bin2hex(signature)), bin2hex(pubkey))
  • Argh, I could not figure it out. And I'm the resident pybitcointools expert – Wizard Of Ozzie Nov 12 '15 at 1:00
  • @WizardOfOzzie in that case i have another question for you :) will post tonight (i also live in aus). – mulllhausen Nov 12 '15 at 3:15
  • 1
    Sounds good mate. There's a bunch of new PRs for pybitcointools which I've submitted recently, so I'm certainly familiar with all the code once again – Wizard Of Ozzie Nov 14 '15 at 3:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.