<p><code>OP_CHECKMULTISIG</code> <a href="https://github.com/bitcoin/bips/blob/master/bip-0011.mediawiki#Specification" rel="noreferrer">contains a bug</a> which consumes one extra element from the stack. Due to this, an additional <code>OP_FALSE</code> (0x00) is pushed for multisig scripts to make the script evaluation valid.</p>

CC BY-SA 4.0
2018-05-08T14:12:38.957Z
2018-05-08T14:12:38.957Z
Raghav Sood
<p>I created a P2SH transaction and signed it using coinb.in.</p>

<p>The sigScript field for this transaction is:</p>

<pre><code>    da
      00
      47
        3044
          0220
            33fb7d92f07516a788465dc5e4becabd5a7a5279efd008d004516ca575f00d1d
          0220
            3ad7cd3a4e9a0a5fec9db40b7348681705780e3bfd9bb862ca919342018d2dbb
        01
      48
        3045
          0221
            008a71a625891fca3d693c60881a6e5d946663253b47567d7309ade68208b37e3e
          0220
            1d078abd7d3e49d34c25e8181dbdba02356b1a55e97a3f50d8218381a99978ff
        01
      47
        5221025fd4ecaecef546156b694115406b61e03dec7e36917bb81a68b01b13d7eb289c2102b29cd1868e4b7c23e7c4aaecace46b28678e0138e736ea66848e0f28906cc66552ae
</code></pre>

<p>Why does this field contain a preprended 0x00 value?</p>

<signature><multi-signature><p2sh>
Why is my P2SH sigScript field prepended with 0x00?
Thorkil Værge
# Why is my P2SH sigScript field prepended with 0x00?

(Asked by: username_0 on 2018-05-08)

I created a P2SH transaction and signed it using coinb.in.
The sigScript field for this transaction is:
    da
      00
      47
        3044
          0220
            33fb7d92f07516a788465dc5e4becabd5a7a5279efd008d004516ca575f00d1d
          0220
            3ad7cd3a4e9a0a5fec9db40b7348681705780e3bfd9bb862ca919342018d2dbb
        01
      48
        3045
          0221
            008a71a625891fca3d693c60881a6e5d946663253b47567d7309ade68208b37e3e
          0220
            1d078abd7d3e49d34c25e8181dbdba02356b1a55e97a3f50d8218381a99978ff
        01
      47
        5221025fd4ecaecef546156b694115406b61e03dec7e36917bb81a68b01b13d7eb289c2102b29cd1868e4b7c23e7c4aaecace46b28678e0138e736ea66848e0f28906cc66552ae

Why does this field contain a preprended 0x00 value?

**Tags:** signature, multi-signature, p2sh


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## 1 answers

### Answer by username_1 on 2018-05-08. Score: 7 | Accepted answer

`OP_CHECKMULTISIG` [contains a bug](https://github.com/bitcoin/bips/blob/master/bip-0011.mediawiki#Specification) which consumes one extra element from the stack. Due to this, an additional `OP_FALSE` (0x00) is pushed for multisig scripts to make the script evaluation valid.


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