<p>I found the answer. This 'unknown bytes' described in <a href="https://github.com/bitcoin/bips/blob/master/bip-0144.mediawiki#serialization" rel="nofollow noreferrer">bip144</a></p>

CC BY-SA 3.0
2016-11-20T14:15:07.750Z
2016-11-20T14:15:07.750Z
axvm
<p>I am working on blk file parser and there is problem with one of coinbase tx.</p>

<p>hex:</p>

<pre><code>00000000: 0b11 0907 cf44 0e00 0000 0020 7f00 6e33  .....D..... ..n3
00000010: 4287 2eb8 c047 5d7c 16de 070e 5d88 1958  B....G]|....]..X
00000020: 91c2 6460 7104 0000 0000 0000 bef7 a5e4  ..d`q...........
00000030: 017b 7455 9f92 e883 d556 e21f ce14 aeb7  .{tU.....V......
00000040: 88c9 b2e2 ffec 2c6f 4b14 a901 0cb5 1358  ......,oK......X
00000050: cc2c 051a e9b8 2286 fdaf 0201 0000 0000  .,....".........
00000060: 0101 0000 0000 0000 0000 0000 0000 0000  ................
00000070: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000080: 0000 ffff ffff 3603 7e76 0f00 040c b513  ......6.~v......
00000090: 5804 b761 0630 0ce8 3a09 58c5 f700 0000  X..a.0..:.X.....
000000a0: 0000 000a 636b 706f 6f6c 122f 4e69 6e6a  ....ckpool./Ninj
000000b0: 6150 6f6f 6c2f 5345 4757 4954 2fff ffff  aPool/SEGWIT/...
000000c0: ff02 0e2a d213 0000 0000 1976 a914 876f  ...*.......v...o
</code></pre>

<p>Let's decode it according to bitcoin developer reference specification.</p>

<p><code>0b11 0907</code> - testnet3 magic number <br>
<code>cf44 0e00</code> - block size <br></p>

<p>Block header begins:<br>
<code>0000 0020</code> - block version <br>
<code>7f00 6e33 4287 2eb8 c047 5d7c 16de 070e 5d88 1958 91c2 6460 7104 0000 0000 0000</code> - previous block hash <br>
<code>bef7 a5e4 017b 7455 9f92 e883 d556 e21f ce14 aeb7 88c9 b2e2 ffec 2c6f 4b14 a901</code> - merkle root hash <br>
<code>0cb5 1358</code> - time <br>
<code>cc2c 051a</code> - bits <br>
<code>e9b8 2286</code> - nonce <br>
Block header ends; <br></p>

<p><code>fdaf 02</code> - transactions in block</p>

<p>And now the problem:<br>
<code>01 0000 00</code> - transaction version<br>
<code>00</code> - inputs counter<br>
<code>0101</code> - 2 unknown bytes.<br></p>

<p>I didn't found any information about this 2 unknown bytes. Any help appreciated.</p>

CC BY-SA 3.0
2016-11-20T10:56:14.333Z
this block is valid. blk file from bitcoin-core client
axvm
<transactions><bitcoind><bitcoin-core><coinbase-transaction>
Extra bytes in coinbase
axvm
# Extra bytes in coinbase

(Asked by: username_0 on 2016-11-20)

I am working on blk file parser and there is problem with one of coinbase tx.

hex:

```
00000000: 0b11 0907 cf44 0e00 0000 0020 7f00 6e33  .....D..... ..n3
00000010: 4287 2eb8 c047 5d7c 16de 070e 5d88 1958  B....G]|....]..X
00000020: 91c2 6460 7104 0000 0000 0000 bef7 a5e4  ..d`q...........
00000030: 017b 7455 9f92 e883 d556 e21f ce14 aeb7  .{tU.....V......
00000040: 88c9 b2e2 ffec 2c6f 4b14 a901 0cb5 1358  ......,oK......X
00000050: cc2c 051a e9b8 2286 fdaf 0201 0000 0000  .,....".........
00000060: 0101 0000 0000 0000 0000 0000 0000 0000  ................
00000070: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000080: 0000 ffff ffff 3603 7e76 0f00 040c b513  ......6.~v......
00000090: 5804 b761 0630 0ce8 3a09 58c5 f700 0000  X..a.0..:.X.....
000000a0: 0000 000a 636b 706f 6f6c 122f 4e69 6e6a  ....ckpool./Ninj
000000b0: 6150 6f6f 6c2f 5345 4757 4954 2fff ffff  aPool/SEGWIT/...
000000c0: ff02 0e2a d213 0000 0000 1976 a914 876f  ...*.......v...o

```

Let's decode it according to bitcoin developer reference specification.

`0b11 0907` - testnet3 magic number   
`cf44 0e00` - block size

Block header begins:  
`0000 0020` - block version   
`7f00 6e33 4287 2eb8 c047 5d7c 16de 070e 5d88 1958 91c2 6460 7104 0000 0000 0000` - previous block hash   
`bef7 a5e4 017b 7455 9f92 e883 d556 e21f ce14 aeb7 88c9 b2e2 ffec 2c6f 4b14 a901` - merkle root hash   
`0cb5 1358` - time   
`cc2c 051a` - bits   
`e9b8 2286` - nonce   
Block header ends;

`fdaf 02` - transactions in block

And now the problem:  
`01 0000 00` - transaction version  
`00` - inputs counter  
`0101` - 2 unknown bytes.

I didn't found any information about this 2 unknown bytes. Any help appreciated.

**Tags:** transactions, bitcoind, bitcoin-core, coinbase-transaction

> **Comments:**
> **username_0**: this block is valid. blk file from bitcoin-core client  

---

## 1 answers

### Answer by username_0 on 2016-11-20. Score: 3 | Accepted answer

I found the answer. This 'unknown bytes' described in [bip144](https://github.com/bitcoin/bips/blob/master/bip-0144.mediawiki#serialization)


---

