<p>Last time I <a href="http://sourceforge.net/mailarchive/forum.php?thread_name=20110707194007.GA27416%40ulyssis.org&amp;forum_name=bitcoin-development">heard of it</a>, the future of version bytes was still unsettled.
Currently, they are used to force incompatibilities between several base58-encoded data structures:</p>

<ul>
<li>addresses / private keys</li>
<li>testnet / realnet</li>
<li>alternative-chains variants (namecoin etc…)</li>
</ul>

<p>This way, you cannot misuse one for the other.</p>

<p>Someday, it might also be used as a real version number (the current SHA-256 + RIPEMD-160 + base58-encoding for keys could become obsolete).</p>

CC BY-SA 3.0
2011-09-04T14:35:32.117Z
2011-09-04T15:11:27.110Z
2011-09-04T15:11:27.110Z
Stéphane Gimenez
<p>Bitcoin address versions are described on the <a href="https://en.bitcoin.it/wiki/Address">Address</a> wiki page:</p>

<blockquote>
  <p>Normal addresses currently always start with 1, though this might change in a future version. Testnet addresses usually start with m or n.</p>
</blockquote>

<p>The <a href="https://en.bitcoin.it/wiki/Protocol_specification#Addresses">Protocol specification</a> gives a bit more technical detail:</p>

<blockquote>
  <p>Version = 1 byte of 0 (zero); on the test network, this is 1 byte of 111</p>
</blockquote>

<p>Aside from distinguishing real and testnet addresses, what is the meaning and purpose of the address version? How and why will it change in future?</p>

<development><address>
What is the meaning of the Bitcoin address version?
Ash Moran
# What is the meaning of the Bitcoin address version?

(Asked by: username_0 on 2011-09-04)

Bitcoin address versions are described on the [Address](https://en.bitcoin.it/wiki/Address) wiki page:

> Normal addresses currently always start with 1, though this might change in a future version. Testnet addresses usually start with m or n.

The [Protocol specification](https://en.bitcoin.it/wiki/Protocol_specification#Addresses) gives a bit more technical detail:

> Version = 1 byte of 0 (zero); on the test network, this is 1 byte of 111

Aside from distinguishing real and testnet addresses, what is the meaning and purpose of the address version? How and why will it change in future?

**Tags:** development, address


---

## 1 answers

### Answer by username_1 on 2011-09-04. Score: 6 | Accepted answer

Last time I [heard of it](http://sourceforge.net/mailarchive/forum.php?thread_name=20110707194007.GA27416%40ulyssis.org&forum_name=bitcoin-development), the future of version bytes was still unsettled.
Currently, they are used to force incompatibilities between several base58-encoded data structures:

* addresses / private keys
* testnet / realnet
* alternative-chains variants (namecoin etc…)

This way, you cannot misuse one for the other.

Someday, it might also be used as a real version number (the current SHA-256 + RIPEMD-160 + base58-encoding for keys could become obsolete).


---

