<p>The address space has 2<sup>160</sup> possible addresses, so to fully benefit from that space, you'd need to surpass a space of </p>

<blockquote>
  <p>2<sup>160</sup> = 1.46E48 combinations.</p>
</blockquote>

<p>This is achieved by picking 26 numbers from your toy bingo machine as </p>

<blockquote>
  <p>90!/64! = 1.17E49</p>
</blockquote>

<p>while you keep track of the order in which they are picked.</p>

<hr>

<p>To achieve at least 64 bit of entropy, you'd need 10 numbers (order recorded) from your toy bingo machine:</p>

<blockquote>
  <p>90!/80! = 2.07E19 > 1.84E19 = 2<sup>64</sup></p>
</blockquote>

<p>Which was suggested as a minimum on the related question: <a href="https://bitcoin.stackexchange.com/q/22159/5406">How many throws of a dice are necessary to defeat a brute force attack?</a></p>

<p>All numbers are assuming that the toy bingo machine acts reasonably random.</p>

CC BY-SA 3.0
2016-02-15T23:11:37.883Z
2016-02-15T23:19:54.687Z
2017-04-13T12:47:33.283Z
Murch
<p>Am I right in thinking there are 90! possibilities.
Would it be random?
Would you trust this technique?</p>

<p><a href="https://i.sstatic.net/4RYbc.jpg" rel="nofollow noreferrer">https://i.sstatic.net/4RYbc.jpg</a></p>

CC BY-SA 3.0
2016-02-15T23:01:14.803Z
But only if you always fill up all 90 fields. If you also allow shorter combinations there are even more! ;)
Murch
<private-key>
How secure would it be to use my toy bingo machine to generate a bitcoin private key?
AndyM
# How secure would it be to use my toy bingo machine to generate a bitcoin private key?

(Asked by: username_0 on 2016-02-15)

Am I right in thinking there are 90! possibilities.
Would it be random?
Would you trust this technique?

<https://i.sstatic.net/4RYbc.jpg>

**Tags:** private-key

> **Comments:**
> **username_1**: But only if you always fill up all 90 fields. If you also allow shorter combinations there are even more! ;)  

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## 1 answers

### Answer by username_1 on 2016-02-15. Score: 0 | Accepted answer

The address space has 2160 possible addresses, so to fully benefit from that space, you'd need to surpass a space of

> 2160 = 1.46E48 combinations.

This is achieved by picking 26 numbers from your toy bingo machine as

> 90!/64! = 1.17E49

while you keep track of the order in which they are picked.

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To achieve at least 64 bit of entropy, you'd need 10 numbers (order recorded) from your toy bingo machine:

> 90!/80! = 2.07E19 > 1.84E19 = 264

Which was suggested as a minimum on the related question: [How many throws of a dice are necessary to defeat a brute force attack?](https://bitcoin.stackexchange.com/q/22159/5406)

All numbers are assuming that the toy bingo machine acts reasonably random.


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