<p>Check sum is a result of 2 hash-functions: SHA256 and RIPEMD160. The length of checksum is 4 bytes. Hash functions are indistinguishable from random oracle, so it is possible, if you make 1 mistake in non-checksum character, you get the same checksum. But probability of this is 1/2^32.</p>

<p>Added later: not exactly correct due to base58 encoding. Correction in the another answer.</p>

CC BY-SA 3.0
2014-02-28T12:54:28.773Z
To add to this: whether you make 1 mistake or 20, the probability that the address is valid is still 1/2^32.
Tim S.
CC BY-SA 3.0
2014-02-28T20:26:44.723Z
I'm afraid this is the wrong answer. The solution is NOT to find two addresses with the same checksum, but with the same sequence of base58-encoded characters for  the large integer represented by the hash concatenated with checksum. See my answer for examples.
uminatsu
CC BY-SA 3.0
2014-03-01T21:06:14.697Z
I agree that you are right. Base58 encoding deforms last check sum bytes. But my calculation of probability is correct anyway.
Zergatul
CC BY-SA 3.0
2014-02-28T09:25:07.373Z
2014-03-01T21:08:21.127Z
2014-03-01T21:08:21.127Z
Zergatul
<p>Here's an example of a pair of valid addresses that differ by only one character.</p>

<pre><code>1xxxxxxxxxxxxxxxxxxxy1wqmDWjatp7t
1xxxxxxxxxxxxxxxxxxxy1wqmDWgatp7t
</code></pre>

<p>another example pair</p>

<pre><code>1xxxxxxxxxxxxxxxxxxxxyE4zW1N3nMx2
1xxxxxxxxxxxxxxxxxxxxyE4zW1U3nMx2
</code></pre>

<p>For both pairs, the 32-bit checksums are NOT the same, but they satisfy the condition that</p>

<pre><code>(checksum1 % 656356768) == ((checksum2 + 356826688) % 656356768)
</code></pre>

CC BY-SA 3.0
2014-02-28T19:23:42.540Z
2014-02-28T19:53:41.963Z
2014-02-28T19:53:41.963Z
uminatsu
<p>Is it known the minimum amount of characters you need to mistype to get another valid address?</p>

<p>Addresses contain checksums, and also must follow some specific rules, so I guess this could be calculated: I wonder if someone did.</p>

<address>
How many characters you need to mistype at minimum to get another valid address?
o0'.
# How many characters you need to mistype at minimum to get another valid address?

(Asked by: username_0 on 2014-02-28)

Is it known the minimum amount of characters you need to mistype to get another valid address?

Addresses contain checksums, and also must follow some specific rules, so I guess this could be calculated: I wonder if someone did.

**Tags:** address


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## 2 answers

### Answer by username_1 on 2014-02-28. Score: 5

Check sum is a result of 2 hash-functions: SHA256 and RIPEMD160. The length of checksum is 4 bytes. Hash functions are indistinguishable from random oracle, so it is possible, if you make 1 mistake in non-checksum character, you get the same checksum. But probability of this is 1/2^32.

Added later: not exactly correct due to base58 encoding. Correction in the another answer.

> **Comments:**
> **username_2**: To add to this: whether you make 1 mistake or 20, the probability that the address is valid is still 1/2^32.  
> **username_3**: I'm afraid this is the wrong answer. The solution is NOT to find two addresses with the same checksum, but with the same sequence of base58-encoded characters for  the large integer represented by the hash concatenated with checksum. See my answer for examples.  
> **username_1**: I agree that you are right. Base58 encoding deforms last check sum bytes. But my calculation of probability is correct anyway.  

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### Answer by username_3 on 2014-02-28. Score: 3

Here's an example of a pair of valid addresses that differ by only one character.
1xxxxxxxxxxxxxxxxxxxy1wqmDWjatp7t
1xxxxxxxxxxxxxxxxxxxy1wqmDWgatp7t

another example pair
1xxxxxxxxxxxxxxxxxxxxyE4zW1N3nMx2
1xxxxxxxxxxxxxxxxxxxxyE4zW1U3nMx2

For both pairs, the 32-bit checksums are NOT the same, but they satisfy the condition that
(checksum1 % 656356768) == ((checksum2 + 356826688) % 656356768)


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