<p>It's really 160 bit hash (<code>RIPEMD160</code>) of an already hashed (<code>SHA256</code>) public secp256k1 elliptic curve key. And yes, on the average, every address has about 2<sup>256-160</sup>=2<sup>96</sup> pairs of private/public keys.</p>

CC BY-SA 4.0
2018-07-30T20:14:33.310Z
There is a possibility that it might be easier for quantum computing to 1st identify any one of the overlapping 2^96 public keys, with an already known companion private key, satisfying the associated P2PKH transaction redemption criteria than trying to factor a 256-bit private key.
skaht
CC BY-SA 4.0
2018-07-26T17:18:38.820Z
2018-07-30T19:59:39.663Z
2018-07-30T19:59:39.663Z
Zergatul
<p>Bitcoin addresses are essentially 160-bit hashes of a 256-bit public key. Huh? How can all possible numbers in 256-bit space be squeezed into 160-bit space? Does that mean any given bitcoin address could be derived from more than just one public key?</p>

CC BY-SA 4.0
2018-07-28T23:34:32.543Z
I’m not sure I understand your question but if it means what I think it does then it will be beneficial for you to read about hash functions in a general setting. They are by design non injective (since they have a finite codomain and a larger domain) meaning there will be two different inputs that hash to the same output but a good hash function is designed so that the probability of one person being able to find two such inputs is epsilon small
Prince M
<wallet><address><security><private-key>
How can all possible numbers in 256-bit space be squeezed into 160-bit space?
abattia
# How can all possible numbers in 256-bit space be squeezed into 160-bit space?

(Asked by: username_0 on 2018-07-26)

Bitcoin addresses are essentially 160-bit hashes of a 256-bit public key. Huh? How can all possible numbers in 256-bit space be squeezed into 160-bit space? Does that mean any given bitcoin address could be derived from more than just one public key?

**Tags:** wallet, address, security, private-key

> **Comments:**
> **username_1**: I’m not sure I understand your question but if it means what I think it does then it will be beneficial for you to read about hash functions in a general setting. They are by design non injective (since they have a finite codomain and a larger domain) meaning there will be two different inputs that hash to the same output but a good hash function is designed so that the probability of one person being able to find two such inputs is epsilon small  

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## 1 answers

### Answer by username_2 on 2018-07-26. Score: 4 | Accepted answer

It's really 160 bit hash (`RIPEMD160`) of an already hashed (`SHA256`) public secp256k1 elliptic curve key. And yes, on the average, every address has about 2256-160=296 pairs of private/public keys.

> **Comments:**
> **username_3**: There is a possibility that it might be easier for quantum computing to 1st identify any one of the overlapping 2^96 public keys, with an already known companion private key, satisfying the associated P2PKH transaction redemption criteria than trying to factor a 256-bit private key.  

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