<p>A 1... address encodes the hash of a public key (specifically <code>RIPEMD160(SHA256(key))</code>). Since cryptographic hashes aren't easily invertible, the address alone cannot be used to convert between compressed and uncompressed keys. If however the owner of this address has spent coins belonging to it (or has otherwise published the public key), the public key is now known and can be used to construct an address from both its compressed and uncompressed version.</p>
<p>You should never actually do this though, for reasons explained by Pieter in the comments.</p>

CC BY-SA 4.0
2022-03-04T19:26:07.717Z
Even if it is possible after seeing the public key, it is a terrible idea. The receiver may not be able to spend coins sent to the converted address, and may not consider coins sent there to be a valid payment. The advice in matters like this should be: as the sender, you should never ever attempt to convert someone else's address. As the receiver you can "convert" by upgrading to wallet software that gives out such addresses in the first place.
Pieter Wuille
CC BY-SA 4.0
2022-03-04T19:53:20.273Z
@PieterWuille By "may not be able to spend the coins" you mean simply that the receiver may lack a convenient method of spending them, or that they truly have no way of spending them? And how would that happen?
Vojtěch Strnad
CC BY-SA 4.0
2022-03-04T20:10:24.840Z
For example if their private key is on a security module or HSM, which only supports signing in certain ways.
Pieter Wuille
CC BY-SA 4.0
2022-03-04T19:12:52.033Z
2022-10-17T10:01:17.767Z
2022-10-17T10:01:17.767Z
Vojtěch Strnad
<p>Is this possible with just an address; if so how?</p>

CC BY-SA 4.0
2022-03-05T14:37:52.763Z
Peter Wuille's comments are canon, and in case you haven't seen this tool, for learning  https://iancoleman.io/bitcoin-key-compression
HansBKK
<address>
Converting Bitcoin compressed address to uncompressed or vice versa?
lepy
# Converting Bitcoin compressed address to uncompressed or vice versa?

(Asked by: username_0 on 2022-03-04)

Is this possible with just an address; if so how?

**Tags:** address

> **Comments:**
> **username_1**: Peter username_3's comments are canon, and in case you haven't seen this tool, for learning  https://iancoleman.io/bitcoin-key-compression  

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## 1 answers

### Answer by username_2 on 2022-03-04. Score: 1 | Accepted answer

A 1... address encodes the hash of a public key (specifically `RIPEMD160(SHA256(key))`). Since cryptographic hashes aren't easily invertible, the address alone cannot be used to convert between compressed and uncompressed keys. If however the owner of this address has spent coins belonging to it (or has otherwise published the public key), the public key is now known and can be used to construct an address from both its compressed and uncompressed version.

You should never actually do this though, for reasons explained by username_3 in the comments.

> **Comments:**
> **username_3**: Even if it is possible after seeing the public key, it is a terrible idea. The receiver may not be able to spend coins sent to the converted address, and may not consider coins sent there to be a valid payment. The advice in matters like this should be: as the sender, you should never ever attempt to convert someone else's address. As the receiver you can "convert" by upgrading to wallet software that gives out such addresses in the first place.  
> **username_2**: @username_3 By "may not be able to spend the coins" you mean simply that the receiver may lack a convenient method of spending them, or that they truly have no way of spending them? And how would that happen?  
> **username_3**: For example if their private key is on a security module or HSM, which only supports signing in certain ways.  

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