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I've searched really hard for a Python script that coverts a compressed public key into uncompressed one, since I don't know how to code this. I stumbled upon these links:

https://stackoverflow.com/questions/43629265/deriving-an-ecdsa-uncompressed-public-key-from-a-compressed-one

How to uncompress a public key?

https://bitcointalk.org/index.php?topic=644919.0

but all python scripts/functions either don't work or outputting incorrect values. I tried to debug them and failed. Could you point out how to code something like this in Python or give an example of the working code? Here are the values to play with (HEX):

#Test case 1
#Compressed Pubkey: 025A2146590B80D1F0D97CC7104E702011AFFF21BFAF817F5C7002446369BA9DDC
'''
Right Uncompressed Pubkey:
045A2146590B80D1F0D97CC7104E702011AFFF21BFAF817F5C7002446369BA9DDC9BD5DCD1B4A737244D6BB7B96E256391B8597D3A7972A6F8CA9096D4AEA1F37E
'''

#Test case 2
#Compressed Pubkey: 035728F4692D85D411DF3643CD69FE05C411A0D507C7D814008F56C8F260AD7ED9
'''
Right Uncompressed Pubkey:
045728F4692D85D411DF3643CD69FE05C411A0D507C7D814008F56C8F260AD7ED99E2DF8D9CB1A575D55264692629AE22E518BC14AD02592941C13BE6755C72973
'''


#Test case 3
#Compressed Pubkey:039E87EB177890FDD788B95843ED53AD4FB6E877E3F730EF1E73593964C2AB9D15
'''
Right Uncompressed Pubkey:
049E87EB177890FDD788B95843ED53AD4FB6E877E3F730EF1E73593964C2AB9D15A3B647C8C4A0766420917B7B445CDCD6BFEC2900175C5534C6113954F3FF00D9
'''
Maltoon Yezi
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1 Answers1

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Using this library (disclaimer: I am the author):

>>> from cryptotools import PublicKey

>>> PublicKey.from_hex('025A2146590B80D1F0D97CC7104E702011AFFF21BFAF817F5C7002446369BA9DDC').hex(compressed=False)
'045a2146590b80d1f0d97cc7104e702011afff21bfaf817f5c7002446369ba9ddc9bd5dcd1b4a737244d6bb7b96e256391b8597d3a7972a6f8ca9096d4aea1f37e'
Mike D
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  • When trying to input an compressed PubKey in 0x hex format and later converted to string with str() into this function it outputs the following error:

    in decode assert len(key) == 33, 'A compressed public key must be 33 bytes long' AssertionError: A compressed public key must be 33 bytes long So the compressed key has to be a string with '' single quotes. This way it works. Nevertheless, thanks!

     – Maltoon Yezi Aug 30 '22 at 18:56