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I was looking thru Block explorer at an address with a balance. It has never been spent from thus the public key is unknown. If the public key is unknown, how can Block explorer calculate the hash160 of the public key?

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Because an address is the Hash160 (=RIPEMD160(SHA256(x))) of the public key. The transaction output lists that 160-bit hash directly.

When redeeming such an output, you provide both the public key (which must hash to the value given in the output) and a signature (which must be valid for the given public key).

  • i'm used to seeing hash algos referred to as SHA256 or RIPEMD. what is Hash160? – joe Mar 8 '13 at 4:02
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    @joe Hash160 = RIPEMD160(SHA256(m)) (note that plain RIPEMD is a different, broken hash and bitcoin doesn't use it) – CodesInChaos Mar 8 '13 at 11:19
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    Edited. In Bitcoin-speak, Hash(x) = SHA256(SHA256(x)) and Hash160(x) = RIPEMD160(SHA256(x)). – Pieter Wuille Mar 10 '13 at 16:13
  • as a related question, what is really stored in a wallet in regards to keys? just the priv keys or priv keys and pub keys? i ask since the pub keys can be derived from the priv keys. – joe Mar 16 '13 at 15:43
  • The Public Key Hash is equivalent to the bitcoin address, without the Base58Check encoding. RIPEMD160(SHA256(PubK)) == Base58.decode(Address) ? – Haddar Macdasi Mar 24 '15 at 23:27

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