# Gavin Andresen
# 2011-01-07 15:29:58
# https://bitcointalk.org/index.php?topic=2657.msg36128#msg36128

The smartcard-generates-a-private-key-itself seems like overkill.  No matter what, you have to trust the smartcard manufacturer.  Because even if the smartcard generates a private key, you have to trust that the smartcard manufacturer didn't: @p{brk}
 + Add a backdoor that lets them read the private key @p{brk}
 + Break the implementation so the private key created is predictable @p{par}

If you have to trust the smartcard manufacturer anyway, it seems to me a much simpler solution is to just associated a bitcoin address with a tangible bitcoin. @p{par}

Redeeming the tangible bitcoin then means turning it over to the issuer and having them send the bitcoins to one of your addresses. @p{par}

It is easy to solve half of the "is this valid" problem@p{--} you can easily check to see if bitcoins have been sent to that address and are still unspent. @p{par}

The other half of the problem is "is there another unredeemed copy out there?" @p{par}

Perhaps the issuer could publish a public database of unredeemed tangible bitcoins that is: @p{brk}
  bitcoin address @p{--}@s{gt}  hash of information that the tangible bitcoin purchaser provides @p{par}

I could then check that database to see if bitcoin address 1abc was sold ONLY to SHA256("Gavin Andresen 1-Jan-2011").  That stops the issuer from selling the same bitcoins over and over again. @p{par}

I still have to trust that the issuer won't decide to spend all the bitcoins (since they have the private keys) and disappear.  But that's really no different from trusting your smartcard manufacturer. @p{par}

(interesting thing to think about:  the issuer could actually use just one private key and generate as many public keys as they like that can all be signed using that one private key...) @p{par}