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I just purchased a pair of CryoBit cards and it occurred to me that, while I know how to send money to a cold storage wallet, I am not exactly sure how to send money out. I assume I import the private key into an online wallet, like BlockChain, and then do a full sweep to another address in the BlockChain wallet.

But if I import the CryoBit private key doesn't that expose the private key on my CryoBit card, reducing the full trust of that card? I've read on other answers that once a cold storage private key is imported into an online wallet that wallet should never be used again... At $30 per CryoBit card that seems like an expensive waste to discard the card after one use.

Also, if I do import the private key on the CryoBit card into BlockChain, do I have to do a full sweep or can I just send some of the CryoBit private key funds out?

Say for example I have $1000 on my CryoBit card and I import the private key into BlockChain. Then I send $500 to an external address leaving $500 on the CryoBit address. Then to clean up the cold storage I delete the private key from BlockChain. Will I still have a trustworthy cold storage wallet in CryoBit with the remaining $500?

Dscoduc
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  • I'm under the same impression, that once you sweep a cold storage wallet that you are no longer meant to use it as a receiving wallet. I think the name "storage" implies that, too. – frеdsbend Jun 06 '14 at 06:01
  • possible duplicate of [How do I transfer BTC in cold storage?](http://bitcoin.stackexchange.com/questions/16599/how-do-i-transfer-btc-in-cold-storage) – frеdsbend Jun 06 '14 at 06:07
  • The other answers don't address the concept of cold storage "cards" and what to do with them after importing the private keys. They also don't talk about whether it's okay to send partial funds directly from the cold storage address without doing a full sweep of the funds into a different local wallet. – Dscoduc Jun 06 '14 at 06:09
  • You referring to [these?](https://www.cryobit.co/cold-storage-products/cryo-card/) – frеdsbend Jun 06 '14 at 06:22
  • Yes, but there are other similar cards like [Bit-Card](http://www.bit-card.de/cards/encrypted-cards.html) – Dscoduc Jun 06 '14 at 06:28
  • I assume it is the type with the private key on the back, not just the address on the front, right? – frеdsbend Jun 06 '14 at 06:33
  • The private key is on the back but is encrypted with a passphrase. – Dscoduc Jun 06 '14 at 06:41
  • What we have here is a terminology problem. Those cards, strictly speaking, are not cold storage. By definition, cold storage must never allow an unencrypted private key to touch an online system, which these cards don't do. When you spend from them, the (presumably online) spending device MUST decrypt the key. What you have here is just a non-paper version of a BIP38 encrypted Paper Wallet. This should be helpful: http://bitcoin.stackexchange.com/questions/19545/which-wallet-applications-implement-bip38-private-key-password-encryption – David Perry Jun 30 '14 at 20:53

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Yes, you would simply import the private key to your client or online wallet.

I think the purpose is to move funds to the address on the card, then keep the card in a place somewhere safe and not use it. For everyday use, I think high grade steel, ceramic cast engraving, fireproofing, etc. is overkill.

You can always send more money to the address after you have swept the balance, but like you said, using it once may compromise the private key.

However, I don't see why you can't use the card to send to an address in your Multibit wallet (or other client). This means only your own computer "saw" the private key. As long as you feel comfortable with that, I see no reason why you can't reuse the card. But, and I am not sure about the following, I think private keys change with every transaction, which might be why you have to sweep the address, rather than just take a portion, and also why you cannot reuse it.

I will post more once I learn more on this topic. Also, another user may clarify in the meantime.

Community
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frеdsbend
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  • I agree with "...keep the card in a place somewhere safe and not use it." but I would expect that I would need to dip into my savings (aka cold storage) from time to time depending on how much I have in my online wallet... – Dscoduc Jun 06 '14 at 07:09