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Author Topic: Minimal wallet file size?  (Read 2178 times)
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July 22, 2011, 02:33:48 PM

It seems that a fresh wallet.dat is around 140kB, but AFAIK it contains already 100 keys. In order to secure an offline wallet, I see two very distinct threats:
1- getting the wallet stolen
2- losing the wallet

The easiest way to address No1 is to bring the wallet offline. Yet, suddenly, it becomes a lot harder to end-up with super-durable storage.

At 140kB, printing the wallet is rather cumbersome, but assuming that it could be brought down to 1.4kB (with only 1 key), it would be much easier to backup, possibly through super-naive Base64 encoding combined with plain text print (and OCR for recovery, with the option of doing it the manual way if OCR fails for whatever reason).

Are my numbers correct? Any thoughts in providing such an option to produce such thin wallets for the sole purpose of offline saving?

Best regards,
Joannes Vermorel
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July 23, 2011, 01:15:12 AM

For a single address offline wallet, you can just generate a private key and record it. This takes only 32 bytes (64 digits in hex, 44 in padded Base64) and is short enough to be stored in a QR code or even written down by hand. People already use this for offline savings. Casascius sells paper wallets containing nine addresses and their private keys on one sheet of paper. BitBills are similar and store the keys in QR codes.
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July 23, 2011, 06:04:43 AM

This is a great reason for deterministic key generation.
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July 25, 2011, 01:42:59 AM

I would be interested btw. in the opposite:
What's the maximum wallet size (if there is one), how many privkeys + adresses can you store in a (for example) 1 TB wallet approximately, how hard are the performance hits of huge (multi GB/TB) wallet.dat files and when would they occur (at every block that is received?)? <-- leveraged trading of BTCUSD, LTCUSD and LTCBTC (long and short) - 10% discount on fees for the first 30 days with this refcode: x5K9YtL3Zb
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July 26, 2011, 09:55:42 AM

With bitcoin -poolsize=0 you'll get 32kb wallet (see

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July 26, 2011, 11:16:42 AM

If you print the wallet you should extract the private keys and print those. They are pretty small (as EricJ says, 32 bytes a piece) so you print it as 1 line/key, or a sheet full of QR codes.

Please don't print the binary database file entirely, it also contains unrelated info (such as configuration) and index structures/padding for efficiency that you don't need on paper.

Bitcoin Core developer [PGP] Warning: For most, coin loss is a larger risk than coin theft. A disk can die any time. Regularly back up your wallet through FileBackup Wallet to an external storage or the (encrypted!) cloud. Use a separate offline wallet for storing larger amounts.
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