Hi pointbiz,

I noticed that there are a lot of people that think about virtual wallet that no data needed to save in local or other server. The best way to do this is to specify a memorizable but not easy to guess string by the end user and the string can be used to generate private/public key pair.  When the user want to know his/her private/public key pair, he/she can generate them again with the same string.

Can you consider about that function in your website?

I'm leaving the redeeming problem to others, I figure the sipa private key import patch for bitcoin will probably make it into the official build at some point because there is so much demand.

If you plan to completely clear out an address and never use it again then this tool, by Joric, is useful:
https://bitcointools.appspot.com/
It uploads your private key to the server and returns you a wallet.dat file you can use with the bitcoin client.

EDIT: However, pyWallet is probably the best option since you don't have to trust an online service.

request for QR code to give balance from blockexplorer: https://blockexplorer.com/q/addressbalance/

I wrote a deterministic wallet generator for Casascius Bitcoin Utility.  Here are my thoughts.

My utility pre-fills the passphrase field with randomized alphabetic characters as a default.  If the user doesn't care, the alphabetic characters suffice.  The Microsoft .NET framework offers a RNG specifically suited for cryptographic functions, and this is the source of the entropy for this random passphrase.  Chances are decent that it's a good one.

If the user chooses a short passphrase, I warn him persistently about why that's a problem.  I recommend to him that he simply mash keys into the text box if he must not accept the default.  I don't remember the precise rules, but I require either 30+ characters of any type, or 20+ characters with at least two of each of three classes (uppercase, lowercase, numbers, and symbols).

A deterministic generation function does one more very valuable thing from an auditability perspective that has nothing to do with recreating wallets.  Supporting deterministic generation from a passphrase allows the average user to control for the possibility that the RNG in your generator isn't rigged or flawed in a non-obvious manner.  If your RNG turns out to be flawed at any time down the road, it would turn into a huge liability for anyone who has ever used your generator.  (Google "Debian OpenSSL key flaw" for an example of a past occurrence of this mess). On the other hand, if it produces the same deterministic wallet as any other program made for the same purpose, it can be conclusively deemed to operate as advertised.

casascius and peak, very good points you've convinced me.

I like the idea of pregenerating something the user could then alter.
Thanks for the enlightenment on the Debian issue.

I might look into adding more entropy by calling the seedTime in more elaborate ways.

Honestly, for the time being, I would be happy just with a QR code. It would be the easiest way to get a paper wallet.

Of course there are other ways. I could just copy the private key, paste it at wolfram alpha and print the QR Code. But having a complete wallet just by opening an html file is a much more clean and attractive solution.

V0.4

2011-09-18:
bitaddress.org-v0.4-SHA1-9d3afda22f8cf526330c0387a77e4016fd050323.html
 -Known bug: Bitcoin.Base58.encode is not working in IE7
 -Removed Private Key Hex
 -Added QRCode for Bitcoin Address
 -Added QRCode for Private Key Wallet Import Format
 -Added extra entrophy with mouse movement technique
 -Footer now hides when printing
 -QRCode shows with canvas, if canvas is not supported (IE8) then it shows
  with a table. Printing of the table is not supported by most browsers.

Hum... It doesn't work on my iPhone. Maybe because I can't move my mouse around? It hangs on "Generating Bitcoin Address...".

Anyway, a cellphone probably isn't the best place to use this.