Quote from: J35st3r on October 12, 2013, 07:50:35 AM

Quote from: chriswilmer on October 09, 2013, 07:02:01 PM

Sorry if this has been asked 1000 times already...

And its actually pretty close to the subject of the very first question I asked on this forum ...

bitaddress.org lets you input a hexadecimal private key, and trying some different values (including all FFFF and all 0000) I thought I'd found a collision. It actually turned out that all 0000 broke the (bitaddress.org) algorithm and just returned the same key as the previous try. But further playing confirmed that the key values do wrap around at the n value (at least in the sense of generating the same public key value, and hence address, from the private key). This is also the case with the version of the ECDSA algorithm used by pywallet. As for bitcoin-qt, I'll leave it to the developers to comment as I haven't got my head around that code yet.

Oh, and some advice. Don't use SHA256 for your brainwallet. Far too many crooks generating rainbow tables and sweeping transactions. If you must, then at the very least use some sort of salt to make their job harder.

Thanks for the reply and the advice.

It's interesting what semi-technical users are interested in. I think there are many users that don't really want to know how ECDSA works, but they do want to know what a "valid" private key is. Not too many places say that it is any integer from 1 to n-1 and specify the n value (and what's worse, I found a few places that mentioned that SHA256 output is a valid key, which is wrong... and probability has nothing to do with it if it leads a user to think that "all FFFF values" typed manually is valid).