How to steal Bitcoins that are protected by weak passphrases
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Re: How to steal Bitcoins that are protected by weak passphrases
#2Or: why not to use brainwallets.
Re: How to steal Bitcoins that are protected by weak passphrases
#3Yes, if you use a weak seed on a service like brainwallet to deterministically generate your keypair then it is quite easy to brute force / dictionary attack your private key. This is why clients like Electrum force you to use a long passphrase that they themselves generate. This really isn't new or novel.
Side note: I ran this attack months ago and you would be shocked at how many weak passphrases actually had money in them at some point.
Re: How to steal Bitcoins that are protected by weak passphrases
#4Or: why not to use brainwallets.
What about a high entropy set of 4 words for the passphrase?
This should give you fairly decent security.
Re: How to steal Bitcoins that are protected by weak passphrases
#5The directory.io thing is really interesting. I assume the idea is that the site does the calculation in some way that in theory produces a full set of results and they hope that Google will index more and more of them over time, thus allowing a search for some public keys to find the corresponding private key. It seems like Google does index a few pages (including some higher number ones), but not too many.
Edit: redit threads: http://www.reddit.com/r/Bitcoin/comments/1rua34/all_bitcoin_... http://www.reddit.com/r/Bitcoin/comments/1ruk0z/dont_panic_d...
Edit2: This is one of those basic security things I have trouble getting an intuitive grasp of (but need to). How much can being able to determine a random small part of a random large key space hurt? I've worried about this before with 256-bit key spaces and been reassured with calculations, but I still don't intuitively get it.
Re: How to steal Bitcoins that are protected by weak passphrases
#6Re: How to steal Bitcoins that are protected by weak passphrases
#7Or: why not to use brainwallets.
What about a high entropy set of 4 words for the passphrase? This should give you fairly decent security.
According to the classic xkcd on this subject (https://xkcd.com/936/) 4 random common words provides 44 bits of entropy which is easily crackable (you can do a hell of a lot more than 1000 guesses/sec)
Something that uses key stretching like WarpWallet might be acceptable: https://keybase.io/warp/
Re: How to steal Bitcoins that are protected by weak passphrases
#8Or: why not to use brainwallets.
What about a high entropy set of 4 words for the passphrase? This should give you fairly decent security.
Not if those 4 words are in the dictionary. Crackers are definitely aware of this password generation technique and it isn't hard to run through 4 word combinations from a dictionary.
In the end, the best password right now is a 16+ random password made up of uppercase letters, lowercase letters, numbers and symbols. Use a password manager to manage and store your passwords.
Re: How to steal Bitcoins that are protected by weak passphrases
#9I have spent quite a lot of time (~250h) on this problem as part of my dissertation and found ~18k brainwallets. Most of the 10k brainwallets found by the author have probably been made by another 'researcher' who is actively probing the network to look for thieves. There are many other similar analyses online which have better and more interesting results than this.
Edit: I can upload some rather large and confusing transaction network diagrams if anyone wishes to see them.
Re: How to steal Bitcoins that are protected by weak passphrases
#10The directory.io thing is really interesting. I assume the idea is that the site does the calculation in some way that in theory produces a full set of results and they hope that Google will index more and more of them over time, thus allowing a search for some public keys to find the corresponding private key. It seems like Google does index a few pages (including some higher number ones), but not too many. Edit: re…
It's not interesting really, it just takes the page number and generates the keys for that particular page on the fly. Google will most certainly never find anything, if nothing else the CPU of the server is a severe bottleneck when you're talking about 2^160 keys. You could load pages on that webserver until the sun becomes a red giant and consumes the earth, and you wouldn't have covered even the smallest percentage of the keyspace.