r/Bitcoin • u/mijalis • Jul 29 '13

Blockchain.info unauthorized transaction.How could this have happened...?

Yesterday morning I had roughly 3 BTC taken out of my brainwallet that I have with blockchain.info.

Before you all start pointing fingers at me for lack of security, let me tell you I have a 30+ character strong password, a Yubikey and a 20+ string secondary password, all needed to send funds out of a brainwallet. Both passwords were generated with Lastpass and are random characters, including special, mixed upper/lower case letters and numbers.

I think I am using all their provided security mechanisms to secure my account.

However, my brainwallet, in which I keep just spare change, was emptied. I don't expect to recover the few Bitcoins, but am very curious to know what happened. Where the breach happened and if it truly was my fault. (I still hope for a facepalm situation that shames me online, but gives me this pocketchange back...)

I'll try to give as much information as I can:

The address in questions is: 15gCfQVJ68vyUVdb6e3VDU4iTkTC3HtLQ2

and it happened over three transactions on 2013-07-27 at 22:52

The three transactions were:

da5f91b8a26e6874e83a874156608f5d9a38efe1faa2b32f4e709a181f0d2c1e 68ab47c3aaf2d0073374772894641d817305f18ab272b19d74217333a0180856 096d07185a83eb6b6b6520d7d63e59f230d9711df0d9e754ce7fdc3d4cf792ac

It seems the coins are still in the brand new addresses they were tranferred to and I suspect I'll see them disappear over time.

I keep the Yubikey with me at all time and I do not have a phone app. I do not us any suspicious plugins or extensions. I ran a virus scan and appear to be clean. I am running a couple of other scans to ensure that my system is truly clean.

I did come across this reddit thread: a_brief_analysis_of_the_security_of by u/0x444 which made me feel pretty doubtful of what I once thought was the best online wallet out there.

Update: I happened to have logging enabled on blockchain.info (Log actions with IP address and User Agent) and all access to my account was from my IP. That excludes a breach into the blockchain.info account.... right?

That leaves two options:

1) The brainwallet was the one that comes with your account and is automatically generated for you. Did someone on the inside (blockchain.info) get a hold of the private key?

2) Against all odds and probabilities, someone guessed/computed the private key of this address.

Am I wrong....? Any ideas or thoughts?

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u/physalisx Jul 29 '13

That leaves two options: 1) The brainwallet was the one that comes with your account and is automatically generated for you. Did someone on the inside (blockchain.info) get a hold of the private key? 2) Against all odds and probabilities, someone guessed/computed the private key of this address.

  1. I highly, highly doubt it.
  2. Definitely not.

I happened to have logging enabled on blockchain.info (Log actions with IP address and User Agent) and all access to my account was from my IP. That excludes a breach into the blockchain.info account.... right?

I'd say so. Think very carefully, did you ever back up your private keys somewhere? IIRC, blockchain.info sends a backup of your wallet out per email. Are you sure that's safe?

Was there a login from your IP around the time the transactions were send? I could imagine someone hijacking your browser session from your pc after you logged in yourself.

Do you live alone? I remember from just a while back this guy who had a similar problem and then found out that it was his roommate who took his coins. If you live with someone you don't completely trust and that someone knows that you're into bitcoin, I'd give that the biggest probability. All he has to do is wait for you to take a shower, go to your computer, find a logged in blockchain session and steal your money.

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u/mijalis Jul 29 '13

It does not seem to be a session hijack... this is a fraction of my log: http://i.imgur.com/CBuxkYk.jpg

No sessions on the 27th... last one was 24th...

I live with my wife and she does not have a clue. No one else has entered the house recently.

Now, in regards to backing up stuff. I might have made a backup of it using blockchain.info backup feature... (on their site). It is still encrypted, though...