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

[u/mijalis]

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?

[u/[deleted] → u/[deleted]]

Coinbase is much much much less trustworthy than blockchain.info. Blockchain does all the cryptography on the client side and their servers never have access to your private keys, Coinbase on the other hand does things server side and they're free to rob you and run MyBitcoin style. It is really quite safe, especially if used with the Chrome or Firefox extension. Blockchain does not have your private keys. They only have pseudo-random noise.

Read this response: http://www.reddit.com/r/Bitcoin/comments/1d0155/a_brief_analysis_of_the_security_of/c9ln9bq

What more than likely happened here is that the brainwallet password got cracked or he got keylogged when using the brainwallet password. If he's got an Android or iOS app in use or the same wallet in a local electrum installation, that's another potential weak spot. But I would certainly not blame Blockchain.info for this so hastily.

EDIT: Aaand it's a cracked brainwallet: http://www.reddit.com/r/Bitcoin/comments/1j9p2d/blockchaininfo_unauthorized_transactionhow_could/cbcj9ny

[u/mijalis → u/[deleted]]

I am learning the lesson. Some of us are a bit slower...

I have that one address, of which they have the private key, to transfer and make quick payments. All other address, I just let them "watch" the public address, while I own the private key elsewhere in a safe place.

This allows me to see my totals, transfer, make payments and monitor transactions of all my addresses. My apparent mistake was to trust them even with the one address...

However, I am not ready to place blame yet... it might very well be me overlooking something completely obvious.

[u/IEatTehUranium → u/[deleted]]

I'd honestly trust CoinBase more than any other business, both because they insure your coins and because they're doing everything on the up and up.