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Author Topic: Blockchain.info - Bitcoin Block explorer & Currency Statistics  (Read 311907 times)
paraipan
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October 19, 2013, 10:46:16 AM
 #2741

Great work piuk, keep it up  Kiss

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piuk
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October 19, 2013, 11:53:52 AM
 #2742

Sharedcoin trustless mixing now available for testing

Sharedcoin uses a technique known as coinjoin to provide coin mixing without needing to trust any third party with your funds. The service still relies on a centralised server but that server only co-ordinates transactions without any funds passing through it. The main advantages are significantly less risk for both the user and operator and no requirement to keep any logs.

Anyone interested in testing can login using the following link:

https://blockchain.info/wallet/login?enable_sharedcoin=true

Please test with small amounts only (0.5 BTC max). 0.1 BTC is the minimum send amount. If you experience any errors please record the output from the javascript console.

The current client stages are:

- The client will submit its "offer", which is the inputs it wants mixing and the desired outputs.
- The server waits a certain amount of time for other clients to submit their offers.
- The server combines everyone's offers and creates a "proposal".
- The clients check they are happy with the proposal and signs their inputs.
- The server submits the final transaction.

The entire process takes about 40 seconds.

Features currently supported:

- Variable number of inputs and outputs per client
- Variable input and output values.
- Randomised fees.
- Ability to draw upon reserve funds when no other participants are available for mixing.
- Taint analysis determines the appropriate inputs to mix.

Features planned:

- Multiple iterations using temporary addresses never saved inside wallets.
- Better randomisation of change outputs and splitting of outputs between multiple iterations.
- Better progress indication.
- Documented Client APIs and SDK.

Example sharedcoin transaction:
 https://blockchain.info/tx/72316782bf48d0cd232b888a7b9ea03f88ba79fac28273cd2aa1804683235412?show_adv=true

The amount currently available in the reserve pool is low, this will be gradually increased over time but during the testing phase if anyone manages to manipulate the client to withdraw excess funds from the pool they can keep that amount.

Client source available at: https://github.com/blockchain/My-Wallet/blob/master/sharedcoin.js
Server status can be viewed while testing at: https://api.sharedcoin.com/

Lohoris
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October 19, 2013, 12:53:01 PM
 #2743

You could even get fancy and give us the option to pick our exchange (for price) and give the option to enter a % premium or % discount.
This would be really great, the feature of picking your price in your home currency is great, but unless you can chose which exchange to trust for the price, it isn't really useful.

The current client stages are:

- The client will submit its "offer", which is the inputs it wants mixing and the desired outputs.
- The server waits a certain amount of time for other clients to submit their offers.
- The server combines everyone's offers and creates a "proposal".
- The clients check they are happy with the proposal and sign their inputs.
- The server submits the final transaction.

The entire process takes about 40 seconds.
Does this imply that you only "mix" your coin with people also trying to mix them in those 40 seconds?
i.e. it works much better within peak activity?

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zebedee
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October 19, 2013, 01:16:14 PM
 #2744

Feature suggestion: When creating a payment request (by clicking the "Request Payment" button on an address page) it would be great if one could enter a EUR or USD amount. Right now you can only enter BTC amounts, but I do know several merchants who price their products in Euro and would like to be able to create payment requestsbased on Euro amounts.
Well duh, blockchain.info has no control whatsoever over what rate you're exchanging at with whatever exchange counterparty you agreed of your own free will.  So if blockchain were to claim you'd get 10 EUR and you got 9, I guess you'd blame them for that too?

Hopefully you can see the problem in your suggestion.  The best that could be done is that blockchain say the rate is indicative.  You should expect an indicative rate to be 5% or more wrong worst case.  Are you happy?  If so, you understand.  If not happy, you need to think more.
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October 19, 2013, 02:39:34 PM
 #2745

Is it important to use whole increments (like 0.1 BTC) when using this? If so, you should enforce that in the user interface.
(if you can send arbitrary amounts, that's cool, I don't know how this works)
dillpicklechips
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October 19, 2013, 02:40:48 PM
 #2746

Sharedcoin trustless mixing now available for testing

Sharedcoin uses a technique known as coinjoin to provide coin mixing without needing to trust any third party with your funds. The service still relies on a centralised server but that server only co-ordinates transactions without any funds passing through it. The main advantages are significantly less risk for both the user and operator and no requirement to keep any logs.
Cool! Does it allow other users not using blockchain.info to join a coinjoin transaction?
piuk
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October 19, 2013, 06:34:30 PM
 #2747

Does this imply that you only "mix" your coin with people also trying to mix them in those 40 seconds?
i.e. it works much better within peak activity?

As the transactions are large and incur high network fees, paid by the operator, there is an advantage to the operator to have multiple participants in one transaction.

But for users themselves as long as the coins in the sharedcoin wallet are being consistently swapped with fresh coins (tainted by many sources) it doesn't necessarily matter if another user is directly involved in your transaction or not. In fact the server can provide better anonymity (see below).

Is it important to use whole increments (like 0.1 BTC) when using this? If so, you should enforce that in the user interface.
(if you can send arbitrary amounts, that's cool, I don't know how this works)

Only if you are mixing with other users who want to send different amounts. When mixing with the sharedcoin pool the server doesn't desire any particular output size so can deliberately add input and output combinations which mimic your own. Then when you include randomised fees into the mix it makes it almost impossible to determine the inputs used from the value of one output.

Cool! Does it allow other users not using blockchain.info to join a coinjoin transaction?

Yes there will be a browser extension available which you can input a private key.

molecular
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October 19, 2013, 07:57:28 PM
 #2748

Sharedcoin trustless mixing now available for testing

Cool. Thanks for going forward on this.

Do I understand correctly that the pool server still knows which inputs and outputs were provided by who? So you still trust the server regarding privacy, just not coins, right?

PGP key molecular F9B70769 fingerprint 9CDD C0D3 20F8 279F 6BE0  3F39 FC49 2362 F9B7 0769
Peter Todd
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October 19, 2013, 09:58:52 PM
 #2749

Only if you are mixing with other users who want to send different amounts. When mixing with the sharedcoin pool the server doesn't desire any particular output size so can deliberately add input and output combinations which mimic your own. Then when you include randomised fees into the mix it makes it almost impossible to determine the inputs used from the value of one output.

One issue with the current version is that the blockchain.info wallet app only uses uncompressed keys, especially for sharedcoin change addresses, while internally the pool uses compressed keys.

I know iPhone compatibility is a problem, but maybe you could make the pool at least occasionally use uncompressed keys, or add compressed key change as an advanced experts-only option?

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October 20, 2013, 12:09:15 AM
 #2750

Then when you include randomised fees into the mix it makes it almost impossible to determine the inputs used from the value of one output.

How about being able to specify multiple outputs?

ThePiachu
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October 20, 2013, 08:48:08 AM
 #2751

Feature suggestion - Blockchain Wallet API List Addresses should include an optional field $confirmations

Reasoning:
If I am keeping track of multiple accounts looking for full confirmations I first have to make an API call to get 0 confirmation balance for every address and then make individual call for every wallet with balance >0 to check if their balance has 6 or more confirmations. Including $confirmations optional flag in List Addresses API call would cut down on the API calls from potentially many to just 1 API call.

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malevolent
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October 20, 2013, 09:36:15 PM
 #2752

(Yet Another) Feature Suggestion — would it possible for blockchain.info to include an option in account settings, that when enabled, the user would be asked for 2FA (email, sms, gauth, yubikey, etc.) also upon trying to withdraw BTC (with the ability to set up a daily transaction threshold (in BTC of fiat), above which the user would be asked for 2FA)?

This would protect people from some more sophisticated malware that waits till the user logs in with his credentials and 2FA, and only then sends funds to the attacker's address.

There is still a possibility that the attacker could wait till the user tries to make a transaction and would replace the user-specified address with his own one. To protect against this, people who have SMS or email as 2FA (hopefully accessing the email account from a different device) could get transaction information about the addresses that are involved along with the code.

It would be also nice to be able to set ranges of IP addresses from which the user should be allowed to log in (for those with dynamic IP addresses). Wink

I'll also post this here again in case piuk last time missed it:
Minor feature request: Please print out a text version of the TOTP secret key below the qr code image on the two factor authentication settings page.

I'll pass this suggestion along, but in the meantime you can use a different QR scanner app to get a copy of the secret key. If you ever need to reset two factor authentication, then you can just submit a 2FA reset request. We usually process these within 12-24 hours max (I check them multiple times a day).

Yes, please print a text version of the key, it would be very convenient for users with older phones for which there are alternative Gauth implementations but none of them can scan QR codes. Other QR scanning apps are also problematic to work with.
VTC
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October 21, 2013, 06:09:04 PM
 #2753

(Yet Another) Feature Suggestion — would it possible for blockchain.info to include an option in account settings, that when enabled, the user would be asked for 2FA (email, sms, gauth, yubikey, etc.) also upon trying to withdraw BTC (with the ability to set up a daily transaction threshold (in BTC of fiat), above which the user would be asked for 2FA)?

This would protect people from some more sophisticated malware that waits till the user logs in with his credentials and 2FA, and only then sends funds to the attacker's address.

There is still a possibility that the attacker could wait till the user tries to make a transaction and would replace the user-specified address with his own one. To protect against this, people who have SMS or email as 2FA (hopefully accessing the email account from a different device) could get transaction information about the addresses that are involved along with the code.


This won't help security. One you successfully login, your wallet is fully decrypted locally, and all the private keys become exposed to your computer,  unless you are using a secondary password.  Make a transaction and use a secondary password and now all your private keys are potentially exposed to malware.  I suggested earlier that secondary password should act like a PIN, and only be used to sign the transaction and never saved in memory.  So multiple transaction would require re-entering the secondary password.  This can potentially help a bit more. 
dillpicklechips
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October 21, 2013, 09:37:22 PM
 #2754

Can blockchain.info somehow integrate with the Trezor? Have the trezor and web browser interact with it so the private keys aren't even on the computer?
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October 22, 2013, 02:13:39 PM
 #2755

Can blockchain.info somehow integrate with the Trezor? Have the trezor and web browser interact with it so the private keys aren't even on the computer?

Piuk actually posted about this - https://bitcointalk.org/index.php?topic=40264.msg3308975#msg3308975. I'm sure more details will be released as Trezor starts to be used.

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mb300sd
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October 22, 2013, 06:32:35 PM
 #2756

Is there any way to pull full raw transaction or block data in hex? I'm trying to use http://blockchain.info/rawtx/$tx_index but the scriptsig and scriptpubkey are missing. Being able to pull the information is the same format as sendrawtransaction would be very useful.

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dillpicklechips
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October 22, 2013, 07:16:44 PM
 #2757

Can blockchain.info somehow integrate with the Trezor? Have the trezor and web browser interact with it so the private keys aren't even on the computer?

Piuk actually posted about this - https://bitcointalk.org/index.php?topic=40264.msg3308975#msg3308975. I'm sure more details will be released as Trezor starts to be used.
This will change everything! All the convienance of blockchain.info and impossible to steal the private keys! Sweet!
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October 24, 2013, 04:58:30 PM
 #2758

Feature suggestion - Blockchain Wallet API List Addresses should include an optional field $confirmations

It does take the server significantly more effort to filter by confirmations but I'll look into adding this.

(Yet Another) Feature Suggestion — would it possible for blockchain.info to include an option in account settings, that when enabled, the user would be asked for 2FA (email, sms, gauth, yubikey, etc.) also upon trying to withdraw BTC (with the ability to set up a daily transaction threshold (in BTC of fiat), above which the user would be asked for 2FA)?

This isn't possible without multisig private keys. Adding restrictions to the user interface would prevent basic attacks, but sophisticated malware could just extract the private key directly out of the browser memory and import it into another bitcoin client.

We've made the decision that we don't want to hold any unencrypted private keys server side which means multisig is especially complicated. The keys not only have to be kept isolated from us but also from each of the user's devices as well. Having said that it would certainly possible to implement with a smartphone app. But for the moment I would prefer to prioritise Hardware wallet support over multisig.

Can blockchain.info somehow integrate with the Trezor? Have the trezor and web browser interact with it so the private keys aren't even on the computer?

I hope we will be able to add support for trezor soon after its release.

This will change everything!

If I had a satoshi for everytime I heard a bitcoiner say "This will change everything" I'd be richer than Satoshi himself Smiley

Is there any way to pull full raw transaction or block data in hex? I'm trying to use http://blockchain.info/rawtx/$tx_index but the scriptsig and scriptpubkey are missing. Being able to pull the information is the same format as sendrawtransaction would be very useful.

This isn't possible at the moment. But you can use /q/outscript to fetch the output scripts e.g.

https://blockchain.info/q/outscript?tx_index=94640319&tx_output_n=0
https://blockchain.info/q/outscript?tx_index=94640319&tx_output_n=1

Cool. Thanks for going forward on this.

Do I understand correctly that the pool server still knows which inputs and outputs were provided by who? So you still trust the server regarding privacy, just not coins, right?

Correct the server has the ability to log the inputs and outputs and de-anonymize you, so it is not trust-less in that regard. There are a number of potential solutions to this some mentioned in the original coinjoin thread. My preferred solution would be to give clients the ability to trade inputs and outputs before submitting them to the server, then proxy back to the client they traded with when asked to sign the inputs.

One issue with the current version is that the blockchain.info wallet app only uses uncompressed keys, especially for sharedcoin change addresses, while internally the pool uses compressed keys.

Good catch, both the client and server will now randomly alternate between compressed and uncompressed keys.

In the following sharedcoin transaction 10 BTC was sent to 19BgLUEFhKAxbcELVMafbvZb4RCzGAkraa:

https://blockchain.info/tx/4602e0c7a0ecb9def7d2f88540a326a4a4bf424622edb2d629c303dc2cb676bb

I'm offering a bounty of 4 BTC to anyone who can successfully predict the senders inputs. The transaction was made using multiple sharedcoin repetitions.


 

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October 24, 2013, 11:13:46 PM
 #2759

eh, that's a lot of swiss nodes

129.132.230.70   8333   168.27    CH (Zurich)   vbitcoin-01.inf.ethz.ch
129.132.230.74   45606   191.75    CH (Zurich)   vbitcoin-05.inf.ethz.ch
129.132.230.77   55486   51.60    CH (Zurich)   vbitcoin-08.inf.ethz.ch
129.132.230.78   37142   80.95    CH (Zurich)   vbitcoin-09.inf.ethz.ch
129.132.230.79   53164   59.93    CH (Zurich)   vbitcoin-0a.inf.ethz.ch
129.132.230.81   60287   15.05    CH (Zurich)   vbitcoin-0c.inf.ethz.ch
129.132.230.83   55054   43.25    CH (Zurich)   vbitcoin-0e.inf.ethz.ch
129.132.230.84   46816   32.85    CH (Zurich)   vbitcoin-0f.inf.ethz.ch
129.132.230.85   46846   30.87    CH (Zurich)   vbitcoin-10.inf.ethz.ch
129.132.230.86   56112   34.03    CH (Zurich)   vbitcoin-11.inf.ethz.ch
129.132.230.87   52520   26.70    CH (Zurich)   vbitcoin-12.inf.ethz.ch
129.132.230.88   34230   145.58    CH (Zurich)   vbitcoin-13.inf.ethz.ch
129.132.230.89   33692   2.12    CH (Zurich)   vbitcoin-14.inf.ethz.ch
129.132.230.91   50123   64.12    CH (Zurich)   vbitcoin-16.inf.ethz.ch
129.132.230.92   48314   22.68    CH (Zurich)   vbitcoin-17.inf.ethz.ch
129.132.230.93   38011   189.43    CH (Zurich)   vbitcoin-18.inf.ethz.ch
129.132.230.95   35183   69.72    CH (Zurich)   vbitcoin-1a.inf.ethz.ch
129.132.230.97   39092   24.58    CH (Zurich)   vbitcoin-1c.inf.ethz.ch
129.132.230.98   48489   8.93    CH (Zurich)   vbitcoin-1d.inf.ethz.ch
129.132.230.99   57714   13.55    CH (Zurich)   vbitcoin-1e.inf.ethz.ch

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October 25, 2013, 07:58:00 AM
 #2760

ETH Zürich has some guys researching Bitcoin.
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