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Today's Topics:
1. Re: Proposal for P2P Wireless (Bluetooth LE) transfer of
Payment URI (Eric Voskuil)
2. Proposal: Requiring a miner's signature in the block header
(Hector Chu)
3. Re: Proposal: Requiring a miner's signature in the block
header (Natanael)
----------------------------------------------------------------------
Message: 1
Date: Tue, 10 Feb 2015 09:56:39 -0800
From: Eric Voskuil <eric@voskuil.org>
Subject: Re: [Bitcoin-development] Proposal for P2P Wireless
(Bluetooth LE) transfer of Payment URI
To: M?rtin H?bo??tiak <martin.habovstiak@gmail.com>
Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>, Paul Puey
<paul@airbitz.co>
Message-ID: <54DA4657.5080604@voskuil.org>
Content-Type: text/plain; charset="utf-8"
On 02/10/2015 09:16 AM, M?rtin H?bo??tiak wrote:
> I'm not sure if I was clear enough. Handshake should be used to
> establish authenticated AND encrypted communication using ECDH (or
> just DH, but I think it's easier to use ECDH, since required functions
> are already used in Bitcoin protocol), like RedPhone does. BTW
> knowledge of verification string is useless to the attacker.
Yes, I think this was clear from your description.
> Yes, the customer must verify it verbally and the merchant shouldn't
> send the transaction before verification. Other possibility is that in
> case of differing verification strings new address is generated, so
> attacker doesn't know the address. But in this case, amount is leaked
> and there is quite high probability it can be found in the Blockchain.
Yes, for each handshake the payment request would need to contain a
different address, mitigating some of the privacy loss.
> Anyway, I don't believe the transaction can be made securely without
> such interaction except with white-listing public keys, so I see no
> reason why interaction should be problematic.
It can be done securely and privately by transfer of a shared secret
through a private channel.
> We don't have such strict regulations but I agree that security is
> important. Currently I think that verbal verification and manual
> confirmation is the best way to achieve high security and reasonable
> user-friendliness.
I think for a broadcast model (e.g. Bluetooth only) that is the only
want to ensure integrity and privacy. A narrow cast can use proximity to
establish trust.
> 2015-02-10 17:55 GMT+01:00 Eric Voskuil <eric@voskuil.org>:
>> Martin,
>>
>> I like your idea for the commit protocol in that it resolves the
>> vandalous address substitution attack. However, I don't see a way to
>> prevent privacy loss without adverse impact to the scenario.
>>
>> Anyone could perform the handshake and thereby obtain the payment
>> request. Therefore to prevent inadvertent disclosure the customer must
>> visually confirm the "phrase" and then verbally tell the merchant to
>> proceed by sending the payment request.
>>
>> One might argue that it's sufficient to preserve the integrity of the
>> transaction while suffering the privacy loss, especially given that a
>> hijacked handshake should never result in a completed transaction -
>> unless of course the hijacker pays.
>>
>> But imagine someone purchasing their meds. HIPAA requires the checkout
>> queue to form behind a yellow line. That speaks directly to this question.
>>
>> e
>>
>> On 02/06/2015 01:07 AM, M?rtin H?bo??tiak wrote:
>>> 2015-02-06 2:29 GMT+01:00 Eric Voskuil <eric@voskuil.org>:
>>>> On 02/05/2015 04:36 PM, Martin Habov?tiak wrote:
>>>>> I believe, we are still talking about transactions of physical
>>>>> people in physical world. So yes, it's proximity based - people
>>>>> tell the words by mouth. :)
>>>>
>>>> Notice from my original comment:
>>>>
>>>>>>>> A MITM can substitute the key. If you don't have verifiable
>>>>>>>> identity associated with the public key (PKI/WoT), you need
>>>>>>>> a shared secret (such as a secret phrase).
>>>>
>>>> I said this could only be accomplished using a shared secret or a
>>>> trusted public key. Exchanging a value that is derived from a pair of
>>>> public keys is a distinction without a difference. The problem remains
>>>> that the parties must have a secure/out-of-band channel for
>>>> communicating this value.
>>>>
>>>> The fact that they are face-to-face establishes this channel, but that
>>>> brings us back to the original problem, as it requires manual
>>>> verification - as in visual/audible scanning of the two values for
>>>> comparison. At that point the visual comparison of the address, or some
>>>> value derived from it, is simpler.
>>>
>>> I have never been against manual verification. What I'm trying to say
>>> is let's just make manual verification easier and more secure.
>>> Comparison of address is simpler for the coder but also simpler to
>>> attack. It has these problems:
>>> - Addresses broadcasted in plaintext (privacy issue)
>>> - Amounts broadcasted in plaintext (privacy issue)
>>> - Address is long - takes lot of time to verify (user experience issue)
>>> - Address prefix can be brute-forced, if too short or used to make
>>> "black hole" address if longer (vandalism issue)
>>>
>>> Commit protocol can be used for both the encryption and the
>>> authentication while user experience is not bad and everything is
>>> still secure.
>>>
>>>>
>>>>> In case of RedPhone, you read those words verbally over not-yet-
>>>>> verified channel relying on difficulty of spoofing your voice. Also
>>>>> the app remembers the public keys, so you don't need to verify
>>>>> second time.
>>>>
>>>> This is reasonable, but wouldn't help in the case of an ad-hoc
>>>> connection between parties who don't know each other well.
>>>>
>>>>> I suggest you to try RedPhone (called Signal on iPhone) yourself.
>>>>> It's free/open source, Internet-based and end-to-end encrypted. You
>>>>> may find it useful some day. Also I'm willing to help you with
>>>>> trying it after I wake up. (~8 hours: Send me private e-mail if
>>>>> you want to.)
>>>>
>>>> I appreciate the offer. I really don't trust *any* smartphone as a
>>>> platform for secure communication/data. But encrypting on the wire does
>>>> of course shrink the attack surface and increase the attacker's cost.
>>>>
>>>> e
>>>>
>>>>> D?a 6. febru?ra 2015 1:22:23 CET pou??vate? Eric Voskuil
>>>> <eric@voskuil.org> nap?sal:
>>>>
>>>>>> On 02/05/2015 04:04 PM, M?rtin H?bo??tiak wrote:
>>>>>>> That's exactly what I though when seeing the RedPhone code, but after
>>>>>>> I studied the commit protocol I realized it's actually secure and
>>>>>>> convenient way to do it. You should do that too. :)
>>>>>
>>>>>> I was analyzing the model as you described it to me. A formal analysis
>>>>>> of the security model of a particular implementation, based on
>>>>>> inference
>>>>> >from source code, is a bit beyond what I signed up for. But I'm
>>>>>> perfectly willing to comment on your description of the model if you
>>>>>> are
>>>>>> willing to indulge me.
>>>>>
>>>>>>> Shortly, how it works:
>>>>>>> The initiator of the connection sends commit message containing the
>>>>>>> hash of his temporary public ECDH part, second party sends back their
>>>>>>> public ECDH part and then initiator sends his public ECDH part in
>>>>>>> open. All three messages are hashed together and the first two bytes
>>>>>>> are used to select two words from a shared dictionary which are
>>>>>>> displayed on the screen of both the initiator and the second party.
>>>>>
>>>>>>> The parties communicate those two words and verify they match.
>>>>>
>>>>>> How do they compare words if they haven't yet established a secure
>>>>>> channel?
>>>>>
>>>>>>> If an attacker wants to do MITM, he has a chance of choosing right
>>>>>>> public parts 1:65536. There is no way to brute-force it, since that
>>>>>>> would be noticed immediately. If instead of two words based on the
>>>>>>> first two bytes, four words from BIP39 wordlist were chosen, it would
>>>>>>> provide entropy of 44 bits which I believe should be enough even for
>>>>>>> paranoid people.
>>>>>>>
>>>>>>> How this would work in Bitcoin payment scenario: user's phone
>>>>>>> broadcasts his name, merchant inputs amount and selects the name from
>>>>>>> the list, commit message is sent (and then the remaining two
>>>>>>> messages), merchant spells four words he sees on the screen and buyer
>>>>>>> confirms transaction after verifying that words match.
>>>>>
>>>>>> So the assumption is that there exists a secure (as in proximity-based)
>>>>>> communication channel?
>>>>>
>>>>>> e
>>>>>
>>>>>>> 2015-02-06 0:46 GMT+01:00 Eric Voskuil <eric@voskuil.org>:
>>>>>>>> On 02/05/2015 03:36 PM, M?rtin H?bo??tiak wrote:
>>>>>>>>>> A BIP-70 signed payment request in the initial broadcast can
>>>>>> resolve the
>>>>>>>>>> integrity issues, but because of the public nature of the
>>>>>> broadcast
>>>>>>>>>> coupled with strong public identity, the privacy compromise is
>>>>>> much
>>>>>>>>>> worse. Now transactions are cryptographically tainted.
>>>>>>>>>>
>>>>>>>>>> This is also the problem with BIP-70 over the web. TLS and other
>>>>>>>>>> security precautions aside, an interloper on the communication,
>>>>>> desktop,
>>>>>>>>>> datacenter, etc., can capture payment requests and strongly
>>>>>> correlate
>>>>>>>>>> transactions to identities in an automated manner. The payment
>>>>>> request
>>>>>>>>>> must be kept private between the parties, and that's hard to do.
>>>>>>>>>
>>>>>>>>> What about using encryption with forward secrecy? Merchant would
>>>>>>>>> generate signed request containing public ECDH part, buyer would
>>>>>> send
>>>>>>>>> back transaction encrypted with ECDH and his public ECDH part. If
>>>>>>>>> receiving address/amount is meant to be private, use commit
>>>>>> protocol
>>>>>>>>> (see ZRTP/RedPhone) and short authentication phrase (which is hard
>>>>>> to
>>>>>>>>> spoof thanks to commit protocol - see RedPhone)?
>>>>>>>>
>>>>>>>> Hi Martin,
>>>>>>>>
>>>>>>>> The problem is that you need to verify the ownership of the public
>>>>>> key.
>>>>>>>> A MITM can substitute the key. If you don't have verifiable identity
>>>>>>>> associated with the public key (PKI/WoT), you need a shared secret
>>>>>> (such
>>>>>>>> as a secret phrase). But the problem is then establishing that
>>>>>> secret
>>>>>>>> over a public channel.
>>>>>>>>
>>>>>>>> You can bootstrap a private session over the untrusted network using
>>>>>> a
>>>>>>>> trusted public key (PKI/WoT). But the presumption is that you are
>>>>>>>> already doing this over the web (using TLS). That process is subject
>>>>>> to
>>>>>>>> attack at the CA. WoT is not subject to a CA attack, because it's
>>>>>>>> decentralized. But it's also not sufficiently deployed for some
>>>>>> scenarios.
>>>>>>>>
>>>>>>>> e
>>>>>>>>
>>>>>
>>>>>
>>>>
>>
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Message: 2
Date: Wed, 11 Feb 2015 08:54:15 +0000
From: Hector Chu <hectorchu@gmail.com>
Subject: [Bitcoin-development] Proposal: Requiring a miner's signature
in the block header
To: bitcoin-development@lists.sourceforge.net
Message-ID:
<CAAO2FKEFxC_byt4xVJb0S-7yy0M7M-Av7MHUH-RBDuri_GAFtw@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
A proposal for stemming the tide of mining centralisation -- Requiring a
miner's signature in the block header (the whole of which is hashed), and
paying out coinbase to the miner's public key.
Please comment on whether this idea is feasible, has been thought of before,
etc., etc. Thank you.
Motivation
----------
Mining is centralising to a handful of pool operators. This is bad for a
number of political reasons, which we won't go into right now. But I have
always believed that some years down the line, they could hold the users
hostage and change the rules to suit themselves. For instance by eliminating
the halving of the block reward.
Solution
--------
Currently the block header is formed by the pool operator and distributed
for
hashing by the pooled miners. It is possible to divide the work among the
miners as the only thing that is used to search the hash space is by
changing
a nonce or two.
I propose that we require each miner to sign the block header prior to
hashing. The signature will be included in the data that is hashed. Further,
the coinbase for the block must only pay out to the public key counterpart
of
the private key used to sign the block header.
A valid block will therefore have a signature in the block header that is
verified by the public key being paid by the coinbase transaction.
Ramifications
-------------
Work can no longer be divided among the pooled miners as before, without
sharing the pool's private key amongst all of them. If the pool does try to
take this route, then any of the miners may redeem the coinbase when it
matures. Therefore, all miners will use their own key pair.
This will make it difficult to form a cooperating pool of miners who may not
trust each other, as the block rewards will be controlled by disparate
parties
and not by the pool operator. Only a tight clique of trusted miners would be
able to form their own private pool in such an environment.
Attacks
-------
Pooled hashpower, instead of earning bitcoins legitimately may try to break
the system instead. They may try a double-spending attack, but in order to
leverage the pool to its full potential the pool operator would again have
to
share their private key with the whole pool. Due to the increased
cooperation
and coordination required for an attack, the probability of a 51% attack is
much reduced.
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Message: 3
Date: Wed, 11 Feb 2015 10:25:27 +0100
From: Natanael <natanael.l@gmail.com>
Subject: Re: [Bitcoin-development] Proposal: Requiring a miner's
signature in the block header
To: Hector Chu <hectorchu@gmail.com>
Cc: bitcoin-development@lists.sourceforge.net
Message-ID:
<CAAt2M1_qj0r03=Ref9mN7bJLg-odep3m5teZ7JWDLC+zknQdQQ@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Den 11 feb 2015 09:55 skrev "Hector Chu" <hectorchu@gmail.com>:
>
> A proposal for stemming the tide of mining centralisation -- Requiring a
> miner's signature in the block header (the whole of which is hashed), and
> paying out coinbase to the miner's public key.
>
> Please comment on whether this idea is feasible, has been thought of
before,
> etc., etc. Thank you.
>
> Motivation
> ----------
>
> Mining is centralising to a handful of pool operators. This is bad for a
> number of political reasons, which we won't go into right now. But I have
> always believed that some years down the line, they could hold the users
> hostage and change the rules to suit themselves. For instance by
eliminating
> the halving of the block reward.
[...]
> I propose that we require each miner to sign the block header prior to
> hashing. The signature will be included in the data that is hashed.
Further,
> the coinbase for the block must only pay out to the public key
counterpart of
> the private key used to sign the block header.
[...]
> This will make it difficult to form a cooperating pool of miners who may
not
> trust each other, as the block rewards will be controlled by disparate
parties
> and not by the pool operator. Only a tight clique of trusted miners would
be
> able to form their own private pool in such an environment.
People already trust things like cloud mining, so your solution with
increasing technical trust requirements won't help. But you will however
break P2Pool instead.
Also, note that threshold signatures (group signatures) could probably be
used by an actual distrusting pool's miners. There are already a proof of
concept for this implemented with secp256k1 that works with Bitcoin clients
silently. This wouldn't prevent such a pool from working.
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