Re: [Bitcoin-development] Bitcoin-development Digest, Vol 45, Issue 37

[Joshua <josh@root.bz>]

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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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> End of Bitcoin-development Digest, Vol 45, Issue 37
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