-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 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. :)
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. 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.) Dňa 6. februára 2015 1:22:23 CET používateľ Eric Voskuil <e...@voskuil.org> napísal: > >On 02/05/2015 04:04 PM, MⒶrtin HⒶboⓋštiak 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 <e...@voskuil.org>: >>> On 02/05/2015 03:36 PM, MⒶrtin HⒶboⓋštiak 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 >>> - -- Odoslané z môjho Android zariadenia pomocou K-9 Mail. -----BEGIN PGP SIGNATURE----- Version: APG v1.1.1 iI8EAREKADcFAlTUDKEwHE1hcnRpbiBIYWJvdmF0aWFrIDxtYXJ0aW4uaGFib3Zz dGlha0BnbWFpbC5jb20+AAoJED6C3NvqapyUfUgA/2j6jQELBtSrNsle7ybGq1D8 uWgGwevguCnjPd0pEpWgAP42sS/ekCqs1v9wbART9fLprZTBk4YPllwXifss+9sa zQ== =J4w/ -----END PGP SIGNATURE----- ------------------------------------------------------------------------------ Dive into the World of Parallel Programming. The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. 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