Re: [sfc] proof-of-transit: continue with both approaches, or choose one?

["Diego R. Lopez" <[e-mail]>]

Hi,

I agree with Stephen and Joel. In fact, finding a "happier" solution for OPOT was what moved us to explore the ideas introduced in Montreal.

Be goode,

--
"Esta vez no fallaremos, Doctor Infierno"

Dr Diego R. Lopez
Telefonica I+D
https://www.linkedin.com/in/dr2lopez/

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On 20/12/2018, 19:52, "sfc on behalf of Adrian Farrel" <[e-mail] on behalf of [e-mail]> wrote:

    I think I agree with Joel on this point.

    The nested encryption approach really did smell a bit :-) It was functional,
    but a rather sad solution.

    Since the 4S approach can now meet the requirement (that is quite important
    in security applications of SFC) to show ordered proof of transit, I should
    think the decision easy.

    Cheers,
    Adrian

    -----Original Message-----
    From: sfc <[e-mail]> On Behalf Of Joel M. Halpern
    Sent: 16 December 2018 20:53
    To: Frank Brockners (fbrockne) <[e-mail]>; [e-mail]
    Subject: Re: [sfc] proof-of-transit: continue with both approaches, or
    choose one?

    <no hats>
    Personally, the argument for just using SSSS, given that it now can
    provide ordered verification, seems quite persuasive to me.
    Yours,
    Joel
    <hat floating back on slowly>

    On 12/15/18 3:19 PM, Frank Brockners (fbrockne) wrote:
    > During the SFC WG at IETF 103 in Bangkok we raised the question, whether
    > we could simplify the draft and choose a single algorithm for
    > proof-of-transit only (see also
    > https://datatracker.ietf.org/meeting/103/materials/minutes-103-sfc-01).
    > Given that we could not come to a conclusion, we decided to take the
    > discussion to the list.
    >
    > Background:
    >
    > draft-ietf-sfc-proof-of-transit-01 describes two different approaches:
    > "nested encryption" and "Shamir's secret sharing scheme (SSSS)".. We
    > documented both approaches in the initial version of the draft, because
    > the two approaches had different qualities: While SSSS was
    > computationally cheaper (each node only needs to perform two additions,
    > a multiplication and a modulo-division), nested-encryption allowed to
    > verify that packets traversed a set of nodes in a particular order
    > ("ordered POT - OPOT") - something that the SSSS-approach in the initial
    > version of the draft did not offer. With the changes discussed in IETF
    > 102 and now documented in draft-ietf-sfc-proof-of-transit-01, both
    > approaches offer order preservation.
    >
    > In summary, we can now observe the following qualities of the two
    > approaches:
    >
    >   * SSSS: Allows verification that a given set of nodes has been
    >     traversed in a specific order (POT and OPOT). SSSS without order
    >     preservation requires 2 additions, 1 multiplication, 1 division per
    >     node participating in POT. Order preservation on top of that
    >     requires an additional XOR (or similar).
    >   * Nested-encryption: Allows verification that a given set of nodes has
    >     been traversed in a specific order (POT and OPOT). The computational
    >     effort of nested encryption depends on the crypto algorithm chosen
    >     and typically higher than SSSS, i.e.. it requires/benefits from
    >     hardware with specific capabilities (e.g. AES-NI).
    >
    > Question:
    >
    > Given that both approaches both solve the problem of POT and ordered
    > POT, should we consider simplifying the draft and describe only a single
    > approach? If so, which approach should we choose?
    >
    > I.e. when taking the computational effort into account and the fact that
    > options increase the burden for any implementor, we could decide to only
    > describe the SSSS approach in the draft.
    >
    > Thoughts? Opinions?
    >
    > Many thanks, Frank
    >
    >
    >
    > _______________________________________________
    > sfc mailing list
    > [e-mail]
    > https://www.ietf.org/mailman/listinfo/sfc
    >

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