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

As a co-author and implementor of the SSSS approach, I would also prefer keeping it as the only approach for proof of transit and remove the nested encryption related text.

Thanks,
Shwetha

From: <ao.ting@zte.com.cn>
To: <jmh@joelhalpern.com>
Cc: <fbrockne@cisco.com>, <sfc@ietf.org>
Subject: Re: [sfc] =?utf-8?q?proof-of-transit=3A_continue_with_both_approache?= =?utf-8?q?s=2Cor_choose_one=3F?=

I agree with Joel. Since SSSS already has mechanism to provide ordered verification requirment, only this one approach is enough.

Regards.

敖婷 Ting Ao

原始邮件

发件人：JoelM.Halpern <jmh@joelhalpern.com><mailto:jmh@joelhalpern.com&gt>;

收件人：Frank Brockners (fbrockne) <fbrockne@cisco.com>;sfc@ietf.org <sfc@ietf.org><mailto:sfc@ietf.org&gt>;;

日 期 ：2018年12月17日 04:53

主 题 ：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

>

>

>

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