Re: [Detnet] DetNet Use Cases comment - time properties of cryptographic algorithms used to verify traffic

["Black, David" <[e-mail]>]

Hi Pascal,

I would not preclude that, but I would discourage it, as, if I understand what is proposed, it involves checking a digital signature on each packet at arbitrary intermediate points along the flow, which is indeed rather expensive.

If only endpoint checks or checks at a small number of intermediate points are required, a more effective approach is to use asymmetric crypto to authenticate distribution or exchange of a secret key for symmetric crypto - a successful check based on that key provides traffic origin verification as long as the key is kept secret by the participants.  Both TLS and IKE (for IPsec) are examples of this for endpoint checks.

In both cases, origin verification also requires replay detection mechanism as part of the security protocol to prevent an attacker from recording and resending traffic, e.g., as a denial of service attack on flow forwarding resources.

Thanks, --David

From: detnet [mailto:[e-mail]] On Behalf Of Pascal Thubert (pthubert)
Sent: Thursday, December 20, 2018 2:34 AM
To: Black, David; Grossman, Ethan A.; [e-mail]
Cc: [e-mail]
Subject: Re: [Detnet] DetNet Use Cases comment - time properties of cryptographic algorithms used to verify traffic


[EXTERNAL EMAIL]
Hello David :

Asymmetric is a lot more expensive, I'm hearing, but could be very useful to ensure that the packets in a DetNet flow are from the proper source.
Say that the DetNet flow is associated with a keypair, and that the private key is available to the source of the flow whereas the public key is distributed with the flow information.
We should not preclude that should we? As long as the crypto time is bounded we should be OK.

All the best

pascal

From: detnet <[e-mail]<mailto:[e-mail]>> On Behalf Of Black, David
Sent: jeudi 20 décembre 2018 03:47
To: Grossman, Ethan A. <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Cc: [e-mail]<mailto:[e-mail]>
Subject: Re: [Detnet] DetNet Use Cases comment - time properties of cryptographic algorithms used to verify traffic

> Good question, for example do such algorithms have deterministic execution times?

Generally, yes, to a first approximation, as the algorithms used to encrypt and verify traffic are usually symmetric crypto algorithms such as AES and SHA-2 which perform the same computation regardless of input.   Non-deterministic execution times are associated with asymmetric crypto algorithms (e.g., public key algorithms), which are not typically used on a packet-by-packet basis - they're used for session setup, including key exchange, from which keys are derived for the symmetric algorithms.

Thanks, --David

From: detnet [mailto:[e-mail]] On Behalf Of Grossman, Ethan A.
Sent: Wednesday, December 19, 2018 7:42 PM
To: [e-mail]<mailto:[e-mail]>
Cc: [e-mail]<mailto:[e-mail]>
Subject: [Detnet] DetNet Use Cases comment - time properties of cryptographic algorithms used to verify traffic


[EXTERNAL EMAIL]

Hi All,

In going over the remaining IESG review comments, there is this question on Sec 11.5 (Security). I don't think it is worth holding up the Use Cases draft for, but it seems worth a conversation on the list.



Text from Section 11.5:

>      addition to arriving with the data content as intended, the data must

>      also arrive at the expected time.  This may present "new" security

>      challenges to implementers, and must be addressed accordingly.  There

>      are other security implications, including (but not limited to) the

>      change in attack surface presented by packet replication and

>      elimination.



Reviewer's Comment:

Do these requirements impose new requirements on the cryptographic algorithms used to verify traffic?



Ethan's thoughts:

Good question, for example do such algorithms have deterministic execution times? Is there a large spread between best- and worst-case execution times? Is this a topic for the Security draft? The Architecture draft? Or is this a more general matter of network (or network silicon) design/implementation/performance, and thus doesn't get covered in DetNet drafts?
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