[Ndn-interest] Describe the HMAC algorithm in SignatureHmacWithSha256?

[Thompson, Jeff]

> I think the purpose is to allow both ends to uniquely identify the key. Is there any particular reason of using the first 4 bytes of the digest?

Using a short identifier (4 bytes) is to keep the packet short for low-power devices. Making a short identifier from the digest is an easy way to get a unique identifier instead of maintaining a separate list of sequential ID numbers. Does that answer your question?

- Jeff T

From: Yingdi Yu <yingdi at cs.ucla.edu<mailto:yingdi at cs.ucla.edu>>
Date: Monday, June 8, 2015 at 16:44
To: Jeff Thompson <jefft0 at remap.ucla.edu<mailto:jefft0 at remap.ucla.edu>>
Cc: Marc Mosko <Marc.Mosko at parc.com<mailto:Marc.Mosko at parc.com>>, "Ndn-interest at lists.cs.ucla.edu<mailto:Ndn-interest at lists.cs.ucla.edu>" <Ndn-interest at lists.cs.ucla.edu<mailto:Ndn-interest at lists.cs.ucla.edu>>
Subject: Re: [Ndn-interest] Describe the HMAC algorithm in SignatureHmacWithSha256?

Hi Jeff,

On Jun 8, 2015, at 2:57 PM, Thompson, Jeff <jefft0 at remap.ucla.edu<mailto:jefft0 at remap.ucla.edu>> wrote:

If the application uses a truncated key digest (e.g. the first 4 bytes of the digest), do you think we can still use the KeyDigest field?  Or, if we treat the truncated key digest as a KeyId and put it in a Name, should the spec suggest a format for the Name?

I would prefer to keep KeyDigest literally (i.e., the real sha256 digest of a key), so that it is consistent with other scenarios (e.g., KeyDigest of public key).

For the key name, I think the purpose is to allow both ends to uniquely identify the key. Is there any particular reason of using the first 4 bytes of the digest?

Yingdi
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