[Ndn-interest] KeyLocator name vs Certificate name

Lan Wang (lanwang) lanwang at memphis.edu
Wed Oct 2 05:51:55 PDT 2019

It seems to me that a separate system is needed to find the latest certificate name (e.g., through NDNS).  That’s an orthogonal issue to the KeyLocator format which seems to be fine the way it is.


On Oct 1, 2019, at 12:51 PM, Junxiao Shi <shijunxiao at email.arizona.edu<mailto:shijunxiao at email.arizona.edu>> wrote:

Dear folks

I wonder what's the relation between KeyLocator name and Certificate name?

Packet format spec<https://named-data.net/doc/NDN-packet-spec/0.3/signature.html#keylocator> says this on KeyLocator name:
The specific definition of the usage of Name and KeyDigest options in KeyLocator field is outside the scope of this specification. Generally, Name names the Data packet with the corresponding certificate. However, it is up to the specific trust model to define whether this name is a full name of the Data packet or a prefix that can match multiple Data packets. For example, the hierarchical trust model<https://named-data.net/publications/techreports/trpublishkey-rev2/> uses the latter approach, requiring clients to fetch the latest version of the Data packet pointed by the KeyLocator (the latest version of the public key certificate) in order to ensure that the public key was not yet revoked.

Certificate format spec<https://named-data.net/doc/ndn-cxx/0.6.6/specs/certificate-format.html#name> defines certificate name to be:

KeyId is an opaque name component to identify an instance of the public key for the certificate namespace. The value of Key ID is controlled by the namespace owner and can be an 8-byte random number, SHA-256 digest of the public key, timestamp, or a simple numerical identifier.

Issuer Id is an opaque name component to identify issuer of the certificate. The value is controlled by the certificate issuer and, similar to KeyId, can be an 8-byte random number, SHA-256 digest of the issuer’s public key, or a simple numerical identifier.

In today's testbed, most applications are setting the KeyLocator name to be /<SubjectName>/KEY/[KeyId].
For example, ivoosh server's Data packet /ndn/web/video/research_questions/hls/playlist.m3u8/%FD01/%00%00 uses KeyLocator name /ndn/web/KEY/%29%964%F6%11%12%1C%9A .
After expressing an Interest for that name, I receive a certificate named  /ndn/web/KEY/%29%964%F6%11%12%1C%9A/NA/%FD%00%00%01i%FE%FD~%BF .

Everything seems to be working fine. However, what if there are more than one certificates associated with the key?
Suppose the namespace owner requests me to issue a new certificate to his existing public key, I could execute:
ndnpeek /ndn/web/KEY/%29%964%F6%11%12%1C%9A/NA/%FD%00%00%01i%FE%FD~%BF | base64 | ndnsec cert-gen -i X - | base64 -d > X.data
and then let him publish the new certificate: /ndn/web/KEY/%29%964%F6%11%12%1C%9A/X/%FD%00%00%01m%88%1E%0A%07

Now, anyone who asks for a certificate using the KeyLocator name /ndn/web/KEY/%29%964%F6%11%12%1C%9A could receive either of the two certificates.
The validator, depending on the trust model, could be expecting one of these certificates.
If it happens to receive the other certificate, validation would fail because the signer does not match policy.

So, what's the solution space?

Trying to ensure there is only one issuer per key defeats the purpose of having IssuerId name component in the first place.
The reason to have IssuerId is that, a namespace owner can obtain certificates from multiple issuers on the same public key, so that the same content can be made available under multiple trust models.

Adding IssuerId to KeyLocator name seems to fix the problem of validator receiving the wrong certificate.
However, this would require the namespace owner to generate separate Data packets for each trust model.
In this case, she may as well use separate keys.

Providing all certificates in a bundle could solve the problem.
The producer would include certificates from multiple distinct trust models in the certificate bundle<https://redmine.named-data.net/issues/2766#note-30>, and then the validator should attempt to validate the original packet using each certificate matching the KeyLocator name, and accept the original packet if any certificate chain leads to a trust anchor configured in the validator.
A drawback of this solution is inflation of certificate bundle size.

Appending an IssuerId component in the validator appears to be the best solution. The validator needs to know, through static configuration, what IssuerId to append to each KeyLocator name.
For example, a validator configured to work with ndncert-legacy's certificate chain could be configured to always append 'NA' as IssuerId. Given the KeyLocator name shown above, the validator would fetch certificate using /ndn/web/KEY/%29%964%F6%11%12%1C%9A/NA and it would receive the expected certificate.

Please REPLY-ALL with your thoughts on this topic.

Yours, Junxiao

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