[Ndn-interest] KeyLocator name vs Certificate name

[Junxiao Shi]

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:
/<SubjectName>/KEY/[KeyId]/[IssuerId]/[Version]

*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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.lists.cs.ucla.edu/pipermail/ndn-interest/attachments/20191001/0c851971/attachment.html>