On 08/25/2016 04:11 PM, Rob Crittenden wrote:
Ben Lipton wrote:
On 08/23/2016 03:54 AM, Jan Cholasta wrote:
On 8.8.2016 22:23, Ben Lipton wrote:
On 07/25/2016 07:45 AM, Jan Cholasta wrote:
On 25.7.2016 13:11, Alexander Bokovoy wrote:
On Mon, 25 Jul 2016, Jan Cholasta wrote:
On 20.7.2016 16:05, Ben Lipton wrote:

Thanks very much for the feedback! Some responses below; I hope
let me know what you think of my reasoning.

On 07/20/2016 04:20 AM, Jan Cholasta wrote:

On 17.6.2016 00:06, Ben Lipton wrote:
On 06/14/2016 08:27 AM, Ben Lipton wrote:
Hello all,

I have written up a design proposal for making certificate
easier to generate when using alternate certificate profiles:

The use case for this is described in
https://fedorahosted.org/freeipa/ticket/4899. I will be
working on
implementing this design over the next couple of months. If you
the time and interest, please take a look and share any
comments or
concerns that you have.



Just a quick update to say that I've created a new document that
the proposed schema additions in a more descriptive way (with
I'm very new to developing with LDAP, so some more experienced
eyes on
the proposal would be very helpful, even if you don't have time to
absorb the full design. Please take a look at

if you have a chance.

I finally had a chance to take a look at this, here are some

1) I don't like how transformation rules are tied to a particular
helper and have to be duplicated for each of them. They should be
generic and work with any helper, as helpers are just an
implementation detail and their resulting data is the same.

In fact, I think I would prefer if the CSR was generated using
python-cryptography's CertificateSigningRequestBuilder [1] rather
openssl or certutil or any other command line tool.

There are lots of tools that users might want to use to manage their
private keys, so I don't know if we can assume that whatever
library we
prefer will actually be able to access the private key to sign a
which is why I thought it would be useful to support more than one.

python-cryptography has the notion of backends, which allow it to
support multiple crypto implementations. Upstream it currently
supports only OpenSSL [2], but some work has been done on PKCS#11
backend [3], which provides support for HSMs and soft-tokens (like

Alternatively, for NSS databases (and other "simple" cases), you can
generate the private key with python-cryptography using the default
backend, export it to a file and import the file to the target
database, so you don't actually need the PKCS#11 backend for them.

So, the only thing that's currently lacking is HSM support, but given
that we don't support HSMs in IPA nor in certmonger, I don't think
it's an issue for now.

purpose of the mapping rule is to tie together the transformation
that produce the same data into an object that's
implementation-agnostic, so that profiles referencing those rules
automatically compatible with all the helper options.

They are implementation-agnostic, as long as you consider `openssl`
and `certutil` the only implementations :-) But I don't think this
solution scales well to other possible implementations.

Anyway, my main grudge is that the transformation rules shouldn't
really be stored on and processed by the server. The server should
know the *what* (mapping rules), but not the *how* (transformation
rules). The *how* is an implementation detail and does not change in
time, so there's no benefit in handling it on the server. It
should be
handled exclusively on the client, which I believe would also make
whole thing more robust (it would not be possible for a bug on the
server to break all the clients).
This is a good point. However, for the scope of Ben's project can we
limit it by openssl and certutil support? Otherwise Ben wouldn't be
to complete the project in time.

I'm fine with that, but I don't think it's up to me :-)

This is turning out to be a common (and, I think, reasonable)
to the proposal. It is rather complex, and I worry that it will be
difficult to configure. On the other hand, there is some hidden
complexity to enabling a simpler config format, as well. One of the
goals of the project as it was presented to me was to allow the
of profiles that add certificate extensions *that FreeIPA doesn't
know about*. With the current proposal, one only has to add a rule
generating text that the helper will understand.

... which will be possible only as long as the helper understands the
extension. Which it might not, thus the current proposal works only
for *some* extensions that FreeIPA doesn't yet support.
We can go ad infinitum here but with any helper implementation, be it python-cryptography or anything else, you will need to have a support
there as well.

My point was that the current proposal is not any better than my
proposal in this regard, as neither of them allows one to use an
arbitrary extension.

The idea with unknown extensions was to allow mapping
their acceptance to a specific relationship between IPA objects
(optionally) and an input from the CSR. A simplest example would be an identity rule that would copy an ASN.1 encoded content from the CSR to
the certificate.

That's on the mapping side, not on the CSR generation side, but it
go similarly for the CSR if you would be able to enter unknown but
otherwise correct ASN.1 stream. There is no difference at which helper type we are talking about because all of them support inserting ASN.1

With your suggestion,
if there's a mapping between "san_directoryname" and the
API calls or configuration lines, we need some way for users to
that mapping without changing the code. If there's no mapping, and
just done with text processing, we need enough in the config
format to
be able to generate fairly complex structures:

builder = builder.subject_name(x509.Name(u'CN=user,O=EXAMPLE.COM'))
builder =

x509.DirectoryName(x509.Name(u'CN=user,O=EXAMPLE.COM'))]), False)

and we need to do it without it being equivalent to calling
eval() on
the config attributes. I'm not sure how to achieve this (is it
safe to
call getattr(x509, extensiontype)(value) where extensiontype and
are user-specified?) and it definitely would have to be tied to a
particular library/tool.

As I pointed out above, this needs to be figured out for the generic
case for both the current proposal and my suggestion.
I have a proof of concept[1] for using openssl-based rules to add a
subject alt name extension without using openssl's knowledge of that
extension. It's not extremely pretty, and it took some trial and error,
but no code changes. So, I think this actually is a difference between
the two proposals.

With the obvious catch being that it works only with OpenSSL, which
might not work for everyone, e.g. when using HSMs or SmartCards, due
to a limited PKCS#11 support in OpenSSL.

Very true. Even certutil's equivalent feature (--extGeneric) doesn't
seem like it would work very well in this context, as you are supposed
to pass in an already-encoded extension, so text-based templating
wouldn't be able to do much.

Yeah, I struggled with this myself. I ended up writing a pyasn1 script to generate the extension I needed, wrote that to a file, and passed it to certutil using:


Next we have the easy case, extensions that we as FreeIPA developers
know are important and build support for. For these, the two proposals
work equivalently well, but yours is simpler to configure because the
knowledge of how to make a san_rfc822name is built into the library
instead of being stored on the server as a set of rules.

Finally, we have the case of extensions that are known to the helper,
but not to FreeIPA. In the existing proposal, new rules can be written
to support these extensions under a particular helper. Further, those
rules can be used by reference in many profiles, reducing duplication of

As I understand it, the main objections in this thread are that
transformation rules are implementation (i.e. helper) specific data
stored in the IPA server, and that the system has several levels of
schema when it could just embed rules in the profile. But without
helper-specific rules, administrators could not take advantage of the
additional extensions supported by the helper they are using.

There is *no* advantage in forcing the user to choose between helpers
which differ only in the set of limitations on the CSR they are able
to produce. The user should specify a) where the private key is
located and b) what profile to use, and that's it, it should just work.
Ok, this is a good point about usability. The user creating the CSR
shouldn't have to care about helpers, and I agree that the current way
they are exposed is clunky. I do think that an administrator creating
custom rules might want to take advantage of a helper, so they wouldn't
need to understand the ASN.1 representation of their chosen certificate
extension. Of course, the desired extension might not be supported by
the helper either. Since I don't know what specific extensions people
will want to use this for, I don't know how to balance the better
administrator experience of adding extensions via a helper with the
limited extension support.

The original reason we arrived at the concept of "helpers" was to
support different ways of getting at private keys, but perhaps this
should not be the concern of the CSR data generator. In your opinion,
would it be sufficient to support just one key format (PKCS#12? PEM?)
and let the user deal with putting those keys into whatever
formats/databases they need? If that's ok, maybe we can stop having
*multiple* helpers, but if we want to replace helpers entirely I'm still
not certain what to replace them with.

I'd just add an option to specify the output format, e.g PEM, NSS, Java keystore, PKCS#12, whatever. You can probably get away with the first two for starters. Different output format is going to mean different options but that is probably not a big deal.

My point was that if we want to get rid of all the helpers but one, or replace helpers with something else entirely like somehow templating ASN1 structures directly, it will get harder to support all those formats (or even both of the first two). For example, if we drop certutil as a helper, how will we sign CSRs with keys stored in NSS databases?

Remember that the private key will be at rest for some period of time while the CSR is being approved. The key needs to be protected at that time.


without the separation of profiles from mapping rules in the schema,
rules would need to be copy+pasted among profiles, and grouping rules
with the same effect under different helpers would be much uglier. We
can and should discuss whether these are the right tradeoffs, but this
is where those decisions came from.

OTOH, I think we could use GSER encoding of the extension value:

   { rfc822Name:"u...@example.com",
directoryName:rdnSequence:"CN=user,O=EXAMPLE.COM" }
GSER is not really used widely and does not have standardized encoding
rules beyond its own definition. If you want to allow transformation
rules in GSER that mention existing content in IPA objects, you would
need to deal with templating anyway. At this point it becomes
what you are templating, though.

True, but the goal here is not to avoid templating, but rather to
avoid implementation-specific bits on the server, and GSER is the only
thing that is textual, implementation-neutral and, as a bonus,

As I said elsewhere, we could use GSER as a textual output format
instead of openssl or certutil, but it still needs its own "helper" to
build the CSR, and unlike the other options, it seems like we might need
to implement that helper. I'm not sure it's fair to call it
implementation-neutral if no implementation exists yet :)

Right. Like I said, using GSER was just a quick idea off the top of my
head. I would actually rather use some sort of data structure
templating rather than textual templating on top of any kind of
textual representation of said data structures. I don't know if there
is such a thing, though.

This sounds interesting, can you give an example of what this might look

I learned that there's also an XML encoding for ASN.1, XER, but that's
still a textual representation and we'd have to insert the data
textually. It doesn't seem to be supported by any python libraries,
either, but it does look like it's supported by the asn1 compiler in the
IPA source distribution. I could imagine an implementation that builds
an XML representation of the CSR via python templating, then makes a
signed CSR out of it in C. I'm a little concerned about it because it
would have to implement the whole CSR structure from scratch, but is
this a prototype that you'd be interested in seeing?

On further investigation, it turns out the version of python-cryptography in F24 includes a feature allowing arbitrary extensions to be added by adding an UnrecognizedExtension to the CertificateSigningRequestBuilder. This makes me feel somewhat better both about python-cryptography as a tool for this task and about the solution I just proposed. But I still don't have a clear idea that answers 1) how to make templates that we can turn into encoded extensions, and 2) how to deal with all the desired key formats.

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