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:Hi,Thanks very much for the feedback! Some responses below; I hope you'll let me know what you think of my reasoning. On 07/20/2016 04:20 AM, Jan Cholasta wrote:There are lots of tools that users might want to use to manage theirHi, 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 requests easier to generate when using alternate certificate profiles:http://www.freeipa.org/page/V4/Automatic_Certificate_Request_Generation.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 have the time and interest, please take a look and share any comments or concerns that you have. Thanks! BenJust a quick update to say that I've created a new document that covers the proposed schema additions in a more descriptive way (with diagrams!) I'm very new to developing with LDAP, so some more experienced eyes onthe proposal would be very helpful, even if you don't have time toabsorb the full design. Please take a look athttp://www.freeipa.org/page/V4/Automatic_Certificate_Request_Generation/Schemaif you have a chance.I finally had a chance to take a look at this, here are some comments: 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 than openssl or certutil or any other command line tool.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 CSR,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 NSS databases).Alternatively, for NSS databases (and other "simple" cases), you cangenerate 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 giventhat we don't support HSMs in IPA nor in certmonger, I don't think it's an issue for now.The purpose of the mapping rule is to tie together the transformation rules that produce the same data into an object that's implementation-agnostic, so that profiles referencing those rules are 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* (transformationrules). The *how* is an implementation detail and does not change intime, 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 the 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 able to complete the project in time.I'm fine with that, but I don't think it's up to me :-)We can go ad infinitum here but with any helper implementation, be it python-cryptography or anything else, you will need to have a supportThis is turning out to be a common (and, I think, reasonable) reaction to the proposal. It is rather complex, and I worry that it will be difficult to configure. On the other hand, there is some hiddencomplexity to enabling a simpler config format, as well. One of thegoals of the project as it was presented to me was to allow the creation of profiles that add certificate extensions *that FreeIPA doesn't yet 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 theextension. Which it might not, thus the current proposal works only for *some* extensions that FreeIPA doesn't yet 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 tothe certificate. That's on the mapping side, not on the CSR generation side, but it would go similarly for the CSR if you would be able to enter unknown butotherwise correct ASN.1 stream. There is no difference at which helper type we are talking about because all of them support inserting ASN.1content.With your suggestion, if there's a mapping between "san_directoryname" and the corresponding API calls or configuration lines, we need some way for users to augment that mapping without changing the code. If there's no mapping, and it's 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 =builder.add_extension(x509.SubjectAlternativeName([x509.RFC822Name(u'u...@example.com'),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 value 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 genericcase 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 thatextension. 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:--extGeneric 2.5.29.17:not-critical:/path/to/msupn.derNext 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, thoserules can be used by reference in many profiles, reducing duplication ofeffort/data/errors. 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?
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.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.robAnd 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.GSER is not really used widely and does not have standardized encodingOTOH, I think we could use GSER encoding of the extension value: { rfc822Name:"u...@example.com", directoryName:rdnSequence:"CN=user,O=EXAMPLE.COM" }rules beyond its own definition. If you want to allow transformationrules in GSER that mention existing content in IPA objects, you wouldneed to deal with templating anyway. At this point it becomes irrelevant what you are templating, though.True, but the goal here is not to avoid templating, but rather toavoid implementation-specific bits on the server, and GSER is the onlything that is textual, implementation-neutral and, as a bonus, standardized.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" tobuild the CSR, and unlike the other options, it seems like we might needto 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 like? 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?
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