[Freeipa-devel] CSR autogeneration next steps
Jan Cholasta
jcholast at redhat.com
Tue Jan 10 06:58:12 UTC 2017
On 19.12.2016 21:59, Ben Lipton wrote:
>
> On 12/15/2016 11:11 PM, Ben Lipton wrote:
>>
>> On 12/12/2016 03:52 AM, Jan Cholasta wrote:
>>> On 5.12.2016 16:48, Ben Lipton wrote:
>>>> Hi Jan, thanks for the comments.
>>>>
>>>>
>>>> On 12/05/2016 04:25 AM, Jan Cholasta wrote:
>>>>> Hi Ben,
>>>>>
>>>>> On 3.11.2016 00:12, Ben Lipton wrote:
>>>>>> Hi everybody,
>>>>>>
>>>>>> Soon I'm going to have to reduce the amount of time I spend on new
>>>>>> development work for the CSR autogeneration project, and I want to
>>>>>> leave
>>>>>> the project in as organized a state as possible. So, I'm taking
>>>>>> inventory of the work I've done in order to make sure that what's
>>>>>> ready
>>>>>> for review can get reviewed and the ideas that have been discussed
>>>>>> get
>>>>>> prototyped or at least recorded so they won't be forgotten.
>>>>>
>>>>> Thanks, I have some questions and comments, see below.
>>>>>
>>>>>>
>>>>>> Code that's ready for review (I will continue to put in as much
>>>>>> time as
>>>>>> needed to help get these ready for submission):
>>>>>>
>>>>>> - Current PR: https://github.com/freeipa/freeipa/pull/10
>>>>>
>>>>> How hard would it be to update the PR to use the "new" interface from
>>>>> the design thread? By this I mean that currently there is a command
>>>>> (cert_get_requestdata), which creates a CSR from profile id +
>>>>> principal + helper, but in the design we discussed a command which
>>>>> creates a CertificationRequestInfo from profile id + principal +
>>>>> public key.
>>>>>
>>>>> Internally it could use the OpenSSL helper, no need to implement the
>>>>> full "new" design. With your build_requestinfo.c code below it looks
>>>>> like it should be pretty straightforward.
>>>>
>>>> This is probably doable with the cffi, but I'm concerned about
>>>> usability. A user can run the current command to get a (reusable)
>>>> script, and run the script to get a CSR. It works with keys in both PEM
>>>> files and NSS databases already. If we change to outputting a
>>>> CertificationRequestInfo, in order to make this usable on the command
>>>> line, we'll need:
>>>> - An additional tool to sign a CSR given a CertificationRequestInfo
>>>> (for
>>>> both types of key storage).
>>>> - A way to extract a SubjectPublicKeyInfo structure from a key within
>>>> the ipa command (like [1] but we need it for both types of key storage)
>>>> Since as far as I know there's no standard encoding for files
>>>> containing
>>>> only a CertificationRequestInfo or a SubjectPublicKeyInfo, we'll be
>>>> writing and distributing these ourselves. I think that's where most of
>>>> the extra work will come in.
>>>
>>> For PEM files, this is easily doable using python-cryptography (to
>>> extract SubjectPublicKeyInfo and sign CertificationRequestInfo) and
>>> PyASN1 (to create a CSR from the CertificationRequestInfo and the
>>> signature).
>>
>> I didn't realize that python-cryptography knew about
>> SubjectPublicKeyInfo structures, but indeed this seems to be pretty
>> straightforward:
>>
>> key = load_pem_private_key(key_bytes, None, default_backend())
>> pubkey_info = key.public_key().public_bytes(Encoding.DER,
>> PublicFormat.SubjectPublicKeyInfo)
>>
>> Thanks for letting me know this functionality already existed.
>>>
>>> For NSS databases, this will be trickier and will require calling C
>>> functions, as neither certutil nor python-nss provide a way to a)
>>> address existing keys in the database by key ID b) get
>>> SubjectPublicKeyInfo for a given key.
This can be worked around by:
1. Generating a key + temporary certificate:
n=$(head -c 40 /dev/urandom | base32)
certutil -S -n $n -s CN=$n -x -t ,,
2. Extracting the public key from the certificate:
certutil -L -n $n -a >temp.crt
(extract the public key using python-cryptography)
3. Deleting the temporary certificate:
certutil -D -n $n
4. Importing the newly issued certificate:
certutil -A -n $n -t ,, -a <new.crt
>>>
>>> As for encoding, the obvious choice is DER. It does not really matter
>>> there is no standard file format, as we won't be transferring these
>>> as files anyway.
>>
>> Agreed. I just meant there aren't tools already because this isn't a
>> type of file one often needs to process.
>>>
>>>>
>>>> Would it be ok to stick with the current design in this PR? I'd feel
>>>> much better if we could get the basic functionality into the repo and
>>>> then iterate on it rather than changing the plan at this point. I can
>>>> create a separate PR to change cert_get_requestdata to this new
>>>> interface and at the same time add the necessary adapters (bullet
>>>> points
>>>> above) to make it user-friendly.
>>>
>>> Works for me.
>>
>> Updated the PR to fix conflicts with master. Had some trouble with CI
>> but creating a new PR with the same commits fixed it
>> (https://github.com/freeipa/freeipa/pull/337). Not sure if it's fixed
>> permanently, so I guess I'll just keep the two PRs synchronized now,
>> or we could close the old one.
You can close the old one.
Just to make sure we are on the same page, you want this PR to be merged
before submitting additional PRs built on top of it?
>>>
>>>>
>>>> I would probably just implement the adapters within the
>>>> cert_build/cert_request client code unless you think having standalone
>>>> tools is valuable. I suppose certmonger is going to need these features
>>>> too, but I don't know how well sharing code between them is going to
>>>> work.
>>>
>>> cert-request is exactly the place where it should be :-) I wouldn't
>>> bother with certmonger until we have a server-side csrgen.
>>>
>>>>>
>>>>>>
>>>>>> - Allow some fields to be specified by the user at creation time:
>>>>>> https://github.com/LiptonB/freeipa/commits/local-user-data
>>>>>
>>>>> Good idea :-)
>>>>>
>>>>>>
>>>>>> - Automation for the full process from getting CSR data to requesting
>>>>>> cert: https://github.com/LiptonB/freeipa/commits/local-cert-build
>>>>>
>>>>> LGTM, although I would prefer if this was a client-side extension of
>>>>> cert-request rather than a completely new command.
>>>>
>>>> I did try that at first, but I struggled to figure out the interface
>>>> for
>>>> the modified cert-request. (Not that the current solution is so great,
>>>> what with the copying of options from cert_request and certreq.) If I
>>>> remember correctly, I was uncertain how to implement parameters that
>>>> are
>>>> required/invalid based on other parameters: the current cert-request
>>>> takes a signed CSR (required), a principal (required), and a profile
>>>> ID;
>>>> the new cert-request (what I implemented as cert-build) takes a
>>>> principal (required), a profile ID (required), and a key location
>>>> (required). I can't remember if that was the only problem, but I'll try
>>>> again to merge the commands and get back to you.
>>>
>>> To make the CSR argument optional on the client, you can do this:
>>>
>>> def get_options(self):
>>> for option in super(cert_request, self).get_options():
>>> if option.name == 'csr':
>>> option = option.clone(required=False)
>>> yield
>>>
>>> IMO profile ID should default to caIPAserviceCert on the client as well.
>>
>> I originally had it doing so, but changed it to a required option
>> based on feedback in this email:
>> https://www.redhat.com/archives/freeipa-devel/2016-August/msg00021.html:
>> "In general use I think that 'caIPAserviceCert' is unlikely to be used
>> a majory of the time, and it is a new command so there are no
>> compatibility issues; therefore why not make the profile option
>> mandatory?" I guess since we're talking about cert-request now, the
>> compatibility issues are back.
>>
>> https://github.com/LiptonB/freeipa/commits/local-cert-build has now
>> been updated to change the cert_request command rather than adding a
>> new command. It seems to work now (thanks for the advice on making the
>> argument optional), the only thing I'm having trouble with is the
>> default for the profile_id argument. Previously, the default was
>> applied by this code in cert_request.execute:
>>
>> profile_id = kw.get('profile_id', self.Backend.ra.DEFAULT_PROFILE)
>>
>> But now, in the client, I need the default to pass to
>> cert_get_requestdata if no profile is specified. I'm not sure I can
>> access backends from the client to get it the same way the server code
>> does. Should I just import ipapython/dogtag.py and use the
>> DEFAULT_PROFILE set in there? Is there a way I can give the option a
>> default that will be seen in both the server and the client?
>>>
>>>>>
>>>>>>
>>>>>> Other prototypes and design ideas that aren't ready for submission
>>>>>> yet:
>>>>>>
>>>>>> - Utility written in C to build a CertificationRequestInfo from a
>>>>>> SubjectPublicKeyInfo and an openssl-style config file. The purpose of
>>>>>> this is to take a config that my code already knows how to
>>>>>> generate, and
>>>>>> put it in a form that certmonger can use. This is nearly done and
>>>>>> available at:
>>>>>> https://github.com/LiptonB/freeipa-prototypes/blob/master/build_requestinfo.c
>>>>>>
>>>>>>
>>>>>
>>>>> Nice! As I said above, this could really make implementing the "new"
>>>>> csrgen interface simple.
>>>>>
>>>>>>
>>>>>>
>>>>>> - Ideally it should be possible to use this tool to reimplement
>>>>>> the full
>>>>>> cert-request automation (local-cert-build branch) without a
>>>>>> dependency
>>>>>> on the certutil/openssl tools. However, I don't think any of the
>>>>>> python
>>>>>> crypto libraries have bindings for the functions that deal with
>>>>>> CertificationRequestInfo objects, so I don't think I can do this
>>>>>> in the
>>>>>> short term.
>>>>>
>>>>> You can use python-cffi to write your own minimal bindings. It's
>>>>> fairly straightforward, take a look at FreeIPA commit 500ee7e2 for an
>>>>> example of how to port C code to Python with python-cffi.
>>>>
>>>> Thank you for the example. I will take a look.
>>>>>
>>>>>>
>>>>>> - Certmonger "helper" program that takes in the
>>>>>> CertificationRequestInfo
>>>>>> that certmonger generates, calls out to IPA for profile-specific
>>>>>> data,
>>>>>> and returns an updated CertificationRequestInfo built from the data.
>>>>>> Certmonger doesn't currently support this type of helper, but (if I
>>>>>> understood correctly) this is the architecture Nalin believed
>>>>>> would be
>>>>>> simplest to fit in. This is not done yet, but I intend to complete it
>>>>>> soon - it shouldn't require much code beyond what's in
>>>>>> build_requestinfo.c.
>>>>>
>>>>> To me this sounds like it should be a new operation of the current
>>>>> helper rather than a completely new helper.
>>>>
>>>> Maybe so. I certainly wouldn't call this a finished design, I just
>>>> wanted to have some kind of proof of concept for how the certmonger
>>>> integration could work. For what it's worth, that prototype is now
>>>> available at [2].
>>>
>>> OK.
>>>
>>>>>
>>>>> Anyway, the ultimate goal is to move the csrgen code to the server,
>>>>> which means everything the helper will have to do is call a command
>>>>> over RPC.
>>>>>
>>>>>>
>>>>>> - Tool to convert an XER-encoded cert extension to DER, given the
>>>>>> ASN.1
>>>>>> description of the extension. This would unblock Jan Cholasta's
>>>>>> idea of
>>>>>> using XSLT for templates rather than text-based formatting. I
>>>>>> should be
>>>>>> able to implement the conversion tool, but it may be a while before I
>>>>>> have time to demo the full XSLT idea.
>>>>>
>>>>> Was there any progress on this?
>>>>
>>>> I have started working on implementing it with asn1c, and I'm already
>>>> seeing some of the inconvenience (security issues aside) of building on
>>>> the server. Libtasn1 seems like a much better model, but doesn't
>>>> seem to
>>>> have XER support. Anyway, don't quite have results here yet but I think
>>>> I should have the XER->DER demo with asn1c ready in a week or two.
>>>
>>> Implementing XER codec on top of libtasn1 shouldn't be too hard; I
>>> have a WIP which I will post soon.
>
> It took me some experimentation to get this to work, but the solution
> with asn1c is actually quite simple because the tool automatically
> provides a sample C file that converts between different formats. So,
> this very basic shell script is able to do the conversion:
> https://github.com/LiptonB/freeipa-prototypes/blob/master/xer2der.sh
>
> $ cat ExtKeyUsage.xer
> <ExtKeyUsageSyntax>
> <KeyPurposeId>1.3.6.1.5.5.7.3.2</KeyPurposeId>
> <KeyPurposeId>1.3.6.1.5.5.7.3.4</KeyPurposeId>
> </ExtKeyUsageSyntax>
>
> $ cat KeyUsage.asn1
> KUModule DEFINITIONS ::=
> BEGIN
>
> KeyUsage ::= BIT STRING {
> digitalSignature (0),
> nonRepudiation (1), -- recent editions of X.509 have
> -- renamed this bit to contentCommitment
> keyEncipherment (2),
> dataEncipherment (3),
> keyAgreement (4),
> keyCertSign (5),
> cRLSign (6),
> encipherOnly (7),
> decipherOnly (8) }
>
> ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId
>
> KeyPurposeId ::= OBJECT IDENTIFIER
>
> END
>
> $ ./xer2der.sh KeyUsage.asn1 ExtKeyUsageSyntax ExtKeyUsage.xer
> 2>/dev/null | xxd
> 00000000: 3014 0608 2b06 0105 0507 0302 0608 2b06 0...+.........+.
> 00000010: 0105 0507 0304 ......
So far I don't have a working example using libtasn1. I have something
close to it, but it's hacky, as the libtasn1 API is pretty limited, and
I didn't have time to work on it in the last few weeks.
>
>>>
>>>>>
>>>>>>
>>>>>> So: currently on my to do list are the certmonger helper and the
>>>>>> XER->DER conversion tool. Do you have any comments about these plans,
>>>>>> and is there anything else I can do to wrap up the project neatly?
>>>>>>
>>>>>> Thanks,
>>>>>> Ben
>>>>>>
>>>>>
>>>>> Honza
>>>>>
>>>> [1]
>>>> https://github.com/LiptonB/freeipa-prototypes/blob/master/key2spki.c
>>>> [2]
>>>> https://github.com/LiptonB/freeipa-prototypes/blob/master/cm_ipa_csrgen.c
>>>>
>>>
>>
>
--
Jan Cholasta
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