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Date: Wed, 1 Oct 2014 21:46:30 -0700
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Subject: Re: Two open issues on Kafka security
From: Jay Kreps <jay.kreps@gmail.com>
To: "dev@kafka.apache.org" <dev@kafka.apache.org>
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Hey Michael,

WRT question 2, I think for SASL you do need the mechanism information
but what I was talking about was the challenge/response byte[] that is
sent back and forth from the client to the server. My understanding is
that SASL gives you an api for the client and server to use to produce
these byte[]'s but doesn't actually specify any way of exchanging them
(that is protocol specific). I could be wrong here since my knowledge
of this stuff is pretty weak. But according to my understanding you
must be imagining some protocol for exchanging challenge/response
information. This protocol would have to be clearly documented for
client implementors. What is that protocol?

-Jay

On Wed, Oct 1, 2014 at 2:36 PM, Michael Herstine
<mherstine@linkedin.com.invalid> wrote:
> Regarding question #1, I=E2=80=99m not sure I follow you, Joe: you=E2=80=
=99re proposing (I
> think) that the API take a byte[], but what will be in that array? A
> serialized certificate if the client authenticated via SSL and the
> principal name (perhaps normalized) if the client authenticated via
> Kerberos?
>
> Regarding question #2, I think I was unclear in the meeting yesterday: I
> was proposing a separate port for each authentication method (including
> none). That is, if a client wants no authentication, then they would
> connect to port N on the broker. If they wanted to talk over SSL, then
> they connect to port N+1 (say). Kerberos: N+2. This would remove the need
> for a new request, since the authentication type would be implicit in the
> port on which the client connected (and it was my understanding that it
> was desirable to not introduce any new messages).
>
> Perhaps the confusion comes from the fact, correctly pointed out by Jay,
> that when you want to use SASL on a single port, there does of course nee=
d
> to be a way for the incoming client to signal which mechanism it wants to
> use, and that=E2=80=99s out of scope of the SASL spec. I didn=E2=80=99t s=
ee there being a
> desire to add new SASL mechanisms going forward, but perhaps I was
> incorrect?
>
> In any event, I=E2=80=99d like to suggest we keep the =E2=80=9Copen=E2=80=
=9D or =E2=80=9Cno auth=E2=80=9D port
> separate, both to make it easy for admins to force the use of security (b=
y
> shutting down that port) and to avoid downgrade attacks (where an attacke=
r
> intercepts the opening packet from a client requesting security & alters
> it to request none).
>
> I=E2=80=99ll update the Wiki with my notes from yesterday=E2=80=99s meeti=
ng this afternoon.
>
> Thanks,
>
> On 10/1/14, 9:35 AM, "Jonathan Creasy" <Jonathan.Creasy@turn.com> wrote:
>
>>This is not nearly as deep as the discussion so far, but I did want to
>>throw this idea out there to make sure we=C2=B9ve thought about it.
>>
>>The Kafka project should make sure that when deployed alongside a Hadoop
>>cluster from any major distributions that it can tie seamlessly into the
>>authentication and authorization used within that cluster. For example,
>>Apache Sentry.
>>
>>This may present additional difficulties that means a decision is made to
>>not do that or alternatively the Kerberos authentication and the
>>authorization schemes we are already working on may be sufficient.
>>
>>I=C2=B9m not sure that anything I=C2=B9ve read so far in this discussion =
actually
>>poses a problem, but I=C2=B9m an Ops guy and being able to more easily
>>integrate more things, makes my life better. :)
>>
>>-Jonathan
>>
>>On 9/30/14, 11:26 PM, "Joe Stein" <joe.stein@stealth.ly> wrote:
>>
>>>inline
>>>
>>>On Tue, Sep 30, 2014 at 11:58 PM, Jay Kreps <jay.kreps@gmail.com> wrote:
>>>
>>>> Hey Joe,
>>>>
>>>> For (1) what are you thinking for the PermissionManager api?
>>>>
>>>> The way I see it, the first question we have to answer is whether it
>>>> is possible to make authentication and authorization independent. What
>>>> I mean by that is whether I can write an authorization library that
>>>> will work the same whether you authenticate with ssl or kerberos.
>>>
>>>
>>>To me that is a requirement. We can't tie them together.  We have to
>>>provide the ability for authorization to work regardless of the
>>>authentication.  One *VERY* important use case is level of trust in
>>>authentication from the authorization perpsective.  e.g. I authorize
>>>"identity" based on the how you authenticated.... Alice is able to view
>>>topic X if Alice authenticated over kerberos.  Bob isn't allowed to view
>>>topic X no matter what. Alice can authenticate over not kerberos (uses
>>>cases for that) and in that case Alice wouldn't see topic X.  A concrete
>>>use case for this with Kafka would be a third party bank consuming data
>>>to
>>>a broker.  The service provider would have some kerberos local auth for
>>>that bank to-do back up that would also have access to other topics
>>>related
>>>to that banks data.... the bank itself over SSL wants a stream of events
>>>(some specific topic) and that banks identity only sees that topic.  It
>>>is
>>>important to not confuse identity, authentication and authorization.
>>>
>>>
>>>> If
>>>> so then we need to pick some subset of identity information that we
>>>> can extract from both and have this constitute the identity we pass
>>>> into the authorization interface. The original proposal had just the
>>>> username/subject. But maybe we should add the ip address as well as
>>>> that is useful. What I would prefer not to do is add everything in the
>>>> certificate. I think the assumption is that you are generating these
>>>> certificates for Kafka so you can put whatever identity info you want
>>>> in the Subject Alternative Name. If that is true then just using that
>>>> should be okay, right?
>>>>
>>>
>>>I think we should just push the byte[] and let the plugin deal with it.
>>>So, if we have a certificate object then pass that along with whatever
>>>other meta data (e.g. IP address of client) we can.  I don't think we
>>>should do any parsing whatsover and let the plugin deal with that.  Any
>>>parsing we do on the identity information for the "security object"
>>>forces
>>>us into specific implementations and I don't see any reason to-do that..=
.
>>>If plug-ins want an "easier" time to deal with certs and parsing and bla=
h
>>>blah blah then we can implement some way they can do this without much
>>>fuss.... we also need to make sure that crypto library is plugable too
>>>(so
>>>we can expose an API for them to call) so that HSM can be easily dropped
>>>in
>>>without Kafka caring... so in the plugin we could provide a
>>>indentity.getAlternativeAttribute() and then that use case is solved (an=
d
>>>we can use bouncy castle or whatever to parse it for them to make it
>>>easier).... and always give them raw bytes so they could do it
>>>themselves.
>>>
>>>
>>>>
>>>> -Jay
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On Tue, Sep 30, 2014 at 4:09 PM, Joe Stein <joe.stein@stealth.ly>
>>>>wrote:
>>>> > 1) We need to support the most flexibility we can and make this
>>>> transparent
>>>> > to kafka (to use Gwen's term).  Any specific implementation is going
>>>>to
>>>> > make it not work with some solution stopping people from using Kafka=
.
>>>> That
>>>> > is a reality because everyone just does it slightly differently
>>>>enough.
>>>> If
>>>> > we have an "identity" byte structure (lets not use string because
>>>>some
>>>> > security objects are bytes) this should just fall through to the
>>>> > implementor.  For certs this is the entire x509 object (not just the
>>>> > certificate part as it could contain an ASN.1 timestamp) and inside
>>>>you
>>>> > parse and do what you want with it.
>>>> >
>>>> > 2) While I think there are many benefits to just the handshake
>>>>approach I
>>>> > don't think it outweighs the cons Jay expressed. a) We can't lead th=
e
>>>> > client libraries down a new path of interacting with Kafka.  By
>>>> > incrementally adding to the wire protocol we are directing a very
>>>>clear
>>>> and
>>>> > expect ted approach.  We already have issues with implementation eve=
n
>>>> with
>>>> > the wire protocol in place and are trying to improve that aspect of
>>>>the
>>>> > community as a whole.  Lets not take a step backwards with this
>>>>there...
>>>> > also we need to not add more/different hoops to
>>>> > debugging/administering/monitoring kafka so taking advantage (as Jay
>>>> says)
>>>> > of built in logging (etc) is important... also for the client
>>>>librariy
>>>> > developers too :)
>>>> >
>>>> > On Tue, Sep 30, 2014 at 6:44 PM, Gwen Shapira <gshapira@cloudera.com=
>
>>>> wrote:
>>>> >
>>>> >> Re #1:
>>>> >>
>>>> >> Since the auth_to_local is a kerberos config, its up to the admin t=
o
>>>> >> decide how he likes the user names and set it up properly (or leave
>>>> >> empty) and make sure the ACLs match. Simplified names may be needed
>>>>if
>>>> >> the authorization system integrates with LDAP to get groups or
>>>> >> something fancy like that.
>>>> >>
>>>> >> Note that its completely transparent to Kafka - if the admin sets u=
p
>>>> >> auth_to_local rules, we simply see a different principal name. No
>>>>need
>>>> >> to do anything different.
>>>> >>
>>>> >> Gwen
>>>> >>
>>>> >> On Tue, Sep 30, 2014 at 3:31 PM, Jay Kreps <jay.kreps@gmail.com>
>>>>wrote:
>>>> >> > Current proposal is here:
>>>> >> >
>>>> >> > https://cwiki.apache.org/confluence/display/KAFKA/Security
>>>> >> >
>>>> >> > Here are the two open questions I am aware of:
>>>> >> >
>>>> >> > 1. We want to separate authentication and authorization. This
>>>>means
>>>> >> > permissions will be assigned to some user-like
>>>>subject/entity/person
>>>> >> > string that is independent of the authorization mechanism. It
>>>>sounds
>>>> >> > like we agreed this could be done and we had in mind some
>>>>krb-specific
>>>> >> > mangling that Gwen knew about and I think the plan was to use
>>>>whatever
>>>> >> > the user chose to put in the Subject Alternative Name of the cert
>>>>for
>>>> >> > ssl. So in both cases these would translate to a string denoting
>>>>the
>>>> >> > entity whom we are granting permissions to in the authorization
>>>>layer.
>>>> >> > We should document these in the wiki to get feedback on them.
>>>> >> >
>>>> >> > The Hadoop approach to extraction was something like this:
>>>> >> >
>>>> >>
>>>>
>>>>http://docs.hortonworks.com/HDPDocuments/HDP1/HDP-1.3.1/bk_installing_m=
a
>>>>n
>>>>ually_book/content/rpm-chap14-2-3-1.html
>>>> >> >
>>>> >> > But actually I'm not sure if just using the full kerberos
>>>>principal is
>>>> >> > so bad? I.e. having the user be jennifer@athena.mit.edu versus
>>>>just
>>>> >> > jennifer. Where this would make a difference would be in a case
>>>>where
>>>> >> > you wanted the same user/entity to be able to authenticate via
>>>> >> > different mechanisms (Hadoop auth, kerberos, ssl) and have a
>>>>single
>>>> >> > set of permissions.
>>>> >> >
>>>> >> > 2. For SASL/Kerberos we need to figure out how the communication
>>>> >> > between client and server will be handled to pass the
>>>> >> > challenge/response byte[]. I.e.
>>>> >> >
>>>> >> >
>>>> >>
>>>>
>>>>http://docs.oracle.com/javase/7/docs/api/javax/security/sasl/SaslClient=
.
>>>>h
>>>>tml#evaluateChallenge(byte[])
>>>> >> >
>>>> >>
>>>>
>>>>http://docs.oracle.com/javase/7/docs/api/javax/security/sasl/SaslServer=
.
>>>>h
>>>>tml#evaluateResponse(byte[])
>>>> >> >
>>>> >> > I am not super expert in this area but I will try to give my
>>>> >> > understanding and I'm sure someone can correct me if I am
>>>>confused.
>>>> >> >
>>>> >> > Unlike SSL the transmission of this is actually outside the scope
>>>>of
>>>> >> > SASL so we have to specify this. Two proposals
>>>> >> >
>>>> >> > Original Proposal: Add a new "authenticate" request/response
>>>> >> >
>>>> >> > The proposal in the original wiki was to add a new "authenticate"
>>>> >> > request/response to pass this information. This matches what was
>>>>done
>>>> >> > in the kerberos implementation for zookeeper. The intention is
>>>>that
>>>> >> > the client would send this request immediately after establishing
>>>>a
>>>> >> > connection, in which case it acts much like a "handshake", howeve=
r
>>>> >> > there is no requirement that they do so.
>>>> >> >
>>>> >> > Whether the authentication happens via SSL or via Kerberos, the
>>>>effect
>>>> >> > will just be to set the username in their session. This will
>>>>default
>>>> >> > to the "anybody" user. So in the default non-secure case we will
>>>>just
>>>> >> > be defaulting "anybody" to have full permission. So to answer the
>>>> >> > question about whether changing user is required or not, I don't
>>>>think
>>>> >> > it is but I think we kind of get it for free in this approach.
>>>> >> >
>>>> >> > In this approach there is no particular need or advantage to
>>>>having a
>>>> >> > separate port for kerberos I don't think.
>>>> >> >
>>>> >> > Alternate Proposal: Create a Handshake
>>>> >> >
>>>> >> > The alternative I think Michael was proposing was to create a
>>>> >> > handshake that would happen at connection time on connections
>>>>coming
>>>> >> > in on the SASL port. This would require a separate port for SASL
>>>>since
>>>> >> > otherwise you wouldn't be able to tell if the bytes you were
>>>>getting
>>>> >> > were for SASL or were the first request of an unauthenticated
>>>> >> > connection.
>>>> >> >
>>>> >> > Michael it would be good to work out the details of how this
>>>>works.
>>>> >> > Are we just sending size-delimited byte arrays back and forth
>>>>until
>>>> >> > the challenge response terminates?
>>>> >> >
>>>> >> > My Take
>>>> >> >
>>>> >> > The pro I see for Michael's proposal is that it keeps the
>>>> >> > authentication logic more localized in the socket server.
>>>> >> >
>>>> >> > I see two cons:
>>>> >> > 1. Since the handshake won't go through the normal api layer it
>>>>won't
>>>> >> > go through the normal logging (e.g. request log), jmx monitoring,
>>>> >> > client trace token, correlation id, etc that we get for other
>>>> >> > requests. This could make operations a little confusing and make
>>>> >> > debugging a little harder since the client will be blocking on
>>>>network
>>>> >> > requests without the normal logging.
>>>> >> > 2. This part of the protocol will be inconsistent with the rest o=
f
>>>>the
>>>> >> > Kafka protocol so it will be a little odd for client implementors
>>>>as
>>>> >> > this will effectively be a request/response that they will have t=
o
>>>> >> > implement that will be different from all the other
>>>>request/responses
>>>> >> > they implement.
>>>> >> >
>>>> >> > In practice these two alternatives are not very different except
>>>>that
>>>> >> > in the original proposal the bytes you send are prefixed by the
>>>>normal
>>>> >> > request header fields such as the client id, correlation id, etc.
>>>> >> > Overall I would prefer this as I think it is a bit more consisten=
t
>>>> >> > from the client's point of view.
>>>> >> >
>>>> >> > Cheers,
>>>> >> >
>>>> >> > -Jay
>>>> >>
>>>>
>>
>