[19674] in Kerberos_V5_Development
Re: Incompatibility between krb's AES256-CTS-HMAC-SHA1-96 and
daemon@ATHENA.MIT.EDU (Andreas Schneider)
Thu Nov 9 09:54:58 2017
From: Andreas Schneider <asn@samba.org>
To: krbdev@mit.edu
Date: Thu, 09 Nov 2017 15:47:06 +0100
Message-ID: <1510264356.bVFtXIL4PB@krikkit.cryptomilk.site>
In-Reply-To: <1509459618.7682.126.camel@redhat.com>
MIME-Version: 1.0
Cc: Simo Sorce <simo@redhat.com>
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Errors-To: krbdev-bounces@mit.edu
On Tuesday, 31 October 2017 15:20:18 CET Simo Sorce wrote:
> On Tue, 2017-10-31 at 10:55 +0300, Ido Shlomo wrote:
> > I am trying to upgrade our system's kerberos encryption from RC4 to
> > AES256.
> > I've set up a Microsoft Windows Domain user with AES256 encryption
> > support.
> > I'm creating a keytab for kinit using ktutil on Linux:
> >
> > ADD_ENTRY="addent -password -p $DOMAIN_LOCAL_USER@$DOMAIN_UPCASE -k 2
> > -e AES256-CTS-HMAC-SHA1-96\n$DOMAIN_LOCAL_PASS\n"
> > echo -e "$ADD_BASE_ENTRY\n$ADD_ENTRY\nwkt user.keytab\nquit\n" | ktutil
> >
> > kinit works well with that keytab.
> >
> > However, when I'm creating an SPN for this user using ktutil on Linux
> >
> > ADD_BASE_ENTRY="addent -password -p
> > MSSQLSvc/$SHORT_HOSTNAME.$DOMAIN_LOWCASE@$DOMAIN_UPCASE -k 2 -e
> > RC4-HMAC\n$DOMAIN_PASSWORD\n"
> > echo -e "rkt spns.keytab\n$ADD_BASE_ENTRY\n$ADD_ENTRY\nwkt
> > spns.keytab\nquit\n" | ktutil > /dev/null 2>&1
> >
> > then I'm unable to accept incoming connections using krb 1.15.2:
> >
> > GSS-API major_status:000d0000, minor_status:000186a6
> > GetGSSError(): GSS Error ERR_MAX: Unspecified GSS failure. Minor code
> > may provide more information
> > GetGSSError(): GSS Error ERR_MIN: Request ticket server
> >
> > > MSSQLSvc/greensqlcent21.kerberosdc.msft:1434@KERBEROSDC.MSFT kvno 2
> >
> > enctype aes256-cts found in keytab but cannot decrypt ticket
> >
> > This has worked well when I was using RC4_HMAC for everything.
> >
> > *Some background:*
> >
> > My application mimics an MSSQL server. I'm running as a User (not as the
> > computer) and I have set this user to login with AES256. Initially, I have
> > kept the SPNs in the incoming keytab file with RC4_HMAC (this used to work
> > when the domain user was also authenticating using RC4_HMAC), but I got an
> > error that the gssapi accept function is looking for an AES256 entry in
> > the
> > SPN keytab file. So I changed the SPN keytab file to also use AES256 and
> > got the above error.
> >
> > Tested with both Windows 2k8 and 2k12 as Domain Controllers. Both fail.
>
> One of the differences with AES is that those keys are generated using
> a SALT, unlike RC4_HMAC. So if the salt is not properly computed your
> key will not match.
> IIRC for SPNs in AD the Salt is always the computer name (as stored in
> the SamAccountName attribute), while in most krb implementation the
> SALT is the principal name, this may be why your key generation doesn't
> work.
There are different salt principals depending on the type, the most commond
are:
host/somehost.example.com@EXAMPLE.COM
SomeAccount@EXAMPLE.COM
SomePrincipal@EXAMPLE.COM
However you need to convert the salt principal to a salt data blob which is
passed to krb5_c_string_to_key(). Those need to be in the following form:
EXAMPLE.COMhost/somehost.example.com
EXAMPLE.COMSomeAccount
EXAMPLE.COMSomePrincipal
Andreas
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