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Message-ID: <478C0E0D.3000406@secure-endpoints.com> Date: Mon, 14 Jan 2008 20:36:13 -0500 From: Jeffrey Altman <jaltman@secure-endpoints.com> MIME-Version: 1.0 To: srinivas.kakde@yahoo.com In-Reply-To: <673189.72562.qm@web46016.mail.sp1.yahoo.com> X-Envelope-From: jaltman@secure-endpoints.com X-MDaemon-Deliver-To: kerberos@mit.edu Cc: kerberos@mit.edu Reply-To: jaltman@secure-endpoints.com Content-Type: multipart/mixed; boundary="===============1480089261==" Errors-To: kerberos-bounces@mit.edu This is a cryptographically signed message in MIME format. --===============1480089261== Content-Type: multipart/signed; protocol="application/x-pkcs7-signature"; micalg=sha1; boundary="------------ms080708010603050300090606" This is a cryptographically signed message in MIME format. --------------ms080708010603050300090606 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Srinivas Kakde wrote: > > Jeffrey Altman wrote: >> The security of the authentication is based upon the name. By asking >> you to authenticate to a name selected by the attacker, you can be >> tricked into using a KDC that is in fact under the control of the >> attacker. > > > Are you sure this is right? I think in Kerberos, knowledge of a > shared secret (not knowledge of the principal name) is the foundation > for trust? In the case of a AS-REQ/AS-REP exchange, what would the malicious KDC > use to encrypt the EncKDCRepPart of the KDC-REP such that the decrypted > nonce would match what the client supplied in the KDC-REQ? Knowledge of a shared secret is how you prove the identity but the shared secret comes from a third party and which secret the third party is going to give you depends upon the name that you request. For example, if you are trying to authenticate to the ftp server at ftp.secure-endpoints.com you should be asking for the shared secret for host/ftp.secure-endpoints.com@SECURE-ENDPOINTS.COM. But what if you didn't ask for that but instead waited for the server to give you a name. Let's say that there is a user "john" who has a personal machine keyed by the SECURE-ENDPOINTS.COM realm and he is able to get you to connect to his machine by spoofing DNS or some other means. You have now connected to johns-machine.secure-endpoints.com but think you are connected to ftp.secure-endpoints.com and john tells you to authenticate to "host/johns-machine.secure-endpoints.com@SECURE-ENDPOINTS.COM". This authentication is going to succeed but you are not connected to the host you wanted to connect to. There are other scenarios as well. Since the realm you contact is determined by the domain name of the host, if the server tells you to authenticate to ftp.compromised.com, the attacker can convince you to authenticate using a compromised KDC that might be accessible via a cross-realm relationship. 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charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline ________________________________________________ Kerberos mailing list Kerberos@mit.edu https://mailman.mit.edu/mailman/listinfo/kerberos --===============1480089261==--
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