JEP-0165: Prevention of JID Spoofing

Peter Saint-Andre

Email: stpeter@jabber.org
JID: stpeter@jabber.org

1. Introduction

2. Recommendations

2.1. Presentation of JIDs

2.2. The Jabber Roster as a Petname System

2.3. Further Securing the Petname System

2.4. Subscription Requests

2.5. Referrals

3. Security Considerations

4. IANA Considerations

5. Jabber Registrar Considerations

Notes

Revision History

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2.1 Presentation of JIDs

Every human user of Jabber/XMPP technologies presumably has a preferred language (or, in some cases, a small set of preferred languages), which an XMPP application SHOULD gather either explicitly from the user or implicitly via the user's operating system. Furthermore, every language has a range of characters normally used to represent that language in textual form. Therefore, an XMPP application SHOULD warn the user when presenting a JID that uses characters outside the normal range of the user's preferred language(s). [5]

2.2 The Jabber Roster as a Petname System

As explained in Introduction to Petname Systems [6], no one naming or address scheme can provide names that are simultaneously global, memorable, and securely unique. However, certain combinations of names and addresses can provide all three properties, and such combinations are commonly called "petname systems". Consider the following combination of names:

1. The JID "stpeter@jabber.org" is globally unique on the Jabber network, but it is not necessarily memorable.
2. The nickname "psa" (asserted by the user associated with the address "stpeter@jabber.org") is memorable but it is neither unique nor global.
3. The alias or petname "that JSF dude" (assigned by a contact who adds "stpeter@jabber.org" to her contact list) is memorable and securely unique but by no means global since it has meaning only to the person who assigns it.

A client SHOULD require an end user to assign a petname for every contact added to the person's roster, which SHOULD be stored as the value of the <item/> element's 'name' attribute qualified by the 'jabber:iq:roster' namespace. A client SHOULD then present that petname instead of or in addition to the contact's JID or nickname (e.g., in the user's roster and in chat interfaces). This will help to prevent mimicked addresses from being presented as equivalent to the address that is being mimicked.

2.3 Further Securing the Petname System

Although a Jabber ID can be considered globally unique, the petname system in which it is embedded can be strengthened by associating that JID with a key or certificate that can be used for signing and encryption (such as a PGP key or X.509 certificate), preferably a key or certificate that encapsulates the associated XMPP address (e.g., as described in Section 5.1.1 of RFC 3920). A client SHOULD associate a key or certificate with the user of that client, and SHOULD generate such a key or certificate if the user does not have one.

Unfortunately, keys, certificates, and fingerprints are even less memorable than JIDs, which makes the specification of a petname or alias even more important. Therefore, a client SHOULD keep track of the keys or certificates associated with the contacts in a user's roster in order to further strengthen the petname system.

2.4 Subscription Requests

We have seen that, at a minimum, three name or address types are needed to provide a petname system: a JID, a nickname, and an alias (preferably strengthened by inclusion of a key or certificate). However, at present a subscription request contains only the JID of the sender:

Example 1. A Basic Subscription Request

<presence from='stpeter@jabber.org to='MaineBoy@jabber.org' type='subscribe'/>
    

Naturally, based on the JID, it is possible to pull information about the sender from a persistent data store such as an LDAP database, vcard-temp [7] node, or future profile system. However, to speed interactions, this document recommends that when a client sends a subscription request, it SHOULD include the preferred nickname of the sender, encapsulated via the Profile Data Representation [8] format: [9]

Example 2. Subscription Request With Nickname

<presence from='stpeter@jabber.org to='MaineBoy@jabber.org' type='subscribe'>
  <x xmlns='jabber:x:data' type='submit'>
    <field var='FORM_TYPE' type='hidden'><value>http://jabber.org/protocol/profiledata</value></field>
    <field var='nickname'><value>psa</value></field>
  </x>
</presence>
    

In addition, the subscription request SHOULD also include the fingerprint of a key or certificate associated with the sender (encapsulated via the fingerprint protocol described below):

Example 3. Subscription Request With Nickname and Fingerprint

<presence from='stpeter@jabber.org to='MaineBoy@jabber.org' type='subscribe'>
  <x xmlns='jabber:x:data' type='submit'>
    <field var='FORM_TYPE' type='hidden'><value>http://jabber.org/protocol/profiledata</value></field>
    <field var='nickname'><value>psa</value></field>
    <field var='x509_fingerprint_sha1'>
      <value>C3 88 33 27 F3 47 3B 8B 07 71 3E 96 44 A7 EE E2 E0 50 4A 5B</value>
    </field>
  </x>
</presence>
    

The key or certificate SHOULD include the user's XMPP address, e.g. as described in Section 5.1.1 of RFC 3920.

2.5 Referrals

In order to strengthen the web of interaction and trust between Jabber/XMPP users, it is helpful for them to share roster items. In particular, when a user wants to subscribe to the presence of a potential contact, the user SHOULD seek a referral from a third person who knows both the user and the contact. Such a referral consists of a roster item sent from the third person to the potential contact, encapsulated using the Roster Item Exchange [10] protocol:

Example 4. A Basic Referral

<message from='peter@saint-andre.com' to='MaineBoy@jabber.org'>
  <x xmlns='http://jabber.org/protocol/rosterx'>
    <item jid='stpeter@jabber.org' name='Peter Saint-Andre'/>
  </x>
</message>
    

Here, the 'name' attribute encapsulates what in petname systems is known as an "alleged name", that is, the name for an entity proposed by a third party.

Such a referral SHOULD also include the nick and fingerprint of the user as understood by the third person:

Example 5. Referral With Nickname and Fingerprint

<message from='peter@saint-andre.com' to='MaineBoy@jabber.org'>
  <x xmlns='http://jabber.org/protocol/rosterx'>
    <item jid='stpeter@jabber.org' name='Peter Saint-Andre'/>
  </x>
  <x xmlns='jabber:x:data' type='submit'>
    <field var='FORM_TYPE' type='hidden'><value>http://jabber.org/protocol/profiledata</value></field>
    <field var='nickname'><value>psa</value></field>
    <field var='x509_fingerprint_sha1'>
      <value>C3 88 33 27 F3 47 3B 8B 07 71 3E 96 44 A7 EE E2 E0 50 4A 5B</value>
    </field>
  </x>
</message>
    

Here again, when a Jabber/XMPP client receives a referral, it SHOULD warn the contact if the JID uses characters outside the normal range of the contact's preferred language(s).

1. Naturally, there is no way to distinguish with full certainty which is the fake JID and which is the real JID. For example, in some communication contexts, the Cherokee JID may be the real JID and the US-ASCII JID may thus appear to be the fake JID.

2. RFC 3920: Extensible Messaging and Presence Protocol (XMPP): Core <http://www.ietf.org/rfc/rfc3920.txt>.

3. Phishing has been defined as "a broadly launched social engineering attack in which an electronic identity is misrepresented in an attempt to trick individuals into revealing personal credentials that can be used fraudulently against them" (see Financial Services Technology Consortium Counter-Phishing Initiative: Phase I). To be precise, the current document (1) does not assume that such attacks will be broadly launched and (2) focuses on the misrepresentation only of Jabber IDs within the context of Jabber/XMPP systems.

4. This document does not cover handling of non-XMPP addresses, for example HTTP URLs. Jabber/XMPP clients SHOULD handle such addresses in accordance with best practices for the relevant non-XMPP technology.

5. This recommendation is not intended to discourage communication across language communities; instead, it simply recognizes the existence of such language communities and encourages due caution when presenting unfamiliar character sets to human users.

6. Introduction to Petname Systems <http://www.skyhunter.com/marcs/petnames/IntroPetNames.html>.

7. JEP-0054: vcard-temp <http://www.jabber.org/jeps/jep-0054.html>.

8. JEP-0154: Profile Data Representation <http://www.jabber.org/jeps/jep-0154.html>.

9. While it could be argued that a less verbose format would be preferable (e.g., a specialized XML format), presence subscription requests are infrequent enough that the slightly more verbose format of Profile Data Representation is acceptable in this context.

10. JEP-0144: Roster Item Exchange <http://www.jabber.org/jeps/jep-0144.html>.

11. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

12. The Jabber Registrar maintains a list of reserved Jabber protocol namespaces as well as registries of parameters used in the context of protocols approved by the Jabber Software Foundation. For further information, see <http://www.jabber.org/registrar/>.

Version 0.1 (2005-11-16)

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Version 0.0.1 (2005-09-28)