End-to-End Object Encryption for the Extensible Messaging and Presence Protocol (XMPP)
draft-miller-xmpp-e2e-00
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| Author | Matthew A. Miller | ||
| Last updated | 2012-02-29 | ||
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draft-miller-xmpp-e2e-00
Network Working Group M. Miller
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track February 29, 2012
Expires: August 14, 2012
End-to-End Object Encryption for the Extensible Messaging and Presence
Protocol (XMPP)
draft-miller-xmpp-e2e-00
Abstract
This document defines a method of end-to-end object encryption for
the Extensible Messaging and Presence Protocol (XMPP).
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 14, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (http://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Encrypting XMPP Stanzas . . . . . . . . . . . . . . . . . . . 2
3.1. Prerequisites . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Process . . . . . . . . . . . . . . . . . . . . . . . . . 3
Miller std [Page 1]
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3.3. Example Securing a Message . . . . . . . . . . . . . . . . 4
4. Requesting Content Keys . . . . . . . . . . . . . . . . . . . 6
4.1. Request Process . . . . . . . . . . . . . . . . . . . . . 6
4.2. Accept Process . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Error Conditions . . . . . . . . . . . . . . . . . . . . . 8
4.4. Example of Successful Key Request . . . . . . . . . . . . 8
5. Handling of Inbound Encrypted Stanzas . . . . . . . . . . . . 10
5.1. Protocol Not Understood . . . . . . . . . . . . . . . . . 11
5.2. Insufficient Information . . . . . . . . . . . . . . . . . 11
5.3. Failed Decryption . . . . . . . . . . . . . . . . . . . . 12
5.4. Timestamp Not Acceptable . . . . . . . . . . . . . . . . . 12
5.5. Successful Decryption . . . . . . . . . . . . . . . . . . 13
6. Inclusion and Checking of Timestamps . . . . . . . . . . . . . 13
7. Interaction with Stanza Semantics . . . . . . . . . . . . . . 14
8. Mandatory-to-Implement Cryptographic Algorithms . . . . . . . 14
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9.1. Storage of Encrypted Stanzas . . . . . . . . . . . . . . . 14
9.2. Re-use of Content Encryption Keys . . . . . . . . . . . . 14
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
10.1. XML Namespace Name for e2e Data in XMPP . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
11.1. Normative References . . . . . . . . . . . . . . . . . . 15
11.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Schema for urn:ietf:params:xml:ns:xmpp-e2e:1 . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
End-to-end encryption of traffic sent over the Extensible Messaging
and Presence Protocol [RFC6120] is a desirable goal. Requirements
and a threat analysis for XMPP encryption are provided in [E2E-REQ].
Many possible approaches to meet those (or similar) requirements have
been proposed over the years, including methods based on PGP, S/MIME,
SIGMA, and TLS.
Most proposals have not been able to support multiple end-points for
a given recipient. As more devices support XMPP, it becomes more
desirable to allow an entity to communicate with another in a more
secure manner, regardless of the number of agents th entity is
employing. This document specifies an approach for encrypting
communications between two entities which each might have multiple
end-points.
2. Terminology
This document inherits terminology defined in [RFC6120].
Security-related terms are to be understood in the sense defined in
[SECTERMS].
The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[KEYWORDS].
3. Encrypting XMPP Stanzas
Miller std [Page 2]
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The process that a sending agent follows for securing stanzas is the
same regardless of the form of stanza (i.e., <iq/>, <message/>, or
<presence/>).
3.1. Prerequisites
First, the sending agent prepares and retains the following:
o The JID of the sender (i.e. its own JID). This SHOULD be the
bare JID (localpart@domainpart).
o The JID of the recipient. This SHOULD be the bare JID
(localpart@domainpart).
o A random Content Encryption Key (CEK). The CEK MUST have a length
at least equal to that of the required encryption keys and MUST be
generated randomly. See [RFC4086] for considerations on
generating random values.
o A CEK identifier (CID). The CID MUST be unique for a given
(sender, recipient, CEK) tuple, and MUST NOT be derived from CEK
itself.
3.2. Process
For a given plaintext stanza (S), the sending agent performs the
following:
1. Notes the current UTC date and time N when this stanza is
constructed, formatted as described under [timestamps].
2. Constructs a forwarding envelope P using a <forwarded/> element
qualified by the "urn:xmpp:forward:0" namespace (as defined in
[MSG-FWD]) as follows:
* The child element <delay/> qualified by the "urn:xmpp:delay"
namespace (as defined in [DELAY]) with the attribute 'stamp' set
to the UTC date and time value N
* The plaintext stanza S
3. Generates any additional unprotected block cipher factors (IV);
e.g. initialization vector, nonce, and/or associated
authentication data. A sending agent MUST ensure that no two
sets of factors are used with the same CEK, and SHOULD NOT reuse
such factors for other stanzas.
4. Constructs a partial [JOSE-JWE] header (H) with the following
information:
* The property 'enc' indicating the algorithm used to encrypt the
content.
Miller std [Page 3]
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* The property 'iv' indicating the initialization vector, if
required by the algorithm.
NOTE: this header is intentionally lacking required attributes. The
receiving agent is responsible for assembling a final, valid JWE
header.
5. Convert the stanza to a UTF-8 encoded string (P'), optionallly
removing line breaks and other insignificant whitespace between
elements and attributes, i.e. P' = UTF8-encode(P). We call P' a
"stanza-string" because for purposes of encryption and decryption
it is treated not as XML but as an opaque string (this avoids the
need for complex canonicalization of the XML input).
6. Encrypts P' using the intended block cipher, i.e. T = block-
encrypt(CEK, IV, P').
7. Constructs an <e2e/> element qualified by the
"urn:ietf:params:xml:ns:xmpp-e2e:1" namespace as follows:
* The attribute 'id' set to the identifier value CID.
* The child element <header/> qualified by the
"urn:ietf:params:xml:ns:xmpp-e2e:1" namespace and with XML
character data as the base64url-encoded form of H.
* The child element <data/> qualified by the "urn:ietf:params:xml:ns
:xmpp-e2e:1" namespace and with XML character data as the
base64url-encoded form of T.
8. Sends the <e2e/> element as the payload of a stanza that SHOULD
match the stanza from step 1 in kind (e.g., <message/>), type
(e.g., "chat"), and addressing (e.g. to="romeo@montague.net"
from="juliet@capulet.net/balcony"). If the original stanza (S)
has a value for the "id" attribute, this stanza MUST NOT use the
same value for its "id" attribute.
3.3. Example Securing a Message
NOTE: unless otherwise indicated, all line breaks are included for
readability.
The sending agent begins with the plaintext version of the <message/>
stanza 'S':
Miller std [Page 4]
Internet-Draft XMPP E2E February 2012
<message xmlns='jabber:client'
from='juliet@capulet.lit/balcony'
to='romeo@montegue.lit/garden'
type='chat'>
<thread>35740be5-b5a4-4c4e-962a-a03b14ed92f4</thread>
<body>
But to be frank, and give it thee again.
And yet I wish but for the thing I have.
My bounty is as boundless as the sea,
My love as deep; the more I give to thee,
The more I have, for both are infinite.
</body>
</message>
and the following prerequisites:
o Sender JID as "juliet@capulet.lit"
o Recipient JID as "romeo@montegue.lit"
o Content encryption key 'CEK' as (base64 encoded)
"-ElMo6FndEkMxWP3TIkp1dDfVKqmqAAgrlcvVnUVpOc="
o CEK identifier CID as "835c92a8-94cd-4e96-b3f3-b2e75a438f92"
The sending agent performs steps 1 and 2 to generate the envelope:
<forwarded xmlns='urn:xmpp:forward:0'>
<delay xmlns='urn:xmpp:delay'
stamp='1492-05-12T20:07:37.012Z'/>
<message xmlns='jabber:client'
from='juliet@capulet.lit/balcony'
to='romeo@montegue.lit/garden'
type='chat'>
<thread>35740be5-b5a4-4c4e-962a-a03b14ed92f4</thread>
<body>
But to be frank, and give it thee again.
And yet I wish but for the thing I have.
My bounty is as boundless as the sea,
My love as deep; the more I give to thee,
The more I have, for both are infinite.
</body>
</message>
</forwarded>
Then the sending agent performs steps 3 and 4 to generate the [JOSE-
JWE] header:
{
"enc":"A256CCM",
"iv":"B7waCj2vF_sLaJfe-1GHrA==",
"adata":"1492-05-12T20:07:37.012Z",
"msize":"16"
Miller std [Page 5]
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}
Then the sending agent performs steps 5 and 6 to generate the
protected content:
7LlMXd-qqPAQ_LZm6u9AR2csyDgT09z5DWdn8K5GLr_qbWRDKw2ufZrmO9YZ-jHl
1IDeXeQ9azbNNViv8gpa-prDYkXOo3QoqYOJiA0RAkPU-UjN41wqqVvV62gad_OB
Dd9q2xsNnK1PI5frIGTCZSexOIeSD3EcP0cDI_0MzMEKqpVnPbYQDkWQNrtxPs2b
lE15KcQXbHVxA9rEz7y0a-ITXruV_fOXGftkRVDuiF1yVh2xNRPa-TQxDegZh1D_
u_c2mwPLO6ED_1ZlvL7075_VL0DT01YGtDDQeyzrQWnQNEBJ4G5jFpCyqtCszbgx
9kjWjxLYNLLGxbMOtwF45OLCd8JFUIQAHoLeKp4aIWr5yp7aATX8dKvQm5_TFICt
nLonaM1e5mRPnRgg5zNeMErx6FFkqowOI1h7hVl_QHF8Ofoy99CmWKiVT3Nq5ngL
74Xm4CtiJMHnAEn2Q-10-fWuIHIEA0u4GwBaXo0ToBw4uCM4ZhG1SFSKyCKkjXmr
7TL-5jwSuuQHX6efS8Hhi7fujmqw9VXekeubsY2btl5put0SWT8_0S8ZBDMjrkXj
y7iI5NUOhQMms3ou1r01NZdzNVKcqiX5q3z1eB1FLWmGymnnj_gE_HalWUL0HoqL
93Fr1nfFLNhXLCZYhZ7By6T9NN8omp4ZYE92HMpPzgo-eCGP
Then the sending agent performs step 7 and sends the following:
<message xmlns='jabber:client'
from='juliet@capulet.lit/balcony'
id='fJZd9WFIIwNjFctT'
to='romeo@montegue.lit/garden'
type='chat'>
<e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e:1'
id='835c92a8-94cd-4e96-b3f3-b2e75a438f92'>
<header>
eyJlbmMiOiJBMjU2Q0NNIiwiaXYiOiJCN3dhQ2oydkZfc0xhSmZlLTFHSHJBPT0i
LCJhZGF0YSI6IjQ5Mi0wNS0xMlQyMDowNzozNy4wMTJaIiwibXNpemUiOiIxNiJ9
</header>
<data>
7LlMXd-qqPAQ_LZm6u9AR2csyDgT09z5DWdn8K5GLr_qbWRDKw2ufZrmO9YZ-jHl
1IDeXeQ9azbNNViv8gpa-prDYkXOo3QoqYOJiA0RAkPU-UjN41wqqVvV62gad_OB
Dd9q2xsNnK1PI5frIGTCZSexOIeSD3EcP0cDI_0MzMEKqpVnPbYQDkWQNrtxPs2b
lE15KcQXbHVxA9rEz7y0a-ITXruV_fOXGftkRVDuiF1yVh2xNRPa-TQxDegZh1D_
u_c2mwPLO6ED_1ZlvL7075_VL0DT01YGtDDQeyzrQWnQNEBJ4G5jFpCyqtCszbgx
9kjWjxLYNLLGxbMOtwF45OLCd8JFUIQAHoLeKp4aIWr5yp7aATX8dKvQm5_TFICt
nLonaM1e5mRPnRgg5zNeMErx6FFkqowOI1h7hVl_QHF8Ofoy99CmWKiVT3Nq5ngL
74Xm4CtiJMHnAEn2Q-10-fWuIHIEA0u4GwBaXo0ToBw4uCM4ZhG1SFSKyCKkjXmr
7TL-5jwSuuQHX6efS8Hhi7fujmqw9VXekeubsY2btl5put0SWT8_0S8ZBDMjrkXj
y7iI5NUOhQMms3ou1r01NZdzNVKcqiX5q3z1eB1FLWmGymnnj_gE_HalWUL0HoqL
93Fr1nfFLNhXLCZYhZ7By6T9NN8omp4ZYE92HMpPzgo-eCGP
</data>
</e2e>
</message>
4. Requesting Content Keys
A receiving agent might not have the conetnt encryption key to
decrypt the stanza.
Miller std [Page 6]
Internet-Draft XMPP E2E February 2012
4.1. Request Process
Before a CEK can be requested, the receiving agent MUST have at least
one public key for which it also has the private key.
To request a CEK, the receiving agent performs the following:
1. Constructs a [JOSE-JWK] container object (KS), containing
information about each public key the requesting agent wishes to
use. Each key SHOULD include a value for the property 'kid'
which uniquely identifies it within the context of all provided
keys. Each key MUST include a value for the property 'kid' if
any two keys use the same algorithm.
2. Constructs a <keyreq/> element qualified by the
"urn:ietf:params:xml:ns:xmpp-e2e:1" namespace as follows:
* The attribute 'id' set to the CEK identifier value CID.
* The child element <pkey/> qualified by the "urn:ietf:params:xml:ns
:xmpp-e2e:1" namespace and with XML character data as the
base64url-encoded form of KS.
3. Sends the <keyreq/> element as the payload of an <iq/> stanza
with the attribute 'type' set to "get", the attribute 'to' set to
the full JID of the original encrypted stanza's sender, and the
attribute 'id' set to an opaque string value the receiving agent
uses to track the <iq/> response.
4.2. Accept Process
If the sending agent approves the request, it performs the following:
1. Chooses a key (PK) from the list provided via KS, and notes its
identifier value 'kid'.
2. Constructs a parial [JOSE-JWE] header (H) as follows:
* The property 'alg' set to the cryptographic algorithm for PK,
which is used to secure the content encryption key CEK.
* The property 'kid' set to the identifier matching PK.
NOTE: this header is intentionally lacking required attributes. The
receiving agent is responsible for assembling a final, valid JWE
header.
3. Encrypts the content encryption key CEK using the key PK, i.e.
CEK' = pki-encrypt(PK, CEK).
4. Constructs a <keyreq/> element qualified by the
"urn:ietf:params:xml:ns:xmpp-e2e:1" namespace as follows:
Miller std [Page 7]
Internet-Draft XMPP E2E February 2012
* The attribute 'id' set to the CEK identifier CID.
* The child element <header/> qualified by the
"urn:ietf:params:xml:ns:xmpp-e2e:1" namespace and with XML
cahracter data as the base64url-encoded form of H.
* The child element <cek/> qualified by the "urn:ietf:params:xml:ns
:xmpp-e2e:1" namespace and with XML character data as the
base64url-encoded form of CEK'.
5. Sends the <keyreq/> element as the payload of an <iq/> stanza
with the attribute 'type' set to "result", the attribute 'to' set
to the full JID from the request <iq/>'s 'from' attribute, and
the attribute 'id' set to the value of the request <iq/>'s 'id'
attribute.
4.3. Error Conditions
If the sending agent does not approve of the request, it sends an <iq
/> stanza of type "error" and containing the reason for denying the
request:
o <forbidden/>: the key request is made by an entity that is not
authorized to decrypt stanzas from the sending agent and/or for
the indicated CID.
o <item-not-found/>: the requested CID is no longer valid.
o <not-acceptable/>: the key request did not contain any keys the
sending agent understands.
4.4. Example of Successful Key Request
NOTE: unless otherwise indicated, all line breaks are included for
readability.
To begin a key request, the receiving agent performs step 1 from
request process [keyreq-process-request] to generate the [JOSE-JWK]:
[{
"alg":"RSA",
"mod":"AL7ano5DBdNYfKChGh3xxGDtAtozO3iEm20rzbNEjSLWFjuhm46SXzeJXV8Nr6V
UXcrJ8FN85OqNv0g9GAh9VoHriNECtZJzEw3TUl8edntXOAU8IZQPIh7rrU1pqQ
anrJ9RjWZqgd42LCTpFQWMAibZAfQD2gb5NIrZUbYs4wn9Rx52ru5xkrcrIYLvP
rK8Yv3fKwuU0y0gf809Yunz_H8A5aHplzrQtFOuW8uT_tWR8Wn_2w_H6Y6bOoME
oHZGSjCQCNGzlmVrjKadp7amtMCwezXcW9iI63qIP7ObLAKEolw1XaLMEm6d-mT
_tZZwpNo_r2eKm4WhYOW2bYLfoME=",
"exp":"AQAB",
"kid":"romeo@montegue.lit/garden"
}]
Miller std [Page 8]
Internet-Draft XMPP E2E February 2012
Then the receiving agent performs step 2 to generate the <keyreq/>:
<keyreq xmlns='urn:ietf:params:xml:ns:xmpp-e2e:1'
id='835c92a8-94cd-4e96-b3f3-b2e75a438f92'>
<pkey>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</pkey>
</keyreq>
Then the receiving agent performs step 3 and sends the following:
<iq xmlns='jabber:client'
from='romeo@montegue.lit/garden'
id='xdJbWMA+'
to='juliet@capulet.lit/balcony'
type='get'>
<keyreq xmlns='urn:ietf:params:xml:ns:xmpp-e2e:1'
id='835c92a8-94cd-4e96-b3f3-b2e75a438f92'>
<pkey>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</pkey>
</keyreq>
</iq>
If the sending agent accepts this key request, it performs steps 1
and 2 from accept process [keyreq-process-accept] to generate the
partial [JOSE-JWE] header:
{
"alg":"RSA-OEAP",
"kid":"romeo@montegue.lit/garden"
}
Then the sending agent performs step 3 to generate the encrypted CEK:
Miller std [Page 9]
Internet-Draft XMPP E2E February 2012
DCKrJpLd8XYze7joNKsyvpzGD4MffVQF7apQMkPK8_vKx4J3xEqWB3tXxp6oxJF
4YHla4SFiMp44LccMEd6JchPp_23OXrBo8i7Fwo8jVH6QoQa71T_1rQj6CWQ1eF
vXiU4Qmp52F-gjuUhlKfe3qccdlFp3kLy8Mpq5mDdq6deOq0_qusqr8QTqrT5LN
IgsXYzrdiDdKx8KSKpI4FBB_H1x-A1C97DfJk9s5H7GzKVm2BRWVXWjJfO4lckE
Z45ZJkA3CKq86Yth3YBetoScPVLhoRoO2qqBg4gR9dDO5mXnOgPslVfXWvegexH
AyhHmJZsj3yV_pW1Rlb5jn5J4Rw==
Then the sending agent performs step 4 to generate the <keyreq/>
response:
<keyreq xmlns='urn:ietf:params:xml:ns:xmpp-e2e:1'
id='835c92a8-94cd-4e96-b3f3-b2e75a438f92'>
<header>
eyJhbGciOiJSU0EtT0VBUCIsImtpZCI6InJvbWVvQG1vbnRlZ3VlLmxpc3QvZ2F
yZGVuIn0=
</header>
<cek>
DCKrJpLd8XYze7joNKsyvpzGD4MffVQF7apQMkPK8_vKx4J3xEqWB3tXxp6oxJF
4YHla4SFiMp44LccMEd6JchPp_23OXrBo8i7Fwo8jVH6QoQa71T_1rQj6CWQ1eF
vXiU4Qmp52F-gjuUhlKfe3qccdlFp3kLy8Mpq5mDdq6deOq0_qusqr8QTqrT5LN
IgsXYzrdiDdKx8KSKpI4FBB_H1x-A1C97DfJk9s5H7GzKVm2BRWVXWjJfO4lckE
Z45ZJkA3CKq86Yth3YBetoScPVLhoRoO2qqBg4gR9dDO5mXnOgPslVfXWvegexH
AyhHmJZsj3yV_pW1Rlb5jn5J4Rw==
</cek>
</keyreq>
Then the sending agent performs step 5 and sends the following:
<iq xmlns='jabber:client'
from='juliet@capulet.lit/balcony'
id='xdJbWMA+'
to='romeo@montegue.lit/garden'
type='result'>
<keyreq xmlns='urn:ietf:params:xml:ns:xmpp-e2e:1'
id='835c92a8-94cd-4e96-b3f3-b2e75a438f92'>
<header>
eyJhbGciOiJSU0EtT0VBUCIsImtpZCI6InJvbWVvQG1vbnRlZ3VlLmxpc3QvZ2F
yZGVuIn0=
</header>
<cek>
DCKrJpLd8XYze7joNKsyvpzGD4MffVQF7apQMkPK8_vKx4J3xEqWB3tXxp6oxJF
4YHla4SFiMp44LccMEd6JchPp_23OXrBo8i7Fwo8jVH6QoQa71T_1rQj6CWQ1eF
vXiU4Qmp52F-gjuUhlKfe3qccdlFp3kLy8Mpq5mDdq6deOq0_qusqr8QTqrT5LN
IgsXYzrdiDdKx8KSKpI4FBB_H1x-A1C97DfJk9s5H7GzKVm2BRWVXWjJfO4lckE
Z45ZJkA3CKq86Yth3YBetoScPVLhoRoO2qqBg4gR9dDO5mXnOgPslVfXWvegexH
AyhHmJZsj3yV_pW1Rlb5jn5J4Rw==
</cek>
</keyreq>
</iq>
5. Handling of Inbound Encrypted Stanzas
Several scenarios are possible when an entity receives an encrypted
stanza:
Miller std [Page 10]
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o The receiving agent does not understand the protocol.
o The receiving agent understands the protocol but does not have
enough infomration to decrypt the payload.
o The receiving agent understands the protocol but is unable to
decrypt the payload.
o The receiving agent understands the protocol and is able to
decrypt the payload, but the timestamps fail the checks specified
under [timestamps].
o The receiving agent understands the protocol and is able to
decrypt the payload (success case).
5.1. Protocol Not Understood
In the case where the receiving agent does not understand the
protocol, it MUST do one and only one of the following: (1) ignore
the <e2e/> extension, (2) ignore the entire stanza, or (3) return a
<service-unavailable/> error to the sender, as described in
[RFC6120].
NOTE: If the inbound stanza is an <iq/>, the receiving agent MUST
return an error to the sending agent, to comply with the exchanging
of IQ stanzas in [RFC6121].
5.2. Insufficient Information
In the case where the protocol is understood but the receiving agent
does not have enough information to decrypt the payload, it SHOULD
request the additional information as described in [keyreq].
If the key request fails, or the receiving agent could not otherwise
determine the additional information, it MAY return a <bad-request/>
error to the sending agent (as described in [RFC6120]), optionally
supplemented by an application-specific error condition element of
<insufficient-information/>:
<message xmlns='jabber:client'
from='juliet@capulet.lit/balcony'
id='fJZd9WFIIwNjFctT'
to='romeo@montegue.lit/garden'
type='chat'>
<e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e:1'
id='835c92a8-94cd-4e96-b3f3-b2e75a438f92'>
<header>[XML character data]</header>
<data>[XML character data]</header>
</e2e>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<insufficient-information xmlns='urn:ietf:params:xml:ns:xmpp-e2e'/>
</error>
</message>
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In addition to returning an error, the receiving agent SHOULD NOT
present the stanza to the intended recipient (human or application)
and SHOULD provide some explicit alternate processing of the stanza
(which MAY be to display a message informing the recipient that it
has received a stanza that cannot be decrypted).
5.3. Failed Decryption
In the case where the protocol is understood but the receiving agent
is unable to decrypt the payload, the receiving agent SHOULD return a
<bad-request/> error to the sending agent (as described in
[RFC6120]), optionally supplemented by an application-specific error
condition element of <decryption-failed/> (previously defined in
[RFC3923]):
<message xmlns='jabber:client'
from='juliet@capulet.lit/balcony'
id='fJZd9WFIIwNjFctT'
to='romeo@montegue.lit/garden'
type='chat'>
<e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e:1'
id='835c92a8-94cd-4e96-b3f3-b2e75a438f92'>
<header>[XML character data]</header>
<data>[XML character data]</header>
</e2e>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<decryption-failed xmlns='urn:ietf:params:xml:ns:xmpp-e2e'/>
</error>
</message>
In addition to returning an error, the receiving agent SHOULD NOT
present the stanza to the intended recipient (human or application)
and SHOULD provide some explicit alternate processing of the stanza
(which MAY be to display a message informing the recipient that it
has received a stanza that cannot be decrypted).
5.4. Timestamp Not Acceptable
In Case #4, the receiving agent MAY return a <not-acceptable/> error
to the sender (as described in [RFC6120]), optionally supplemented by
an application-specific error condition element of <bad-timestamp/>
(previously defined in [RFC3923]):
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<message xmlns='jabber:client'
from='juliet@capulet.lit/balcony'
id='fJZd9WFIIwNjFctT'
to='romeo@montegue.lit/garden'
type='chat'>
<e2e xmlns='urn:ietf:params:xml:ns:xmpp-e2e:1'
id='835c92a8-94cd-4e96-b3f3-b2e75a438f92'>
<header>[XML character data]</header>
<data>[XML character data]</header>
</e2e>
<error type='modify'>
<bad-request xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
<bad-timestamp xmlns='urn:ietf:params:xml:ns:xmpp-e2e'/>
</error>
</message>
5.5. Successful Decryption
In the case where the protocol is understood and the receiving agent
successfully decrypted the payload, it MUST NOT return a stanza
error.
If the payload is an <iq/> of type "get" or "set", and the response
is an error, the receiving agent MUST send the encrypted response in
an <iq/> of type "result", to prevent exposing information about the
payload.
6. Inclusion and Checking of Timestamps
Timestamps are included to help prevent replay attacks. All
timestamps MUST conform to [DATETIME] and be presented as UTC with no
offset, and SHOULD include the seconds and fractions of a second to
three digits. Absent a local adjustment to the sending agent's
perceived time or the underlying clock time, the sending agent MUST
ensure that the timestamps it sends to the receiver increase
monotonically (if necessary by incrementing the seconds fraction in
the timestamp if the clock returns the same time for multiple
requests). The following rules apply to the receiving agent:
o It MUST verify that the timestamp received is within five minutes
of the current time, except as described below for offline
messages.
o It SHOULD verify that the timestamp received is greater than any
timestamp received in the last 10 minutes which passed the
previous check.
o If any of the foregoing checks fails, the timestamp SHOULD be
presented to the receiving entity (human or application) marked as
"old timestamp", "future timestamp", or "decreasing timestamp",
and the receiving entity MAY return a stanza error to the sender.
Miller std [Page 13]
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The foregoing timestamp checks assume that the recipient is online
when the message is received. However, if the recipient is offline
then the server will probably store the message for delivery when the
recipient is next online (offline storage does not apply to <iq/> or
<presence/> stanzas, only <message/> stanzas). As described in
[OFFLINE], when sending an offline message to the recipient, the
server SHOULD include delayed delivery data as specified in [DELAY]
so that the recipient knows that this is an offline message and also
knows the original time of receipt at the server. In this case, the
recipient SHOULD verify that the timestamp received in the encrypted
message is within five minutes of the time stamped by the recipient's
server in the <delay/> element.
7. Interaction with Stanza Semantics
The following limitations and caveats apply:
o Undirected <presence/> stanzas SHOULD NOT be encrypted. Such
stanzas are delivered to anyone the sender has authorized, and can
generate a large volume of key requests.
o Stanzas directed to multiplexing services (e.g. multi-user chat)
SHOULD NOT be encrypted, unless the sender has established an
acceptable trust relationship with the multiplexing service.
8. Mandatory-to-Implement Cryptographic Algorithms
All algorithms that MUST be implemented for [JOSE-JWE] also MUST be
implemented for this specification.
9. Security Considerations
9.1. Storage of Encrypted Stanzas
The recipient's server might store any <message/> stanzas received
until the recipient is next available; this duration could be
anywhere from a few minutes to several months.
9.2. Re-use of Content Encryption Keys
A sender SHOULD NOT use the same CEK for stanzas intended for
different recipients.
A sender MAY re-use a CEK for several stanzas to the same recpient.
In this case, the CID remains the same, but MUST generate a new IV
(and other data) for each encrypted stanza. The sender SHOULD
periodically generate a new CEK; however, this specification does not
mandate any specific algorithms or processes.
10. IANA Considerations
10.1. XML Namespace Name for e2e Data in XMPP
Miller std [Page 14]
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A URN sub-namespace of encrypted content for the Extensible Messaging
and Presence Protocol (XMPP) is defined as follows.
URI: urn:ietf:params:xml:ns:xmpp-e2e:1
Specification: RFC XXXX
Description: This is an XML namespace name of encrypted content for
the Extensible Messaging and Presence Protocol as defined by RFC
XXXX.
Registrant Contact: IESG, <iesg@ietf.org>
11. References
11.1. Normative References
[BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[CMS-AES] Schaad, J., "Use of the Advanced Encryption Standard (AES)
Encryption Algorithm in Cryptographic Message Syntax
(CMS)", RFC 3565, July 2003.
[DATETIME]
Saint-Andre, P., "XMPP Date and Time Profiles", XSF XEP
0082, May 2003.
[DELAY] Saint-Andre, P., "Delayed Delivery", XSF XEP 0203,
September 2009.
[E2E-REQ] Saint-Andre, P, "Requirements for End-to-End Encryption in
the Extensible Messaging and Presence Protocol (XMPP)",
Internet-Draft draft-saintandre-xmpp-e2e-requirements-01,
March 2010.
[MSG-FWD] Wild, M. and K. Smith, "Message Forwarding", XSF XEP 0297,
July 2011.
[KEYWORDS]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[HMAC] Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and HMAC-SHA)", RFC 4634, July 2006.
[JOSE-JWA]
Jones, M., "JSON Web Algorithms (JWA)", Internet-Draft
draft-ietf-jose-json-web-algorithms-00, January 2012.
[JOSE-JWE]
Jones, M., Rescola, E. and J. Hildebrand, "JSON Web
Encryption (JWE)", Internet-Draft draft-ietf-jose-json-
web-encryption-00, January 2012.
[JOSE-JWK]
Jones, M., "JSON Web Key (JWK)", Internet-Draft draft-
ietf-jose-json-web-key-00, January 2012.
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[PKIX] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R. and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[SECTERMS]
Shirey, R., "Internet Security Glossary, Version 2", RFC
4949, August 2007.
[X509-ALGO]
Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
11.2. Informative References
[OFFLINE] Saint-Andre, P., "Best Practices for Handling Offline
Messages", XSF XEP 0160, January 2006.
[RFC3923] Saint-Andre, P., "End-to-End Signing and Object Encryption
for the Extensible Messaging and Presence Protocol
(XMPP)", RFC 3923, October 2004.
[RFC4086] Eastlake, D., Schiller, J. and S. Crocker, "Randomness
Requirements for Security", RFC 4086, June 2005.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6121, March 2011.
[RFC6121] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence", RFC
6121, March 2011.
Appendix A. Schema for urn:ietf:params:xml:ns:xmpp-e2e:1
The following XML schema is descriptive, not normative.
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<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-e2e:1'
xmlns='urn:ietf:params:xml:ns:xmpp-e2e:1'
elementFormDefault='qualified'>
<xs:element name='e2e'>
<xs:complexType>
<xs:attribute name='id' type='xs:string' use='required'/>
<xs:sequence>
<xs:element ref='header' minOccurs='1' maxOccurs='1'/>
<xs:element ref='data' minOccurs='1' maxOccurs='1'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='keyreq'>
<xs:complexType>
<xs:attribute name='id' type='xs:string' use='required'/>
<xs:sequence>
<xs:element ref='header' minOccurs='0' maxOccurs='1'/>
<xs:element ref='pkey' minOccurs='0' maxOccurs='1'/>
<xs:element ref='cek' minOccurs='0' maxOccurs='1'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='cek'>
<xs:complexType>
<xs:simpleType>
<xs:extension base='xs:string'>
</xs:extension>
</xs:simpleType>
</xs:complexType>
</xs:element>
<xs:element name='data'>
<xs:complexType>
<xs:simpleType>
<xs:extension base='xs:string'>
</xs:extension>
</xs:simpleType>
</xs:complexType>
</xs:element>
<xs:element name='header'>
<xs:complexType>
<xs:simpleType>
<xs:extension base='xs:string'>
</xs:extension>
</xs:simpleType>
</xs:complexType>
</xs:element>
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<xs:element name='pkey'>
<xs:complexType>
<xs:simpleType>
<xs:extension base='xs:string'>
</xs:extension>
</xs:simpleType>
</xs:complexType>
</xs:element>
<xs:element name='bad-timestamp' type='empty'/>
<xs:element name='decryption-failed' type='empty'/>
<xs:element name='insufficient-information' type='empty'/>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
Author's Address
Matthew Miller
Cisco Systems, Inc.
1899 Wyknoop Street, Suite 600
Denver, CO 80202
USA
Phone: +1-303-308-3204
Email: mamille2@cisco.com
Miller std [Page 18]