One document matched: draft-barnes-atoca-escape-00.txt
ATOCA R. Barnes
Internet-Draft BBN Technologies
Intended status: Informational October 6, 2011
Expires: April 8, 2012
Encoding of Secure Common Alert Protocol Entities (ESCAPE)
draft-barnes-atoca-escape-00.txt
Abstract
Recipients of emergency alerts need to be able to verify that an
alert they receive was issued by an authorized source. The Common
Alerting Protocol (CAP) provides a standard way of encoding alert
information, but does not provide any security features that would
support authentication of alert originators. This document describes
a security wrapper for Common Alerting Protocol objects to allow
alerts to be signed by alert originators.
Please send feedback to the atoca@ietf.org mailing list.
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/.
Internet-Drafts are draft documents valid for a maximum of six months
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 April 8, 2012.
Copyright Notice
Copyright (c) 2011 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
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to this document. Code Components extracted from this document must
include Simplified BSD License text 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Open Questions . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. new section . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Basic MIME encoding . . . . . . . . . . . . . . . . . . . 4
3.2. Alert Tokens . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. S/MIME Encapsulation . . . . . . . . . . . . . . . . . . . 5
3.4. Validity . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Processing Rules . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Alert Originator (Signer) . . . . . . . . . . . . . . . . 6
4.2. Alert Relay (Re-signer) . . . . . . . . . . . . . . . . . 7
4.3. Alert Recipient (Verifier) . . . . . . . . . . . . . . . . 8
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
Emergency alerting is an increasingly important function of
telecommunications networks, allowing authorities to distribute
warnings of impending danger to large numbers of end users in a short
period of time. However, because emergency alerts are such important
messages to users, there is much more potential for abuse of alerting
than other messaging systems. If an attacker can introduce a false
emergency alert, he may be able to cause mass action, such as the
evacuation of a building or city.
Traditionally, the security of alerting systems has been based mainly
on the security of the system by which authorities provide alerts to
broadcast points, and on the link-layer security of broadcast media
that deliver alerts to end users. In the context of the Internet, it
is impossible to rely on link-layer security because IP runs over
many types of link that have no analogous access control. While it
is still important for the "staging" or "distribution" step be
secure, the alerting system would be more robust if security were
provided end-to-end, from the original authority to the end
recipient.
This document describes ESCAPE, a secure container format for the
Common Alerting Protocol (CAP) [CAP]. CAP documents provide
information about an emergency alert; ESCAPE-wrapped CAP documents
also provide security information that can authenticate the
originator of the alert. Using this additional information, end
alert recipients can verify that ESCAPE-wrapped alerts were
originated by entities they trust, and reject false alerts from
untrusted entities.
The ESCAPE format defines only a mechanism for signing alerts. It
does not define how an alert recipient discovers public keys for
entities that it should trust to originate alerts, such as local
network operators or local alert authorities. This document assumes
that cryptographic parameters such as public keys and "alert tokens"
have been provisioned through some other mechanism, e.g., [ATOCA-DOC-
TBD].
1.1. Open Questions
Should we always apply GZIP to the entire encoded message? Pro:
Slightly smaller message size. Con: Will need to require GZIP for
all messages or add content indication.
Should we allow DER-encoded CAP as well as XML-encoded CAP? Pro:
Smaller message size. Con: Clients need to support two encodings.
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Should we constrain crypto algorithms. Pro: Marginally simpler
implementation. Con: Need to maintain a list of supported
algorithms.
Should we require a public-key signature, or allow reliance on token
checks alone? Pro: Enables cases with no public-key operations.
Con: Risk of replay attacks using old tokens.
Should we move the Alert-Token field from the inner (signed) MIME
entity to the outer (unsigned) MIME entity? Pro: Allows relays to
add tokens. Con: Allows relays and attackers to remove or change
tokens.
2. Definitions
The 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 RFC 2119 [RFC2119].
3. new section
The ESCAPE format encapsulates a CAP document as an S/MIME object
[RFC5751]. First, the CAP document is encoded as a MIME entity
[RFC2045], then the MIME entity is signed using S/MIME.
3.1. Basic MIME encoding
CAP XML documents have MIME type "application/cap+xml". An alert
originator may choose to apply the gzip compression scheme to the
alert before sending it. If the alert is compressed, the originator
must encode the compressed alert using the base64 encoding scheme
before transmitting it [RFC1952][RFC4648]. A CAP MIME body thus has
the following properties:
o A "Content-Type" header field MUST be present, with the single
value "application/cap+xml".
o A "Content-Encoding" header field MAY be present. If present, it
MUST have the value "gzip", and there MUST be a "Content-Transfer-
Encoding" header with the value "base64".
o The body of the MIME entity MUST be a CAP document, either
directly, or processed through the gzip and base64 encodings.
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3.2. Alert Tokens
ESCAPE introduces a new MIME header, Alert-Token, which provides a
rough form of authentication. If alert recipients are configured
with a list of valid tokens (or an algorithm for checkign the
validity of a token), the recipient of an alert message can check the
validity of the value in the Alert-Token field before performing full
S/MIME validation on the ESCAPE object. The Alert-Token field
contains a single opaque binary string, encoded in base64. The ABNF
syntax for the field is as follows, where "base64" is as defined in
RFC 4566 [RFC4566][RFC2234]. (Here we also follow the usual
conventions with regard to whitespace in MIME headers.)
Alert-Token = "Alert-Token" ":" base64
An ESCAPE MIME entity MAY contain one or more Alert-Token header
fields. Any header fields other than "Content-Type", "Content-
Encoding", "Content-Transfer-Encoding", and "Alert-Token" MAY be
ignored by alert recipients.
3.3. S/MIME Encapsulation
After a CAP message has been encoded into a MIME entity, an S/MIME
signature is applied, following the S/MIME procedures for
constructing a signed message of type "multipart/signed" (Section 3.4
of RFC 5751 [RFC5751]). The following constraints apply to the
S/MIME encoding used in ESCAPE messages.
o The ESCAPE message MUST have type "multipart/signed".
o If the ESCAPE message contains header fields other than "Content-
Type", then they MAY be ignored.
o The S/MIME body part SHOULD NOT include certificates for signers,
in order to minimize message size.
o The S/MIME body part SHOULD identify signers by subject key
identifier rather than by subject name, in order to allow for both
certified and uncertified public keys [RFC5652].
Except the constraints above, software to verify ESCAPE alerts MUST
include full S/MIME support, including all defined cryptographic
algorithms [RFC3370][RFC5754]. Implementations MAY include
additional algorithms, but alert signers SHOULD NOT sign alerts with
non-standard algorithms, since some recipients may not be able to
process them.
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3.4. Validity
An ESCAPE object is valid if and only if all of the following
conditions are true:
o If the verifying entity is configured with valid tokens, then
there must be at least one Alert-Token header field containing a
valid token.
o If the verifying entity is configured with trusted public keys,
then the S/MIME signature on the object must be valid, and must be
verified using a trusted public key.
An entity verifying an ESCAPE object MUST verify both of these
criteria, but MAY check them in either order and omit further checks
after the object fails one check. In particular, performing the
token check before decoding and verifying the CMS signature may avoid
the work of signature verification. A verifying entity SHOULD NOT
accept ESCAPE objects if it is configured with neither trusted public
keys nor valid tokens.
4. Processing Rules
There are three main phases in the life-cycle of an ESCAPE object.
First, it is created and signed by an alert originator. Second, it
may pass through an alert relay that adds a signature under its key.
Finally, it is received and verified by an end recipient. This
section describes the steps that each type of entity follows to sign,
re-sign or verify an ESCAPE object.
4.1. Alert Originator (Signer)
Inputs:
o CAP document
o Private key for signing and corresponding subject key ID
o gzip flag
o List of tokens (possibly empty)
Processing steps:
1. Encode the CAP document as a MIME entity.
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A. Add a "Content-Type" header field with value "application/
common-application-protocol+xml".
B. If the gzip flag is set, add a "Content-Encoding" header
field with value "gzip" and a "Content-Transfer-Encoding"
header field with value "base64".
C. Add an "Access-Token" header field for each token in the
list.
D. If the gzip flag is set, gzip the CAP document, then gzip and
base64-encode the CAP document and set it as the message
body.
E. If the gzip flag is not set, set the CAP document as the
message body.
2. Compute the signature over the MIME entity using the signing key
and create a CMS SignedData structure that identifies the signer
using the corresponding subject key ID.
3. Combine the CAP MIME entity and the computed CMS SignedData
structure into a "multipart/signed" S/MIME object.
Output: ESCAPE message
4.2. Alert Relay (Re-signer)
Inputs:
o ESCAPE object
o Private key for signing and corresponding subject key ID
Processing steps:
1. Extract the CAP MIME entity and CMS SignedData object from the
ESCAPE message.
2. Compute the signature over the CAP MIME entity using the signing
key.
3. Append the signature value and subject key ID to the CMS
SignedData object as a new SignerInfo.
4. Combine the CAP MIME entity and the computed CMS SignedData
structure into a "multipart/signed" S/MIME object.
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Output: ESCAPE message
4.3. Alert Recipient (Verifier)
Inputs:
o ESCAPE object
o Set of trusted public keys (possibly empty)
o Set of valid tokens (possibly empty)
Processing steps:
1.
2. Extract the CAP MIME entity and the CMS SignedData object from
the ESCAPE message.
3. Check that the MIME headers for the CAP MIME entity have the
correct values.
* Content-Type must be "application/
common-alerting-protocol+xml"
* Content-Encoding must be "gzip" or absent
* Content-Transfer-Encoding must be present and equal to
"base64" if Content-Encoding is present, otherwise absent.
If any of these headers are invalid, then return the CAP message
is malformed. Return FALSE.
4. Extract the CAP entity body. If the Content-Encoding is "gzip",
then base64-decode and un-gzip the CAP entity body.
5. If the set of valid tokens is non-empty, then verify that at
least one of the Alert-Token values in the CAP MIME entity is
contained within the set of valid tokens. If no Alert-Token
value is valid, then return FALSE.
6. If the set of trusted public keys is non-empty, then verify that
at least one of the SignerInfos within the CMS SignedData object
contains a valid signature under a trusted key. If no valid,
trusted signature is found, then return FALSE.
7. Return TRUE.
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Output: Verification status
5. Examples
Consider the following CAP message:
<?xml version = "1.0" encoding = "UTF-8"?>
<alert xmlns = "urn:oasis:names:tc:emergency:cap:1.1">
<identifier>43b080713727</identifier>
<sender>hsas@dhs.gov</sender>
<sent>2003-04-02T14:39:01-05:00</sent>
<status>Actual</status>
<msgType>Alert</msgType>
<scope>Public</scope>
<info>
<category>Security</category>
<event>Homeland Security Advisory System Update</event>
<urgency>Immediate</urgency>
<severity>Severe</severity>
<certainty>Likely</certainty>
<senderName>U.S. Government,
Department of Homeland Security</senderName>
<headline>Homeland Security Sets Code ORANGE</headline>
<description>The Department of Homeland Security has
elevated the Homeland Security Advisory System threat level
to ORANGE / High in response to intelligence which may
indicate a heightened threat of terrorism.</description>
<instruction> A High Condition is declared when there is a
high risk of terrorist attacks. In addition to the
Protective Measures taken in the previous Threat Conditions,
Federal departments and agencies should consider agency-
specific Protective Measures in accordance with their
existing plans.</instruction>
<web>http://www.dhs.gov/dhspublic/display?theme=29</web>
<parameter>
<valueName>HSAS</valueName>
<value>ORANGE</value>
</parameter>
<resource>
<resourceDesc>Image file (GIF)</resourceDesc>
<uri>http://www.dhs.gov/dhspublic/getAdvisoryImage</uri>
</resource>
<area>
<areaDesc>U.S. nationwide and interests worldwide</areaDesc>
</area>
</info>
</alert>
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Suppose an alert signer has the following RSA key pair, encoded as a
PEM-encoded private key and self-signed certificate [RFC1421]:
-----BEGIN PRIVATE KEY-----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-----END PRIVATE KEY-----
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
Then if the signer signs the alert with the above private key and the
token "foobar", he will create the following ESCAPE message:
Content-Type: multipart/signed;
protocol="application/pkcs7-signature";
micalg="sha1";
boundary="----C16CFF6F1CB606631B8BBD4B5B43051F"
------C16CFF6F1CB606631B8BBD4B5B43051F
Alert-Token: asdfasdfasdf
Content-Type: application/cap+xml
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<?xml version = "1.0" encoding = "UTF-8"?>
<alert xmlns = "urn:oasis:names:tc:emergency:cap:1.1">
<identifier>43b080713727</identifier>
<sender>hsas@dhs.gov</sender>
<sent>2003-04-02T14:39:01-05:00</sent>
<status>Actual</status>
<msgType>Alert</msgType>
<scope>Public</scope>
<info>
<category>Security</category>
<event>Homeland Security Advisory System Update</event>
<urgency>Immediate</urgency>
<severity>Severe</severity>
<certainty>Likely</certainty>
<senderName>U.S. Government,
Department of Homeland Security</senderName>
<headline>Homeland Security Sets Code ORANGE</headline>
<description>The Department of Homeland Security has
elevated the Homeland Security Advisory System threat level
to ORANGE / High in response to intelligence which may
indicate a heightened threat of terrorism.</description>
<instruction> A High Condition is declared when there is a
high risk of terrorist attacks. In addition to the
Protective Measures taken in the previous Threat Conditions,
Federal departments and agencies should consider agency-
specific Protective Measures in accordance with their
existing plans.</instruction>
<web>http://www.dhs.gov/dhspublic/display?theme=29</web>
<parameter>
<valueName>HSAS</valueName>
<value>ORANGE</value>
</parameter>
<resource>
<resourceDesc>Image file (GIF)</resourceDesc>
<uri>http://www.dhs.gov/dhspublic/getAdvisoryImage</uri>
</resource>
<area>
<areaDesc>U.S. nationwide and interests worldwide</areaDesc>
</area>
</info>
</alert>
------C16CFF6F1CB606631B8BBD4B5B43051F
Content-Type: application/pkcs7-signature; name="smime.p7s"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="smime.p7s"
MIIBxQYJKoZIhvcNAQcCoIIBtjCCAbICAQMxCTAHBgUrDgMCGjALBgkqhkiG9w0B
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BwExggGTMIIBjwIBA4AUKcxEepHj4Yr7+WDTS28DWxXcIvMwBwYFKw4DAhqggdgw
GAYJKoZIhvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMTExMDA0
MTUzMzM4WjAjBgkqhkiG9w0BCQQxFgQUG0dU/Z+LJg/29/4nvzkou4Bion4weQYJ
KoZIhvcNAQkPMWwwajALBglghkgBZQMEASowCwYJYIZIAWUDBAEWMAsGCWCGSAFl
AwQBAjAKBggqhkiG9w0DBzAOBggqhkiG9w0DAgICAIAwDQYIKoZIhvcNAwICAUAw
BwYFKw4DAgcwDQYIKoZIhvcNAwICASgwDQYJKoZIhvcNAQEBBQAEgYBDIjpmJ2uP
nbFJqb35p7dGKdoWyh0Q0LUKr9SxOWkmvK9K6AB/Bodzlo1U5hGVqX10p7HqUWW9
SMt3DXB8sxSbEOrD0HUsdsQvmoulfWNAX5ZphS7jvy1LeR9qrYp8zyzUd1bWSOZA
kQKwpg6PRyVYArqG8uAD00CW0elL34WKLQ==
------C16CFF6F1CB606631B8BBD4B5B43051F--
If the signer also applies the GZIP encoding and attaches the token,
he will create the following ESCAPE message:
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Content-Type: multipart/signed;
protocol="application/pkcs7-signature";
micalg="sha1";
boundary="----C6A0932DF53B0609D38DC49A7E492DB3"
------C6A0932DF53B0609D38DC49A7E492DB3
Alert-Token: foobar
Content-Type: application/cap+xml
Content-Transfer-Encoding: base64
Content-Encoding: gzip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6. IANA Considerations
This document requires no action by IANA.
7. Security Considerations
[TODO]
[Dependency on external configuration of keys/TAs and (optionally)
tokens]
8. Acknowledgements
[TODO]
9. References
9.1. Normative References
[CAP] Botterell, A. and E. Jones, "Common Alerting Protocol
v1.1", October 2005.
[RFC1421] Linn, J., "Privacy Enhancement for Internet Electronic
Mail: Part I: Message Encryption and Authentication
Procedures", RFC 1421, February 1993.
[RFC1952] Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G.
Randers-Pehrson, "GZIP file format specification version
4.3", RFC 1952, May 1996.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC3370] Housley, R., "Cryptographic Message Syntax (CMS)
Algorithms", RFC 3370, August 2002.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
Barnes Expires April 8, 2012 [Page 14]
Internet-Draft ESCAPE October 2011
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, September 2009.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, January 2010.
[RFC5754] Turner, S., "Using SHA2 Algorithms with Cryptographic
Message Syntax", RFC 5754, January 2010.
9.2. Informative References
[I-D.ietf-atoca-requirements]
Schulzrinne, H., Norreys, S., Rosen, B., and H.
Tschofenig, "Requirements, Terminology and Framework for
Exigent Communications", draft-ietf-atoca-requirements-01
(work in progress), January 2011.
Author's Address
Richard Barnes
BBN Technologies
9861 Broken Land Parkway
Columbia, MD 21046
US
Phone: +1 410 290 6169
Barnes Expires April 8, 2012 [Page 15]
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