draft-ietf-tls-oob-pubkey-01.txt   draft-ietf-tls-oob-pubkey-02.txt 
IETF P. Wouters TLS P. Wouters
Internet-Draft No Hats Corporation Internet-Draft No Hats Corporation
Intended status: Standards Track J. Gilmore Intended status: Standards Track J. Gilmore
Expires: July 10, 2012 Expires: September 12, 2012
S. Weiler S. Weiler
SPARTA, Inc. SPARTA, Inc.
T. Kivinen T. Kivinen
AuthenTec AuthenTec
H. Tschofenig H. Tschofenig
Nokia Siemens Networks Nokia Siemens Networks
January 20, 2012 March 11, 2012
TLS Out-of-Band Public Key Validation TLS Out-of-Band Public Key Validation
draft-ietf-tls-oob-pubkey-01.txt draft-ietf-tls-oob-pubkey-02.txt
Abstract Abstract
This document specifies a new TLS certificate type for exchanging raw This document specifies a new TLS certificate type for exchanging raw
public keys in Transport Layer Security (TLS) and Datagram Transport public keys in Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS) for use with out-of-band authentication. Layer Security (DTLS) for use with out-of-band public key validation.
Currently, TLS authentication can only occur via PKIX or OpenPGP Currently, TLS authentication can only occur via X.509-based Public
certificates. By specifying a minimum resource for raw public key Key Infrastructure (PKI) or OpenPGP certificates. By specifying a
exchange, implementations can use alternative authentication methods. minimum resource for raw public key exchange, implementations can use
alternative public key validation methods.
One such method is using DANE Resource Records secured by DNSSEC, One such alternative public key valiation method is offered by the
Another use case is to provide authentication functionality when used DNS-Based Authentication of Named Entities (DANE) together with DNS
with devices in a constrained environment that use whitelists and Security. Another alternative is to utilize pre-configured keys, as
blacklists, as is the case with sensors and other embedded devices is the case with sensors and other embedded devices. The usage of
that are constrained by memory, computational, and communication raw public keys, instead of X.509-based certificates, leads to a
limitations where the usage of PKIX is not feasible. smaller code footprint.
The new certificate type specified can also be used to reduce the The support for raw public keys is introduced into TLS via a new non-
latency of a TLS client that is already in possession of a validated PKIX certificate type.
public key of the TLS server before it starts a (non-resumed) TLS
handshake.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 10, 2012. This Internet-Draft will expire on September 12, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 5 3. TLS Handshake Extension . . . . . . . . . . . . . . . . . . . . 5
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Client Hello . . . . . . . . . . . . . . . . . . . . . . . 5
2. Changes to the Handshake Message Contents . . . . . . . . . . 5 3.2. Server Hello . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Client Hello . . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Certificate Request . . . . . . . . . . . . . . . . . . . . 7
2.2. Server Hello . . . . . . . . . . . . . . . . . . . . . . . 7 3.4. Other Handshake Messages . . . . . . . . . . . . . . . . . 7
2.3. Certificate Request . . . . . . . . . . . . . . . . . . . 7 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
2.4. Other Handshake Messages . . . . . . . . . . . . . . . . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
3. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 8 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8.2. Informative References . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
1.1. Motivation
Traditionally, TLS server public keys are obtained in PKIX containers Traditionally, TLS server public keys are obtained in PKIX containers
in-band using the TLS connection and validated using trust anchors in-band using the TLS handshake and validated using trust anchors
based on a [PKIX] certification authority (CA). This method can add based on a [PKIX] certification authority (CA). This method can add
a complicated trust relationship that is difficult to validate. a complicated trust relationship that is difficult to validate.
Examples of such complexity can be seen in [Defeating-SSL]. Examples of such complexity can be seen in [Defeating-SSL].
Alternative methods are available that allow a TLS client to obtain Alternative methods are available that allow a TLS client to obtain
the TLS server public key: the TLS server public key:
o The TLS server public key is obtained from a DNSSEC secured RRset o The TLS server public key is obtained from a DNSSEC secured
using [DANE] resource records using DANE [I-D.ietf-dane-protocol].
o The TLS server public key is obtained from a [PKIX] certificate o The TLS server public key is obtained from a [PKIX] certificate
chain from an [LDAP] server chain from an Lightweight Directory Access Protocol (LDAP) [LDAP]
server.
o The TLS server public key is provisioned by the operating system
and updated via software updates
o A TLS client has connected to the TLS server before and has cached
the TLS server certificate chain or TLS server public key for re-
use
[RFC5246] does not provide a mechanism for a TLS client to tell the
TLS server it is already in possession of the authenticated public
key. Therefore, a TLS server must always send a list of trusted CA
keys and its EE certificate containing its public key, even when the
TLS client does not require or desire that data for authentication.
[RFC6066] allows suppression of the certificate trust anchor chain,
but not suppression of the PKIX EE certificate container. These
certificate chains are large opaque blocks of data containing much
more than the public key of the TLS server. Since the TLS client
might only be able to validate the PKIX SubjectPublicKeyInfo via an
out-of-band method such as [DANE], it has to ignore any additional
information received that was sent by the server that it could not
validate. Furthermore, information that comes in via these
certificate chains could contain contradicting or additional
information that the TLS client cannot validate or trust, such as an
expiry date that conflicts with information obtained from DNS or
LDAP. This document specifies a method to suppress sending this
additional information.
Some small embedded devices use the UDP based [CoAP], a specialized
constrained networks and nodes for machine-to-machine applications.
These devices interact with a Web server to upload data such as
temperature sensor readings at a regular intervals. Constrained
Application Protocol (CoAP) [CoAP] can utilize DTLS for its
communication security. As part of the provisioning procedure, the
embeded device is configured with the address and public key of a
dedicated CoAP server to upload sensor data. Receiving PKIX
information [PKIX] from a webserver would be an unneccesarry burden
on a sensor networking deployment environment that requires pre-
configured client-server public keys. These devices often also lack
a real-time clock to perform any PKIX epixry checks.
1.2. Applicability o The TLS client and server public key is provisioned into the
operating system firmware image, and updated via software updates.
The Transport Layer Security (TLS) Protocol Version 1.2 is specified Some smart objects use the UDP-based Constrained Application Protocol
in [RFC5246] and provides a framework for extensions to TLS as well (CoAP) [I-D.ietf-core-coap] to interact with a Web server to upload
as considerations for designing such extensions. [RFC6066] defines sensor data at a regular intervals, such as temperature readings.
several new TLS extensions. This document extends the specifications CoAP [I-D.ietf-core-coap] can utilize DTLS for securing the client-
of those RFCs with one new TLS Certificate Type to facilitate to-server communication. As part of the manufacturing process, the
suppressing unneeded [PKIX] information from being sent during the embeded device may be configured with the address and the public key
TLS handshake when this information is not required to authenticate of a dedicated CoAP server, as well as a public key for the client
the TLS server. itself. The usage of X.509-based PKIX certificates [PKIX] may not
suit all smart object deployments and would therefore be an
unneccesarry burden.
1.3. Terminology The Transport Layer Security (TLS) Protocol Version 1.2 [RFC5246]
provides a framework for extensions to TLS as well as guidelines for
designing such extensions. This document uses the TLS Certificate
Type extension point to define a new non-X.509 certificate type for
carrying raw public keys.
Most security-related terms in this document are to be understood in 2. Terminology
the sense defined in [SECTERMS]; such terms include, but are not
limited to, "attack", "authentication", "authorization",
"certification authority", "certification path", "certificate",
"credential", "identity", "self-signed certificate", "trust", "trust
anchor", "trust chain", "validate", and "verify".
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Changes to the Handshake Message Contents 3. TLS Handshake Extension
This section describes the changes to the TLS handshake message This section describes the changes to the TLS handshake message
contents when raw public keys are to be used for authentication. contents when raw public key certificates are to be used. Figure 1
Figure 1 illustrates the exchange of messages as described in the illustrates the exchange of messages as described in the sub-sections
sub-sections below. The new "RawPublicKey" value in the cert_type below. The new "RawPublicKey" value in the cert_type extension
extension indicates the ability and desire to exchange raw public indicates the ability and desire to exchange raw public keys, which
keys, which are then exchanged as part of the certificate payloads. are then exchanged as part of the certificate payloads. Note that
the certificate payloads only contain the SubjectPublicKeyInfo
structure instead of the entire certificate.
client_hello, client_hello,
cert_type="RawPublicKey" -> cert_type="RawPublicKey" ->
<- server_hello, <- server_hello,
cert_type="RawPublicKey", cert_type="RawPublicKey",
certificate, certificate,
server_key_exchange, server_key_exchange,
certificate_request, certificate_request,
server_hello_done server_hello_done
skipping to change at page 6, line 28 skipping to change at page 5, line 39
change_cipher_spec, change_cipher_spec,
finished -> finished ->
<- change_cipher_spec, <- change_cipher_spec,
finished finished
Application Data <-------> Application Data Application Data <-------> Application Data
Figure 1: Example Message Flow Figure 1: Example Message Flow
2.1. Client Hello 3.1. Client Hello
In order to indicate the support of out-of-band raw public keys, In order to indicate the support of out-of-band raw public keys,
clients MUST include an extension of type "cert_type" to the extended clients MUST include an extension of type "cert_type" to the extended
client hello message. The "cert_type" TLS extension, which is client hello message. The "cert_type" TLS extension, which is
defined in [RFC6091], is assigned the value of 9 from the TLS defined in [RFC6091], is assigned the value of 9 from the TLS
ExtensionType registry. This value is used as the extension number ExtensionType registry. This value is used as the extension number
for the extensions in both the client hello message and the server for the extensions in both the client hello message and the server
hello message. The hello extension mechanism is described in hello message. The hello extension mechanism is described in
[RFC5246]. [RFC5246].
skipping to change at page 7, line 24 skipping to change at page 6, line 36
CertificateType certificate_types<1..2^8-1>; CertificateType certificate_types<1..2^8-1>;
case server: case server:
CertificateType certificate_type; CertificateType certificate_type;
} }
} CertificateTypeExtension; } CertificateTypeExtension;
No new cipher suites are required to use raw public keys. All No new cipher suites are required to use raw public keys. All
existing cipher suites that support a key exchange method compatible existing cipher suites that support a key exchange method compatible
with the defined extension can be used. with the defined extension can be used.
2.2. Server Hello 3.2. Server Hello
If the server receives a client hello that contains the "cert_type" If the server receives a client hello that contains the "cert_type"
extension and chooses a cipher suite then two outcomes are possible. extension and chooses a cipher suite then two outcomes are possible.
The server MUST either select a certificate type from the The server MUST either select a certificate type from the
certificate_types field in the extended client hello or terminate the CertificateType field in the extended client hello or terminate the
session with a fatal alert of type "unsupported_certificate". session with a fatal alert of type "unsupported_certificate".
The certificate type selected by the server is encoded in a The certificate type selected by the server is encoded in a
CertificateTypeExtension structure, which is included in the extended CertificateTypeExtension structure, which is included in the extended
server hello message using an extension of type "cert_type". Servers server hello message using an extension of type "cert_type". Servers
that only support X.509 certificates MAY omit including the that only support X.509 certificates MAY omit including the
"cert_type" extension in the extended server hello. "cert_type" extension in the extended server hello.
If the negotiated certificate type is RawPublicKey the TLS server If the negotiated certificate type is RawPublicKey the TLS server
MUST send a CertificateTypeExtension structure with a PKIX [PKIX] MUST place the SubjectPublicKeyInfo structure into the Certificate
certificate containing ONLY the SubjectPublicKeyInfo. The public key payload. The public key MUST match the selected key exchange
MUST match the selected key exchange algorithm. algorithm.
2.3. Certificate Request 3.3. Certificate Request
The semantics of this message remain the same as in the TLS The semantics of this message remain the same as in the TLS
specification. However, if this message is sent, and the negotiated specification.
certificate type is RawPublicKey, the "certificate_authorities" list
MUST be empty.
2.4. Other Handshake Messages 3.4. Other Handshake Messages
All the other handshake messages are identical to the TLS All the other handshake messages are identical to the TLS
specification. specification.
3. Security Considerations 4. Security Considerations
The TLS cert_type extension defined here lets a TLS client attempt to
supress the sending of server certificate as well as the
certification chain for that certificate.
A client using this cert_type needs to be confident in the The transmission of raw public keys, as described in this document,
authenticity of the public key it is using. Since those public keys provides benefits by lowering the over-the-air transmission overhead
were obtained out-of-band extension), the authentication must also be since raw public keys are quite naturally smaller than an entire
out-of-band. certificate. There are also advantages from a codesize point of view
for parsing and processing these keys. The crytographic procedures
for assocating the public key with the possession of a private key
also follows standard procedures.
Depending on exactly how the public keys were obtained, it may be The main security challenge is, however, how to associate the public
appropriate to use authentication mechanisms tied to the public key key with a specific entity. This information will be needed to make
transport. For example, if public keys were obtained using [DANE] it authorization decisions. Without a secure binding, man-in-the-middle
is appropriate to use DNSSEC to authenticate the public keys. attacks may be the consequence. This document assumes that such
binding can be made out-of-band and we list a few examples in
Section 1. DANE [I-D.ietf-dane-protocol] offers one such approach.
If public keys are obtained using DANE, these public keys are
authenticated via DNSSEC. Pre-configured keys is another out of band
method for authenticating raw public keys. While pre-configured keys
are not suitable for a generic Web-based e-commerce environment such
keys are a reasonable approach for many smart object deployments
where there is a close relationship between the software running on
the device and the server-side communication endpoint. Regardless of
the chosen mechanism for out-of-band public key validation an
assessment of the most suitable approach has to be made prior to the
start of a deployment to ensure the security of the system.
4. IANA Considerations 5. IANA Considerations
We request that IANA assign a TLS cert_type value for RawPublicKey. This document requests IANA to assign a TLS cert_type value for
RawPublicKey. The cert_type registry is established with [RFC6091].
5. Contributors 6. Contributors
The following individuals made important contributions to this The following individuals made important contributions to this
document: Paul Hoffman. document: Paul Hoffman.
6. Acknowledgements 7. Acknowledgements
This document is based on material from RFC 6066 for which the author
is Donald Eastlake 3rd. Contributions to that document also include
Joseph Salowey, Alexey Melnikov, Peter Saint-Andre, and Adrian
Farrel.
The feedback from the TLS working group meeting at IETF#81 has The feedback from the TLS working group meeting at IETF#81 has
substantially shaped the document and we would like to thank the substantially shaped the document and we would like to thank the
meeting participants for their input. The support for hashes of meeting participants for their input. The support for hashes of
public keys has been removed after the discussions at the IETF#82 public keys has been moved to [I-D.ietf-tls-cached-info] after the
meeting and the feedback from Eric Rescorla. discussions at the IETF#82 meeting and the feedback from Eric
Rescorla.
7. References We would like to thank Martin Rex, Bill Frantz, Zach Shelby, Carsten
Bormann, Cullen Jennings, Rene Struik, Alper Yegin, and Jim Schaad.
7.1. Normative References 8. References
8.1. Normative References
[PKIX] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [PKIX] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008. (CRL) Profile", RFC 5280, May 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
[SECTERMS] 8.2. Informative References
Shirey, R., "Internet Security Glossary, Version 2",
RFC 4949, August 2007.
7.2. Informative References
[CoAP] Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
"Constrained Application Protocol",
draft-ietf-core-coap-07 (work in progress), July 2011.
[DANE] Hoffman, P. and J. Schlyter, "Using Secure DNS to
Associate Certificates with Domain Names For TLS",
draft-ietf-dane-protocol-14 (work in progress),
September 2011.
[Defeating-SSL] [Defeating-SSL]
Marlinspike, M., "New Tricks for Defeating SSL in Marlinspike, M., "New Tricks for Defeating SSL in
Practice", February 2009, <http://www.blackhat.com/ Practice", February 2009, <http://www.blackhat.com/
presentations/bh-dc-09/Marlinspike/ presentations/bh-dc-09/Marlinspike/
BlackHat-DC-09-Marlinspike-Defeating-SSL.pdf>. BlackHat-DC-09-Marlinspike-Defeating-SSL.pdf>.
[I-D.ietf-core-coap]
Frank, B., Bormann, C., Hartke, K., and Z. Shelby,
"Constrained Application Protocol (CoAP)",
draft-ietf-core-coap-08 (work in progress), October 2011.
[I-D.ietf-dane-protocol]
Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Protocol for Transport Layer
Security (TLS)", draft-ietf-dane-protocol-18 (work in
progress), March 2012.
[I-D.ietf-tls-cached-info]
Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension",
draft-ietf-tls-cached-info-11 (work in progress),
December 2011.
[LDAP] Sermersheim, J., "Lightweight Directory Access Protocol [LDAP] Sermersheim, J., "Lightweight Directory Access Protocol
(LDAP): The Protocol", RFC 4511, June 2006. (LDAP): The Protocol", RFC 4511, June 2006.
[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011.
[RFC6091] Mavrogiannopoulos, N. and D. Gillmor, "Using OpenPGP Keys [RFC6091] Mavrogiannopoulos, N. and D. Gillmor, "Using OpenPGP Keys
for Transport Layer Security (TLS) Authentication", for Transport Layer Security (TLS) Authentication",
RFC 6091, February 2011. RFC 6091, February 2011.
Authors' Addresses Authors' Addresses
Paul Wouters Paul Wouters
No Hats Corporation No Hats Corporation
Email: paul@nohats.ca Email: paul@nohats.ca
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