draft-ietf-tls-cached-info-13.txt   draft-ietf-tls-cached-info-14.txt 
TLS S. Santesson TLS S. Santesson
Internet-Draft 3xA Security AB Internet-Draft 3xA Security AB
Intended status: Standards Track H. Tschofenig Intended status: Standards Track H. Tschofenig
Expires: March 16, 2013 Nokia Siemens Networks Expires: September 29, 2013 Nokia Siemens Networks
September 12, 2012 March 28, 2013
Transport Layer Security (TLS) Cached Information Extension Transport Layer Security (TLS) Cached Information Extension
draft-ietf-tls-cached-info-13.txt draft-ietf-tls-cached-info-14.txt
Abstract Abstract
Transport Layer Security (TLS) handshakes often include fairly static Transport Layer Security (TLS) handshakes often include fairly static
information, such as the server certificate and a list of trusted information, such as the server certificate and a list of trusted
Certification Authorities (CAs). This information can be of Certification Authorities (CAs). This information can be of
considerable size, particularly if the server certificate is bundled considerable size, particularly if the server certificate is bundled
with a complete certificate path (including all intermediary with a complete certificate path (including all intermediary
certificates up to the trust anchor public key). certificates up to the trust anchor public key).
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 16, 2013. This Internet-Draft will expire on September 29, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Cached Information Extension . . . . . . . . . . . . . . . . . 5 3. Cached Information Extension . . . . . . . . . . . . . . . . . 5
4. Exchange Specification . . . . . . . . . . . . . . . . . . . . 7 4. Exchange Specification . . . . . . . . . . . . . . . . . . . . 7
4.1. Fingerprint of the Certificate Chain . . . . . . . . . . . 7 4.1. Omitting the Certificate Chain . . . . . . . . . . . . . . 7
4.2. Fingerprint for Trusted CAs . . . . . . . . . . . . . . . 8 4.2. Omitting the Trusted CAs . . . . . . . . . . . . . . . . . 8
5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7.1. New Entry to the TLS ExtensionType Registry . . . . . . . 13 7.1. New Entry to the TLS ExtensionType Registry . . . . . . . 12
7.2. New Registry for CachedInformationType . . . . . . . . . . 13 7.2. New Registry for CachedInformationType . . . . . . . . . . 12
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . . 15 9.1. Normative References . . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . . 15 9.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
Transport Layer Security (TLS) handshakes often include fairly static Transport Layer Security (TLS) handshakes often include fairly static
information, such as the server certificate and a list of trusted information, such as the server certificate and a list of trusted
Certification Authorities (CAs). This information can be of Certification Authorities (CAs). This information can be of
considerable size, particularly if the server certificate is bundled considerable size, particularly if the server certificate is bundled
with a complete certificate path (including all intermediary with a complete certificate path (including all intermediary
certificates up to the trust anchor public key). certificates up to the trust anchor public key).
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rate. These types of networks exist, for example, when smart objects rate. These types of networks exist, for example, when smart objects
are connected using a low power IEEE 802.15.4 radio. For more are connected using a low power IEEE 802.15.4 radio. For more
information about the challenges with smart object deployments please information about the challenges with smart object deployments please
see [RFC6574]. see [RFC6574].
This specification defines a TLS extension that allows a client and a This specification defines a TLS extension that allows a client and a
server to exclude transmission of cached information from the TLS server to exclude transmission of cached information from the TLS
handshake. handshake.
A typical example exchange may therefore look as follows. First, the A typical example exchange may therefore look as follows. First, the
TLS exchange executes the usual TLS handshake. It may decide to client and the server executes the usual TLS handshake. The client
store the certificate provided by the server for a future exchange. may, for example, decide to cache the certificate provided by the
When the TLS client then connects to the TLS server some time in the server. When the TLS client connects to the TLS server some time in
future, without using session resumption, it then attaches the the future, without using session resumption, it then attaches the
cached_information extension defined in this document to the client cached_information extension defined in this document to the client
hello message to indicate that it had cached the certificate, and it hello message to indicate that it had cached the certificate, and it
provides the fingerprint of it. If the server's certificate had not provides the fingerprint of it. If the server's certificate had not
changed then the TLS server does not need to send the full changed then the TLS server does not need to send the full
certificate to the client again. In case the information had certificate to the client again. In case the information had
changed, the certificate payload is transmitted to the client to changed, the certificate payload is transmitted to the client to
allow the client to update it's state information. allow the client to update it's state information.
2. Terminology 2. Terminology
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This document establishes a registry for CachedInformationType types This document establishes a registry for CachedInformationType types
and additional values can be added following the policy described in and additional values can be added following the policy described in
Section 7. Section 7.
4. Exchange Specification 4. Exchange Specification
Clients supporting this extension MAY include the Clients supporting this extension MAY include the
"cached_information" extension in the (extended) client hello, which "cached_information" extension in the (extended) client hello, which
MAY contain zero or more CachedObject attributes. MAY contain zero or more CachedObject attributes.
Server supporting this extension MAY include the "cached_information" A server supporting this extension MAY include the
extension in the (extended) server hello, which MAY contain one or "cached_information" extension in the (extended) server hello, which
more CachedObject attributes. By returning the "cached_information" MAY contain one or more CachedObject attributes it supports. By
extension the server indicates that it supports caching of each returning the "cached_information" extension the server indicates
present CachedObject that matches the specified hash value. The that it supports caching of each present CachedObject that matches
server MAY support other cached objects that are not present in the the specified hash value. The server MAY support other cached
extension. objects that are not present in the extension.
Note: Clients may need the ability to cache different values Note: If clients make use of the Server Name Indication [RFC6066]
depending on other information in the Client Hello that modify what then clients may need to cache multiple data items for a single
values the server uses, in particular the Server Name Indication server since servers may host multiple 'virtual' servers at a single
[RFC6066] value. underlying network address.
Following a successful exchange of "cached_information" extensions, Following a successful exchange of the "cached_information"
the server MAY send fingerprints of the cached information in the extensions in the client and server hello, the server omits sending
handshake exchange as a replacement for the exchange of the full the corresponding handshake message. How information is omitted from
data. Section 4.1 and Section 4.2 defines the syntax of the the handshake message is defined per cached info type. Section 4.1
fingerprinted information. and Section 4.2 defines the syntax of the fingerprinted information.
The handshake protocol MUST proceed using the information as if it The handshake protocol MUST proceed using the information as if it
was provided in the handshake protocol. The Finished message MUST be was provided in the handshake protocol. The Finished message MUST be
calculated over the actual data exchanged in the handshake protocol. calculated over the actual data exchanged in the handshake protocol.
That is, the Finished message will be calculated over the hash values That is, the Finished message will be calculated over the information
of cached information objects and not over the cached information that was omitted from transmission by means of its present hash in
that were omitted from transmission. the client hello and not through its presence in the handshake
exchange.
The server MUST NOT include more than one fingerprint for a single The server MUST NOT include more than one fingerprint for a single
information element, i.e., at maximum only one CachedObject structure information element, i.e., at maximum only one CachedObject structure
per replaced information is provided. per replaced information is provided.
4.1. Fingerprint of the Certificate Chain 4.1. Omitting the Certificate Chain
When an object of type 'certificate_chain' is provided in the client When an object of type 'certificate_chain' is provided in the client
hello, the server MAY send a fingerprint instead of the complete hello, the server MAY replace the sequence of certificates with an
certificate chain as shown below. empty sequence with an actual length field of zero (=empty vector).
The original handshake message syntax is defined in RFC 5246 The original handshake message syntax is defined in RFC 5246
[RFC5246] and has the following structure: [RFC5246] and has the following structure:
opaque ASN.1Cert<1..2^24-1>; opaque ASN.1Cert<1..2^24-1>;
struct { struct {
ASN.1Cert certificate_list<0..2^24-1>; ASN.1Cert certificate_list<0..2^24-1>;
} Certificate; } Certificate;
By using the extension defined in this document the following Note that [I-D.ietf-tls-oob-pubkey] allows the certificate payload to
information is sent: contain only the SubjectPublicKeyInfo instead of the full information
struct {
CachedObject cached_objects<1..2^24-1>;
} Certificate;
The certificate_list vector of opaque ASN.1Cert elements in the
original syntax is replaced with a vector holding CachedObject
structures as defined in this document.
Note: [I-D.ietf-tls-oob-pubkey] allows a PKIX certificate containing
only the SubjectPublicKeyInfo instead of the full information
typically found in a certificate. Hence, when this specification is typically found in a certificate. Hence, when this specification is
used in combination with [I-D.ietf-tls-oob-pubkey] and the negotiated used in combination with [I-D.ietf-tls-oob-pubkey] and the negotiated
certificate type is a raw public key then the TLS server sends the certificate type is a raw public key then the TLS server omits
hashed Certificate payload that contains a ASN.1Cert structure of the sending a Certificate payload that contains an ASN.1Cert structure of
SubjectPublicKeyInfo. the SubjectPublicKeyInfo.
4.2. Fingerprint for Trusted CAs 4.2. Omitting the Trusted CAs
When a hash for an object of type 'trusted_cas' is provided in the When a fingerprint for an object of type 'trusted_cas' is provided in
client hello, the server MAY send a fingerprint instead of the the client hello, the server MAY send a DistinguishedName in the
complete certificate authorities information as shown below. Certificate Request message with an actual length field of zero
(=empty vector).
The original handshake message syntax is defined in RFC 5246 The original handshake message syntax is defined in RFC 5246
[RFC5246] and has the following structure: [RFC5246] and has the following structure:
opaque DistinguishedName<1..2^16-1>; opaque DistinguishedName<1..2^16-1>;
struct { struct {
ClientCertificateType certificate_types<1..2^8-1>; ClientCertificateType certificate_types<1..2^8-1>;
SignatureAndHashAlgorithm SignatureAndHashAlgorithm
supported_signature_algorithms<2^16-1>; supported_signature_algorithms<2^16-1>;
DistinguishedName certificate_authorities<0..2^16-1>; DistinguishedName certificate_authorities<0..2^16-1>;
} CertificateRequest; } CertificateRequest;
By using the extension defined in this document the following
information is sent:
struct {
ClientCertificateType certificate_types<1..2^8-1>;
SignatureAndHashAlgorithm
supported_signature_algorithms<2^16-1>;
CachedObject cached_objects<1..2^16-1>;
} CertificateRequest;
The certificate_authorities vector of opaque DistinguishedName
elements in the original syntax is replaced with a vector holding
CachedObject structures as defined in this document.
5. Example 5. Example
Figure 1 illustrates an example exchange using the TLS cached info Figure 1 illustrates an example exchange using the TLS cached info
extension. In the normal TLS handshake exchange shown in flow (A) extension. In the normal TLS handshake exchange shown in flow (A)
the TLS server provides its certificate in the Certificate payload to the TLS server provides its certificate in the Certificate payload to
the client, see step [1]. This allows the client to store the the client, see step [1]. This allows the client to store the
certificate for future use. After some time the TLS client again certificate for future use. After some time the TLS client again
interacts with the same TLS server and makes use of the TLS cached interacts with the same TLS server and makes use of the TLS cached
info extension, as shown in flow (B). The TLS client indicates info extension, as shown in flow (B). The TLS client indicates
support for this specification via the cached_information extension, support for this specification via the cached_information extension,
see [2], and indicates that it has stored the certificate_chain from see [2], and indicates that it has stored the certificate_chain from
the earlier exchange. With [3] the TLS server indicates that it also the earlier exchange. With [3] the TLS server indicates that it also
supports this specification and informs the client that it also supports this specification and informs the client that it also
supports caching of other objects beyond the 'certificate_chain', supports caching of other objects beyond the 'certificate_chain',
namely 'trusted_cas' (also defined in this document), and the 'foo- namely 'trusted_cas' (also defined in this document), and the 'foo-
bar' extension (i.e., an imaginary extension that yet needs to be bar' extension (i.e., an imaginary extension that yet needs to be
defined). With [4] the TLS server provides the fingerprint of the defined). With [4] the TLS server omits sending the certificate
certificate chain as described in Section 4.1. chain, as described in Section 4.1.
(A) Initial (full) Exchange (A) Initial (full) Exchange
client_hello -> client_hello ->
<- server_hello, <- server_hello,
certificate, // [1] certificate, // [1]
server_key_exchange, server_key_exchange,
server_hello_done server_hello_done
client_key_exchange, client_key_exchange,
change_cipher_spec, change_cipher_spec,
finished -> finished ->
<- change_cipher_spec, <- change_cipher_spec,
finished finished
Application Data <-------> Application Data Application Data <-------> Application Data
(B) TLS Cached Extension Usage (B) TLS Cached Extension Usage
client_hello, client_hello,
cached_information=(certificate_chain) -> // [2] cached_information=(certificate_chain) -> // [2]
<- server_hello, <- server_hello,
cached_information= // [3] cached_information= // [3]
(certificate_chain, trusted_cas, foo-bar) (certificate_chain, trusted_cas, foo-bar)
certificate, // [4] certificate, // [4]
server_key_exchange, server_key_exchange,
server_hello_done server_hello_done
client_key_exchange, client_key_exchange,
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 Exchange Figure 1: Example Message Exchange
6. Security Considerations 6. Security Considerations
This specification defines a mechanism to reference stored state This specification defines a mechanism to reference stored state
using a fingerprint. The hash algorithm used in this specification using a fingerprint. Sending a fingerprint of cached information in
is required to have reasonable random properties in order to provide an unencrypted handshake, as the client and server hello is, may
reasonably unique identifiers. There is no requirement that this allow an attacker or observer to correlate independent TLS exchanges.
hash algorithm must have strong collision resistance. While some information elements used in this specification, such as
server certificates, are public objects and usually not sensitive in
this regard, others may be. Those who implement and deploy this
specification should therefore make an informed decision whether the
cached information is inline with their security and privacy goals.
In case of concerns, it is advised to avoid sending the fingerprint
of the data objects in clear.
Caching information in an encrypted handshake (such as a renegotiated The hash algorithm used in this specification is required to have
handshake) and sending a hash of that cached information in an reasonable random properties in order to provide reasonably unique
unencrypted handshake might introduce integrity or data disclosure identifiers. There is no requirement that this hash algorithm must
issues as it enables an attacker to identify if a known object (such have strong collision resistance.
as a known server certificate) has been used in previous encrypted
handshakes. Information object types defined in this specification,
such as server certificates, are public objects and usually not
sensitive in this regard, but implementers should be aware if any
cached information are subject to such security concerns and in such
case SHOULD NOT send a hash over encrypted data in unencrypted
handshake.
7. IANA Considerations 7. IANA Considerations
7.1. New Entry to the TLS ExtensionType Registry 7.1. New Entry to the TLS ExtensionType Registry
IANA is requested to add an entry to the existing TLS ExtensionType IANA is requested to add an entry to the existing TLS ExtensionType
registry, defined in RFC 5246 [RFC5246], for cached_information(TBD) registry, defined in RFC 5246 [RFC5246], for cached_information(TBD)
defined in this document. defined in this document.
7.2. New Registry for CachedInformationType 7.2. New Registry for CachedInformationType
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8. Acknowledgments 8. Acknowledgments
We would like to thank the following persons for your detailed We would like to thank the following persons for your detailed
document reviews: document reviews:
o Paul Wouters and Nikos Mavrogiannopoulos (December 2011) o Paul Wouters and Nikos Mavrogiannopoulos (December 2011)
o Rob Stradling (February 2012) o Rob Stradling (February 2012)
o Ondrej Mikle in March 2012) o Ondrej Mikle (in March 2012)
Additionally, we would like to thank the TLS working group chairs, Additionally, we would like to thank the TLS working group chairs,
Eric Rescorla and Joe Salowey, as well as the security area Eric Rescorla and Joe Salowey, as well as the security area
directors, Sean Turner and Stephen Farrell, for their feedback and directors, Sean Turner and Stephen Farrell, for their feedback and
support. support.
9. References 9. References
9.1. Normative References 9.1. Normative References
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[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.
[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions: [RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011. Extension Definitions", RFC 6066, January 2011.
9.2. Informative References 9.2. Informative References
[I-D.ietf-tls-oob-pubkey] [I-D.ietf-tls-oob-pubkey]
Wouters, P., Gilmore, J., Weiler, S., Kivinen, T., and H. Wouters, P., Tschofenig, H., Gilmore, J., Weiler, S., and
Tschofenig, "Out-of-Band Public Key Validation for T. Kivinen, "Out-of-Band Public Key Validation for
Transport Layer Security", draft-ietf-tls-oob-pubkey-04 Transport Layer Security (TLS)",
(work in progress), July 2012. draft-ietf-tls-oob-pubkey-07 (work in progress),
February 2013.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008. May 2008.
[RFC6574] Tschofenig, H. and J. Arkko, "Report from the Smart Object [RFC6574] Tschofenig, H. and J. Arkko, "Report from the Smart Object
Workshop", RFC 6574, April 2012. Workshop", RFC 6574, April 2012.
Authors' Addresses Authors' Addresses
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