Internet DRAFT - draft-ietf-tls-cached-info
draft-ietf-tls-cached-info
TLS S. Santesson
Internet-Draft 3xA Security AB
Intended status: Standards Track H. Tschofenig
Expires: November 12, 2016 ARM Ltd.
May 11, 2016
Transport Layer Security (TLS) Cached Information Extension
draft-ietf-tls-cached-info-23.txt
Abstract
Transport Layer Security (TLS) handshakes often include fairly static
information, such as the server certificate and a list of trusted
certification authorities (CAs). This information can be of
considerable size, particularly if the server certificate is bundled
with a complete certificate chain (i.e., the certificates of
intermediate CAs up to the root CA).
This document defines an extension that allows a TLS client to inform
a server of cached information, allowing the server to omit already
available information.
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 November 12, 2016.
Copyright Notice
Copyright (c) 2016 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
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Cached Information Extension . . . . . . . . . . . . . . . . 3
4. Exchange Specification . . . . . . . . . . . . . . . . . . . 5
4.1. Server Certificate Message . . . . . . . . . . . . . . . 5
4.2. CertificateRequest Message . . . . . . . . . . . . . . . 6
5. Fingerprint Calculation . . . . . . . . . . . . . . . . . . . 7
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8.1. New Entry to the TLS ExtensionType Registry . . . . . . . 10
8.2. New Registry for CachedInformationType . . . . . . . . . 10
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. Normative References . . . . . . . . . . . . . . . . . . 11
10.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
Reducing the amount of information exchanged during a Transport Layer
Security handshake to a minimum helps to improve performance in
environments where devices are connected to a network with a low
bandwidth, and lossy radio technology. With Internet of Things such
environments exist, for example, when devices use IEEE 802.15.4 or
Bluetooth Smart. For more information about the challenges with
smart object deployments please see [RFC6574].
This specification defines a TLS extension that allows a client and a
server to exclude transmission information cached in an earlier TLS
handshake.
A typical example exchange may therefore look as follows. First, the
client and the server executes the full TLS handshake. The client
then caches the certificate provided by the server. When the TLS
client connects to the TLS server some time in the future, without
using session resumption, it then attaches the cached_info extension
defined in this document to the client hello message to indicate that
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it had cached the certificate, and it provides the fingerprint of it.
If the server's certificate has not changed then the TLS server does
not need to send its certificate and the corresponding certificate
chain again. In case information has changed, which can be seen from
the fingerprint provided by the client, the certificate payload is
transmitted to the client to allow the client to update the cache.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "MUST", "MUST NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This document refers to the TLS protocol but the description is
equally applicable to DTLS as well.
3. Cached Information Extension
This document defines a new extension type (cached_info(TBD)), which
is used in client hello and server hello messages. The extension
type is specified as follows.
enum {
cached_info(TBD), (65535)
} ExtensionType;
The extension_data field of this extension, when included in the
client hello, MUST contain the CachedInformation structure. The
client MAY send multiple CachedObjects of the same
CachedInformationType. This may, for example, be the case when the
client has cached multiple certificates from a server.
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enum {
cert(1), cert_req(2) (255)
} CachedInformationType;
struct {
select (type) {
case client:
CachedInformationType type;
opaque hash_value<1..255>;
case server:
CachedInformationType type;
} body;
} CachedObject;
struct {
CachedObject cached_info<1..2^16-1>;
} CachedInformation;
This document defines the following two types:
'cert' Type for not sending the complete Server Certificate Message:
With the type field set to 'cert', the client MUST include the
fingerprint of the Certificate message in the hash_value field.
For this type the fingerprint MUST be calculated using the
procedure described in Section 5 with the Certificate message as
input data.
'cert_req' Type for not sending the complete CertificateRequest
Message:
With the type set to 'cert_req', the client MUST include the
fingerprint of the CertificateRequest message in the hash_value
field. For this type the fingerprint MUST be calculated using the
procedure described in Section 5 with the CertificateRequest
message as input data.
New cached info types can be added following the policy described in
the IANA considerations section, see Section 8. New message digest
algorithms for use with these types can also be added by registering
a new type that makes use of the updated message digest algorithm.
For practical reasons we recommend to re-use hash algorithms already
available with TLS ciphersuites to avoid additional code and to keep
the collision probably low new hash algorithms MUST NOT have a
collision resistance worse than SHA-256.
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4. Exchange Specification
Clients supporting this extension MAY include the "cached_info"
extension in the (extended) client hello. If the client includes the
extension then it MUST contain one or more CachedObject attributes.
A server supporting this extension MAY include the "cached_info"
extension in the (extended) server hello. By returning the
"cached_info" extension the server indicates that it supports the
cached info types. For each indicated cached info type the server
MUST alter the transmission of respective payloads, according to the
rules outlined with each type. If the server includes the extension
it MUST only include CachedObjects of a type also supported by the
client (as expressed in the client hello). For example, if a client
indicates support for 'cert' and 'cert_req' then the server cannot
respond with a "cached_info" attribute containing support for ('foo-
bar').
Since the client includes a fingerprint of information it cached (for
each indicated type) the server is able to determine whether cached
information is stale. If the server supports this specification and
notices a mismatch between the data cached by the client and its own
information then the server MUST include the information in full and
MUST NOT list the respective type in the "cached_info" extension.
Note: If a server is part of a hosting environment then the client
may have cached multiple data items for a single server. To allow
the client to select the appropriate information from the cache it is
RECOMMENDED that the client utilizes the Server Name Indication
extension [RFC6066].
Following a successful exchange of the "cached_info" extension in the
client and server hello, the server alters sending the corresponding
handshake message. How information is altered from the handshake
messages is defined in Section 4.1, and in Section 4.2 for the types
defined in this specification.
Appendix A shows an example hash calculation and Section 6 shows an
example protocol exchange.
4.1. Server Certificate Message
When a ClientHello message contains the "cached_info" extension with
a type set to 'cert' then the server MAY send the Certificate message
shown in Figure 1 under the following conditions:
o The server software implements the "cached_info" extension defined
in this specification.
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o The 'cert' cached info extension is enabled (for example, a policy
allows the use of this extension).
o The server compared the value in the hash_value field of the
client-provided "cached_info" extension with the fingerprint of
the Certificate message it normally sends to clients. This check
ensures that the information cached by the client is current. The
procedure for calculating the fingerprint is described in
Section 5.
The original Certificate handshake message syntax is defined in
[RFC5246] and has been extended with [RFC7250]. RFC 7250 allows the
certificate payload to contain only the SubjectPublicKeyInfo instead
of the full information typically found in a certificate. Hence,
when this specification is used in combination with [RFC7250] and the
negotiated certificate type is a raw public key then the TLS server
omits sending a Certificate payload that contains an ASN.1
Certificate structure with the included SubjectPublicKeyInfo rather
than the full certificate chain. As such, this extension is
compatible with the raw public key extension defined in RFC 7250.
Note: We assume that the server implementation is able to select the
appropriate certificate or SubjectPublicKeyInfo from the received
hash value. If the SNI extension is used by the client then the
server has additional information to guide the selection of the
appropriate cached info.
When the cached info specification is used then a modified version of
the Certificate message is exchanged. The modified structure is
shown in Figure 1.
struct {
opaque hash_value<1..255>;
} Certificate;
Figure 1: Cached Info Certificate Message.
4.2. CertificateRequest Message
When a fingerprint for an object of type 'cert_req' is provided in
the client hello, the server MAY send the CertificateRequest message
shown in Figure 2 message under the following conditions:
o The server software implements the "cached_info" extension defined
in this specification.
o The 'cert_req' cached info extension is enabled (for example, a
policy allows the use of this extension).
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o The server compared the value in the hash_value field of the
client-provided "cached_info" extension with the fingerprint of
the CertificateRequest message it normally sends to clients. This
check ensures that the information cached by the client is
current. The procedure for calculating the fingerprint is
described in Section 5.
o The server wants to request a certificate from the client.
The original CertificateRequest handshake message syntax is defined
in [RFC5246]. The modified structure of the CertificateRequest
message is shown in Figure 2.
struct {
opaque hash_value<1..255>;
} CertificateRequest;
Figure 2: Cached Info CertificateRequest Message.
The CertificateRequest payload is the input parameter to the
fingerprint calculation described in Section 5.
5. Fingerprint Calculation
The fingerprint for the two cached info objects defined in this
document MUST be computed as follows:
1. Compute the SHA-256 [RFC6234] hash of the input data. The input
data depends on the cached info type. This document defines two
cached info types, described in Section 4.1 and in Section 4.2.
Note that the computed hash only covers the input data structure
(and not any type and length information of the record layer).
Appendix A shows an example.
2. Use the output of the SHA-256 hash.
The purpose of the fingerprint provided by the client is to help the
server select the correct information. For example, in case of the
certificate message the fingerprint identifies the server certificate
(and the corresponding private key) for use for with the rest of the
handshake. Servers may have more than one certificate and therefore
a hash needs to be long enough to keep the probably of hash
collisions low. On the other hand, the cached info design aims to
reduce the amount of data being exchanged. The security of the
handshake depends on the private key and not on the size of the
fingerprint. Hence, the fingerprint is a way to prevent the server
from accidentally selecting the wrong information. If an attacker
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injects an incorrect fingerprint then two outcomes are possible: (1)
The fingerprint does not relate to any cached state and the server
has to fall back to a full exchange. (2) If the attacker manages to
inject a fingerprint that refers to data the client has not cached
then the exchange will fail later when the client continues with the
handshake and aims to verify the digital signature. The signature
verification will fail since the public key cached by the client will
not correspond to the private key that was used by server to sign the
message.
6. Example
In the regular, full TLS handshake exchange, shown in Figure 3, the
TLS server provides its certificate in the Certificate payload to the
client, see step (1). This allows the client to store the
certificate for future use. After some time the TLS client again
interacts with the same TLS server and makes use of the TLS cached
info extension, as shown in Figure 4. The TLS client indicates
support for this specification via the "cached_info" extension, see
step (2), and indicates that it has stored the certificate from the
earlier exchange (by indicating the 'cert' type). With step (3) the
TLS server acknowledges the supports of the 'cert' type and by
including the value in the server hello informs the client that the
content of the certificate payload contains the fingerprint of the
certificate instead of the RFC 5246-defined payload of the
certificate message in step (4).
ClientHello ->
<- ServerHello
Certificate* // (1)
ServerKeyExchange*
CertificateRequest*
ServerHelloDone
Certificate*
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished ->
<- [ChangeCipherSpec]
Finished
Application Data <-------> Application Data
Figure 3: Example Message Exchange: Initial (full) Exchange.
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ClientHello
cached_info=(cert) -> // (2)
<- ServerHello
cached_info=(cert) (3)
Certificate (4)
ServerKeyExchange*
ServerHelloDone
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished ->
<- [ChangeCipherSpec]
Finished
Application Data <-------> Application Data
Figure 4: Example Message Exchange: TLS Cached Extension Usage.
7. Security Considerations
This specification defines a mechanism to reference stored state
using a fingerprint. Sending a fingerprint of cached information in
an unencrypted handshake, as the client and server hello is, may
allow an attacker or observer to correlate independent TLS exchanges.
While some information elements used in this specification, such as
server certificates, are public objects and usually do not contain
sensitive information, other not yet defined types may. 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.
The use of the cached info extension allows the server to send
significantly smaller TLS messages. Consequently, these omitted
parts of the messages are not included in the transcript of the
handshake in the TLS Finish message. However, since the client and
the server communicate the hash values of the cached data in the
initial handshake messages the fingerprints are included in the TLS
Finish message.
Clients MUST ensure that they only cache information from legitimate
sources. For example, when the client populates the cache from a TLS
exchange then it must only cache information after the successful
completion of a TLS exchange to ensure that an attacker does not
inject incorrect information into the cache. Failure to do so allows
for man-in-the-middle attacks.
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Security considerations for the fingerprint calculation are discussed
in Section 5.
8. IANA Considerations
8.1. New Entry to the TLS ExtensionType Registry
IANA is requested to add an entry to the existing TLS ExtensionType
registry, defined in [RFC5246], for cached_info(TBD) defined in this
document.
8.2. New Registry for CachedInformationType
IANA is requested to establish a registry for TLS
CachedInformationType values. The first entries in the registry are
o cert(1)
o cert_req(2)
The policy for adding new values to this registry, following the
terminology defined in [RFC5226], is as follows:
o 0-63 (decimal): Standards Action
o 64-223 (decimal): Specification Required
o 224-255 (decimal): reserved for Private Use
9. Acknowledgments
We would like to thank the following persons for your detailed
document reviews:
o Paul Wouters and Nikos Mavrogiannopoulos (December 2011)
o Rob Stradling (February 2012)
o Ondrej Mikle (March 2012)
o Ilari Liusvaara, Adam Langley, and Eric Rescorla (July 2014)
o Sean Turner (August 2014)
o Martin Thomson (August 2015)
o Jouni Korhonen (November 2015)
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o Matt Miller (December 2015)
We would also to thank Martin Thomson, Karthikeyan Bhargavan, Sankalp
Bagaria and Eric Rescorla for their feedback regarding the
fingerprint calculation.
Finally, we would like to thank the TLS working group chairs, Sean
Turner and Joe Salowey, as well as the responsible security area
director, Stephen Farrell, for their support and their reviews.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/
RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, DOI
10.17487/RFC6066, January 2011,
<http://www.rfc-editor.org/info/rfc6066>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI
10.17487/RFC6234, May 2011,
<http://www.rfc-editor.org/info/rfc6234>.
10.2. Informative References
[ASN.1-Dump]
Gutmann, P., "ASN.1 Object Dump Program", February 2013,
<http://www.cs.auckland.ac.nz/~pgut001/>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC6574] Tschofenig, H. and J. Arkko, "Report from the Smart Object
Workshop", RFC 6574, DOI 10.17487/RFC6574, April 2012,
<http://www.rfc-editor.org/info/rfc6574>.
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[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <http://www.rfc-editor.org/info/rfc7250>.
Appendix A. Example
Consider a certificate containing an NIST P256 elliptic curve public
key displayed using Peter Gutmann's ASN.1 decoder [ASN.1-Dump] in
Figure 5.
0 556: SEQUENCE {
4 434: SEQUENCE {
8 3: [0] {
10 1: INTEGER 2
: }
13 1: INTEGER 13
16 10: SEQUENCE {
18 8: OBJECT IDENTIFIER ecdsaWithSHA256 (1 2 840 10045 4 3 2)
: }
28 62: SEQUENCE {
30 11: SET {
32 9: SEQUENCE {
34 3: OBJECT IDENTIFIER countryName (2 5 4 6)
39 2: PrintableString 'NL'
: }
: }
43 17: SET {
45 15: SEQUENCE {
47 3: OBJECT IDENTIFIER organizationName (2 5 4 10)
52 8: PrintableString 'PolarSSL'
: }
: }
62 28: SET {
64 26: SEQUENCE {
66 3: OBJECT IDENTIFIER commonName (2 5 4 3)
71 19: PrintableString 'Polarssl Test EC CA'
: }
: }
: }
92 30: SEQUENCE {
94 13: UTCTime 24/09/2013 15:52:04 GMT
109 13: UTCTime 22/09/2023 15:52:04 GMT
: }
124 65: SEQUENCE {
126 11: SET {
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128 9: SEQUENCE {
130 3: OBJECT IDENTIFIER countryName (2 5 4 6)
135 2: PrintableString 'NL'
: }
: }
139 17: SET {
141 15: SEQUENCE {
143 3: OBJECT IDENTIFIER organizationName (2 5 4 10)
148 8: PrintableString 'PolarSSL'
: }
: }
158 31: SET {
160 29: SEQUENCE {
162 3: OBJECT IDENTIFIER commonName (2 5 4 3)
167 22: PrintableString 'PolarSSL Test Client 2'
: }
: }
: }
191 89: SEQUENCE {
193 19: SEQUENCE {
195 7: OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
204 8: OBJECT IDENTIFIER prime256v1 (1 2 840 10045 3 1 7)
: }
214 66: BIT STRING
: 04 57 E5 AE B1 73 DF D3 AC BB 93 B8 81 FF 12 AE
: EE E6 53 AC CE 55 53 F6 34 0E CC 2E E3 63 25 0B
: DF 98 E2 F3 5C 60 36 96 C0 D5 18 14 70 E5 7F 9F
: D5 4B 45 18 E5 B0 6C D5 5C F8 96 8F 87 70 A3 E4
: C7
: }
282 157: [3] {
285 154: SEQUENCE {
288 9: SEQUENCE {
290 3: OBJECT IDENTIFIER basicConstraints (2 5 29 19)
295 2: OCTET STRING, encapsulates {
297 0: SEQUENCE {}
: }
: }
299 29: SEQUENCE {
301 3: OBJECT IDENTIFIER subjectKeyIdentifier (2 5 29 14)
306 22: OCTET STRING, encapsulates {
308 20: OCTET STRING
: 7A 00 5F 86 64 FC E0 5D E5 11 10 3B B2 E6 3B C4
: 26 3F CF E2
: }
: }
330 110: SEQUENCE {
332 3: OBJECT IDENTIFIER authorityKeyIdentifier (2 5 29 35)
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337 103: OCTET STRING, encapsulates {
339 101: SEQUENCE {
341 20: [0]
: 9D 6D 20 24 49 01 3F 2B CB 78 B5 19 BC 7E 24
: C9 DB FB 36 7C
363 66: [1] {
365 64: [4] {
367 62: SEQUENCE {
369 11: SET {
371 9: SEQUENCE {
373 3: OBJECT IDENTIFIER countryName (2 5 4 6)
378 2: PrintableString 'NL'
: }
: }
382 17: SET {
384 15: SEQUENCE {
386 3: OBJECT IDENTIFIER organizationName
: (2 5 4 10)
391 8: PrintableString 'PolarSSL'
: }
: }
401 28: SET {
403 26: SEQUENCE {
405 3: OBJECT IDENTIFIER commonName (2 5 4 3)
410 19: PrintableString 'Polarssl Test EC CA'
: }
: }
: }
: }
: }
431 9: [2] 00 C1 43 E2 7E 62 43 CC E8
: }
: }
: }
: }
: }
: }
442 10: SEQUENCE {
444 8: OBJECT IDENTIFIER ecdsaWithSHA256 (1 2 840 10045 4 3 2)
: }
454 104: BIT STRING, encapsulates {
457 101: SEQUENCE {
459 48: INTEGER
: 4A 65 0D 7B 20 83 A2 99 B9 A8 0F FC 8D EE 8F 3D
: BB 70 4C 96 03 AC 8E 78 70 DD F2 0E A0 B2 16 CB
: 65 8E 1A C9 3F 2C 61 7E F8 3C EF AD 1C EE 36 20
509 49: INTEGER
: 00 9D F2 27 A6 D5 74 B8 24 AE E1 6A 3F 31 A1 CA
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: 54 2F 08 D0 8D EE 4F 0C 61 DF 77 78 7D B4 FD FC
: 42 49 EE E5 B2 6A C2 CD 26 77 62 8E 28 7C 9E 57
: 45
: }
: }
: }
Figure 5: ASN.1-based Certificate: Example.
To include the certificate shown in Figure 5 in a TLS/DTLS
Certificate message it is prepended with a message header. This
Certificate message header in our example is 0b 00 02 36 00 02 33 00
02 00 02 30, which indicates:
Message Type: 0b -- 1 byte type field indicating a Certificate
message
Length: 00 02 36 -- 3 byte length field indicating a 566 bytes
payload
Certificates Length: 00 02 33 -- 3 byte length field indicating 563
bytes for the entire certificates_list structure, which may
contain multiple certificates. In our example only one
certificate is included.
Certificate Length: 00 02 30 -- 3 byte length field indicating 560
bytes of the actual certificate following immediately afterwards.
In our example, this is the certificate content with 30 82 02 ....
9E 57 45 shown in Figure 6.
The hex encoding of the ASN.1 encoded certificate payload shown in
Figure 5 leads to the following encoding.
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30 82 02 2C 30 82 01 B2 A0 03 02 01 02 02 01 0D
30 0A 06 08 2A 86 48 CE 3D 04 03 02 30 3E 31 0B
30 09 06 03 55 04 06 13 02 4E 4C 31 11 30 0F 06
03 55 04 0A 13 08 50 6F 6C 61 72 53 53 4C 31 1C
30 1A 06 03 55 04 03 13 13 50 6F 6C 61 72 73 73
6C 20 54 65 73 74 20 45 43 20 43 41 30 1E 17 0D
31 33 30 39 32 34 31 35 35 32 30 34 5A 17 0D 32
33 30 39 32 32 31 35 35 32 30 34 5A 30 41 31 0B
30 09 06 03 55 04 06 13 02 4E 4C 31 11 30 0F 06
03 55 04 0A 13 08 50 6F 6C 61 72 53 53 4C 31 1F
30 1D 06 03 55 04 03 13 16 50 6F 6C 61 72 53 53
4C 20 54 65 73 74 20 43 6C 69 65 6E 74 20 32 30
59 30 13 06 07 2A 86 48 CE 3D 02 01 06 08 2A 86
48 CE 3D 03 01 07 03 42 00 04 57 E5 AE B1 73 DF
D3 AC BB 93 B8 81 FF 12 AE EE E6 53 AC CE 55 53
F6 34 0E CC 2E E3 63 25 0B DF 98 E2 F3 5C 60 36
96 C0 D5 18 14 70 E5 7F 9F D5 4B 45 18 E5 B0 6C
D5 5C F8 96 8F 87 70 A3 E4 C7 A3 81 9D 30 81 9A
30 09 06 03 55 1D 13 04 02 30 00 30 1D 06 03 55
1D 0E 04 16 04 14 7A 00 5F 86 64 FC E0 5D E5 11
10 3B B2 E6 3B C4 26 3F CF E2 30 6E 06 03 55 1D
23 04 67 30 65 80 14 9D 6D 20 24 49 01 3F 2B CB
78 B5 19 BC 7E 24 C9 DB FB 36 7C A1 42 A4 40 30
3E 31 0B 30 09 06 03 55 04 06 13 02 4E 4C 31 11
30 0F 06 03 55 04 0A 13 08 50 6F 6C 61 72 53 53
4C 31 1C 30 1A 06 03 55 04 03 13 13 50 6F 6C 61
72 73 73 6C 20 54 65 73 74 20 45 43 20 43 41 82
09 00 C1 43 E2 7E 62 43 CC E8 30 0A 06 08 2A 86
48 CE 3D 04 03 02 03 68 00 30 65 02 30 4A 65 0D
7B 20 83 A2 99 B9 A8 0F FC 8D EE 8F 3D BB 70 4C
96 03 AC 8E 78 70 DD F2 0E A0 B2 16 CB 65 8E 1A
C9 3F 2C 61 7E F8 3C EF AD 1C EE 36 20 02 31 00
9D F2 27 A6 D5 74 B8 24 AE E1 6A 3F 31 A1 CA 54
2F 08 D0 8D EE 4F 0C 61 DF 77 78 7D B4 FD FC 42
49 EE E5 B2 6A C2 CD 26 77 62 8E 28 7C 9E 57 45
Figure 6: Hex Encoding of the Example Certificate.
Applying the SHA-256 hash function to the Certificate message, which
is starts with 0b 00 02 and ends with 9E 57 45, produces
0x086eefb4859adfe977defac494fff6b73033b4ce1f86b8f2a9fc0c6bf98605af.
Authors' Addresses
Santesson & Tschofenig Expires November 12, 2016 [Page 16]
Internet-Draft TLS Cached Information Extension May 2016
Stefan Santesson
3xA Security AB
Scheelev. 17
Lund 223 70
Sweden
Email: sts@aaa-sec.com
Hannes Tschofenig
ARM Ltd.
Hall in Tirol 6060
Austria
Email: Hannes.tschofenig@gmx.net
URI: http://www.tschofenig.priv.at
Santesson & Tschofenig Expires November 12, 2016 [Page 17]
