draft-ietf-tls-cached-info-20.txt   draft-ietf-tls-cached-info-21.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: April 21, 2016 ARM Ltd. Expires: June 23, 2016 ARM Ltd.
October 19, 2015 December 21, 2015
Transport Layer Security (TLS) Cached Information Extension Transport Layer Security (TLS) Cached Information Extension
draft-ietf-tls-cached-info-20.txt draft-ietf-tls-cached-info-21.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 chain (i.e., the certificates of with a complete certificate chain (i.e., the certificates of
intermediate CAs up to the root CA). intermediate CAs up to the root CA).
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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 April 21, 2016. This Internet-Draft will expire on June 23, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 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
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8.1. New Entry to the TLS ExtensionType Registry . . . . . . . 10 8.1. New Entry to the TLS ExtensionType Registry . . . . . . . 10
8.2. New Registry for CachedInformationType . . . . . . . . . 10 8.2. New Registry for CachedInformationType . . . . . . . . . 10
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. Normative References . . . . . . . . . . . . . . . . . . 11 10.1. Normative References . . . . . . . . . . . . . . . . . . 11
10.2. Informative References . . . . . . . . . . . . . . . . . 12 10.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 12 Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
Reducing the amount of information exchanged during a Transport Layer Reducing the amount of information exchanged during a Transport Layer
Security handshake to a minimum helps to improve performance in Security handshake to a minimum helps to improve performance in
environments where devices are connected to a network with a low environments where devices are connected to a network with a low
bandwidth, and lossy radio technology. With Internet of Things such bandwidth, and lossy radio technology. With Internet of Things such
environments exist, for example, when devices use IEEE 802.15.4 or environments exist, for example, when devices use IEEE 802.15.4 or
Bluetooth Smart. For more information about the challenges with Bluetooth Smart. For more information about the challenges with
smart object deployments please see [RFC6574]. smart object deployments please see [RFC6574].
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handshake. handshake.
A typical example exchange may therefore look as follows. First, the A typical example exchange may therefore look as follows. First, the
client and the server executes the full TLS handshake. The client client and the server executes the full TLS handshake. The client
then caches the certificate provided by the server. When the TLS then caches the certificate provided by the server. When the TLS
client connects to the TLS server some time in the future, without client connects to the TLS server some time in the future, without
using session resumption, it then attaches the cached_info extension using session resumption, it then attaches the cached_info extension
defined in this document to the client hello message to indicate that defined in this document to the client hello message to indicate that
it had cached the certificate, and it provides the fingerprint of it. 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 If the server's certificate has not changed then the TLS server does
not need to send its' certificate and the corresponding certificate not need to send its certificate and the corresponding certificate
chain again. In case information has changed, which can be seen from chain again. In case information has changed, which can be seen from
the fingerprint provided by the client, the certificate payload is the fingerprint provided by the client, the certificate payload is
transmitted to the client to allow the client to update the cache. transmitted to the client to allow the client to update the cache.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "MUST", "MUST NOT", The key words "MUST", "MUST NOT", "REQUIRED", "MUST", "MUST 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 [RFC2119]. document are to be interpreted as described in [RFC2119].
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select (type) { select (type) {
case client: case client:
CachedInformationType type; CachedInformationType type;
opaque hash_value<1..255>; opaque hash_value<1..255>;
case server: case server:
CachedInformationType type; CachedInformationType type;
} body; } body;
} CachedObject; } CachedObject;
struct { struct {
CachedObject cached_info<1..2^16-1>; CachedObject cached_info<1..2^8-1>;
} CachedInformation; } CachedInformation;
This document defines the following two types: This document defines the following two types:
'cert' Type for not sending the complete Server Certificate Message: 'cert' Type for not sending the complete Server Certificate Message:
With the type field set to 'cert', the client MUST include the With the type field set to 'cert', the client MUST include the
fingerprint of the Certificate message in the hash_value field. fingerprint of the Certificate message in the hash_value field.
For this type the fingerprint MUST be calculated using the For this type the fingerprint MUST be calculated using the
procedure described in Section 5 with the Certificate message as procedure described in Section 5 with the Certificate message as
input data. input data.
'cert_req' Type for not sending the complete CertificateRequest 'cert_req' Type for not sending the complete CertificateRequest
Message: Message:
With the type set to 'cert_req', the client MUST include the With the type set to 'cert_req', the client MUST include the
fingerprint of the CertificateRequest message in the hash_value fingerprint of the CertificateRequest message in the hash_value
field. For this type the fingerprint MUST be calculated using the field. For this type the fingerprint MUST be calculated using the
procedure described in Section 5 with the CertificateRequest procedure described in Section 5 with the CertificateRequest
message as input data.. message as input data.
New cached info types can be added following the policy described in New cached info types can be added following the policy described in
the IANA considerations section, see Section 8. New message digest the IANA considerations section, see Section 8. New message digest
algorithms for use with these types can also be added by registering algorithms for use with these types can also be added by registering
a new type that makes use of the updated message digest algorithm. a new type that makes use of the updated message digest algorithm.
There are no specific requirements for the use of specific hash There are no specific requirements for the use of specific hash
algorithms but for practical reason it is useful to re-use algorithms algorithms but for practical reason it is useful to re-use algorithms
already available with TLS ciphersuites to avoid additional code and already available with TLS ciphersuites to avoid additional code and
to keep the collision probably low. to keep the collision probably low.
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A server supporting this extension MAY include the "cached_info" A server supporting this extension MAY include the "cached_info"
extension in the (extended) server hello. By returning the extension in the (extended) server hello. By returning the
"cached_info" extension the server indicates that it supports the "cached_info" extension the server indicates that it supports the
cached info types. For each indicated cached info type the server cached info types. For each indicated cached info type the server
MUST alter the transmission of respective payloads, according to the MUST alter the transmission of respective payloads, according to the
rules outlined with each type. If the server includes the extension rules outlined with each type. If the server includes the extension
it MUST only include CachedObjects of a type also supported by the it MUST only include CachedObjects of a type also supported by the
client (as expressed in the client hello). For example, if a client client (as expressed in the client hello). For example, if a client
indicates support for 'cert' and 'cert_req' then the server cannot indicates support for 'cert' and 'cert_req' then the server cannot
respond with a "cached_info" attribute containing support for ('foo- respond with a "cached_info" attribute containing support for ('foo-
bar'. bar').
Since the client includes a fingerprint of information it cached (for Since the client includes a fingerprint of information it cached (for
each indicated type) the server is able to determine whether cached each indicated type) the server is able to determine whether cached
information is stale. If the server supports this specification and information is stale. If the server supports this specification and
notices a mismatch between the data cached by the client and its own notices a mismatch between the data cached by the client and its own
information then the server MUST include the information in full and information then the server MUST include the information in full and
MUST NOT list the respective type in the "cached_info" extension. MUST NOT list the respective type in the "cached_info" extension.
Note: If a server is part of a hosting environment then the client 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 may have cached multiple data items for a single server. To allow
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o The 'cert' cached info extension is enabled (for example, a policy o The 'cert' cached info extension is enabled (for example, a policy
allows the use of this extension). allows the use of this extension).
o The server compared the value in the hash_value field of the o The server compared the value in the hash_value field of the
client-provided "cached_info" extension with the fingerprint of client-provided "cached_info" extension with the fingerprint of
the Certificate message it normally sends to clients. This check the Certificate message it normally sends to clients. This check
ensures that the information cached by the client is current. The ensures that the information cached by the client is current. The
procedure for calculating the fingerprint is described in procedure for calculating the fingerprint is described in
Section 5. Section 5.
The original Certificate handshake message syntax is defined in RFC The original Certificate handshake message syntax is defined in
5246 [RFC5246] and has been extended with RFC 7250 [RFC7250]. RFC [RFC5246] and has been extended with [RFC7250]. RFC 7250 allows the
7250 allows the certificate payload to contain only the certificate payload to contain only the SubjectPublicKeyInfo instead
SubjectPublicKeyInfo instead of the full information typically found of the full information typically found in a certificate. Hence,
in a certificate. Hence, when this specification is used in when this specification is used in combination with [RFC7250] and the
combination with [RFC7250] and the negotiated certificate type is a negotiated certificate type is a raw public key then the TLS server
raw public key then the TLS server omits sending a Certificate omits sending a Certificate payload that contains an ASN.1
payload that contains an ASN.1 Certificate structure with the Certificate structure with the included SubjectPublicKeyInfo rather
included SubjectPublicKeyInfo rather than the full certificate chain. than the full certificate chain. As such, this extension is
As such, this extension is compatible with the raw public key compatible with the raw public key extension defined in RFC 7250.
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 When the cached info specification is used then a modified version of
the Certificate message is exchanged. The modified structure is the Certificate message is exchanged. The modified structure is
shown in Figure 1. shown in Figure 1.
struct { struct {
opaque hash_value[1..255]; opaque hash_value[1..255];
} Certificate; } Certificate;
Figure 1: Cached Info Certificate Message. Figure 1: Cached Info Certificate Message.
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o The server compared the value in the hash_value field of the o The server compared the value in the hash_value field of the
client-provided "cached_info" extension with the fingerprint of client-provided "cached_info" extension with the fingerprint of
the CertificateRequest message it normally sends to clients. This the CertificateRequest message it normally sends to clients. This
check ensures that the information cached by the client is check ensures that the information cached by the client is
current. The procedure for calculating the fingerprint is current. The procedure for calculating the fingerprint is
described in Section 5. described in Section 5.
o The server wants to request a certificate from the client. o The server wants to request a certificate from the client.
The original CertificateRequest handshake message syntax is defined The original CertificateRequest handshake message syntax is defined
in RFC 5246 [RFC5246]. The modified structure of the in [RFC5246]. The modified structure of the CertificateRequest
CertificateRequest message is shown in Figure 2. message is shown in Figure 2.
struct { struct {
opaque hash_value<1..255>; opaque hash_value<1..255>;
} CertificateRequest; } CertificateRequest;
Figure 2: Cached Info CertificateRequest Message. Figure 2: Cached Info CertificateRequest Message.
The CertificateRequest payload is the input parameter to the The CertificateRequest payload is the input parameter to the
fingerprint calculation described in Section 5. fingerprint calculation described in Section 5.
5. Fingerprint Calculation 5. Fingerprint Calculation
The fingerprint MUST be computed as follows: The fingerprint MUST be computed as follows:
1. Compute the SHA-256 [RFC4634] hash of the input data. The input 1. Compute the SHA-256 [RFC6234] hash of the input data. The input
data depends on the cached info type. This document defines two data depends on the cached info type. This document defines two
cached info types, described in Section 4.1 and in Section 4.2. cached info types, described in Section 4.1 and in Section 4.2.
Note that the computed hash only covers the input data structure Note that the computed hash only covers the input data structure
(and not any type and length information of the record layer). (and not any type and length information of the record layer).
Appendix A shows an example.
2. Truncate the output of the SHA-256 hash. When a hash value is 2. Truncate the output of the SHA-256 hash. When a hash value is
truncated to 32 bits, the leftmost 32 bits (that is, the most truncated to 32 bits, the leftmost 32 bits (that is, the most
significant 32 bits in network byte order) from the binary significant 32 bits in network byte order) from the binary
representation of the hash value MUST be used as the truncated representation of the hash value MUST be used as the truncated
value. An example of a 256-bit hash output truncated to 32 bits value. An example of a 256-bit hash output truncated to 32 bits
is shown in Figure 3. is shown in Figure 3.
256-bit hash: 256-bit hash:
0x265357902fe1b7e2a04b897c6025d7a2265357902fe1b7e2a04b897c6025d7a2 0x265357902fe1b7e2a04b897c6025d7a2265357902fe1b7e2a04b897c6025d7a2
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has to fall back to a full exchange. (2) If the attacker manages to 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 inject a fingerprint that refers to data the client has not cached
then the exchange will fail later when the client continues with the then the exchange will fail later when the client continues with the
handshake and aims to verify the digital signature. The signature handshake and aims to verify the digital signature. The signature
verification will fail since the public key cached by the client will 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 not correspond to the private key that was used by server to sign the
message. message.
6. Example 6. Example
Figure 4 illustrates an example exchange using the TLS cached info In the regular, full TLS handshake exchange, shown in Figure 4, the
extension. In the normal TLS handshake exchange shown in flow (A) TLS server provides its certificate in the Certificate payload to the
the TLS server provides its certificate in the Certificate payload to 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 Figure 5. The TLS client indicates
support for this specification via the "cached_info" extension, see support for this specification via the "cached_info" extension, see
[2], and indicates that it has stored the certificate from the step (2), and indicates that it has stored the certificate from the
earlier exchange (by indicating the 'cert' type). With [3] the TLS earlier exchange (by indicating the 'cert' type). With step (3) the
server acknowledges the supports of the 'cert' type and by including TLS server acknowledges the supports of the 'cert' type and by
the value in the server hello informs the client that the content of including the value in the server hello informs the client that the
the certificate payload contains the fingerprint of the certificate content of the certificate payload contains the fingerprint of the
instead of the RFC 5246-defined payload of the certificate message in certificate instead of the RFC 5246-defined payload of the
message [4]. certificate message in step (4).
(A) Initial (full) Exchange
ClientHello -> ClientHello ->
<- ServerHello <- ServerHello
Certificate* // [1] Certificate* // (1)
ServerKeyExchange* ServerKeyExchange*
CertificateRequest* CertificateRequest*
ServerHelloDone ServerHelloDone
Certificate* Certificate*
ClientKeyExchange ClientKeyExchange
CertificateVerify* CertificateVerify*
[ChangeCipherSpec] [ChangeCipherSpec]
Finished -> Finished ->
<- [ChangeCipherSpec] <- [ChangeCipherSpec]
Finished Finished
Application Data <-------> Application Data Application Data <-------> Application Data
(B) TLS Cached Extension Usage Figure 4: Example Message Exchange: Initial (full) Exchange.
ClientHello ClientHello
cached_info=(cert) -> // [2] cached_info=(cert) -> // (2)
<- ServerHello <- ServerHello
cached_info=(cert) [3] cached_info=(cert) (3)
Certificate [4] Certificate (4)
ServerKeyExchange* ServerKeyExchange*
ServerHelloDone ServerHelloDone
ClientKeyExchange ClientKeyExchange
CertificateVerify* CertificateVerify*
[ChangeCipherSpec] [ChangeCipherSpec]
Finished -> Finished ->
<- [ChangeCipherSpec] <- [ChangeCipherSpec]
Finished Finished
Application Data <-------> Application Data Application Data <-------> Application Data
Figure 4: Example Message Exchange Figure 5: Example Message Exchange: TLS Cached Extension Usage.
7. Security Considerations 7. Security Considerations
This specification defines a mechanism to reference stored state This specification defines a mechanism to reference stored state
using a fingerprint. Sending a fingerprint of cached information in using a fingerprint. Sending a fingerprint of cached information in
an unencrypted handshake, as the client and server hello is, may an unencrypted handshake, as the client and server hello is, may
allow an attacker or observer to correlate independent TLS exchanges. allow an attacker or observer to correlate independent TLS exchanges.
While some information elements used in this specification, such as While some information elements used in this specification, such as
server certificates, are public objects and usually do not contain server certificates, are public objects and usually do not contain
sensitive information, other not yet defined types may. Those who sensitive information, other not yet defined types may. Those who
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initial handshake messages the fingerprints are included in the TLS initial handshake messages the fingerprints are included in the TLS
Finish message. Finish message.
Clients MUST ensure that they only cache information from legitimate Clients MUST ensure that they only cache information from legitimate
sources. For example, when the client populates the cache from a TLS sources. For example, when the client populates the cache from a TLS
exchange then it must only cache information after the successful exchange then it must only cache information after the successful
completion of a TLS exchange to ensure that an attacker does not completion of a TLS exchange to ensure that an attacker does not
inject incorrect information into the cache. Failure to do so allows inject incorrect information into the cache. Failure to do so allows
for man-in-the-middle attacks. for man-in-the-middle attacks.
Security consideratios for the fingerprint calculation are discussed Security considerations for the fingerprint calculation are discussed
in Section 5. in Section 5.
8. IANA Considerations 8. IANA Considerations
8.1. New Entry to the TLS ExtensionType Registry 8.1. 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_info(TBD) defined registry, defined in [RFC5246], for cached_info(TBD) defined in this
in this document. document.
8.2. New Registry for CachedInformationType 8.2. New Registry for CachedInformationType
IANA is requested to establish a registry for TLS IANA is requested to establish a registry for TLS
CachedInformationType values. The first entries in the registry are CachedInformationType values. The first entries in the registry are
o cert(1) o cert(1)
o cert_req(2) o cert_req(2)
The policy for adding new values to this registry, following the The policy for adding new values to this registry, following the
terminology defined in RFC 5226 [RFC5226], is as follows: terminology defined in [RFC5226], is as follows:
o 0-63 (decimal): Standards Action o 0-63 (decimal): Standards Action
o 64-223 (decimal): Specification Required
o 64-223 (decimal): Specification Required
o 224-255 (decimal): reserved for Private Use o 224-255 (decimal): reserved for Private Use
9. Acknowledgments 9. 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 (March 2012)
o Ilari Liusvaara, Adam Langley, and Eric Rescorla (in July 2014) o Ilari Liusvaara, Adam Langley, and Eric Rescorla (July 2014)
o Sean Turner (in August 2014) o Sean Turner (August 2014)
o Martin Thomson (in August 2015) o Martin Thomson (August 2015)
o Jouni Korhonen (November 2015)
o Matt Miller (December 2015)
We would also to thank Martin Thomson, Karthikeyan Bhargavan, Sankalp We would also to thank Martin Thomson, Karthikeyan Bhargavan, Sankalp
Bagaria and Eric Rescorla for their feedback regarding the Bagaria and Eric Rescorla for their feedback regarding the
fingerprint calculation. fingerprint calculation.
Finally, we would like to thank the TLS working group chairs, Sean Finally, we would like to thank the TLS working group chairs, Sean
Turner and Joe Salowey, as well as the responsible security area Turner and Joe Salowey, as well as the responsible security area
director, Stephen Farrell, for their support. director, Stephen Farrell, for their support and their reviews.
10. References 10. References
10.1. Normative References 10.1. Normative References
[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, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997, RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC4634] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and HMAC-SHA)", RFC 4634, DOI 10.17487/RFC4634, July
2006, <http://www.rfc-editor.org/info/rfc4634>.
[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, DOI 10.17487/ (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/
RFC5246, August 2008, RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>. <http://www.rfc-editor.org/info/rfc5246>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS) [RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, DOI Extensions: Extension Definitions", RFC 6066, DOI
10.17487/RFC6066, January 2011, 10.17487/RFC6066, January 2011,
<http://www.rfc-editor.org/info/rfc6066>. <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 10.2. Informative References
[ASN.1-Dump] [ASN.1-Dump]
Gutmann, P., "ASN.1 Object Dump Program", February 2013, Gutmann, P., "ASN.1 Object Dump Program", February 2013,
<http://www.cs.auckland.ac.nz/~pgut001/>. <http://www.cs.auckland.ac.nz/~pgut001/>.
[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,
DOI 10.17487/RFC5226, May 2008, DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>. <http://www.rfc-editor.org/info/rfc5226>.
skipping to change at page 12, line 35 skipping to change at page 12, line 40
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J., [RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250, Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <http://www.rfc-editor.org/info/rfc7250>. June 2014, <http://www.rfc-editor.org/info/rfc7250>.
Appendix A. Example Appendix A. Example
Consider a certificate containing an NIST P256 elliptic curve public Consider a certificate containing an NIST P256 elliptic curve public
key displayed using Peter Gutmann's ASN.1 decoder [ASN.1-Dump] in key displayed using Peter Gutmann's ASN.1 decoder [ASN.1-Dump] in
Figure 5. Figure 6.
0 556: SEQUENCE { 0 556: SEQUENCE {
4 434: SEQUENCE { 4 434: SEQUENCE {
8 3: [0] { 8 3: [0] {
10 1: INTEGER 2 10 1: INTEGER 2
: } : }
13 1: INTEGER 13 13 1: INTEGER 13
16 10: SEQUENCE { 16 10: SEQUENCE {
18 8: OBJECT IDENTIFIER ecdsaWithSHA256 (1 2 840 10045 4 3 2) 18 8: OBJECT IDENTIFIER ecdsaWithSHA256 (1 2 840 10045 4 3 2)
: } : }
skipping to change at page 15, line 31 skipping to change at page 15, line 36
: 65 8E 1A C9 3F 2C 61 7E F8 3C EF AD 1C EE 36 20 : 65 8E 1A C9 3F 2C 61 7E F8 3C EF AD 1C EE 36 20
509 49: INTEGER 509 49: INTEGER
: 00 9D F2 27 A6 D5 74 B8 24 AE E1 6A 3F 31 A1 CA : 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 : 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 : 42 49 EE E5 B2 6A C2 CD 26 77 62 8E 28 7C 9E 57
: 45 : 45
: } : }
: } : }
: } : }
Figure 5: ASN.1-based Certificate: Example. Figure 6: ASN.1-based Certificate: Example.
To include the certificate shown in Figure 5 in a TLS/DTLS To include the certificate shown in Figure 6 in a TLS/DTLS
Certificate message it is prepended with a message header. This 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 Certificate message header in our example is 0b 00 02 36 00 02 33 00
02 00 02 30, which indicates: 02 00 02 30, which indicates:
Message Type: 0b -- 1 byte type field indicating a Certificate Message Type: 0b -- 1 byte type field indicating a Certificate
message message
Length: 00 02 36 -- 3 byte length field indicating a 566 bytes Length: 00 02 36 -- 3 byte length field indicating a 566 bytes
payload payload
skipping to change at page 16, line 4 skipping to change at page 16, line 9
Length: 00 02 36 -- 3 byte length field indicating a 566 bytes Length: 00 02 36 -- 3 byte length field indicating a 566 bytes
payload payload
Certificates Length: 00 02 33 -- 3 byte length field indicating 563 Certificates Length: 00 02 33 -- 3 byte length field indicating 563
bytes for the entire certificates_list structure, which may bytes for the entire certificates_list structure, which may
contain multiple certificates. In our example only one contain multiple certificates. In our example only one
certificate is included. certificate is included.
Certificate Length: 00 02 30 -- 3 byte length field indicating 560 Certificate Length: 00 02 30 -- 3 byte length field indicating 560
bytes of the actual certificate following immediately afterwards. bytes of the actual certificate following immediately afterwards.
In our example, this is the certificate content with 30 82 02 .... In our example, this is the certificate content with 30 82 02 ....
9E 57 45 shown in Figure 6. 9E 57 45 shown in Figure 7.
The hex encoding of the ASN.1 encoded certificate payload shown in The hex encoding of the ASN.1 encoded certificate payload shown in
Figure 5 leads to the following encoding. Figure 6 leads to the following encoding.
30 82 02 2C 30 82 01 B2 A0 03 02 01 02 02 01 0D 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 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 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 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 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 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 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 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 30 09 06 03 55 04 06 13 02 4E 4C 31 11 30 0F 06
skipping to change at page 16, line 47 skipping to change at page 17, line 41
72 73 73 6C 20 54 65 73 74 20 45 43 20 43 41 82 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 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 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 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 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 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 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 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 49 EE E5 B2 6A C2 CD 26 77 62 8E 28 7C 9E 57 45
Figure 6: Hex Encoding of the Example Certificate. Figure 7: Hex Encoding of the Example Certificate.
Applying the SHA-256 hash function to the Certificate message, which Applying the SHA-256 hash function to the Certificate message, which
is starts with 0b 00 02 and ends with 9E 57 45, produces is starts with 0b 00 02 and ends with 9E 57 45, produces
0x086eefb4859adfe977defac494fff6b73033b4ce1f86b8f2a9fc0c6bf98605af. 0x086eefb4859adfe977defac494fff6b73033b4ce1f86b8f2a9fc0c6bf98605af.
Subsequently, this output is truncated to 32 bits, which leads to a Subsequently, this output is truncated to 32 bits, which leads to a
fingerpint of 0x086eefb4. fingerpint of 0x086eefb4.
Authors' Addresses Authors' Addresses
Stefan Santesson Stefan Santesson
3xA Security AB 3xA Security AB
Scheelev. 17 Scheelev. 17
Lund 223 70 Lund 223 70
Sweden Sweden
 End of changes. 40 change blocks. 
65 lines changed or deleted 70 lines changed or added

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