< draft-ietf-tls-oob-pubkey-09.txt   draft-ietf-tls-oob-pubkey-10.txt >
TLS P. Wouters, Ed. TLS P. Wouters, Ed.
Internet-Draft Red Hat Internet-Draft Red Hat
Intended status: Standards Track H. Tschofenig, Ed. Intended status: Standards Track H. Tschofenig, Ed.
Expires: January 31, 2014 Nokia Siemens Networks Expires: April 22, 2014 Nokia Solutions and Networks
J. Gilmore J. Gilmore
S. Weiler S. Weiler
SPARTA, Inc. SPARTA, Inc.
T. Kivinen T. Kivinen
AuthenTec AuthenTec
July 30, 2013 October 19, 2013
Out-of-Band Public Key Validation for Transport Layer Security (TLS) Using Raw Public Keys in Transport Layer Security (TLS) and Datagram
draft-ietf-tls-oob-pubkey-09.txt Transport Layer Security (DTLS)
draft-ietf-tls-oob-pubkey-10.txt
Abstract Abstract
This document specifies a new certificate type and two TLS This document specifies a new certificate type and two TLS extensions
extensions, one for the client and one for the server, for exchanging for exchanging raw public keys in Transport Layer Security (TLS) and
raw public keys in Transport Layer Security (TLS) and Datagram Datagram Transport Layer Security (DTLS) for use with out-of-band
Transport Layer Security (DTLS) for use with out-of-band public key public key validation.
validation.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 31, 2014. This Internet-Draft will expire on April 22, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 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.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. New TLS Extension . . . . . . . . . . . . . . . . . . . . . . 3 3. Structure of the Raw Public Key Extension . . . . . . . . . . 4
4. TLS Handshake Extension . . . . . . . . . . . . . . . . . . . 7 4. TLS Client and Server Handshake Behavior . . . . . . . . . . 6
4.1. Client Hello . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Client Hello . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Server Hello . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Server Hello . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Certificate Request . . . . . . . . . . . . . . . . . . . 7 4.3. Client Authentication . . . . . . . . . . . . . . . . . . 8
4.4. Other Handshake Messages . . . . . . . . . . . . . . . . 8
4.5. Client authentication . . . . . . . . . . . . . . . . . . 8
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5.1. TLS Server uses Raw Public Key . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 5.2. TLS Client and Server use Raw Public Keys . . . . . . . . 9
5.3. Combined Usage of Raw Public Keys and X.509 Certificate . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . 12 9.1. Normative References . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . 13 9.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Example Encoding . . . . . . . . . . . . . . . . . . 13 Appendix A. Example Encoding . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
Traditionally, TLS client and server public keys are obtained in PKIX Traditionally, TLS client and server public keys are obtained in PKIX
containers in-band using the TLS handshake and validated using trust containers in-band as part of the TLS handshake procedure and are
anchors based on a [PKIX] certification authority (CA). This method validated using trust anchors based on a PKIX certification authority
can add a complicated trust relationship that is difficult to (CA) [RFC5280]. This method can add a complicated trust relationship
validate. Examples of such complexity can be seen in that is difficult to validate. Examples of such complexity can be
[Defeating-SSL]. seen in [Defeating-SSL].
Alternative methods are available that allow a TLS clients/servers to Alternative methods are available that allow a TLS clients/servers to
obtain the TLS servers/client public key: obtain the TLS servers/client public key:
o TLS clients can obtain the TLS server public key from a DNSSEC o TLS clients can obtain the TLS server public key from a DNSSEC
secured resource records using DANE [RFC6698]. secured resource records using DANE [RFC6698].
o The TLS client or server public key is obtained from a [PKIX] o The TLS client or server public key is obtained from a certificate
certificate chain from an Lightweight Directory Access Protocol chain via a Lightweight Directory Access Protocol (LDAP) [RFC4511]
(LDAP) [LDAP] server or web page. server or web page.
o The TLS client and server public key is provisioned into the o The TLS client and server public key is provisioned into the
operating system firmware image, and updated via software updates. operating system firmware image, and updated via software updates.
For example: For example:
Some smart objects use the UDP-based Constrained Application Some smart objects use the UDP-based Constrained Application
Protocol (CoAP) [I-D.ietf-core-coap] to interact with a Web server Protocol (CoAP) [I-D.ietf-core-coap] to interact with a Web server
to upload sensor data at a regular intervals, such as temperature to upload sensor data at a regular intervals, such as temperature
readings. CoAP [I-D.ietf-core-coap] can utilize DTLS for securing readings. CoAP [I-D.ietf-core-coap] can utilize DTLS for securing
the client-to-server communication. As part of the manufacturing the client-to-server communication. As part of the manufacturing
process, the embedded device may be configured with the address process, the embedded device may be configured with the address
and the public key of a dedicated CoAP server, as well as a public and the public key of a dedicated CoAP server, as well as a public
key for the client itself. /private key pair for the client itself.
This document introduces the use of raw public keys in TLS/DTLS. Raw
public key thereby means that only a sub-set of the information found
in typical certificates is utilized, namely the SubjectPublicKeyInfo
structure of a PKIX certificates that carries the parameters
necessary to describe the public key. Other parameters also found in
a PKIX certificate are omitted. A consequence of omitting various
certificate related structures is that the resulting raw public key
is fairly small (compared to the original certificate) and does not
require codepaths for the ASN.1 parser, for certificate path
validation and other PKIX related processing tasks. To further
reduce the size of the exchanged information this specification can
be combined with the TLS Cached Info extension
[I-D.ietf-tls-cached-info], which enables TLS endpoints to just
exchange fingerprints of their public keys (rather than the full
public keys).
The mechanism defined herein only provides authentication when an The mechanism defined herein only provides authentication when an
out-of-band mechanism is also used to bind the public key to the out-of-band mechanism is also used to bind the public key to the
entity presenting the key. entity presenting the key.
This document registers a new value to the IANA certificate types This document is structured as follows: Section 3 defines the
registry for the support of raw public keys. It also defines two new structure of the two new TLS extensions "client_certificate_type" and
TLS extensions, "client_certificate_type" and "server_certificate_type", which can be used as part of an extended
"server_certificate_type". TLS handshake when raw public keys are to be used. Section 4 defines
the behavior of the TLS client and the TLS server. Example exchanges
are described in Section 5. Finally, in Section 7 this document also
registers a new value to the IANA certificate types registry for the
support of raw public keys.
2. Terminology 2. Terminology
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].
3. New TLS Extension We use the terms 'TLS server' and 'server' as well as 'TLS client'
and 'client' interchangable.
This section describes the changes to the TLS handshake message 3. Structure of the Raw Public Key Extension
contents when raw public keys are to be used. Figure 4 illustrates
the exchange of messages as described in the sub-sections below. The This section defines the two TLS extensions 'client_certificate_type'
client and the server exchange make use of two new TLS extensions, and 'server_certificate_type', which can be used as part of an
namely 'client_certificate_type' and 'server_certificate_type', and extended TLS handshake when raw public keys are used. Section 4
an already available IANA TLS Certificate Type registry defines the behavior of the TLS client and the TLS server using this
[TLS-Certificate-Types-Registry] to indicate their ability and desire extension.
to exchange raw public keys. These raw public keys, in the form of a
SubjectPublicKeyInfo structure, are then carried inside the This specification reuses the SubjectPublicKeyInfo structure to
Certificate payload. The Certificate and the SubjectPublicKeyInfo encode the raw public key and to convey that information within the
structure is shown in Figure 1. TLS handshake the Certificate payload is utilized as a container, as
shown in Figure 1. The shown Certificate structure is an adaptation
of its original form [RFC5246].
opaque ASN.1Cert<1..2^24-1>; opaque ASN.1Cert<1..2^24-1>;
struct { struct {
select(certificate_type){ select(certificate_type){
// certificate type defined in this document. // certificate type defined in this document.
case RawPublicKey: case RawPublicKey:
opaque ASN.1_subjectPublicKeyInfo<1..2^24-1>; opaque ASN.1_subjectPublicKeyInfo<1..2^24-1>;
// X.509 certificate defined in RFC 5246 // X.509 certificate defined in RFC 5246
case X.509: case X.509:
ASN.1Cert certificate_list<0..2^24-1>; ASN.1Cert certificate_list<0..2^24-1>;
// Additional certificate type based on TLS // Additional certificate type based on TLS
// Certificate Type Registry // Certificate Type Registry
}; };
} Certificate; } Certificate;
Figure 1: TLS Certificate Structure. Figure 1: Certificate Payload as a Container for the Raw Public Key.
The SubjectPublicKeyInfo structure is defined in Section 4.1 of RFC The SubjectPublicKeyInfo structure is defined in Section 4.1 of RFC
5280 [PKIX] and does not only contain the raw keys, such as the 5280 [RFC5280] and does not only contain the raw keys, such as the
public exponent and the modulus of an RSA public key, but also an public exponent and the modulus of an RSA public key, but also an
algorithm identifier. The algorithm identifier can also include algorithm identifier. The algorithm identifier can also include
parameters. The structure, as shown in Figure 2, is encoded in an parameters. The structure, as shown in Figure 2, is represented in a
DER encoded ASN.1 format [X.690] and therefore contains length DER encoded ASN.1 format [X.690] and therefore contains length
information as well. An example is provided in Appendix A. information as well. An example is provided in Appendix A.
SubjectPublicKeyInfo ::= SEQUENCE { SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier, algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING } subjectPublicKey BIT STRING }
AlgorithmIdentifier ::= SEQUENCE { AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER, algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL } parameters ANY DEFINED BY algorithm OPTIONAL }
skipping to change at page 4, line 47 skipping to change at page 5, line 25
The algorithm identifiers are Object Identifiers (OIDs). RFC 3279 The algorithm identifiers are Object Identifiers (OIDs). RFC 3279
[RFC3279] and [RFC5480], for example, define the following OIDs shown [RFC3279] and [RFC5480], for example, define the following OIDs shown
in Figure 3. Note that this list is not exhaustive and more OIDs may in Figure 3. Note that this list is not exhaustive and more OIDs may
be defined in future RFCs. RFC 5480 also defines a number of OIDs. be defined in future RFCs. RFC 5480 also defines a number of OIDs.
Key Type | Document | OID Key Type | Document | OID
-----------------------+----------------------------+------------------- -----------------------+----------------------------+-------------------
RSA | Section 2.3.1 of RFC 3279 | 1.2.840.113549.1.1 RSA | Section 2.3.1 of RFC 3279 | 1.2.840.113549.1.1
.......................|............................|................... .......................|............................|...................
Digital Signature | | Digital Signature | |
Algorithm (DSS) | Section 2.3.2 of RFC 3279 | 1.2.840.10040.4.1 Algorithm (DSA) | Section 2.3.2 of RFC 3279 | 1.2.840.10040.4.1
.......................|............................|................... .......................|............................|...................
Elliptic Curve | | Elliptic Curve | |
Digital Signature | | Digital Signature | |
Algorithm (ECDSA) | Section 2 of RFC 5480 | 1.2.840.10045.2.1 Algorithm (ECDSA) | Section 2 of RFC 5480 | 1.2.840.10045.2.1
-----------------------+----------------------------+------------------- -----------------------+----------------------------+-------------------
Figure 3: Example Algorithm Object Identifiers. Figure 3: Example Algorithm Object Identifiers.
The message exchange in Figure 4 shows the 'client_certificate_type' The extension format for extended client hellos and extended server,
and 'server_certificate_type' extensions added to the client and via the "extension_data" field, is used to carry the
server hello messages. ClientCertTypeExtension and the ServerCertTypeExtension structures.
These two structures are shown in Figure 4. The CertificateType
structure is an enum with values taken from the 'TLS Certificate
Type' registry [TLS-Certificate-Types-Registry].
struct {
select(ClientOrServerExtension)
case client:
CertificateType client_certificate_types<1..2^8-1>;
case server:
CertificateType client_certificate_type;
}
} ClientCertTypeExtension;
struct {
select(ClientOrServerExtension)
case client:
CertificateType server_certificate_types<1..2^8-1>;
case server:
CertificateType server_certificate_type;
}
} ServerCertTypeExtension;
Figure 4: CertTypeExtension Structure.
4. TLS Client and Server Handshake Behavior
This specification extends the ClientHello and the ServerHello
messages, according to the extension procedures defined in [RFC5246].
It does not extend or modify any other TLS message.
Note: No new cipher suites are required to use raw public keys. All
existing cipher suites that support a key exchange method compatible
with the defined extension can be used.
The high-level message exchange in Figure 5 shows the
'client_certificate_type' and 'server_certificate_type' extensions
added to the client and server hello messages.
client_hello, client_hello,
client_certificate_type client_certificate_type,
server_certificate_type -> server_certificate_type ->
<- server_hello, <- server_hello,
client_certificate_type, client_certificate_type,
server_certificate_type, server_certificate_type,
certificate, certificate,
server_key_exchange, server_key_exchange,
certificate_request, certificate_request,
server_hello_done server_hello_done
certificate, certificate,
client_key_exchange, client_key_exchange,
certificate_verify, certificate_verify,
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 5: Basic Raw Public Key TLS Exchange.
Figure 4: Basic Raw Public Key TLS Exchange. 4.1. Client Hello
The semantic of the two extensions is defined as follows:
The 'client_certificate_type' and 'server_certificate_type' sent
in the client hello, may carry a list of supported certificate
types, sorted by client preference. It is a list in the case
where the client supports multiple certificate types. These
extension MUST be omitted if the client only supports X.509
certificates. The 'client_certificate_type' sent in the client
hello indicates the certificate types the client is able to
provide to the server, when requested using a certificate_request
message. The 'server_certificate_type' in the client hello
indicates the type of certificates the client is able to process
when provided by the server in a subsequent certificate payload.
The 'client_certificate_type' returned in the server hello
indicates the certificate type found in the attached certificate
payload. Only a single value is permitted. The
'server_certificate_type' in the server hello indicates the type
of certificates the client is requested to provide in a subsequent
certificate payload. The value conveyed in the
'server_certificate_type' MUST be selected from one of the values
provided in the 'server_certificate_type' sent in the client
hello. If the server does not send a certificate_request payload
or none of the certificates supported by the client (as indicated
in the 'server_certificate_type' in the client hello) match the
server-supported certificate types the 'server_certificate_type'
payload sent in the server hello is omitted.
The "extension_data" field of this extension contains the
ClientCertTypeExtension or the ServerCertTypeExtension structure, as
shown in Figure 5. The CertificateType structure is an enum with
with values from TLS Certificate Type Registry.
struct {
select(ClientOrServerExtension)
case client:
CertificateType client_certificate_types<1..2^8-1>;
case server:
CertificateType client_certificate_type;
}
} ClientCertTypeExtension;
struct {
select(ClientOrServerExtension)
case client:
CertificateType server_certificate_types<1..2^8-1>;
case server:
CertificateType server_certificate_type;
}
} ServerCertTypeExtension;
Figure 5: CertTypeExtension Structure. In order to indicate the support of raw public keys, clients include
the 'client_certificate_type' and/or the 'server_certificate_type'
extensions in an extended client hello message. The hello extension
mechanism is described in Section 7.4.1.4 of TLS 1.2 [RFC5246].
No new cipher suites are required to use raw public keys. All The 'client_certificate_type' sent in the client hello indicates the
existing cipher suites that support a key exchange method compatible certificate types the client is able to provide to the server, when
with the defined extension can be used. requested using a certificate_request message.
4. TLS Handshake Extension The 'server_certificate_type' in the client hello indicates the types
of certificates the client is able to process when provided by the
server in a subsequent certificate payload.
4.1. Client Hello The 'client_certificate_type' and 'server_certificate_type' sent in
the client hello may carry a list of supported certificate types,
sorted by client preference. It is a list in the case where the
client supports multiple certificate types.
In order to indicate the support of out-of-band raw public keys, The TLS client MUST omit the 'client_certificate_type' extension in
clients MUST include the 'client_certificate_type' and the client hello if it does not possess a client certificate or is
'server_certificate_type' extensions in an extended client hello not configured to use one with the given TLS server. The TLS client
message. The hello extension mechanism is described in TLS 1.2 MUST omit the 'server_certificate_type' extension in the client hello
[RFC5246]. if it is unable to process any certificate types from the server
(which is a situation that should not occur in normal circumstances).
4.2. Server Hello 4.2. Server Hello
If the server receives a client hello that contains the If the server receives a client hello that contains the
'client_certificate_type' and 'server_certificate_type' extensions 'client_certificate_type' and 'server_certificate_type' extensions
and chooses a cipher suite then three outcomes are possible: and chooses a cipher suite then three outcomes are possible:
1. The server does not support the extension defined in this 1. The server does not support the extension defined in this
document. In this case the server returns the server hello document. In this case the server returns the server hello
without the extensions defined in this document. without the extensions defined in this document.
2. The server supports the extension defined in this document and 2. The server supports the extension defined in this document but it
does not have a certificate type in common with the client. Then
the server terminates the session with a fatal alert of type
"unsupported_certificate".
3. The server supports the extensions defined in this document and
has at least one certificate type in common with the client. In has at least one certificate type in common with the client. In
this case it returns the 'server_certificate_type' and indicates this case the processing rules described below are followed.
the selected certificate type value.
3. The server supports the extension defined in this document but If the client hello indicates support of raw public keys in the
does not have a certificate type in common with the client. In 'client_certificate_type' extension and the server chooses to use raw
this case the server terminate the session with a fatal alert of public keys then the TLS server MUST place the SubjectPublicKeyInfo
type "unsupported_certificate". structure into the Certificate payload.
If the TLS server also requests a certificate from the client (via If the TLS server also requests a certificate from the client (via
the certificate_request) it MUST include the the certificate_request message) it MUST include the
'client_certificate_type' extension with a value chosen from the list 'client_certificate_type' extension with a value chosen from the list
of client-supported certificates types (as provided in the of client-supported certificates types (as provided in the
'client_certificate_type' of the client hello). 'client_certificate_type' of the client hello).
If the client hello indicates support of raw public keys in the If the server does not send a certificate_request payload (for
'client_certificate_type' extension and the server chooses to use raw example, because client authentication happens at the application
public keys then the TLS server MUST place the SubjectPublicKeyInfo layer or no client authentication is required) or none of the
structure into the Certificate payload. certificates supported by the client (as indicated in the
'server_certificate_type' in the client hello) match the server-
supported certificate types then the 'server_certificate_type'
payload in the server hello is omitted.
4.3. Certificate Request 4.3. Client Authentication
The semantics of this message remain the same as in the TLS
specification.
4.4. Other Handshake Messages Authentication of the TLS client to the TLS server is supported only
through authentication of the received client SubjectPublicKeyInfo
via an out-of-band method.
All the other handshake messages are identical to the TLS 5. Examples
specification.
4.5. Client authentication This section illustrates a number of possible usage scenarios.
Client authentication by the TLS server is supported only through 5.1. TLS Server uses Raw Public Key
authentication of the received client SubjectPublicKeyInfo via an
out-of-band method.
5. Examples This section shows an example where the TLS client indicates its
ability to receive and validate raw public keys from the server. In
our example the client is quite restricted since it is unable to
process other certificate types sent by the server. It also does not
have credentials (at the TLS layer) it could send to the server and
therefore omits the 'client_certificate_type' extension. Hence, the
client only populates the 'server_certificate_type' extension with
the raw public key type, as shown in [1].
Figure 6, Figure 7, and Figure 8 illustrate example exchanges. When the TLS server receives the client hello it processes the
extension. Since it has a raw public key it indicates in [2] that it
had chosen to place the SubjectPublicKeyInfo structure into the
Certificate payload [3].
The first example shows an exchange where the TLS client indicates The client uses this raw public key in the TLS handshake together
its ability to receive and validate raw public keys from the server. with an out-of-band validation technique, such as DANE, to verify it.
In our example the client is quite restricted since it is unable to
process other certificate types sent by the server. It also does not
have credentials (at the TLS layer) it could send. The
'client_certificate_type' extension indicates this in [1]. When the
TLS server receives the client hello it processes the
'client_certificate_type' extension. Since it also has a raw public
key it indicates in [2] that it had chosen to place the
SubjectPublicKeyInfo structure into the Certificate payload [3]. The
client uses this raw public key in the TLS handshake and an out-of-
band technique, such as DANE, to verify its validity.
client_hello, client_hello,
server_certificate_type=(RawPublicKey) -> // [1] server_certificate_type=(RawPublicKey) // [1]
->
<- server_hello, <- server_hello,
server_certificate_type=(RawPublicKey), // [2] server_certificate_type=(RawPublicKey), // [2]
certificate, // [3] certificate, // [3]
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 6: Example with Raw Public Key provided by the TLS Server Figure 6: Example with Raw Public Key provided by the TLS Server.
In our second example the TLS client as well as the TLS server use 5.2. TLS Client and Server use Raw Public Keys
raw public keys. This is a use case envisioned for smart object
networking. The TLS client in this case is an embedded device that This section shows an example where the TLS client as well as the TLS
is configured with a raw public key for use with TLS and is also able server use raw public keys. This is a use case envisioned for smart
to process raw public keys sent by the server. Therefore, it object networking. The TLS client in this case is an embedded device
that is configured with a raw public key for use with TLS and is also
able to process raw public keys sent by the server. Therefore, it
indicates these capabilities in [1]. As in the previously shown indicates these capabilities in [1]. As in the previously shown
example the server fulfills the client's request, indicates this via example the server fulfills the client's request, indicates this via
the "RawPublicKey" value in the server_certificate_type payload, and the "RawPublicKey" value in the server_certificate_type payload, and
provides a raw public key into the Certificate payload back to the provides a raw public key into the Certificate payload back to the
client (see [3]). The TLS server, however, demands client client (see [3]). The TLS server, however, demands client
authentication and therefore a certificate_request is added [4]. The authentication and therefore a certificate_request is added [4]. The
certificate_type payload in [2] indicates that the TLS server accepts certificate_type payload in [2] indicates that the TLS server accepts
raw public keys. The TLS client, who has a raw public key pre- raw public keys. The TLS client, who has a raw public key pre-
provisioned, returns it in the Certificate payload [5] to the server. provisioned, returns it in the Certificate payload [5] to the server.
skipping to change at page 9, line 47 skipping to change at page 10, line 18
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 7: Example with Raw Public Key provided by the TLS Server and Figure 7: Example with Raw Public Key provided by the TLS Server and
the Client the Client.
In our last example we illustrate a combination of raw public key and 5.3. Combined Usage of Raw Public Keys and X.509 Certificate
X.509 usage. The client uses a raw public key for client
This section shows an example combining raw public keys and X.509
certificates. The client uses a raw public key for client
authentication but the server provides an X.509 certificate. This authentication but the server provides an X.509 certificate. This
exchange starts with the client indicating its ability to process exchange starts with the client indicating its ability to process
X.509 certificates provided by the server, and the ability to send X.509 certificates provided by the server, and the ability to send
raw public keys (see [1]). The server provides the X.509 certificate raw public keys (see [1]). The server provides the X.509 certificate
in [3] with the indication present in [2]. For client authentication in [3] with the indication present in [2]. For client authentication
the server indicates in [4] that it selected the raw public key the server indicates in [4] that it selected the raw public key
format and requests a certificate from the client in [5]. The TLS format and requests a certificate from the client in [5]. The TLS
client provides a raw public key in [6] after receiving and client provides a raw public key in [6] after receiving and
processing the TLS server hello message. processing the TLS server hello message.
skipping to change at page 10, line 32 skipping to change at page 11, line 4
server_certificate_type=(X.509)//[2] server_certificate_type=(X.509)//[2]
certificate, // [3] certificate, // [3]
client_certificate_type=(RawPublicKey)//[4] client_certificate_type=(RawPublicKey)//[4]
certificate_request, // [5] certificate_request, // [5]
server_key_exchange, server_key_exchange,
server_hello_done server_hello_done
certificate, // [6] certificate, // [6]
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 8: Hybrid Certificate Example Figure 8: Hybrid Certificate Example.
6. Security Considerations 6. Security Considerations
The transmission of raw public keys, as described in this document, The transmission of raw public keys, as described in this document,
provides benefits by lowering the over-the-air transmission overhead provides benefits by lowering the over-the-air transmission overhead
since raw public keys are quite naturally smaller than an entire since raw public keys are quite naturally smaller than an entire
certificate. There are also advantages from a code size point of certificate. There are also advantages from a code size point of
view for parsing and processing these keys. The cryptographic view for parsing and processing these keys. The cryptographic
procedures for associating the public key with the possession of a procedures for associating the public key with the possession of a
private key also follows standard procedures. private key also follows standard procedures.
The main security challenge is, however, how to associate the public The main security challenge is, however, how to associate the public
key with a specific entity. Without a secure binding between key with a specific entity. Without a secure binding between
identity and key the protocol will be vulnerable to masquerade and identity and key, the protocol will be vulnerable to masquerade and
man-in-the-middle attacks. This document assumes that such binding man-in-the-middle attacks. This document assumes that such binding
can be made out-of-band and we list a few examples in Section 1. can be made out-of-band and we list a few examples in Section 1.
DANE [RFC6698] offers one such approach. In order to address these DANE [RFC6698] offers one such approach. In order to address these
vulnerabilities, specifications that make use of the extension MUST vulnerabilities, specifications that make use of the extension MUST
specify how the identity and public key are bound. In addition to specify how the identity and public key are bound. In addition to
ensuring the binding is done out-of-band an implementation also needs ensuring the binding is done out-of-band an implementation also needs
to check the status of that binding. to check the status of that binding.
If public keys are obtained using DANE, these public keys are If public keys are obtained using DANE, these public keys are
authenticated via DNSSEC. Pre-configured keys is another out of band authenticated via DNSSEC. Pre-configured keys is another out of
method for authenticating raw public keys. While pre-configured keys band method for authenticating raw public keys. While pre-
are not suitable for a generic Web-based e-commerce environment such configured keys are not suitable for a generic Web-based
keys are a reasonable approach for many smart object deployments e-commerce environment such keys are a reasonable approach for
where there is a close relationship between the software running on many smart object deployments where there is a close relationship
the device and the server-side communication endpoint. Regardless of between the software running on the device and the server-side
the chosen mechanism for out-of-band public key validation an communication endpoint. Regardless of the chosen mechanism for
assessment of the most suitable approach has to be made prior to the out-of-band public key validation an assessment of the most
start of a deployment to ensure the security of the system. suitable approach has to be made prior to the start of a
deployment to ensure the security of the system.
A downgrading attack is another possibility for an adversary to gain
advantages. Thereby, an attacker might try to influence the
handshake exchange to make the parties select different certificate
types than they would normally choose.
For this attack, an attacker must actively change one or more
handshake messages. If this occurs, the client and server will
compute different values for the handshake message hashes. As a
result, the parties will not accept each others' Finished messages.
Without the master_secret, the attacker cannot repair the Finished
messages, so the attack will be discovered.
7. IANA Considerations 7. IANA Considerations
IANA is asked to register a new value in the "TLS Certificate Types" IANA is asked to register a new value in the "TLS Certificate Types"
registry of Transport Layer Security (TLS) Extensions registry of Transport Layer Security (TLS) Extensions
[TLS-Certificate-Types-Registry], as follows: [TLS-Certificate-Types-Registry], as follows:
Value: 2 Value: 2
Description: Raw Public Key Description: Raw Public Key
Reference: [[THIS RFC]] Reference: [[THIS RFC]]
skipping to change at page 12, line 18 skipping to change at page 12, line 40
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 moved to [I-D.ietf-tls-cached-info] after the public keys has been moved to [I-D.ietf-tls-cached-info] after the
discussions at the IETF#82 meeting. discussions at the IETF#82 meeting.
We would like to thank the following persons for their review We would like to thank the following persons for their review
comments: Martin Rex, Bill Frantz, Zach Shelby, Carsten Bormann, comments: Martin Rex, Bill Frantz, Zach Shelby, Carsten Bormann,
Cullen Jennings, Rene Struik, Alper Yegin, Jim Schaad, Barry Leiba, Cullen Jennings, Rene Struik, Alper Yegin, Jim Schaad, Barry Leiba,
Paul Hoffman, Robert Cragie, Nikos Mavrogiannopoulos, Phil Hunt, John Paul Hoffman, Robert Cragie, Nikos Mavrogiannopoulos, Phil Hunt, John
Bradley, Klaus Hartke, Stefan Jucker, Kovatsch Matthias, Daniel Kahn Bradley, Klaus Hartke, Stefan Jucker, Kovatsch Matthias, Daniel Kahn
Gillmor, Peter Sylvester, Hauke Mehrtens, and James Manger. Nikos Gillmor, Peter Sylvester, Hauke Mehrtens, Alexey Melnikov, and James
Mavrogiannopoulos contributed the design for re-using the certificate Manger. Nikos Mavrogiannopoulos contributed the design for re-using
type registry. Barry Leiba contributed guidance for the IANA the certificate type registry. Barry Leiba contributed guidance for
consideration text. Stefan Jucker, Kovatsch Matthias, and Klaus the IANA consideration text. Stefan Jucker, Kovatsch Matthias, and
Hartke provided implementation feedback regarding the Klaus Hartke provided implementation feedback regarding the
SubjectPublicKeyInfo structure. SubjectPublicKeyInfo structure.
Christer Holmberg provided the General Area (Gen-Art) review, Yaron
Sheffer provided the Security Directorate (SecDir) review, Bert
Greevenbosch provided the Applications Area Directorate review, and
Linda Dunbar provided the Operations Directorate review.
We would like to thank our TLS working group chairs, Eric Rescorla We would like to thank our TLS working group chairs, Eric Rescorla
and Joe Salowey, for their guidance and support. Finally, we would and Joe Salowey, for their guidance and support. Finally, we would
like to thank Sean Turner, who is the responsible security area like to thank Sean Turner, who is the responsible security area
director for this work for his review comments and suggestions. director for this work for his review comments and suggestions.
9. References 9. References
9.1. Normative References 9.1. Normative References
[PKIX] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(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.
[RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and [RFC3279] Bassham, L., Polk, W., and R. Housley, "Algorithms and
Identifiers for the Internet X.509 Public Key Identifiers for the Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 3279, April 2002. (CRL) Profile", RFC 3279, April 2002.
[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.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
[RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk, [RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
"Elliptic Curve Cryptography Subject Public Key "Elliptic Curve Cryptography Subject Public Key
Information", RFC 5480, March 2009. Information", RFC 5480, March 2009.
[TLS-Certificate-Types-Registry] [TLS-Certificate-Types-Registry]
, "TLS Certificate Types Registry", February 2013, <http:/ , "TLS Certificate Types Registry", February 2013, <http:/
/www.iana.org/assignments/tls-extensiontype-values#tls- /www.iana.org/assignments/tls-extensiontype-values#tls-
extensiontype-values-2>. extensiontype-values-2>.
[X.690] , "Information technology - ASN.1 encoding rules: > [X.690] ITU, "ITU-T Recommendation X.690 (2002) | ISO/IEC
Specification of Basic Encoding Rules (BER), Canonical > 8825-1:2002, Information technology - ASN.1 encoding
Encoding Rules (CER) and Distinguished Encoding Rules > rules: Specification of Basic Encoding Rules (BER),
(DER).", RFC 5280, 2002. Canonical Encoding Rules (CER) and Distinguished Encoding
Rules (DER)", 2002.
9.2. Informative References 9.2. 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/>.
[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/
skipping to change at page 13, line 35 skipping to change at page 14, line 25
-Marlinspike-Defeating-SSL.pdf>. -Marlinspike-Defeating-SSL.pdf>.
[I-D.ietf-core-coap] [I-D.ietf-core-coap]
Shelby, Z., Hartke, K., and C. Bormann, "Constrained Shelby, Z., Hartke, K., and C. Bormann, "Constrained
Application Protocol (CoAP)", draft-ietf-core-coap-18 Application Protocol (CoAP)", draft-ietf-core-coap-18
(work in progress), June 2013. (work in progress), June 2013.
[I-D.ietf-tls-cached-info] [I-D.ietf-tls-cached-info]
Santesson, S. and H. Tschofenig, "Transport Layer Security Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension", draft-ietf-tls- (TLS) Cached Information Extension", draft-ietf-tls-
cached-info-14 (work in progress), March 2013. cached-info-15 (work in progress), October 2013.
[LDAP] Sermersheim, J., "Lightweight Directory Access Protocol [RFC4511] Sermersheim, J., "Lightweight Directory Access Protocol
(LDAP): The Protocol", RFC 4511, June 2006. (LDAP): The Protocol", RFC 4511, June 2006.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication [RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS) of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, August 2012. Protocol: TLSA", RFC 6698, August 2012.
Appendix A. Example Encoding Appendix A. Example Encoding
For example, the following hex sequence describes a The following example hex sequence describes a SubjectPublicKeyInfo
SubjectPublicKeyInfo structure inside the certificate payload: structure inside the certificate payload:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9
---+------+-----+-----+-----+-----+-----+-----+-----+-----+----- ---+------+-----+-----+-----+-----+-----+-----+-----+-----+-----
1 | 0x30, 0x81, 0x9f, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48, 1 | 0x30, 0x81, 0x9f, 0x30, 0x0d, 0x06, 0x09, 0x2a, 0x86, 0x48,
2 | 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x01, 0x05, 0x00, 0x03, 0x81, 2 | 0x86, 0xf7, 0x0d, 0x01, 0x01, 0x01, 0x05, 0x00, 0x03, 0x81,
3 | 0x8d, 0x00, 0x30, 0x81, 0x89, 0x02, 0x81, 0x81, 0x00, 0xcd, 3 | 0x8d, 0x00, 0x30, 0x81, 0x89, 0x02, 0x81, 0x81, 0x00, 0xcd,
4 | 0xfd, 0x89, 0x48, 0xbe, 0x36, 0xb9, 0x95, 0x76, 0xd4, 0x13, 4 | 0xfd, 0x89, 0x48, 0xbe, 0x36, 0xb9, 0x95, 0x76, 0xd4, 0x13,
5 | 0x30, 0x0e, 0xbf, 0xb2, 0xed, 0x67, 0x0a, 0xc0, 0x16, 0x3f, 5 | 0x30, 0x0e, 0xbf, 0xb2, 0xed, 0x67, 0x0a, 0xc0, 0x16, 0x3f,
6 | 0x51, 0x09, 0x9d, 0x29, 0x2f, 0xb2, 0x6d, 0x3f, 0x3e, 0x6c, 6 | 0x51, 0x09, 0x9d, 0x29, 0x2f, 0xb2, 0x6d, 0x3f, 0x3e, 0x6c,
7 | 0x2f, 0x90, 0x80, 0xa1, 0x71, 0xdf, 0xbe, 0x38, 0xc5, 0xcb, 7 | 0x2f, 0x90, 0x80, 0xa1, 0x71, 0xdf, 0xbe, 0x38, 0xc5, 0xcb,
skipping to change at page 14, line 23 skipping to change at page 15, line 13
11 | 0xa2, 0x84, 0xf8, 0x65, 0xc7, 0xce, 0x2d, 0x96, 0x17, 0xaa, 11 | 0xa2, 0x84, 0xf8, 0x65, 0xc7, 0xce, 0x2d, 0x96, 0x17, 0xaa,
12 | 0x91, 0xf8, 0x61, 0x04, 0x50, 0x70, 0xeb, 0xb4, 0x43, 0xb7, 12 | 0x91, 0xf8, 0x61, 0x04, 0x50, 0x70, 0xeb, 0xb4, 0x43, 0xb7,
13 | 0xdc, 0x9a, 0xcc, 0x31, 0x01, 0x14, 0xd4, 0xcd, 0xcc, 0xc2, 13 | 0xdc, 0x9a, 0xcc, 0x31, 0x01, 0x14, 0xd4, 0xcd, 0xcc, 0xc2,
14 | 0x37, 0x6d, 0x69, 0x82, 0xd6, 0xc6, 0xc4, 0xbe, 0xf2, 0x34, 14 | 0x37, 0x6d, 0x69, 0x82, 0xd6, 0xc6, 0xc4, 0xbe, 0xf2, 0x34,
15 | 0xa5, 0xc9, 0xa6, 0x19, 0x53, 0x32, 0x7a, 0x86, 0x0e, 0x91, 15 | 0xa5, 0xc9, 0xa6, 0x19, 0x53, 0x32, 0x7a, 0x86, 0x0e, 0x91,
16 | 0x82, 0x0f, 0xa1, 0x42, 0x54, 0xaa, 0x01, 0x02, 0x03, 0x01, 16 | 0x82, 0x0f, 0xa1, 0x42, 0x54, 0xaa, 0x01, 0x02, 0x03, 0x01,
17 | 0x00, 0x01 17 | 0x00, 0x01
Figure 9: Example SubjectPublicKeyInfo Structure Byte Sequence. Figure 9: Example SubjectPublicKeyInfo Structure Byte Sequence.
The decoded byte-sequence shown in Figure 9 (for example using We used Peter Gutmann's ASN.1 decoder [ASN.1-Dump] to turn the above-
Peter's ASN.1 decoder [ASN.1-Dump]) illustrates the structure, as shown byte-sequence into an ASN.1 structure, as shown in of the
shown in Figure 10. Figure 10.
Offset Length Description Offset Length Description
------------------------------------------------------------------- -------------------------------------------------------------------
0 3+159: SEQUENCE { 0 3+159: SEQUENCE {
3 2+13: SEQUENCE { 3 2+13: SEQUENCE {
5 2+9: OBJECT IDENTIFIER Value (1 2 840 113549 1 1 1) 5 2+9: OBJECT IDENTIFIER Value (1 2 840 113549 1 1 1)
: PKCS #1, rsaEncryption : PKCS #1, rsaEncryption
16 2+0: NULL 16 2+0: NULL
: } : }
18 3+141: BIT STRING, encapsulates { 18 3+141: BIT STRING, encapsulates {
skipping to change at page 15, line 4 skipping to change at page 15, line 36
22 3+137: SEQUENCE { 22 3+137: SEQUENCE {
25 3+129: INTEGER Value (1024 bit) 25 3+129: INTEGER Value (1024 bit)
157 2+3: INTEGER Value (65537) 157 2+3: INTEGER Value (65537)
: } : }
: } : }
: } : }
Figure 10: Decoding of Example SubjectPublicKeyInfo Structure. Figure 10: Decoding of Example SubjectPublicKeyInfo Structure.
Authors' Addresses Authors' Addresses
Paul Wouters (editor) Paul Wouters (editor)
Red Hat Red Hat
Email: paul@nohats.ca Email: paul@nohats.ca
Hannes Tschofenig (editor) Hannes Tschofenig (editor)
Nokia Siemens Networks Nokia Solutions and Networks
Linnoitustie 6 Linnoitustie 6
Espoo 02600 Espoo 02600
Finland Finland
Phone: +358 (50) 4871445 Phone: +358 (50) 4871445
Email: Hannes.Tschofenig@gmx.net Email: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at URI: http://www.tschofenig.priv.at
John Gilmore John Gilmore
PO Box 170608 PO Box 170608
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