Internet Engineering Task Force P. Hallam-Baker
Internet-Draft Comodo Group Inc.
Intended status: Standards Track June 12, 2013
Expires: December 14, 2013
JSON Service Connect (JCX) Protocol
draft-hallambaker-wsconnect-01
Abstract
JSON Service Connect (JCX) is a JSON/REST Web Service that may be
used to establish and maintain a 'connection binding' of a device to
an account held with a Web Service Provider. Multiple connection
bindings may be established under the same account to support
multiple devices and/or multiple users of a single device. A
connection binding permits a device to securely connect to one or
more services offered by the Web Service Provider with support for
protocol and protocol version agilty and fault tollerance.
The protocol is presented as a HTTP/JSON Web Service and uses the
HTTP session continuation mechanism for authentication of transaction
messages and supports negotiation of a HTTP session continuation
mechanism context for the established endpoint connections.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 14, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Introduction and Purpose . . . . . . . . . . . . . . . . . . 3
2.1. Establishing a Web Service Provider Account . . . . . . . 4
2.2. Establishing a Connection Binding . . . . . . . . . . . . 4
2.2.1. PIN Code Establishement. . . . . . . . . . . . . . . 5
2.2.2. Out of Band Completion. . . . . . . . . . . . . . . . 5
2.2.3. QR Code Preauthorization. . . . . . . . . . . . . . . 5
3. Example Uses . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. PIN code establishment . . . . . . . . . . . . . . . . . 6
3.2. Unbinding . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3. Out of Band Completion . . . . . . . . . . . . . . . . . 12
4. OBPConnection . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. Message: Message . . . . . . . . . . . . . . . . . . . . 13
4.2. Message: Response . . . . . . . . . . . . . . . . . . . . 13
4.3. Message: ErrorResponse . . . . . . . . . . . . . . . . . 13
4.4. Message: Request . . . . . . . . . . . . . . . . . . . . 13
4.5. Structure: Cryptographic . . . . . . . . . . . . . . . . 13
4.6. Structure: ImageLink . . . . . . . . . . . . . . . . . . 13
4.7. Structure: Connection . . . . . . . . . . . . . . . . . . 14
4.8. Bind . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.9. Message: BindRequest . . . . . . . . . . . . . . . . . . 14
4.10. Message: BindResponse . . . . . . . . . . . . . . . . . . 15
4.11. Message: OpenRequest . . . . . . . . . . . . . . . . . . 15
4.12. Message: OpenResponse . . . . . . . . . . . . . . . . . . 16
4.13. Message: TicketRequest . . . . . . . . . . . . . . . . . 16
4.14. Message: TicketResponse . . . . . . . . . . . . . . . . . 16
4.15. Unbind . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.16. Message: UnbindRequest . . . . . . . . . . . . . . . . . 16
4.17. Message: UnbindResponse . . . . . . . . . . . . . . . . . 16
5. Mutual Authentication . . . . . . . . . . . . . . . . . . . . 17
5.1. PIN Authentication . . . . . . . . . . . . . . . . . . . 17
5.2. Example: Latin PIN Code . . . . . . . . . . . . . . . . . 20
5.3. Example: Cyrillic PIN Code . . . . . . . . . . . . . . . 20
5.4. Out of Band Confirmation . . . . . . . . . . . . . . . . 20
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
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7. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7.1. Denial of Service . . . . . . . . . . . . . . . . . . . . 21
7.2. Breach of Trust . . . . . . . . . . . . . . . . . . . . . 21
7.3. Coercion . . . . . . . . . . . . . . . . . . . . . . . . 21
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9. Normative References . . . . . . . . . . . . . . . . . . . . 21
Appendix A. Stateless server . . . . . . . . . . . . . . . . . . 22
A.1. Temporary ID . . . . . . . . . . . . . . . . . . . . . . 22
A.2. Connection Binding ID . . . . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 23
1. Definitions
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Introduction and Purpose
JSON Service Connect (JCX) is a JSON/REST Web Service that may be
used to establish and maintain a 'connection binding' of a device to
an account held with a Web Service Provider (WSP).
A Connection Binding comprises a set of long term credentials used to
authenticate interactions with the JCX service itself and a set of
'Service Connections' to specific services offered by the Web Service
Provider.
Each service connection in turn comprises a collection of 'Instance
Connections' which describe a specific instances of the Web Service.
For example Alice is a consumer and example.com a provider of a range
of Web Services including anti-malware protection and management of
home automation devices. Alice has 42 devices of different types
that each make use of one or more of the Web Services proviced by
example.com. All the devices are enrolled in the same JCX account
'alice@example.com' but each device has a unique connection binding
and different devices make use of different Web Services.
The centralized account provides Alice with a single point of control
from which she can authorize the addition of new devices to the
account or the removal of devices that are deactivated. This allows
Alice to avoid the need to manage a device such as a network-enabled
lightswitch through the lightswitch itself.
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To ensure continuity of service in case of network failure or
administration work, example.com provides multiple instances of its
Web Services hosted on different machines. Different users MAY be
granted access to a different collection of service instances
according to their needs and the service tier they are subscribed to.
2.1. Establishing a Web Service Provider Account
The means by which the Web Service Provider Account is established is
outside the scope of this document.
In a typical case the user would establish an account with their
chosen Web Service Provider through the normal process of using a Web
Browser to access the Web Service Provider's site and entering such
data as the Web Service Provider requires into a HTML form.
Depending on the circumstances, the data provided by the applicant
may require verification before the account is created.
[Default accounts for appliances that are going to be implicitly
authenticated by reference to the network they are on.]
2.2. Establishing a Connection Binding
A connection binding represents a long term association between a
device and an account at the Web Service Provider. The association
includes the establishment of an authentication context between the
device and the JCX service.
An authentication context consists of:
A Context Identifier.
An authentication algorithm.
A secret key.
The context identifier is an opaque string assigned by the JCX
service. Following the approach introduced in Kerberos, a JCX
service MAY eliminate the need to store authentication context
information by encoding the authentication algorithm and encrypted
secret key in the context identifier.
The authentication context can ensure that future communications are
secured against impersonation if and only if the original process of
establishing a connection binding was secured against communication.
Mutual authentication is therefore an essential requirement.
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The means by which the connection binding is established depend on
the affordances of the device in question. Establishing a connection
binding to a device with a keyboard is easily accomplished through
use of a one-time PIN code. But many embedded devices do not provide
a keyboard or similar affordance.
The following modes of session establishement are supported:
PIN Code Establishement.
Out of Band Completion.
QR Code Establishement.
2.2.1. PIN Code Establishement.
To establish a connection binding for a new mobile phone, Alice logs
into her JCX account manager and requests a new PIN code. She then
starts the application that makes use of a JCX account and selects
'create new binding'. She is prompted for and enters her account
name (alice@example.com) and PIN.
The client connects to the JCX service and verifies that the TLS
certificate presented is correct for example.com and has been issued
in accordance with issue practices that ensure an appropriately high
degree of trust (e.g. the CABForum Extended Validation requirements).
2.2.2. Out of Band Completion.
To establish a connection binding for her new toaster oven, Alice
plugs the appliance into her local network and enters her account
name into the device. Since she has not obtained a PIN code in
advance, she leaves the entry blank.
To complete the process, Alice logs into her JCX account where she
sees that a new device is available to add to the account. To help
identify the correct device, there is a picture of the toaster oven,
the model name and serial number.
2.2.3. QR Code Preauthorization.
Alice decides to remodel the kitchen completely and plans to install
a dozen new network enabled LED light fixtures. Using an application
on the mobile phone she enabled earlier, Alice scans a QR code
attached to each fixture before the devices are installed. When the
fixtures are installed and powered, the connection binding is
preauthorized.
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3. Example Uses
3.1. PIN code establishment
Alice buys a new laptop computer which she wishes to use with the
malware protection service provided by example.com. Alice has an
existing account 'alice' with this Web Service Provider and obtains a
pin code Q80370-1RA606-F04B from the Web Service Provider Web site.
Alice enters the values alice@example.com and Q80370-1RA606-F04B into
the Web Service client she wishes to use with the Web Service
Provider on the new laptop.
The client obtains the JCX service for example.com using DNS SRV
discovery. The client establishes a TLS connection to the service
and verifies that the certificate provided has a valid certificate
path, has not been revoked and meets the validation criteria of the
client. Since the purpose of this particular Web Service client is
to provide security, the client requires that an Extended Validation
certificate be presented.
Having established a TLS connection to the JCX Service, the client
sends the following HTTP request:
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Post / HTTP/1.1
Host: example.com
Cache-Control: no-store
Content-Type: Application/json;charset=UTF-8
Content-Length: 470
{
"OpenRequest": {
"Encryption": ["HS256",
"HS384",
"HS512",
"HS256T128"],
"Authentication": ["A128CBC",
"A256CBC",
"A128GCM",
"A256GCM"],
"Account": "alice",
"Domain": "example.com",
"HavePasscode": true,
"HaveDisplay": true,
"Challenge": "d2gdVeQesS3UTOgtK4JSEg==",
"DeviceID": "Serial:0002212",
"DeviceURI": "http://comodo.com/dragon/v3.4",
"DeviceName": "Comodo Dragon"}}
To prevent man in the middle attack, the client does not send the PIN
code in the initial request. The PIN code is only sent after the
service responds with a challenge nonce to be used to prevent replay
attack.
The service receives the request, determines that is meets its access
control policy and selects a set of cryptographic parameters from the
set proposed by the client. In this case the service prefers the use
of AES128CBC for encryption and the HS256 Message Authentication Code
for authentication.
The service determines that a PIN code has been issued for the
account and uses the value of that PIN to generate a response to the
challenge presented by the client. A new challenge is generated to
test the client knowledge of the PIN.
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[TBS: Is there a need for the service to be able to support multiple
outstanding PIN codes for the same account? This could be supported
by providing the last 2 significant characters of the PIN code to the
service which could use it as an index. This would enable several
hundred simultaneous outstanding requests which should be enough for
most applications. Large volume applications would need to use a
different scheme.]
The service sends the following response to the client:
HTTP/1.1 203 Passcode
Content-Type: application/json;charset=UTF-8
Content-Length: 500
{ "Status" : "Authenticate",
"OpenResponse": {
"Status": 203,
"StatusDescription": "Passcode",
"Cryptographic": [{
"Secret": "11bmdFi9Et7KIUg8aeN2AQ==",
"Encryption": "A128CBC",
"Authentication": "HS256",
"Ticket":
"TUMnorO0SjHHS7D2uFcGlRYJ0Hd3eibwe0ogptoNMQuCYmCHfHAJcJlyvi
j8WoXDglTSOkctnmoBzl8W0NLSlcgSyZcmsAyoWs8y1Rn2ZlO2WBgoWrFIO
qPa4oB29dgs/ei6ieINZtmvXNCm2NUkWA=="}],
"Challenge": "alX8aAWH6acSqO3FTT94HA==",
"ChallengeResponse": "enT5myMw8w2hV4H32Ntx/g=="}}
To complete the transaction, the client sends a TicketRequest message
to the service containing a response to the PIN challenge sent by the
service (ChallengeResponse).
The TicketRequest message is authenticated using HTTP Session
authentication under the shared secret specified in the OpenResponse
message:
Post / HTTP/1.1
Host: example.com
Cache-Control: no-store
Content-Type: Application/json;charset=UTF-8
Content-Length: 78
Session:
Value=cjkMkfnnYP8JYWZAbRLvtpqImmOK3rsrOT1XcvAgHDk=;
Id=TUMnorO0SjHHS7D2uFcGlRYJ0Hd3eibwe0ogptoNMQuCYmCHfHAJcJlyvi
j8WoXDglTSOkctnmoBzl8W0NLSlcgSyZcmsAyoWs8y1Rn2ZlO2WBgoWrFIOqPa4
oB29dgs/ei6ieINZtmvXNCm2NUkWA==
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{
"TicketRequest": {
"ChallengeResponse": "TctLOG74cwpm26YNpEibcQ=="}}
The service checks the value of ChallengeResponse against the known
PIN and if the result is correct establishes parameters for the
Connection Binding for the device.
In this case the server uses the Session Id parameter to encode
permissions associated with the request as described in
[Appendix TBS]. Accordingly the server must replace the Session Id
whenever the associated permissions change. Accordingly, the server
replaces the cryptographic parameters specified in the OpenResponse
request for use in future JCX service requests. In this case the
server returns three connections, each offering a different transport
protocol option. Each connection specifies its own set of
cryptographic parameters (or will when the code is written for that).
The service also returns a service connection the malware protection
service the client requested access to. This service connection
specifies three different service instances. Each service instance
has its own set of cryptographic parameters for use with HTTP session
authentication. In this case the three different service instances
offer different means of accessing the same service: as a JSON Web
Service over HTTP, using a binary encoding over a UDP transport and
tunnelling via DNS.
HTTP/1.1 200 Complete
Content-Type: application/json;charset=UTF-8
Content-Length: 1907
Session:
Value=nKhjR1r2eYPga0rmDfHT4HOvgQ+EuUoQPwzIl0btljs=;
Id=TUMnorO0SjHHS7D2uFcGlRYJ0Hd3eibwe0ogptoNMQuCYmCHfHAJcJlyvi
j8WoXDglTSOkctnmoBzl8W0NLSlcgSyZcmsAyoWs8y1Rn2ZlO2WBgoWrFIOqPa4
oB29dgs/ei6ieINZtmvXNCm2NUkWA==
{ "Status" : "Success",
"TicketResponse": {
"Status": 200,
"StatusDescription": "Complete",
"Cryptographic": [{
"Protocol": "OBPConnection",
"Secret": "HQuQg4GkzTwTVoGxar0EXg==",
"Encryption": "A128CBC",
"Authentication": "HS256",
"Ticket":
"0ulMVMMfY/pLHZ0FlIy2zDnNycYz9Znvs3JJYQGlZ+dWaxMNxm/jLEsJd/
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0qsAc5qp8fjBoMN49V9DkDgM4UYJxVriqfr64RyTTgug2taHY="}],
"Service": [{
"Name": "obp1.example.com",
"Port": 443,
"Address": "10.1.2.3",
"Priority": 1,
"Weight": 100,
"Transport": "WebService",
"Cryptographic": {
"Protocol": "OBPQuery",
"Secret": "kezeXxhkzXgxY7vpkHUb1g==",
"Encryption": "A128CBC",
"Authentication": "HS256",
"Ticket":
"jpBXvI7/0WTmwI2NN4n7Vvw96nbS9LpSsSNMIkdapiUoLikSkjpgMrtb
VKz5lHOPloCgAyZXxfZpQRsp4oPY4BcRaMw6F5na62IHnBVDeXg="}},
{
"Name": "dns1.example.com",
"Port": 53,
"Address": "10.1.2.2",
"Priority": 1,
"Weight": 100,
"Transport": "DNS",
"Cryptographic": {
"Protocol": "OBPQuery",
"Secret": "Wk3m7DlL/GStBBm3xUjyzg==",
"Encryption": "A128CBC",
"Authentication": "HS256",
"Ticket":
"Q9r4hXefHhLvgpKHVg3w2p7VptVH9qidGiIa4Nw3Zp5hZR816h9+PRj5
sye1jmIhy4sYA/jfK/g4OrSngK9xWO7Qg3/iQ+YTAchKQjdJtN4="}},
{
"Name": "udp.example.com",
"Port": 5000,
"Address": "10.1.2.2",
"Priority": 1,
"Weight": 100,
"Transport": "UDP",
"Cryptographic": {
"Protocol": "OBPQuery",
"Secret": "wBiguG9FGj08nS/c/njp4Q==",
"Encryption": "A128CBC",
"Authentication": "HS256",
"Ticket":
"F8LPKTL+XaAX0eJsM22fdJ37BRS816dKXD66UbD8NAVKOgOu556uS8WW
AMj+dJbJaErUzo/vw7tY0icCu1bw8qHmOO4gzhbSbD4Nga2EAU4="}}]}
}
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3.2. Unbinding
After a year of use, Alice decides to replace the laptop with a new
one. Before selling the old laptop on EBay, she tells the Web
Service client to cancel the connection to the Web Service Provider.
The client sends the following mesasage to the provider:
Post / HTTP/1.1
Host: example.com
Cache-Control: no-store
Content-Type: Application/json;charset=UTF-8
Content-Length: 25
Session:
Value=bZU61eCOW4nVnfdJNS719HL4IsNVxtoTgoRt+mqLbWY=;
ID=0ulMVMMfY/pLHZ0FlIy2zDnNycYz9Znvs3JJYQGlZ+dWaxMNxm/jLEsJd/
0qsAc5qp8fjBoMN49V9DkDgM4UYJxVriqfr64RyTTgug2taHY=
{
"UnbindRequest": {}}
The Session ID specifies the connection binding. Since the Unbind
Request is only valid for that connection binding, there is no need
to specify the connection binding further in the request.
The server verifies that the request was authenticated and returns a
successful response:
HTTP/1.1 200 Complete
Content-Type: application/json;charset=UTF-8
Content-Length: 26
Session:
Value=9P1FmroeFU7y9qHgXdSFXH2qSImh0cQpaSgZrx5IswM=;
Id=0ulMVMMfY/pLHZ0FlIy2zDnNycYz9Znvs3JJYQGlZ+dWaxMNxm/jLEsJd/
0qsAc5qp8fjBoMN49V9DkDgM4UYJxVriqfr64RyTTgug2taHY=
{ "Status" : "Success",
"UnbindResponse": {}}
[TBS: Add in the status response back into the JSON message. ]
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3.3. Out of Band Completion
Alice purchases an Internet enabled coffee pot. The installer
configures the coffee pot in her kitchen but does not have access to
Alice's JCX account or a PIN code to configure it.
The installer configures the coffee pot to use the JCX account
specified by Alice. The coffee pot does not have a pssscode to enter
but does have a link to an image of the coffee pot.
The client sends the following request:
[TBS: non pin code example]
Since the client does not have a PIN code, there is no need to return
a challenge. Instead the service returns the status "OOB" to
indicate that the transaction will be completed out of band.
[TBS: non pin code example]
By default the coffee pot attempts to complete the JCX connection at
ten second intervals for the first ten minutes, every thirty seconds
for the next hour, every five minutes for the following 24 hours and
once an hour thereafter.
The client sends the following request to check the status of the
request:
[TBS: should add in a parameter 'don't call again for x seconds']
The first service response tells the coffee pot not to ask again
until five minutes have elapsed:
[TBS: non pin code example]
The installer calls Alice to tell her that the coffee pot is ready to
connect. Alice authorizes the connection remotely via the Web
Service Provider's Web site. Alice identifies the request to connect
the coffee pot by means of the image provided. She can also use the
same image to help determine which connection to cancel when the
coffee pot is replaced.
The next time the coffee pot requests a status update, the service
responds with the connection binding parameters:
[TBS: non pin code example]
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4. OBPConnection
4.1. Message: Message
4.2. Message: Response
Application layer server status code
Describes the status code (ignored by processors)
4.3. Message: ErrorResponse
An error response MAY be returned in response to any request.
Note that requests MAY be rejected by the code implementing the
transport binding before application processing begins and so a
server is not guaranteed to provide an error response message.
4.4. Message: Request
Opaque ticket issued by the server that identifies the
cryptographic parameters for encryption and authentication of
the message payload.
4.5. Structure: Cryptographic
Parameters describing a cryptographic context.
OBP tickets MAY be restricted to use with either the management
protocol (Management) or the query protocol (Query). If so a
service would typically specify a ticket with a long expiry
time or no expiry for use with the management protocol and a
separate ticket for use with the query protocol.
Shared secret
Encryption Algorithm selected
Authentication Algorithm selected
Opaque ticket issued by the server that identifies the
cryptographic parameters for encryption and authentication of
the message payload.
Date and time at which the context will expire
4.6. Structure: ImageLink
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Image encoding algorithm (e.g. JPG, PNG)
Image data as specified by algorithm
4.7. Structure: Connection
Contains information describing a network connection.
DNS Name. Since one of the functions of an OBP service is name
resolution, a DNS name is only used to establish a connection
if connection by means of the IP address fails.
TCP or UDP port number.
IPv4 (32 bit) or IPv6 (128 bit) service address
Service priority. Services with lower priority numbers SHOULD
be attempted before those with higher numbers.
Weight to be used to select between services of equal priority.
OBP Transport binding to be used valid values are HTTP, DNS and
UDP.
Date and time at which the specified connection context will
expire.
4.8. Bind
Binding a device is a two step protocol that begins with the Start
Query followed by a sequence of Ticket queries.
4.9. Message: BindRequest
The following parameters MAY occur in either a StartRequest or
TicketRequest:
Encryption Algorithm that the client accepts. A Client MAY
offer multiple algorithms. If no algorithms are specified then
support for the mandatory to implement algorithm is assumed.
Otherwise mandatory to implement algorithms MUST be specified
explicitly.
Authentication Algorithm that the client accepts. If no
algorithms are specified then support for the mandatory to
implement algorithm is assumed. Otherwise mandatory to
implement algorithms MUST be specified explicitly.
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4.10. Message: BindResponse
The following parameters MAY occur in either a StartResponse or
TicketResponse:
Cryptographic Parameters.
A Connection describing an OBP service point
4.11. Message: OpenRequest
The OpenRequest Message is used to begin a device binding
transaction. Depending on the authentication requirements of the
service the transaction may be completed in a single query or require
a further Ticket Query to complete.
If authentication is required, the mechanism to be used depends on
the capabilities of the device, the requirements of the broker and
the existing relationship between the user and the broker.
If the device supports some means of data entry, authentication MAY
be achieved by entering a passcode previously delivered out of band
into the device.
The OpenRequest specifies the properties of the service (Account,
Domain) and Device (ID, URI, Name) that will remain constant
throughout the period that the device binding is active and
parameters to be used for the mutual authentication protocol.
Account name of the user at the OBP service
Domain name of the OBP broker service
If 'true', the user has entered a passcode value for use with
passcode authentication.
Specifies if the device is capable of displaying information to
the user or not.
Client challenge value to be used in authentication challenge
Device identifier unique for a particular instance of a device
such as a MAC or EUI-64 address expressed as a URI
Device identifier specifying the type of device, e.g. an
xPhone.
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Descriptive name for the device that would distinguish it from
other similar devices, e.g. 'Alice's xPhone".
4.12. Message: OpenResponse
An Open request MAY be accepted immediately or be held pending
completion of an inband or out-of-band authentication process.
The OpenResponse returns a ticket and a set of cryptographic
connection parameters in either case. If the
Challenge value to be used by the client to respond to the
server authentication challenge.
Server response to authentication challenge by the client
Link to an image to be used in an image verification mechanism.
4.13. Message: TicketRequest
The TicketRequest message is used to (1) complete a binding request
begun with an OpenRequest and (2) to refresh ticket or connection
parameters as necessary.
The response to a server authentication challenge.
4.14. Message: TicketResponse
The TicketResponse message returns cryptographic and/or connection
context information to a client.
4.15. Unbind
Requests that a previous device association be deleted.
4.16. Message: UnbindRequest
Since the ticket identifies the binding to be deleted, the only thing
that the unbind message need specify is that the device wishes to
cancel the binding.
4.17. Message: UnbindResponse
Reports on the success of the unbinding operation.
If the server reports success, the client SHOULD delete the ticket
and all information relating to the binding.
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A service MAY continue to accept a ticket after an unbind request has
been granted but MUST NOT accept such a ticket for a bind request.
5. Mutual Authentication
A Connection Service MAY require that a connection request be
authenticated. Two authentication mechanisms are defined.
PIN Code: The client and server demonstrate mutual knowledge of a
PIN code previously exchanged out of band.
Out of Band Confirmation: The request for access is confirmed out
of band.
In addition, services MAY accept the use of any message or transport
layer authentication scheme. For example HTTP Session Continuation
or Transport Layer Security with client authentication.
5.1. PIN Authentication
PIN code authentication provides users with a simple and often
familiar mechanism for authenticating the connection request. The
means by which the user obtains the PIN code is outside the scope of
this document. Possible methods for distributing the PIN code
include obtaining the code from an account management Web site
provided by the Web Service Provider, letter post, email and in
person.
Although the PIN value is never exposed on the wire in any form, the
protcol considers the PIN value to be text encoded in UTF8 encoding.
To encourage readability, the use of space (0x20) and hyphen (0x2D)
characters to arrange PIN characters into groups of four to seven
characters is encouraged. To avoid the risk of this practice
introducing user error, space and hyphen characters are ignored when
processing the PIN value.
Support for the full UNICODE character set in PIN codes is intended
to facilitate provision of PIN codes in the user's native language.
Web Service Providers MAY make use of any UNICODE characters they
choose but capricious choices are likely to cause users difficulty.
For example a PIN code MAY contain the ZAPF Dingbats thick tick mark
(U+2704) but users would almost certainly find it difficult to enter
and may confuse it with the similar thin tick mark (U+2703).
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Servers that support PIN Authorization SHOULD offer the choice of a
PIN that only uses numeric digits ('0', '1', '2', '3', '4', '5', '6',
'7', '8', '9'). Clients that support PIN Authorization MUST allow
entry of PINS that only contain numeric digits.
The PIN Mechanism is a three step process:
The client sends an OpenRequest message to the Service containing
a challenge value CC.
The service returns an OpenResponse message containing to the
client a server challenge value SV and a server response value SR.
The client sends a TicketRequest message to the service containing
a client response value CR.
Since no prior authentication key has been established the
OpenRequest and OpenResponse messages are sent without message
authentication.
The Challenge values CC, and SC are cryptographic nonces. The nonces
SHOULD be generated using an appropriate cryptographic random source.
The nonces MUST be at least as long as 128 bits, MUST be at least the
minimum key size of the authentication algorithm used and MUST NOT
more than 640 bits in length (640 bits should be enough for anybody).
The server response and client response values are generated using an
authentication algorithm selected by the server from the choices
proposed by the client in the OpenRequest message.
The algorithn chosen may be a MAC algorithm or an encrypt-with-
authentication (EWA) algorithm. If an EWA is specified, the
encrypted data is discarded and only the authentication value is used
in its place.
Let A(d,k) be the authentication value obtained by applying the
authentication algorithm with key k to data d.
To create the Server Response value, the UTF8 encoding of the PIN
value 'P' is first pre-processed to remove space and hyphen
characters, then converted into a symmetric key KPC by using the
Client challenge value as the key truncating if necessary and then
applied to the of the OpenRequest message:
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KPC = A (PIN, CC)
SR = A (Secret + SC + OpenRequest, KPC)
In the Web Service Binding, the Payload of the message is the HTTP
Body as presented on the wire. The Secret and Server Challenge are
presented in their binary format and the '+' operator stands for
simple concatenation of the binary sequences.
This protocol construction ensures that the party constructing SR:
Knows the PIN code value (through the construction of KPC).
Is responding to the Open Request Message (SR depends on
OpenRequest).
Has knowlege of the secret key which MUST be used to authenticate
the following TicketRequest/TicketResponse interaction that will
establish the actual connection.
Does not provide an oracle the PIN value. That is, the protocol
does not provide a service that reveals the (since the value SR
includes the value SC which is a random nonce generated by the
server and cannot be predicted by the client).
To create the Client Response value, secret key is applied to the PIN
value and server Challenge:
CR = A (PIN + SC + OpenRequest, Secret)
Note that the server can calculate the value of the Client Response
token at the time that it generates the Server Challenge. This
minimizes the amount of state that needs to be carried from one
request to the next in the Ticket value when using the stateless
server implementation described in section Appendix A
This protocol construction ensures that the generator of CR
Knows the PIN value.
Is respoding to the OpenResponse generated by the server.
Note that while disclosure of an oracle for the PIN value is a
concern in the construction of CR, this is not the case in the
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construction of SR since the client has already demonstrated
knowledge of the PIN value.
5.2. Example: Latin PIN Code
The Connection Request example of section Section 3 demonstrates the
use of an alphanumeric PIN code using the Latin alphabet.
The PIN code is [Q80370-1RA606-F04B] and the authentication algorithm
is [HS256]. The value KP is thus:
[TBS]
The data over which the hash value is calulated is Secret + SC +
OpenRequest:
[TBS]
Applying the derrived key to the data produces the server response:
The data for the client response is PIN + SC:
[TBS]
Applying the secret key to the data produces the client response:
[TBS]
5.3. Example: Cyrillic PIN Code
If the PIN code in the earlier example was [] the value KP would be:
[TBS]
The Server Response would be:
[TBS]
The rest of the protocol would then continue as before.
5.4. Out of Band Confirmation
The Out Of Band Confirmation mechanism is a three step process in
which:
The client makes an OpenRequest message to the service and obtains
an OpenResponse message.
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The connection binding is authorized through an out of band
process.
The client makes a TicketRequest to the service and obtains a
TicketResponse message to complete the exchange.
Since no prior authentication key has been established the
OpenRequest and OpenResponse messages are sent without
authentication.
The principal concern in the Out Of Band Confirmation mechanism is
ensuring that the party authorizing the request is able to identify
which party originated the request they are attempting to identify.
If a device has the ability to display an image it MAY set the
HasDisplay=true in the OpenRequest message. If the broker recieves
an OpenRequest with the HasDisplay value set to true, the
OpenResponse MAY contain one or more VerificationImage entries
specifying image data that is to be displayed to the user by both the
client and the confirmation interface.
Before confirming the request, the user SHOULD verify that the two
images are the same and reject the request in the case that they are
not.
Many devices do not have a display capability, in particular an
embedded device such as a network switch or a thermostat. In this
case the device MAY be identified by means of the information
provided in DeviceID, DeviceURI, DeviceImage and DeviceName.
6. Acknowledgements
[List of contributors]
7. Security Considerations
7.1. Denial of Service
7.2. Breach of Trust
7.3. Coercion
8. IANA Considerations
[TBS list out all the code points that require an IANA registration]
9. Normative References
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[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 4366, April 2006.
[X.509] International Telecommunication Union , "ITU-T
Recommendation X.509 (11/2008): Information technology -
Open systems interconnection - The Directory: Public-key
and attribute certificate frameworks ", ITU-T
Recommendation X.509, November 2008.
[X.680] International Telecommunication Union , "ITU-T
Recommendation X.680 (11/2008): Information technology -
Abstract Syntax Notation One (ASN.1): Specification of
basic notation ", ITU-T Recommendation X.680, November
2008.
Appendix A. Stateless server
The protocol is designed to permit but not require the server to
store connection binding state in the Session ID of the HTTP Session
Continuation authentication mechanism.
The Session IDs are opaque as far as the client is concerned. The
client receives the Session ID from the service and returns it with
each request. The internal structure of the Session ID is therefore
outside the scope of this specification but is provided here to
assist implementers.
In the PIN Authentication example, two SessionIDs are issued by the
server:
A temporary ID in response to the initial client OpenRequest.
A connection binding ID when the client PIN confirmation is
accepted and the connection binding is created.
A.1. Temporary ID
[TBS]
A.2. Connection Binding ID
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Author's Address
Phillip Hallam-Baker
Comodo Group Inc.
Email: philliph@comodo.com
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