Web Services Connect Protocol
draft-hallambaker-wsconnect-00
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| Author | Phillip Hallam-Baker | ||
| Last updated | 2013-05-17 | ||
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draft-hallambaker-wsconnect-00
Internet Engineering Task Force P. Hallam-Baker
Internet-Draft Comodo Group Inc.
Intended status: Standards Track May 17, 2013
Expires: November 18, 2013
Web Services Connect Protocol
draft-hallambaker-wsconnect-00
Abstract
Many Web Services share a requirement for establishing and
maintaining a persistent connection between the client and service.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 18, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Omnibroker Connection Maintenance Service . . . . . . . . . . 3
3.1. Authentication . . . . . . . . . . . . . . . . . . . . . . 3
3.1.1. Broker Authentication . . . . . . . . . . . . . . . . 3
3.1.2. Device Authentication . . . . . . . . . . . . . . . . 3
3.1.3. Illustrative example . . . . . . . . . . . . . . . . . 4
3.2. OBPConnection . . . . . . . . . . . . . . . . . . . . . . 9
3.2.1. Message: Message . . . . . . . . . . . . . . . . . . . 9
3.2.2. Message: Response . . . . . . . . . . . . . . . . . . 9
3.2.3. Message: ErrorResponse . . . . . . . . . . . . . . . . 9
3.2.4. Message: Request . . . . . . . . . . . . . . . . . . . 10
3.2.5. Structure: Cryptographic . . . . . . . . . . . . . . . 10
3.2.6. Structure: ImageLink . . . . . . . . . . . . . . . . . 10
3.2.7. Structure: Connection . . . . . . . . . . . . . . . . 11
3.2.8. Bind . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2.9. Message: BindRequest . . . . . . . . . . . . . . . . . 12
3.2.10. Message: BindResponse . . . . . . . . . . . . . . . . 12
3.2.11. Message: OpenRequest . . . . . . . . . . . . . . . . . 12
3.2.12. Message: OpenResponse . . . . . . . . . . . . . . . . 14
3.2.13. Message: TicketRequest . . . . . . . . . . . . . . . . 14
3.2.14. Message: TicketResponse . . . . . . . . . . . . . . . 14
3.2.15. Unbind . . . . . . . . . . . . . . . . . . . . . . . . 14
3.2.16. Message: UnbindRequest . . . . . . . . . . . . . . . . 14
3.2.17. Message: UnbindResponse . . . . . . . . . . . . . . . 15
4. Mutual Authentication . . . . . . . . . . . . . . . . . . . . 15
4.1. PIN Authentication . . . . . . . . . . . . . . . . . . . . 15
4.2. Example: Latin PIN Code . . . . . . . . . . . . . . . . . 17
4.3. Example: Cyrillic PIN Code . . . . . . . . . . . . . . . . 18
4.4. Stateless server . . . . . . . . . . . . . . . . . . . . . 18
4.5. Established Key . . . . . . . . . . . . . . . . . . . . . 18
4.6. Out of Band Confirmation . . . . . . . . . . . . . . . . . 18
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 19
6.1. Denial of Service . . . . . . . . . . . . . . . . . . . . 19
6.2. Breach of Trust . . . . . . . . . . . . . . . . . . . . . 19
6.3. Coercion . . . . . . . . . . . . . . . . . . . . . . . . . 19
7. To do . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9. Normative References . . . . . . . . . . . . . . . . . . . . . 20
Appendix A. Example Data. . . . . . . . . . . . . . . . . . . . . 20
A.1. Ticket A . . . . . . . . . . . . . . . . . . . . . . . . . 20
A.2. Ticket B . . . . . . . . . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20
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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. Purpose
3. Omnibroker Connection Maintenance Service
3.1. Authentication
The principle function of the OBP Connection Maintenance Protocol is
to establish and maintain the cryptographic parameters used to
authenticate and encrypt
The user needs to authenticate the broker service regardless of any
authentication requirements of the broker.
3.1.1. Broker Authentication
The OBP connection maintenance protocol transport MUST provide a
trustworthy means of verifying the identity of the broker (e.g. an
Extended Validation SSL certificate).
If the device supports a display capability, authentication of the
device and user MAY be achieved by means of an authentication image.
Such an authentication image is generated by the broker and passed to
the client in the OpenResponse message. The user then verifies that
the image presented on the device display is the same as that
presented on the account maintenance console.
3.1.2. Device Authentication
If device 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 into the device that was
previously delivered to the user out of band.
The passcode authentication mechanism allows the device to establish
a proof that it knows the passcode without disclosing the passcode.
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This property provides protection against Man-In-The-Middle type
disclosure attacks.
3.1.3. Illustrative example
Alice is an employee of Example Inc. which runs its own local
omnibroker service 'example.com'. To configure her machine for use
with this service, Alice contacts her network administrator who
assigns her the account identifier 'alice' and obtains a PIN number
from the service 'Q80370-1RA606-F04B'
Alice enters the values 'alice@example.com' and 'Q80370-1RA606-F04B'
into her Omnibroker-enabled Web browser.
The Web browser uses the local DNS to resolve 'example.com' and
establishes a HTTPS connection to the specified IP address. The
client verifies that the certificate presented has a valid
certificate chain to an embedded trust anchor under an appropriate
certificate policy (e.g. compliant with Extended Validation Criteria
defined by CA-Browser Forum).
Having established an authenticated and encrypted TLS session to the
Omnibroker service, the client sends an OpenRequest message to begin
the process of mutual authentication. This message specifies the
cryptographic parameters supported by the client (Authentication,
Encryption) and a nonce value (Challenge), device identification
parameters (DeviceID, DeviceURI, DeviceName) and the name of the
account being requested.
The client does not specify the PIN code in the request, nor is the
request authenticated. Instead the client informs the server that it
has a PIN code that can be supplied if necessary.
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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"}}
The service receives the request. If the request is consistent with
the access control policy for the server it returns a reply that
specifies the chosen cryptographic parameters (Cryptographic),
responds to the client issued by the client to establish server proof
of knowsledge of the PIN (ChallengeResponse) and issues a challenge
to the client (Challenge).
The cryptographic parameters specify algorithms to be used for
encryption and authentication, a shared secret and a ticket value.
Note that while the shared secret is exchanged in plaintext form in
the HTTP binding, the connection protocol MUST provide encryption.
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HTTP/1.1 203 Passcode
Content-Type: application/json;charset=UTF-8
Content-Length: 500
{
"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 serice containing a response to the PIN challenge sent by the
service (ChallengeResponse). The TicketRequest message is
authenticated 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
Content-Integrity:
mac=cjkMkfnnYP8JYWZAbRLvtpqImmOK3rsrOT1XcvAgHDk=;
ticket=TUMnorO0SjHHS7D2uFcGlRYJ0Hd3eibwe0ogptoNMQuCYmCHfHAJcJlyvi
j8WoXDglTSOkctnmoBzl8W0NLSlcgSyZcmsAyoWs8y1Rn2ZlO2WBgoWrFIOqPa4
oB29dgs/ei6ieINZtmvXNCm2NUkWA==
{
"TicketRequest": {
"ChallengeResponse": "TctLOG74cwpm26YNpEibcQ=="}}
If the response to the PIN challenge is correct, the service responds
with a message that specifies a set of cryptographic parameters to be
used to authenticate future interactions with the service
(Cryptographic) and a set of connection parameters for servers
supporting the Query Service (Service).
In this case the server returns three connections, each offering a
different transport protocol option. Each connection specifies its
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own set of cryptographic parameters (or will when the code is written
for that).
HTTP/1.1 200 Complete
Content-Type: application/json;charset=UTF-8
Content-Length: 1907
Content-Integrity:
mac=nKhjR1r2eYPga0rmDfHT4HOvgQ+EuUoQPwzIl0btljs=;
ticket=TUMnorO0SjHHS7D2uFcGlRYJ0Hd3eibwe0ogptoNMQuCYmCHfHAJcJlyvi
j8WoXDglTSOkctnmoBzl8W0NLSlcgSyZcmsAyoWs8y1Rn2ZlO2WBgoWrFIOqPa4
oB29dgs/ei6ieINZtmvXNCm2NUkWA==
{
"TicketResponse": {
"Status": 200,
"StatusDescription": "Complete",
"Cryptographic": [{
"Protocol": "OBPConnection",
"Secret": "HQuQg4GkzTwTVoGxar0EXg==",
"Encryption": "A128CBC",
"Authentication": "HS256",
"Ticket":
"0ulMVMMfY/pLHZ0FlIy2zDnNycYz9Znvs3JJYQGlZ+dWaxMNxm/jLEsJd/
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",
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"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="}}]}
}
When Alice's machine is to be transfered to another employee, the
Unbind transaction is used. The only parameter is the Ticket
identifying the device association (Ticket).
Post / HTTP/1.1
Host: example.com
Cache-Control: no-store
Content-Type: Application/json;charset=UTF-8
Content-Length: 25
Content-Integrity:
mac=bZU61eCOW4nVnfdJNS719HL4IsNVxtoTgoRt+mqLbWY=;
ticket=0ulMVMMfY/pLHZ0FlIy2zDnNycYz9Znvs3JJYQGlZ+dWaxMNxm/jLEsJd/
0qsAc5qp8fjBoMN49V9DkDgM4UYJxVriqfr64RyTTgug2taHY=
{
"UnbindRequest": {}}
Since the unbind response represents the termination the relationship
with the Omnibroker, the response merely reports the success or
failure of the request.
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HTTP/1.1 0
Content-Type: application/json;charset=UTF-8
Content-Length: 26
Content-Integrity:
mac=9P1FmroeFU7y9qHgXdSFXH2qSImh0cQpaSgZrx5IswM=;
ticket=0ulMVMMfY/pLHZ0FlIy2zDnNycYz9Znvs3JJYQGlZ+dWaxMNxm/jLEsJd/
0qsAc5qp8fjBoMN49V9DkDgM4UYJxVriqfr64RyTTgug2taHY=
{
"UnbindResponse": {}}
The 'Ticket' value presented in the foregoing examples is a sequence
of binary data generated by the service is opaque to the client.
Services MAY generate ticket values with a substructure that enable
the service to avoid the need to maintain server side state.
In the foregoing example, the ticket structures generated by the
service encode the cryptographic parameter data, the shared secret,
account identifier and an authentication value. The initial ticket
value generated additionally encodes the values of the client and
service challeng values for use in calculating the necessary
ChallengeResponse.
3.2. OBPConnection
3.2.1. Message: Message
3.2.2. Message: Response
Status : Integer [0..1]
Application layer server status code
StatusDescription : String [0..1]
Describes the status code (ignored by processors)
3.2.3. 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.
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3.2.4. Message: Request
Ticket : Binary [1..1]
Opaque ticket issued by the server that identifies the
cryptographic parameters for encryption and authentication of
the message payload.
3.2.5. Structure: Cryptographic
Parameters describing a cryptographic context.
Protocol : Label [0..1]
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.
Secret : Binary [1..1]
Shared secret
Encryption : Label [1..1]
Encryption Algorithm selected
Authentication : Label [1..1]
Authentication Algorithm selected
Ticket : Binary [1..1]
Opaque ticket issued by the server that identifies the
cryptographic parameters for encryption and authentication of
the message payload.
Expires : DateTime [0..1]
Date and time at which the context will expire
3.2.6. Structure: ImageLink
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Algorithm : Label [0..1]
Image encoding algorithm (e.g. JPG, PNG)
Image : Binary [0..1]
Image data as specified by algorithm
3.2.7. Structure: Connection
Contains information describing a network connection.
Name : Name [0..1]
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.
Port : Integer [0..1]
TCP or UDP port number.
Address : String [0..1]
IPv4 (32 bit) or IPv6 (128 bit) service address
Priority : Integer [0..1]
Service priority. Services with lower priority numbers SHOULD
be attempted before those with higher numbers.
Weight : Integer [0..1]
Weight to be used to select between services of equal priority.
Transport : Label [0..1]
OBP Transport binding to be used valid values are HTTP, DNS and
UDP.
Expires : DateTime [0..1]
Date and time at which the specified connection context will
expire.
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3.2.8. Bind
Binding a device is a two step protocol that begins with the Start
Query followed by a sequence of Ticket queries.
3.2.9. Message: BindRequest
The following parameters MAY occur in either a StartRequest or
TicketRequest:
Encryption : Label [0..Many]
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 : Label [0..Many]
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.
3.2.10. Message: BindResponse
The following parameters MAY occur in either a StartResponse or
TicketResponse:
Cryptographic : Cryptographic [0..Many]
Cryptographic Parameters.
Service : Connection [0..Many]
A Connection describing an OBP service point
3.2.11. 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.
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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 : String [0..1]
Account name of the user at the OBP service
Domain : Name [0..1]
Domain name of the OBP broker service
HavePasscode : Boolean [0..1] Default =False
If 'true', the user has entered a passcode value for use with
passcode authentication.
HaveDisplay : Boolean [0..1] Default =False
Specifies if the device is capable of displaying information to
the user or not.
Challenge : Binary [0..1]
Client challenge value to be used in authentication challenge
DeviceID : URI [0..1]
Device identifier unique for a particular instance of a device
such as a MAC or EUI-64 address expressed as a URI
DeviceURI : URI [0..1]
Device identifier specifying the type of device, e.g. an
xPhone.
DeviceName : String [0..1]
Descriptive name for the device that would distinguish it from
other similar devices, e.g. 'Alice's xPhone".
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3.2.12. 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 : Binary [0..1]
Challenge value to be used by the client to respond to the
server authentication challenge.
ChallengeResponse : Binary [0..1]
Server response to authentication challenge by the client
VerificationImage : ImageLink [0..Many]
Link to an image to be used in an image verification mechanism.
3.2.13. 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.
ChallengeResponse : Binary [0..1]
The response to a server authentication challenge.
3.2.14. Message: TicketResponse
The TicketResponse message returns cryptographic and/or connection
context information to a client.
3.2.15. Unbind
Requests that a previous device association be deleted.
3.2.16. 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.
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3.2.17. 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.
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.
4. Mutual Authentication
A Connection Service MAY require that a connection request be
authenticated. Three authentication mechanisms are defined.
PIN Code: The client and server demonstrate mutual knowledge of a
PIN code previously exchanged out of band.
Established Key: The client and server demonstrate knowledge of
the private key associated with a credential previously
established. This MAY be a public key or a symmetric key.
Out of Band Confirmation: The request for access is forwarded to
an out of band confirmation service.
4.1. PIN Authentication
[Motivation]
Although the PIN value is never exposed on the wire in any form, the
protcol considers the PIN value to be a text encoded in UTF8
encoding.
[Considerations for PIN character set choice discussed in body of
draft, servers MUST support numeric only, clients SHOULD support full
Unicode]
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.
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Since no prior authentication key has been the OpenRequest and
OpenResponse messages are initially sent without authentication and
authentication values established the Challenge-Response mechanism.
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 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:
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
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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 Section 4.4
This protocol construction ensures that the 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
construction of SR since the client has already demonstrated
knowledge of the PIN value.
4.2. Example: Latin PIN Code
The Connection Request example of section Section 3.1.3 demonstrates
the use of an alphanumeric PIN code using the Latin alphabet.
The PIN code is [] and the authentication algorithm is []. 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]
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4.3. 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.
4.4. Stateless server
The protocol is designed to permit but not require a stateless
implementation by the server using the Ticket value generated by the
server to pass state from the first server transaction to the second.
In the example shown in Section 3.1.3, the server generates a
'temporary ticket' containing the following information:
If a server uses the Ticket to transmit state in this way it MUST
protect the confidentiality of the ticket using a strong means of
encryption and authentication.
4.5. Established Key
The Established Key mechanism is used when the parties have an
existing shared key or public key credential.
The [Open request open response are authenticated under the
respective keys]
SR=CC, CR=SC
4.6. 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.
The service is informed that the service has been authorized
through an out of band process.
The client makes a TicketRequest to the service and obtains a
TicketResponse message to complete the exchange.
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Since no prior authentication key has been 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.
5. Acknowledgements
[List of contributors]
6. Security Considerations
6.1. Denial of Service
6.2. Breach of Trust
6.3. Coercion
7. To do
Formatting of the abstract data items needs to be improved
8. IANA Considerations
[TBS list out all the code points that require an IANA registration]
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9. Normative References
[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. Example Data.
A.1. Ticket A
A.2. Ticket B
Author's Address
Phillip Hallam-Baker
Comodo Group Inc.
Email: philliph@comodo.com
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