| Network Working Group | P. Hallam-Baker |
| Internet-Draft | Comodo Group Inc. |
| Intended status: Informational | May 10, 2017 |
| Expires: November 11, 2017 |
Mesh Confirmation Protocol (Mesh/Confirm)
draft-hallambaker-mesh-confirm-00
Mesh Confirmation Protocol (Mesh/Confirm) is a three-party Web Service that supports a transactional second factor confirmation mechanism that provides a superset of the capabilities of traditional second factor authentication schemes. The three parties in the protocol are Enquirer who posts a confirmation request, a Responder who may or may not respond to the request and the Broker where the requests and responses are posted.
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Authentication of end users is one of the biggest challenges for Internet and Web security today. Despite an abundance of technology that offers authentication mechanisms that are more robust, more secure and easier to use, the default mechanism for user authentication is the use of usernames and passwords.
Unlike traditional schemes, Mesh/Confirm is designed for implementation on a device that has at least the capabilities of a modern 'smartphone'. In particular, a Mesh/Confirm client device must support a display, a means of accepting text input from the user and a connection to the Internet.
While mobile devices offering this degree of functionality were rare in 2007, they have since become ubiquitous. It is thus now a practical proposition for a site requiring second factor authentication to support at least a part of its users using a technology that requires this level of capability. Software applications that emulate traditional second factor authentication protocols on such devices have been available for some time.
Second factor authentication mechanisms offer greater security over the use of passwords alone by combining a first factor (typically a password) with a second factor, typically a biometric or proof of possession of a physical token.
Traditional second factor authentication techniques have suffered from the need to distribute physical tokens and the difficulty of ensuring that a biometric authentication is presented to a trustworthy terminal.
The usability of traditional second factor authentication techniques has been poor or worse. Even the simplest scheme in which the user is required to read in a 'one time use' numeric code from the authentication token device and enter it into a password field. While such operations are relatively simple they require the user to engage in a sequence of operations that bears no necessary or natural relationship to the underlying task for which the authentication is required.
Nor does the act of engaging in a traditional second factor scheme offer proof of anything other than that the user was authenticated. Any correspondence between the act of authentication and the purpose for which the authentication was provided must be maintained separately.
A second factor confirmation service addresses the limitations of traditional second factor authentication schemes.
A confirmation service allows the user experience to be precisely matched to the action that the user is attempted. This is simpler and more secure. Instead of being asked to read a random number from one device and enter it into another, the user is asked if they really want to perform the action for which authentication is requested.
A confirmation service offers better accountability for end users than a traditional authentication service. An authentication service only provides an assertion that the user was present. A confirmation service provides an assertion that the user was present and that they confirmed a specific transaction.
For example, Alice has been granted access to a machine storing classified data. If an authentication service is used for access control, the authentication service log will only record the dates and times that Alice accessed the system. to find out if Alice accessed a particular file on a particular day it is necessary to consult and correlate both the authentication log of the system and the activity log for the application.
If instead a confirmation service is used the confirmation log contains an authenticated record of both the authentication events and the transactions for which the authentication was requested.
A confirmation service complements rather than replaces a traditional authentication scheme. Providing a highly secure and convenient means of authenticating requests that carry a high degree of risk mitigates the risk of using convenient but intrinsically low security techniques for other actions.
If an attacker is to profit from breaching an account with a financial service such as a bank or a brokerage they must find a way to move money out of the account. Thus, adding bill payment recipients, initiating wire transfers and trading in low volume 'penny stocks' represent high risk activities.
For example: Bank of Ethel might permit customers to use a simple username and password scheme to gain access to their account for the purpose of checking their balance or paying bills to existing recipients but require use of the second factor confirmation device for a high-risk transaction such as paying a bill.
A second factor confirmation service may be combined with a machine level authentication scheme to permit a transparent form of authentication for low risk transactions.
For example: Alice stores her low risk authentication credentials (e.g. usernames and passwords) using a 'cloud' service. When she wishes to use those credentials an agent on her personal machine fetches credentials from the cloud service as necessary. When Alice wishes to access a site from a different machine she receives a confirmation request on her mobile device to grant access from that machine.
Use of such a mechanism is clearly more satisfactory when suitable cryptographic protocols such as SAML or Kerberos are employed to limit the disclosure and hence possible compromise of the credentials. The specification of such protocols is outside the scope of this document.
Although Mesh/Confirm is designed for use in a three-party scenario, there are situations in which a two party mode may be preferred.
For example: Bob is a roadwarrior who requires access to confidential documents stored on his laptop device from anywhere in the world, including locations where Internet access is not possible. To permit access in such circumstances, Bob's Mesh/Confirm client supports use of a tethered mode in which the mobile device is plugged into his laptop via a USB port.
For example: Carol is a network manager of a large computing facility that uses Mesh/Confirm to authenticate and track all changes to critical resources. Since Mesh/Confirm is itself a network resource a bootstrap consideration arises: How can Carol confirm her network configuration requests using Mesh/Confirm when the network itself is down? Support for a tethered mode in which the Mesh/Confirm device communicates via USB or similar wired protocol allows this use case to be supported.
While availability of a tethered mode is clearly essential if Mesh/Confirm is to be used in certain applications, support for this feature outside the scope of this version of the specification.
While Mesh/Confirm is designed for deployment on a secondary device, deployment on the same device as the one for which confirmation is being requested is also possible and can provide security benefits.
Modern Web browsers are large and complex with many features such as support for mobile code that are incompatible with a high security environment. Separating the confirmation protocol from the Web Browsing protocol permits implementation in a minimal client designed to permit detailed security analysis. Such a client might be embedded in or support means of secure interaction with a trustworthy operating system component.
While this means of deployment does not provide a true second factor confirmation, it is likely to provide a sufficient degree of authentication for many transactions.
Mesh/Confirm is a Web Service that permits a Enquirer to request that a User confirm or reject a specified action. If the user responds, the response is signed with a digital signature under a key that is unique to the user account, the client and the device.
Each Mesh/Confirm protocol interaction takes place between a connection pair of the following parties:
Enquirer
A party that initiates a confirmation request.
User
The User is the person being asked to grant or refuse confirmation. A User MAY have multiple accounts with multiple Broker Services.
User Device
A device that the user has bound to their broker account.
Broker
A clearing house that stores and forwards requests from Initiators to Users Device and responses from Users to Initiators. The Broker is only trusted to perform routing filtering and recording of requests and responses. The Broker is not trusted with respect to the responses returned.
The communication between the parties is shown in Figure 1.
+-------------+ +------------+ +-------------+
| Enquirer | <-----> | Broker | <------ | Device |
+-------------+ +------------+ +-------------+
^
|
V
+-------------+
| User |
+-------------+
Figure 1. Mesh/Confirm Parties
Users are identified by means of an account identifier. The display presentation of an account identifier is the form of an RFC2822 email address identifier without the enclosing angle braces, for example:
alice@example.com
The account identifier is used by the User when registering the use of the confirmation service with a Broker.
An Mesh/Confirm service MAY be Open or Closed. An Open service provider provides Mesh/Confirm service to the general public. A Closed service provider only provides service to a specific community.
For example: An Internet Service Provider or DNS Registrar might provide an open Mesh/Confirm service as a part of their standard service offering to customers. An employer might operate a closed Mesh/Confirm service to be used for company business.
It is often useful to be able to verify that a service is ready and willing to perform transactions before attempting to perform one. Especially so when the transaction requires considerable amounts of data and may require the use of specific server determined authentication options.
The request message is 'HelloRequest' and has no parameters:
POST /.well-known/confirm/HTTP/1.1
Host: prismproof.org
Content-Length: 23
{
"HelloRequest": {}}
The response message specifies the protocol version(s) supported, the corresponding encodings and bindings:
HTTP/1.1 200 OK
Date: Thu 11 May 2017 03:12:20
Content-Length: 157
{
"HelloResponse": {
"Status": 201,
"StatusDescription": "Operation completed successfully",
"Version": {
"Major": 0,
"Minor": 1}}}
Alice attempts to log into her computer system as administrator. The site policy requires that all administrative logins be confirmed via Mesh/Confirm. Alice's confirmation account is alice@example.com. In this exchange, the computer Alice is trying to access is the Enquirer, the device she uses to respond to the query (her watch) is the Responder and the Mesh/Confirm service at example.com is the broker.
The computer acting as Enquirer (example.net) creates a confirmation request as follows:
<?xml version="1.0" encoding="utf-8" ?> <srml xmlns="http://hallambaker.com/Schemas/srml.xsd"> <h1>Grant Administrator</h1> <p>Host: example.net</p> <button value="Access">Access</button> </srml>
Note that it is not necessary to specify the reject option since this is implicit.
The request message is 'EnquireRequest' which contains an object signed by the Enquirer that specifies the account the request is directed to and the request text.
POST /.well-known/confirm/HTTP/1.1
Host: prismproof.org
Content-Length: 25
{
"EnquireRequest": {}}
The request is accepted and a success response returned specifying the transaction ID.
HTTP/1.1 200 OK
Date: Thu 11 May 2017 03:12:20
Content-Length: 105
{
"EnquireResponse": {
"Status": 201,
"StatusDescription": "Operation completed successfully"}}
Note that while the requirement that request messages be authenticated by means of a digital signature is within the scope of Mesh/Recrypt, the specification of the filtering rules is not.
At present, the only mechanism for determining if there are pending requests is by polling. Provision of a push notification mechanism is an obvious priority for future improvement of the protocol.
Alice's watch regularly polls the broker to determine if there are pending confirmation requests.
POST /.well-known/confirm/HTTP/1.1
Host: prismproof.org
Content-Length: 25
{
"PendingRequest": {}}
The response message contains the number of pending requests meeting the selection criteria and the returned requests.
HTTP/1.1 200 OK
Date: Thu 11 May 2017 03:12:20
Content-Length: 105
{
"PendingResponse": {
"Status": 201,
"StatusDescription": "Operation completed successfully"}}
Each request is signed by the Enquirer that originally generated it.
Alice selects the pending access request and grants herself access to the machine she is attempting to log in to. Her watch creates a signed response message containing the digest of the original request and her response "Accept".
POST /.well-known/confirm/HTTP/1.1
Host: prismproof.org
Content-Length: 25
{
"RespondRequest": {}}
The response message tells Alice that the transaction completed successfully and the broker has her acceptance message.
HTTP/1.1 200 OK
Date: Thu 11 May 2017 03:12:20
Content-Length: 105
{
"RespondResponse": {
"Status": 201,
"StatusDescription": "Operation completed successfully"}}
Note that in future versions of the protocol it may be desirable to make use of additional affordances of the device such as the ability to perform biometric capture such as fingerprint or facial recognition.
Another possibility is that the user might be asked to enter a one time use PIN generated by the Enquirer, thus verifying that the user is indeed responding to the confirmation request they believe they are responding to.
The enquirer obtains the result of the confirmation request by polling using the Status transaction.
POST /.well-known/confirm/HTTP/1.1
Host: prismproof.org
Content-Length: 24
{
"StatusRequest": {}}
Since Alice has responded, the response message contains the signed result:
HTTP/1.1 200 OK
Date: Thu 11 May 2017 03:12:20
Content-Length: 104
{
"StatusResponse": {
"Status": 201,
"StatusDescription": "Operation completed successfully"}}
As with the use of polling on the user side, it is obviously desirable to eliminate the need for polling by introducing a callback registration mechanism.
The Mesh/Confirm confirmation service is a two party protocol. An Enquirer requests a response from the
SRV Prefix:
HTTP Well Known Service Prefix:
Every Confirm Service transaction consists of exactly one request followed by exactly one response.
There is no set sequence in which operations are required to be performed. It is not necessary to perform a Hello transaction prior to a CreateGroup, AddMember or any other transaction.
Base class for all request messages.
Portal: String (Optional)
Base class for all response messages. Contains only the status code and status description fields.
A service MAY return either the response message specified for that transaction or any parent of that message. Thus the RecryptResponse message MAY be returned in response to any request.
Status: Integer (Optional)
StatusDescription: String (Optional)
The following response codes are returned when a transaction has completed successfully.
[201] SuccessOK
[201] SuccessCreated
[202] SuccessUpdated
The following response codes are returned when a transaction did not complete because the target service has been redirected.
In the case that a redirect code is returned, the StatusDescription field contains the URI of the new service. Note however that the redirect location indicated in a status response might be incorrect or even malicious and cannot be considered trustworthy without appropriate authentication.
[303] RedirectPermanent
[307] RedirectTemporary
A response code in the range 400-499 is returned when the service was able to process the transaction but the transaction resulted in an error.
[401] ClientUnauthorized
[404] NotFound
[409] AlreadyExists
A response code in the range 500-599 is returned when the service was unable to process the transaction but the transaction due to an internal failure.
[500] ServerInternal
[503] ServerOverload
The Recrypt Administration Sercice makes use of JSON objects defined in the JOSE Signatgure and Encryption specifications.
The following classes are referenced at multiple points in the protocol.
Describes a protocol version.
Major: Integer (Optional)
Minor: Integer (Optional)
Encodings: Encoding [0..Many]
URI: String [0..Many]
Describes a message content encoding.
ID: String [0..Many]
Dictionary: String [0..Many]
Request: HelloRequest
Response:HelloResponse
Report service and version information.
The Hello transaction provides a means of determining which protocol versions, message encodings and transport protocols are supported by the service.
Request service description.
[None]
Always reports success. Describes the configuration of the service.
Version: Version (Optional)
Alternates: Version [0..Many]
Request: EnquireRequest
Response:EnquireResponse
Post a confirmation request to the broker.
Request: JoseWebEncryption (Optional)
Responder: String (Optional)
Expire: DateTime (Optional)
EnquirerID: String (Optional)
Reports the success or failure of an Enquire transaction.
BrokerID: String (Optional)
Request: StatusRequest
Response:StatusResponse
Request status on a previously posted request
Reports the status or of an Enquire transaction.
Cancel: Boolean (Optional)
BrokerID: String (Optional)
The result of a status request.
RequestStatus: String (Optional)
Response: JoseWebEncryption (Optional)
Request: PendingRequest
Response:PendingResponse
Request a list of pending transactions meeting the specified selection criteria.
Request a list of pending requests for a specified account.
Responder: String (Optional)
MaxResponse: Integer (Optional)
BeforeId: String (Optional)
AfterId: String (Optional)
Contains a list of pending requests.
Entries: RequestEntry (Optional)
Describes a pending request and associated information.
Request: JoseWebEncryption (Optional)
Responder: String (Optional)
Expire: DateTime (Optional)
EnquirerID: String (Optional)
BrokerID: String (Optional)
Request: RespondRequest
Response:RespondResponse
Respond to a confirmation request.
Respond to a confirmation request.
Response: JoseWebEncryption (Optional)
Reports the success or failure of a Respond transaction.
[None]
Confirmation requests are posted in SRML, a deliberately limited subset of HTML. SRML is limited to four elements and one attribute. These are:
The top-level element for an SRML request
Heading
Running text
Paragraph
User option
Button specifying a value that the user can select.
While SRML is loosely based on the HTML forms markup, there are important differences. The HTML markup model supports multiple document types of which forms are only one and a single document may contain multiple forms with multiple different action values. In an SRML document is a single form and the form action to be performed is impicit in the presentation of the document to the user.
The MIME Content Type and schema identifier for SRML are
Content-Type
text/xml
xmlns
http://hallambaker.com/Schemas/srml.xsd
The schema is
<?xml version="1.0" encoding="utf-8"?>
<xs:schema id="SRML"
targetNamespace="http://hallambaker.com/Schemas/srml.xsd"
elementFormDefault="qualified"
xmlns="http://hallambaker.com/Schemas/srml.xsd"
xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="srml" type="SrmlType"/>
<xs:complexType name="SrmlType">
<xs:sequence>
<xs:element name="h1" type="xs:string"
minOccurs="1" maxOccurs="1"/>
<xs:element name="p" type="xs:string" />
<xs:element name="button" type="ButtonType"
minOccurs="1" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="ButtonType">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="value" type="xs:string" />
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:schema>
The capabilities of SRML are intentionally limited to the bare minimum. It should be possible to make use of SRML to display options to the user on a smartwatch or other device with a highly constrained display.
The function of the confirmation service is to provide confirmation of an action that was initiated elsewhere. It is therefore inappropriate for this or any future version of SRML to offer extensive data entry or validation capabilities. SRML applications MUST NOT support any form of scripting or active code extensions to SRML content.
It might prove advantageous in the future to extend the input types to include simple form elements such as checkboxes, numeric fields, text choices and possibly free form text.
Consider spam control, how do users prevent unwanted requests? (EV accreditatio, filtering at Broker)
People deploying Mesh/Confirm as a means of controlling access to networking infrastructure must consider the bootstrap issue. In particular since Mesh/Confirm requires Internet access the network administrator must ensure that it is possible to manage the network resources necessary to support an SXS service when that service is down.