OpenID Provider Authentication Policy Extension 1.0 - Draft 5

Abstract

This extension to the OpenID Authentication protocol provides a mechanism by which a Relying Party can request that particular authentication policies be applied by the OpenID Provider when authenticating an End User. This extension also provides a mechanism by which an OpenID Provider may inform a Relying Party which authentication policies were used. Thus a Relying Party can request that the End User authenticate, for example, using a phishing-resistant or multi-factor authentication method.

This extension is not intended to provide all information regarding the quality of an OpenID Authentication assertion. Rather, it is designed to be balanced with information the Relying Party already has with regard to the OpenID Provider and the level of trust it places in it. If additional information is needed about processes such as new End User enrollment on the OpenID Provider, such information should either be transmitted out-of-band or in other extensions such as OpenID Attribute Exchange. Other aspects (e.g. security characteristics, credential provisioning, etc) could be dealt with in the future.

This extension is optional, though its use is certainly recommended. This extension can be used with OpenID Authentication versions 1.1 and 2.0.

While none of the information transmitted using this extension can be verified by the Relying Party using technology alone, this does not limit the utility of this extension. Because there is no trust model specified by OpenID, Relying Parties must decide for themselves which Providers are trustworthy; likewise, RPs can decide whether to trust authentication policy claims from such OpenID Providers as well. As with other OpenID extensions, it is the Relying Party's responsibility to implement policy relative to the OpenID Provider's response.

Table of Contents

1.  Definitions
    1.1.  Requirements Notation
    1.2.  Conventions
    1.3.  Terminology
2.  Extension Overview
3.  Advertising Supported Policies
4.  Defined Authentication Policies
5.  Authentication Protocol
    5.1.  Request Parameters
    5.2.  Response Parameters
6.  Security Considerations
    6.1.  NIST Assurance Levels
Appendix A.  Examples
Appendix A.1.  Authentication Method Classifications
Appendix B.  Acknowledgements
7.  Normative References
§  Authors' Addresses

1.  Definitions

1.1.  Requirements Notation

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 [RFC2119] (Bradner, B., “Key words for use in RFCs to Indicate Requirement Levels,” 1997.) .

1.2.  Conventions

Throughout this document, values are quoted to indicate that they are to be taken literally. When using these values in protocol messages, the quotes MUST NOT be used as part of the value.

All OpenID 2.0 messages that contain a Provider Authentication Policy Extension (PAPE) element MUST contain the following extension namespace declaration, as specified in the Extensions section of [OpenIDAuthentication2.0] (specs@openid.net, “OpenID Authentication 2.0,” 2007.) .

             openid.ns.<alias>=http://specs.openid.net/extensions/pape/1.0

The actual extension namespace alias should be determined on a per-message basis by the party composing the messages, in such a manner as to avoid conflicts between multiple extensions. For the purposes of this document and when constructing OpenID 1.1 messages, the extension namespace alias SHALL be "pape".

Additionally, this specification uses name spaces for the custom authentication level identification. It is in the form of

             openid.pape.auth_level.ns.<cust>=http://some.authlevel.uri

The actual extension namespace alias should be determined on a per-message basis by the party composing the messages, in such a manner as to avoid conflicts between multiple extensions. For the purposes of this document and when constructing OpenID 1.1 messages, the one custom authentication level identification extension namespace defined by this specification is "nist". Others may also be defined and used by implementations, for example, "jisa".

1.3.  Terminology

The following terms are defined in [OpenIDAuthentication2.0] (specs@openid.net, “OpenID Authentication 2.0,” 2007.) :

• Identifier
• OpenID Provider (OP)
• Relying Party (RP)
• User-Agent

Authentication Method:

A single mechanism by which the End User authenticated to their OpenID Provider. For example, a password or a hardware credential.

Authentication Policy:

An Authentication Policy is a plain-text description of requirements that dictate which Authentication Methods can be used by an End User when authenticating to their OpenID Provider. An Authentication Policy is defined by a URI which must be previously agreed upon by one or more OPs and RPs.

2.  Extension Overview

1. As part of the [Yadis] (Miller, J., Ed., “Yadis Specification 1.0,” 2005.) Discovery process, OpenID Providers can optionally add supported authentication policies to an End User's XRDS document. This aids Relying Parties in choosing between multiple listed OPs depending on authentication policy requirements.
2. The Relying Party includes parameters in the OpenID Authentication request describing its preferences for authentication policy for the current assertion.
3. The OpenID Provider processes the PAPE request, prompting the End User to fulfill the requested policies during the authentication process.
4. As part of the OpenID Provider's response to the Relying Party, the OP includes PAPE information around the End User's authentication. An OP MAY include this response information even if not requested by the RP.
5. When processing the OpenID Provider's response, the Relying Party takes the PAPE information into account when determining if the End User should be sent through additional verification steps or if the OpenID login process cannot proceed due to not meeting policy requirements.

3.  Advertising Supported Policies

Via the use of [Yadis] (Miller, J., Ed., “Yadis Specification 1.0,” 2005.) within OpenID, Relying Parties are able to discover OpenID Provider service information in an automated fashion. This is used within OpenID Authentication for a RP to discover what version of the protocol each OP listed supports as well as any extensions, such as this one, that are supported. To aide in the process of a Relying Party selecting which OP they wish to interact with, it is STRONGLY RECOMMENDED that the following information be added to the End User's XRDS document.

When advertising supported policies, each policy URI MUST be added as the value of an <xrd:Type> element of an OpenID <xrd:Service> element in an XRDS document.

4.  Defined Authentication Policies

The following are defined policies and policy identifiers describing how the End User should authenticate to an OP. Additional policies can be specified elsewhere and used without making changes to this document. The policies described below are designed to be a starting point to cover the most common use-cases. Additional polices can be found at http://schemas.openid.net/pape/policies/.

When multiple policies are listed in the Relying Party's request, it is up to the OpenID Provider to satisfy as many of the policies as it can. This might mean that the OP needs to understand the relationship between policies (such as if one encompasses another or if one is stronger than another). This also means that when the RP processes the OP's response, it will have to make its own determinations as to if its requirements were met. For instance, if the RP requested Multi-Factor Authentication and the OP authentication employed Multi-Factor Physical Authentication, it is recommended that the OP include both policies in the response.

• Phishing-Resistant Authentication

  http://schemas.openid.net/pape/policies/2007/06/phishing-resistant

  An authentication mechanism where a party potentially under the control of the Relying Party can not gain sufficient information to be able to successfully authenticate to the End User's OpenID Provider as if that party were the End User. (Note that the potentially malicious Relying Party controls where the User-Agent is redirected to and thus may not send it to the End User's actual OpenID Provider).

• Multi-Factor Authentication

  http://schemas.openid.net/pape/policies/2007/06/multi-factor

  An authentication mechanism where the End User authenticates to the OpenID Provider by providing over one authentication factor. Common authentication factors are something you know, something you have, and something you are. An example would be authentication using a password and a software token or digital certificate.

• Physical Multi-Factor Authentication

  http://schemas.openid.net/pape/policies/2007/06/multi-factor-physical

  An authentication mechanism where the End User authenticates to the OpenID Provider by providing over one authentication factor where at least one of the factors is a physical factor such as a hardware device or biometric. Common authentication factors are something you know, something you have, and something you are. This policy also implies the Multi-Factor Authentication policy (http://schemas.openid.net/pape/policies/2007/06/multi-factor) and both policies MAY BE specified in conjunction without conflict. An example would be authentication using a password and a hardware token.

5.  Authentication Protocol

5.1.  Request Parameters

The following parameters MUST be included during an OpenID Authentication request (specs@openid.net, “OpenID Authentication 2.0,” 2007.) [OpenIDAuthentication2.0] by the Relying Party unless marked as optional.

• openid.ns.pape

  Value: "http://specs.openid.net/extensions/pape/1.0"

• openid.pape.max_auth_age

  (Optional) If the End User has not actively authenticated to the OP within the number of seconds specified in a manner fitting the requested policies, the OP SHOULD authenticate the End User for this request.

  Value: Integer value greater than or equal to zero in seconds.

  The OP should realize that not adhering to the request for re-authentication most likely means that the End User will not be allowed access to the services provided by the RP. If this parameter is absent in the request, the OP should authenticate the user at its own discretion.

• openid.pape.preferred_auth_policies

  Zero or more authentication policy URIs that the OP SHOULD conform to when authenticating the user. If multiple policies are requested, the OP SHOULD satisfy as many as it can.

  Value: Space separated list of authentication policy URIs.

  If no policies are requested, the RP may be interested in other information such as the authentication age.

  Example:

  openid.pape.preferred_auth_policies=http://schemas.openid.net/pape/policies/2007/06/phishing-resistant http://schemas.openid.net/pape/policies/2007/06/multi-factor

• openid.pape.auth_level.ns.<cust>

  (Optional) The name space for the custom Assurance Level defined by various parties, such as a country or industry specific standards body.

  Value: URL that represents this Assurance Level.

  Example:

  openid.pape.auth_level.ns.nist=http://csrc.nist.gov/publications/nistpubs/800-63/SP800-63V1_0_2.pdf

  openid.pape.auth_level.ns.jisa=http://www.jisa.or.jp/spec/auth_level.html

• openid.pape.preferred_auth_level_types

  (Optional) The space separated list of the name spaces of the custom Assurance Level that RP requests, in the order of its preference.

  Value: The space separated list of the name space aliases of the custom Assurance Level that RP requests, in the order of its preference.

  Example:

  openid.pape.preferred_auth_levels=jisa nist

5.2.  Response Parameters

In response to a Relying Party's request, the following parameters MUST be included in the OpenID Authentication Response. All response parameters MUST be included in the signature of the Authentication Response. It is RECOMMENDED that an OP supporting this extension include the following parameters even if not requested by the Relying Party.

All response parameters MUST describe the End User's current session with the OpenID Provider.

• openid.ns.pape

  Value: "http://specs.openid.net/extensions/pape/1.0"

• openid.pape.auth_policies

  One or more authentication policy URIs that the OP conformed to when authenticating the End User.

  Value: Space separated list of authentication policy URIs.

  Note: If no policies were met though the OP wishes to convey other information in the response, this parameter MUST be included with the value of http://schemas.openid.net/pape/policies/2007/06/none.

  Example:

  openid.pape.auth_policies=http://schemas.openid.net/pape/policies/2007/06/multi-factor http://schemas.openid.net/pape/policies/2007/06/multi-factor-physical

• openid.pape.auth_time

  (Optional) The most recent timestamp when the End User has actively authenticated to the OP in a manner fitting the asserted policies.

  Value: The timestamp MUST be formatted as specified in section 5.6 of [RFC3339] (Klyne, G. and C. Newman, “Date and Time on the Internet: Timestamps,” .) , with the following restrictions:

  • All times must be in the UTC timezone, indicated with a "Z".
  • No fractional seconds are allowed

  Example: 2005-05-15T17:11:51Z

  Note: If the RP's request included the "openid.pape.max_auth_age" parameter then the OP MUST include "openid.pape.auth_time" in its response. If "openid.pape.max_auth_age" was not requested, the OP MAY choose to include "openid.pape.auth_time" in its response.

• openid.pape.auth_level.ns.<cust>

  (Optional) The name space for the custom Assurance Level defined by various parties, such as a country or industry specific standards body.

  Value: URL that represents this Assurance Level.

  Example:

  openid.pape.auth_level.ns.nist=http://csrc.nist.gov/publications/nistpubs/800-63/SP800-63V1_0_2.pdf

  openid.pape.auth_level.ns.jisa=http://www.jisa.or.jp/spec/auth_level.html

• openid.pape.auth_level.<cust>

  (Optional) The Assurance Level as defined by the above standard body that is corresponding to the authentication method and policies employed by the OP when authenticating the End User.

  Value: Strings defined according to this Assurance Level.

  Example:

  openid.pape.auth_level.nist=1

  openid.pape.auth_level.jisa=2

6.  Security Considerations

As to commonly accepted security practices, it should be noted that the overall strength of any authentication is only as strong as its weakest step. It is thus recommended that provisioning of phishing-resistant and other credentials stronger than shared secrets should be accomplished using methods that are at least as strong as the credential being provisioned. By counter-example, allowing people to retrieve a phishing-resistant credential using only a phishable shared secret negates much of the value provided by the phishing-resistant credential itself. Similarly, sometimes using a phishing-resistant method when a phishable method continues to sometimes be employed may still enable phishing attacks to compromise the OpenID.

OpenID Providers need to make smart decisions as to how to describe the authentication performed with respect to that requested by the Relying Party. For example, if the RP were to request phishing-resistant authentication it may or may not make sense for the OP to actually tell it that the End User did in fact perform phishing-resistant, physical multi-factor authentication. Likewise, an OP MAY choose to respond with a level or levels used for the particular authentication even in some cases where this information was explicitly requested.

OPs SHOULD attempt to use the authentication policies requested by the RP and the reply SHOULD minimally contain at least the subset of the requested policies that applied to the authentication performed. The OP MAY also choose to return additional policies that applied to the authentication performed, even if not requested.

If the RP requested that an authentication level or levels be returned and the OP supports those level types, then the OP SHOULD return the actual level values for those types, if available.

6.1.  NIST Assurance Levels

National Institute of Standards and Technology (NIST) in Special Publication 800-63 (Burr, W., Dodson, D., and W. Polk, Ed., “Electronic Authentication Guideline,” April 2006.) [NIST_SP800‑63] defines a set of Assurance Levels from 1 to 4. These may be returned by the OP to the RP to communicate which NIST level the identity proofing, authentication method, and policies employed by the OP when authenticating the End User corresponds to.

Value: Integer value between 0 and 4 inclusive.

Note: Level 0 is not an assurance level defined by NIST, but rather SHOULD be used to signify that the OP recognizes the parameter and the End User authentication did not meet the requirements of Level 1. See Appendix A.1.2 (NIST Authentication Mechanism Levels) for high-level example classifications of authentication methods within the defined levels. Authentication using a long-lived browser cookie, for instance, is one example where the use of "level 0" is appropriate. Authentications with level 0 should never be used to authorize access to any resource of any monetary value whatsoever. The previous sentence should not be construed as implying that any of the other levels are recommended or appropriate for accessing resources with monetary value either without the Relying Party doing an appropriate risk assessment of the particular OpenID provider asserting them and their issuance and authentication procedures as they apply to the particular online interaction in question.

Depending on the particular use case being satisfied by the authentication response and PAPE information, the OpenID Provider will have to make a decision, ideally with the consent of the End User, as if it will include the "openid.pape.auth_level.nist" parameter. This information is designed to give Relying Parties more information around the strength of credentials used without actually disclosing the specific credential type. Disclosing the specific credential type can be considered a potential privacy or security risk.

It is RECOMMENDED that this parameter always be included in the response from the OP. This holds true even in cases where the End User authentication does not meet one of the defined Authentication Policies. For example, if the End User is authenticating using a password via HTTPS there is still value to the RP in knowing if the strength of the Password corresponds to the entropy requirements laid out by Level 1 or 2 or that it does not even meet the minimum requirement for the lowest level. With that said, discretion needs to be used by OP's as conveying that one of their End User's has a weak password to an "un-trustworthy" RP would not generally be considered a good idea.

Appendix A.  Examples

Appendix A.1.  Authentication Method Classifications

This non-normative section illustrates classification of various common authentication methods and their respective conformance within the defined policies and levels.

Appendix A.1.1.  Authentication Policy Examples

This table provides examples of common authentication technologies and their mapping to the Authentication Policies defined in Section 4 (Defined Authentication Policies) .

Appendix A.1.2.  NIST Authentication Mechanism Levels

This section is designed to highlight the Authentication Mechanism Levels described in [NIST_SP800‑63] (Burr, W., Dodson, D., and W. Polk, Ed., “Electronic Authentication Guideline,” April 2006.) . All normative and authoritative text can be found in [NIST_SP800‑63] (Burr, W., Dodson, D., and W. Polk, Ed., “Electronic Authentication Guideline,” April 2006.) . Note that assurance level is not only comprised of Authentication Mechanism employed but also the nature of the identity proofing performed. The overall assurance level is determined as a combination of these factors.

This table is republished from page 39 of [NIST_SP800‑63] (Burr, W., Dodson, D., and W. Polk, Ed., “Electronic Authentication Guideline,” April 2006.) .

This table is republished from page 39 of [NIST_SP800‑63] (Burr, W., Dodson, D., and W. Polk, Ed., “Electronic Authentication Guideline,” April 2006.) .

The following table illustrates the minimum number of factors required at each Authentication Mechanism Level.

In all cases, implementing a commonly accepted nonce and cross-site scripting protection when entering authentication credentials is required to satisfy all four Authentication Mechanism Levels. All examples below assume this requirement is met.

It should be noted that NIST Authentication Mechanism Levels 1 and 2 have differing password entropy requirements. When working with passwords, you should refer to the [NIST_SP800‑63] (Burr, W., Dodson, D., and W. Polk, Ed., “Electronic Authentication Guideline,” April 2006.) specification for more details. All examples below assume the password meets these requirements.

This table provides examples of common authentication technologies and their mapping to NIST Authentication Mechanism Levels, please be aware that there are details not represented in these examples that may bear on the resulting Authentication Mechanism Level.

Appendix B.  Acknowledgements

The authors would like to thank Barry Ferg, Ben Laurie, Dick Hardt, Drummond Reed, George Fletcher, Kim Cameron, Arun Nanda, Allen Tom, Tatsuki Sakushima, Nate Klingstein, Gary Krall, and John Bradley for their feedback when drafting this specification. David Recordon would also like to acknowledge VeriSign who employed him during the original authoring of this specification.

7. Normative References

Authors' Addresses