[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 draft-ietf-oauth-signed-http-request

OAuth Working Group                                       J. Richer, Ed.
Internet-Draft                                     The MITRE Corporation
Intended status: Experimental                                 J. Bradley
Expires: October 26, 2014                                  Ping Identity
                                                           H. Tschofenig
                                                             ARM Limited
                                                          April 24, 2014


            A Method for Signing an HTTP Requests for OAuth
               draft-richer-oauth-signed-http-request-01

Abstract

   This document a method for offering data origin authentication and
   integrity protection of HTTP requests.  To convey the relevant data
   items in the request a JSON-based encapsulation is used and the JSON
   Web Signature (JWS) technique is re-used.  JWS offers integrity
   protection using symmetric as well as asymmetric cryptography.

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 October 26, 2014.

Copyright Notice

   Copyright (c) 2014 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
   to this document.  Code Components extracted from this document must



Richer, et al.          Expires October 26, 2014                [Page 1]


Internet-Draft            HTTP Signed Messages                April 2014


   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Generating a JSON Object from an HTTP Request . . . . . . . .   3
     3.1.  Selection of a hashing algorithm and size . . . . . . . .   4
     3.2.  Calculating the query parameter list and hash . . . . . .   4
     3.3.  Calculating the header list and hash  . . . . . . . . . .   5
   4.  Verifying the Hashes  . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Validating the query parameter list and hash  . . . . . .   6
     4.2.  Validating the header list and hash . . . . . . . . . . .   6
   5.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  The 'pop' OAuth Access Token Type . . . . . . . . . . . .   7
     6.2.  JSON Web Signature and Encryption Type Values
           Registration  . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
     7.1.  Offering Confidentiality Protection for Access to
           Protected       Resources . . . . . . . . . . . . . . . .   8
     7.2.  Authentication of Resource Servers  . . . . . . . . . . .   8
     7.3.  Plaintext Storage of Credentials  . . . . . . . . . . . .   9
     7.4.  Entropy of Keys . . . . . . . . . . . . . . . . . . . . .   9
     7.5.  Denial of Service . . . . . . . . . . . . . . . . . . . .   9
     7.6.  Protecting HTTP Header Fields . . . . . . . . . . . . . .  10
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   In order to protect an HTTP request with a signature, a method for
   conveying various parameters and to compute a signature is needed.
   Ideally, this should be done without replicating the information
   already present in the HTTP request.  This version of the document
   still replicates most of the headers though.

   The keying material required for this signature calculation is
   distributed via mechanisms described in companion documents (see
   [I-D.bradley-oauth-pop-key-distribution] and
   [I-D.hunt-oauth-pop-architecture]).  The JSON Web Signature (JWS)
   specification [I-D.ietf-jose-json-web-signature] is re-used for




Richer, et al.          Expires October 26, 2014                [Page 2]


Internet-Draft            HTTP Signed Messages                April 2014


   computing a digital signature (which uses asymmetric cryptography) or
   a keyed message digest (in case of symmetric cryptography).

   The scope of the mechanism described in this document is shown in
   Figure 1 where a client in possession of keying material that is tied
   to the access token creates a JSON object, signs it, and issues an
   request to a resource server for access to a protected resource.

    +-----------+                                    +------------+
    |           |--(1)- HTTP Request               ->| Resource   |
    | Client    |       (+Signature, +Access Token)->| Server     |
    |           |                                    |            |
    |           |<-(2)- HTTP Response ---------------|            |
    +-----------+                                    +------------+

                          Figure 1: Message Flow.

   Many HTTP application frameworks insert extra headers, query
   parameters, and otherwise manipulate the HTTP request on its way from
   the web server into the application code itself.  It is the goal of
   this draft to have a signature protection mechanism that is
   sufficiently robust against such deployment constraints (while still
   providing sufficient security benefits).

   The method of conveying the token and signed request to the protected
   resource server is undefined by this document, but [RFC6750] could be
   re-used.

   The mechanism described in this document does not provide
   authentication of the resource server to the client.  This version of
   the document does not provide a cryptographic binding to Transport
   Layer Security (TLS) used underneath the an HTTPS request.

2.  Terminology

   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].

   We use the term 'sign' (or 'signature') to denote both a keyed
   message digest and a digital signature operation.

3.  Generating a JSON Object from an HTTP Request

   This section describes how to generate a JSON object below is
   included as a member of the JSON object.  All members are OPTIONAL.





Richer, et al.          Expires October 26, 2014                [Page 3]


Internet-Draft            HTTP Signed Messages                April 2014


   m  The HTTP Method used to make this request.  This MUST be the
      uppercase HTTP verb as a JSON string.

   u  The HTTP URL host component as a JSON string.  This MAY include
      the port separated from the host by a colon in host:port format.

   p  The HTTP URL path component of the request as an HTTP string.

   q  The hashed HTTP URL query parameter map of the request as a two-
      part JSON array.  The first part of this array is a JSON array
      listing all query parameters that were used in the calculation of
      the hash in the order that they were added to the hashed value as
      described below.  The second part of this array is a JSON string
      containing the Base64URL encoded hash itself, calculated as
      described below.

   h  The hashed HTTP request headers as a two-part JSON array.  The
      first part of this array is a JSON array listing all headers that
      were used in the calculation of the hash in the order that they
      were added to the hashed value as described below.  The second
      part of this array is a JSON string containing the Base64URL
      encoded hash itself, calculated as described below.

   b  The base64URL encoded hash of the HTTP Request body, calculated as
      the HMAC of the byte array of the body.

   ts The "ts" (timestamp) element provides replay protection of the
      JSON object.  Its value MUST be a number containing an IntDate
      value representing number of whole integer seconds from midnight,
      January 1, 1970 GMT.

3.1.  Selection of a hashing algorithm and size

   The hashes SHALL be calculated using the HMAC algorithm using a hash
   size equal to the size of the surrounding JWT's alg header field.
   That is, if the JWT uses HS256 or RS256, the HMAC here uses a 256-bit
   HMAC.  If the JWT uses RS512, the HMAC here uses 512-bit HMAC, and so
   forth.

3.2.  Calculating the query parameter list and hash

   To generate the query parameter list and hash, the client creates two
   data objects: an ordered list of strings to hold the query parameter
   names and a string buffer to hold the data to be hashed.

   The client iterates through all query parameters in whatever order it
   chooses and for each query parameter it does the following:




Richer, et al.          Expires October 26, 2014                [Page 4]


Internet-Draft            HTTP Signed Messages                April 2014


   1.  Adds the name of the query parameter to the end of the list.

   2.  Encodes the name and value of the query parameter as "name=value"
       and appends it to the string buffer.  [[Separated by an
       ampersand?  Alternatively we could have this also pulled into an
       ordered list and post-process the concatenation, but that might
       be too deep into the weeds. ]]

   Repeated parameter names are processed separately with no special
   handling.  Parameters MAY be skipped by the client if they are not
   required (or desired) to be covered by the signature.

   The client then calculates the HMAC hash over the resulting string
   buffer.  The list and the hash result are added as the value of the
   "p" member.

3.3.  Calculating the header list and hash

   To generate the header list and hash, the client creates two data
   objects: an ordered list of strings to hold the header names and a
   string buffer to hold the data to be hashed.

   The client iterates through all query parameters in whatever order it
   chooses and for each query parameter it does the following:

   1.  Adds the name of the header to the end of the list.

   2.  Encodes the name and value of the header as "name: value" and
       appends it to the string buffer.  [[Separated by a newline?
       Alternatively we could have this also pulled into an ordered list
       and post-process the concatenation, but that might be too deep
       into the weeds. ]]

   Repeated header names are processed separately with no special
   handling.  Headers MAY be skipped by the client if they are not
   required (or desired) to be covered by the signature.

   The client then calculates the HMAC hash over the resulting string
   buffer.  The list and the hash result are added as the value of the
   "h" member.

4.  Verifying the Hashes

   Validation of the overall signature is done using the standard JWS
   mechanisms for JSON structures.  However, in order to trust any of
   the hashed mechanisms above, an application MUST re-create and verify
   a hash for each component.  Additionally, an application MUST compare
   the replicated values included in various JSON fields with the actual



Richer, et al.          Expires October 26, 2014                [Page 5]


Internet-Draft            HTTP Signed Messages                April 2014


   header fields of the request.  Failure to-do so will allow an
   attacker to modify the underlying request, connect do different
   resources while at the same time having the application layer verify
   the signature correctly.

4.1.  Validating the query parameter list and hash

   The client has at its disposal a map that indexes the query parameter
   names to the values given.  The client creates a string buffer for
   calculating the hash.  The client then iterates through the "list"
   portion of the "p" parameter.  For each item in the list (in the
   order of the list) it does the following:

   1.  Fetch the value of the parameter from the HTTP request parameter
       map.  If a parameter is found in the list of signed parameters
       but not in the map, the validation fails.

   2.  Encode the parameter as "name=value" and concatenate it to the
       end of the string buffer. [[same separator issue as above.]]

   The client calculates the hash of the string buffer and base64url
   encodes it.  The client compares that string to the string passed in
   as the hash.  If the two match, the hash validates, and all named
   parameters and their values are considered covered by the signature.

   There MAY be additional query parameters that are not listed in the
   list and are therefore not covered by the signature.  The client MUST
   decide whether or not to accept a request with these uncovered
   parameters.

4.2.  Validating the header list and hash

   The client has at its disposal a map that indexes the header names to
   the values given.  The client creates a string buffer for calculating
   the hash.  The client then iterates through the "list" portion of the
   "h" parameter.  For each item in the list (in the order of the list)
   it does the following:

   1.  Fetch the value of the header from the HTTP request header map.
       If a header is found in the list of signed parameters but not in
       the map, the validation fails.

   2.  Encode the parameter as "name: value" and concatenate it to the
       end of the string buffer. [[same separator issue as above.]]

   The client calculates the hash of the string buffer and base64url
   encodes it.  The client compares that string to the string passed in




Richer, et al.          Expires October 26, 2014                [Page 6]


Internet-Draft            HTTP Signed Messages                April 2014


   as the hash.  If the two match, the hash validates, and all named
   headers and their values are considered covered by the signature.

   There MAY be additional headers that are not listed in the list and
   are therefore not covered by the signature.  The client MUST decide
   whether or not to accept a request with these uncovered headers.

5.  Example

   Example goes in here but will look like something like this
   (symmetric key case).

      1) HTTP Request (plain)

           POST /request?b5=%3D%253D&a3=a&c%40=&a2=r%20b&c2 HTTP/1.1
           Host: example.com

      2) JWS protected JSON object

         {"typ":"pop",
          "alg":"HS256",
          "kid":"client12345@example.com"}
         .
         {"m":"POST",
          "u":"example.com",
          "p":"request",
          "q":[["a3", "b5", "a2"], "m2398f32i2o3roiu2313aa"],
          "ts":1300819380
         }
         .
         dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk

                          Figure 2: Message Flow.

6.  IANA Considerations

6.1.  The 'pop' OAuth Access Token Type

   Section 11.1 of [RFC6749] defines the OAuth Access Token Type
   Registry and this document adds another token type to this registry.

   Type name:  pop

   Additional Token Endpoint Response Parameters:  (none)

   HTTP Authentication Scheme(s):  Proof-of-possession access token for
      use with OAuth 2.0




Richer, et al.          Expires October 26, 2014                [Page 7]


Internet-Draft            HTTP Signed Messages                April 2014


   Change controller:  IETF

   Specification document(s):  [[ this document ]]

6.2.  JSON Web Signature and Encryption Type Values Registration

   This specification registers the "pop" type value in the IANA JSON
   Web Signature and Encryption Type Values registry
   [I-D.ietf-jose-json-web-signature]:

   o  "typ" Header Parameter Value: "pop"

   o  Abbreviation for MIME Type: None

   o  Change Controller: IETF

   o  Specification Document(s): [[ this document ]]

7.  Security Considerations

7.1.  Offering Confidentiality Protection for Access to Protected
      Resources

   This specification can be used with and without Transport Layer
   Security (TLS).

   Without TLS this protocol provides a mechanism for verifying the
   integrity of requests, it provides no confidentiality protection.
   Consequently, eavesdroppers will have full access to communication
   content and any further messages exchanged between the client and the
   resource server.  This could be problematic when data is exchanged
   that requires care, such as personal data.

   When TLS is used then confidentiality can be ensured; this version of
   the specification does, however, not provide the TLS channel binding
   feature, which ensures that the TLS channel is cryptographically
   bound to the application layer protocol authentication defined in
   this document.

   The use of TLS in combination with the signed HTTP request mechanism
   is highly recommended to ensure the confidentiality of the user's
   data.

7.2.  Authentication of Resource Servers

   This protocol allows clients to verify the authenticity of resource
   servers only when TLS is used.  With TLS the resource server is
   authenticated as part of the TLS handshake.  The mechanism described



Richer, et al.          Expires October 26, 2014                [Page 8]


Internet-Draft            HTTP Signed Messages                April 2014


   in this document does not provide any mechanism for the client to
   authenticate the resource server at the application layer.

7.3.  Plaintext Storage of Credentials

   The mechanism described in this document works similar to many three
   party authentication and key exchange mechanisms.  In order to
   compute the signature over the HTTP request, the client must have
   access to a key bound to the access token (in plaintext form).

   If an attacker were to gain access to these stored secrets at the
   client or (in case of symmetric keys) at the resource server he or
   she would be able to perform any action on behalf of any client.

   It is therefore paramount to the security of the protocol that the
   private keys associated with the access tokens are protected from
   unauthorized access.

7.4.  Entropy of Keys

   Unless TLS is used between the client and the resource server,
   eavesdroppers will have full access to requests sent by the client.
   They will thus be able to mount off-line brute-force attacks to
   recover the session key or private key used to compute the keyed
   message digest or digital signature, respectively.

   This specification assumes that the keying material for use with the
   described HTTP signing mechanism has been distributed via other
   mechanisms, such as [I-D.bradley-oauth-pop-key-distribution].  Hence,
   it is the responsibility of the authorization server and or the
   client to be careful when generating fresh and unique keys with
   sufficient entropy to resist such attacks for at least the length of
   time that the session keys (and the access tokens) are valid.

   For example, if the key bound to the access token is valid for one
   day, authorization servers must ensure that it is not possible to
   mount a brute force attack that recovers that key in less than one
   day.  Of course, servers are urged to err on the side of caution, and
   use the longest key length reasonable.

7.5.  Denial of Service

   This specification includes a number of features which may make
   resource exhaustion attacks against resource servers possible.  For
   example, a resource server may need to need to the resource server
   has to process the incoming request, verify the access token, perform
   signature verification, and might have (in certain circumstances)




Richer, et al.          Expires October 26, 2014                [Page 9]


Internet-Draft            HTTP Signed Messages                April 2014


   consult back-end databases or the authorization server before
   granting access to the protected resource.

   An attacker may exploit this to perform a denial of service attack by
   sending a large number of invalid requests to the server.  The
   computational overhead of verifying the keyed message digest alone
   is, however, not sufficient to mount a denial of service attack since
   keyed message digest functions belong to the computationally fastest
   cryptographic algorithms.  The situation may, however, be different
   when using asymmetric cryptography, which is also supported by the
   JWS.

7.6.  Protecting HTTP Header Fields

   This specification provides flexibility for selectively protecting
   header fields and even the body of the message.  Since all components
   of the HTTP request are only optionally protected by this method, and
   even some components may be protected only in part (e.g., some
   headers but not others) it is up to application developers to verify
   that any parameters in a request are actually covered by the
   signature.

   The application verifying this signature MUST NOT assume that any
   particular parameter is appropriately covered by the signature.  Any
   applications that are sensitive of header or query parameter order
   MUST verify the order of the parameters on their own.  The
   application MUST also compare the values in the JSON container with
   the actual parameters received with the HTTP request.  Failure to
   make this comparison will render the signature mechanism useless.

8.  Acknowledgements

   The authors acknowledge the OAuth Working Group and submit this draft
   for feedback and input into the ongoing work of signed HTTP requests
   for the interaction between clients and resource servers.

9.  References

9.1.  Normative References

   [I-D.ietf-jose-json-web-signature]
              Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", draft-ietf-jose-json-web-signature-25
              (work in progress), March 2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.




Richer, et al.          Expires October 26, 2014               [Page 10]


Internet-Draft            HTTP Signed Messages                April 2014


   [RFC6749]  Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
              6749, October 2012.

   [RFC6750]  Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage", RFC 6750, October 2012.

9.2.  Informative References

   [I-D.bradley-oauth-pop-key-distribution]
              Bradley, J., Hunt, P., Jones, M., and H. Tschofenig,
              "OAuth 2.0 Proof-of-Possession: Authorization Server to
              Client Key Distribution", draft-bradley-oauth-pop-key-
              distribution-00 (work in progress), April 2014.

   [I-D.hunt-oauth-pop-architecture]
              Hunt, P., Richer, J., Mills, W., Mishra, P., and H.
              Tschofenig, "OAuth 2.0 Proof-of-Possession (PoP) Security
              Architecture", draft-hunt-oauth-pop-architecture-00 (work
              in progress), April 2014.

Authors' Addresses

   Justin Richer (editor)
   The MITRE Corporation

   Email: jricher@mitre.org


   John Bradley
   Ping Identity

   Email: ve7jtb@ve7jtb.com
   URI:   http://www.thread-safe.com/


   Hannes Tschofenig
   ARM Limited
   Austria

   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at










Richer, et al.          Expires October 26, 2014               [Page 11]


Html markup produced by rfcmarkup 1.127, available from https://tools.ietf.org/tools/rfcmarkup/