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Versions: 00

Network Working Group                                    A. Backman, Ed.
Internet-Draft                                                    Amazon
Intended status: Standards Track                       November 19, 2019
Expires: May 22, 2020


             Signing HTTP Requests via JSON Web Signatures
                  draft-richanna-http-jwt-signature-00

Abstract

   This document defines a method for generating and validating a
   digital signature or Message Authentication Code (MAC) over a set of
   protocol elements within an HTTP Request, using JSON Web Signatures
   (JWS).

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 https://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 May 22, 2020.

Copyright Notice

   Copyright (c) 2019 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
   (https://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
   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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Generating a HTTP Request Signature Using JWS . . . . . . . .   3
     3.1.  Generating the Payload of the JWS . . . . . . . . . . . .   4
     3.2.  Calculating the query parameter list and hash . . . . . .   5
     3.3.  Calculating the header list and hash  . . . . . . . . . .   6
   4.  Validating the HTTP Request Signature . . . . . . . . . . . .   6
     4.1.  Validating the query parameter list and hash  . . . . . .   7
     4.2.  Validating the header list and hash . . . . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  JSON Web Signature and Encryption Type Values
           Registration  . . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
     6.1.  Offering Confidentiality Protection for Access to
           Protected Resources . . . . . . . . . . . . . . . . . . .   8
     6.2.  Plaintext Storage of Credentials  . . . . . . . . . . . .   9
     6.3.  Entropy of Keys . . . . . . . . . . . . . . . . . . . . .   9
     6.4.  Denial of Service . . . . . . . . . . . . . . . . . . . .   9
     6.5.  Validating the integrity of HTTP message  . . . . . . . .   9
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  10
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Digital signatures and MACs are popular cryptographic tools that can
   be used to address a variety of use cases, such as providing message
   integrity, or establishing proof of possession of a cryptographic
   key.  While several digital signature algorithms exist, they
   generally share the constraint that any party wishing to validate a
   signature must have or be able to produce the exact byte sequence of
   the message that was signed.  Consequently, it is non-trivial to
   create digital signatures over content that may undergo
   transformation, such as can occur with HTTP messages as they pass
   through proxies and software libraries in use by the sender or
   recipient.

   This draft describes a method for generating and validating digital
   signatures or MACs over a set of protocol elements within an HTTP
   Request.  This method consists of:

      Mechanisms for identifying the protocol elements covered by the
      signature.





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      Mechanisms for creating canonical representations of protocol
      elements for the purpose of signing.

      A mechanism creating and encoding a signature over those canonical
      representations using JSON Web Signatures (JWS) [RFC7515].

   Many HTTP application frameworks reorder or insert extra headers,
   query parameters, and otherwise manipulate the HTTP request on its
   way from the web server into the application code itself.  Such
   transformations may be applied by the sender and recipient, as well
   as any proxy through which the message passes.  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.

   This draft is concerned specifically with the generation,
   representation, and validation of signatures over elements within an
   HTTP request, with the expectation that this draft will be profiled
   by later drafts that seek to apply these signatures to address
   specific use cases within a larger application context.
   Consequently, key distribution, signing algorithm selection, and
   determination of which elements must be covered by the signature are
   all out of scope of this draft.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].

   Other terms such as "client", "server", "HTTP request", and "protocol
   element" are inherited from HTTP [RFC7230].

   This document uses the term 'sign' (or 'signature') to denote both a
   keyed message digest and a digital signature operation.

3.  Generating a HTTP Request Signature Using JWS

   This specification uses JSON Web Signature [RFC7515] to sign a set of
   protocol elements taken from an HTTP Request.  When a JWS is created
   for this purpose, its ""typ"" header attribute MUST have the value
   ""http-sig"".

   The JWS MUST be signed with a valid algorithm as defined in
   [RFC7518].  The "none" algorithm MUST NOT be used.





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3.1.  Generating the Payload of the JWS

   The JWS Payload is a JSON object containing the data that will be
   covered by the signature.  In order to include a protocol element
   within the covered data, its value must be represented within this
   JSON object.  Some elements are represented directly, by setting the
   value of a member in the object to the element's value in the HTTP
   Request.  Others are included indirectly, by setting the value of a
   member in the object to a cryptographic hash or other value derived
   from the element's value in the HTTP Request.

   The below list defines the means of inclusion of various protocol
   elements, including the JSON object member that MUST be used when
   including the element, and how the element's value should be
   included.  When present, each of these members MUST be a top-level
   member of the JSON object.

   The JSON object MAY contain other top-level members.  The syntax and
   semantics of members not listed below are out of scope of this
   specification.  Implementations SHOULD consider a signature invalid
   if the JSON object contains members that the implementation does not
   understand.

   ts RECOMMENDED.  The timestamp.  This integer provides replay
      protection of the signed JSON object.  Its value MUST be a number
      containing an integer value representing number of whole integer
      seconds from midnight, January 1, 1970 GMT.

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

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

   q  OPTIONAL.  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  OPTIONAL.  The hashed HTTP request headers as a two-part JSON
      array.  The first part of this array is a JSON array listing all



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      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  OPTIONAL.  The base64URL encoded hash of the HTTP Request body,
      calculated as the SHA256 of the byte array of the body

   All hashes SHALL be calculated using the SHA256 algorithm.

3.2.  Calculating the query parameter list and hash

   To generate the query parameter list and hash, the signer 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 signer 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 query parameter to the end of the list.

   2.  Percent-encodes the name and value of the parameter as specified
       in [RFC3986].  Note that if the name and value have already been
       percent-encoded for transit, they are not re-encoded for this
       step.

   3.  Encodes the name and value of the query parameter as "name=value"
       and appends it to the string buffer separated by the ampersand
       "&" character.

   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 signer then calculates the hash over the resulting string buffer.
   The list and the hash result are added to a list as the value of the
   "q" member.

   For example, the query parameter set of "b=bar", "a=foo", "c=duck" is
   concatenated into the string:

   b=bar&a=foo&c=duck

   When added to the JSON structure using this process, the results are:

   "q": [["b", "a", "c"], "u4LgkGUWhP9MsKrEjA4dizIllDXluDku6ZqCeyuR-JY"]





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3.3.  Calculating the header list and hash

   To generate the header list and hash, the signer 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 signer iterates through all query parameters in whatever order it
   chooses and for each query parameter it does the following:

   1.  Lowercases the header name.

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

   3.  Encodes the name and value of the header as "name: value" and
       appends it to the string buffer separated by a newline "\n"
       character.

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

   For example, the headers "Content-Type: application/json" and "Etag:
   742-3u8f34-3r2nvv3" are concatenated into the string:

   content-type: application/json
   etag: 742-3u8f34-3r2nvv3

   "h": [["content-type", "etag"],
     "bZA981YJBrPlIzOvplbu3e7ueREXXr38vSkxIBYOaxI"]

4.  Validating the HTTP Request Signature

   Validation of the signature is done using normal JWS validation for
   the signature and key type.  Additionally, in order to trust any of
   the hashed components of the HTTP request, the validator MUST re-
   create and verify a hash for each component as described below.  This
   process is a mirror of the process used to create the hashes in the
   first place, with a mind toward the fact that order may have changed
   and that elements may have been added or deleted.  The protected
   resource MUST similarly compare the replicated values included in
   various JSON fields with the corresponding actual values from the
   request.  Failure to do so will allow an attacker to modify the
   underlying request while at the same time having the application
   layer verify the signature correctly.



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4.1.  Validating the query parameter list and hash

   The validator has at its disposal a map that indexes the query
   parameter names to the values given.  The validator creates a string
   buffer for calculating the hash.  The validator 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 query
       parameter map.  If a parameter is found in the list of signed
       parameters but not in the map, the validation fails.

   2.  Percent-encodes the name and value of the parameter as specified
       in [RFC3986].  Note that if the name and value have already been
       percent-encoded for transit, they are not re-encoded for this
       step.

   3.  Encode the parameter as "name=value" and concatenate it to the
       end of the string buffer, separated by an ampersand character.

   The validator calculates the hash of the string buffer and base64url
   encodes it.  The protected resource 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 validator
   MUST decide whether or not to accept a request with these uncovered
   parameters.

4.2.  Validating the header list and hash

   The validator has at its disposal a map that indexes the header names
   to the values given.  The validator creates a string buffer for
   calculating the hash.  The validator 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, separated by a newline character.

   The validator calculates the hash of the string buffer and base64url
   encodes it.  The protected resource compares that string to the



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   string passed in 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 validator MUST
   decide whether or not to accept a request with these uncovered
   headers.

5.  IANA Considerations

5.1.  JSON Web Signature and Encryption Type Values Registration

   This specification registers the "http-sig" type value in the IANA
   JSON Web Signature and Encryption Type Values registry [RFC7515]:

   o  "typ" Header Parameter Value: "http-sig"

   o  Abbreviation for MIME Type: None

   o  Change Controller: IETF

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

6.  Security Considerations

6.1.  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
   server.  This could be problematic when data is exchanged that
   requires care, such as personal data.

   When TLS is used then confidentiality of the transmission can be
   ensured between endpoints, including both the request and the
   response.  The use of TLS in combination with the signed HTTP request
   mechanism is highly recommended to ensure the confidentiality of the
   data returned from the protected resource.







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6.2.  Plaintext Storage of Credentials

   The mechanism described in this document works in a similar way 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 the decryption key 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 server they would be able to forge
   signatures for any HTTP request they wished, effectively allowing
   them to impersonate the client.

   It is therefore paramount to the security of the protocol that any
   private or symmetric keys used to sign HTTP requests are protected
   from unauthorized access.

6.3.  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
   attempt recovery of the session key or private key used to compute
   the keyed message digest or digital signature, respectively.

   Key generation and distribution is out of scope for this document.
   It is the responsibility of users of this specification to ensure
   that keys are generated with sufficient entropy and rotated at an
   appropriate frequency to sufficiently mitigate the risk of such
   attacks, as appropriate for their use case.

6.4.  Denial of Service

   This specification includes a number of features which may make
   resource exhaustion attacks against servers possible.  For example,
   server may need to consult back-end databases or other servers in
   order to verify a signature, or the cryptographic overhead may
   present a significant burden on the server.  An attacker could
   leverage this overhead to attempt a denial of service attack by
   sending a large number of invalid requests to the server, causing the
   server to expend significant resources checking invalid signatures.
   This attack vector must be taken into consideration when implementing
   or deploying this specification.

6.5.  Validating the integrity of HTTP message

   This specification provides flexibility for selectively validating
   the integrity of the HTTP request, including header fields, query
   parameters, and message bodies.  Since all components of the HTTP
   request are only optionally validated by this method, and even some



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   components may be validated only in part (e.g., some headers but not
   others) it is up to developers to verify that any vital parameters in
   a request are actually covered by the signature.  Failure to do so
   could allow an attacker to inject vital parameters or headers into
   the request, ouside of the protection of the signature.

   The application verifying this signature MUST NOT assume that any
   particular parameter is appropriately covered by the signature unless
   it is included in the signed structure and the hash is verified.  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 (using a direct
   comparison or a hash calculation, as appropriate).  Failure to make
   this comparison will render the signature mechanism useless for
   protecting these elements.

   The behavior of repeated query parameters or repeated HTTP headers is
   undefined by this specification.  If a header or query parameter is
   repeated on either the outgoing request from the client or the
   incoming request to the protected resource, that query parameter or
   header name MUST NOT be covered by the hash and signature.

   This specification records the order in which query parameters and
   headers are hashed, but it does not guarantee that order is preserved
   between the client and protected resource.  If the order of
   parameters or headers are significant to the underlying application,
   it MUST confirm their order on its own, apart from the signature and
   HTTP message validation.

7.  Privacy Considerations

   This specification addresses machine to machine communications and
   raises no privacy considerations beyond existing HTTP interactions.

8.  Acknowledgements

   The authors thank the OAuth Working Group for input into this work.

   In particular, the authors thank Justin Richer for his work on
   [I-D.ietf-oauth-signed-http-request], on which this specification is
   based.

9.  Normative References







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   [I-D.ietf-oauth-signed-http-request]
              Richer, J., Bradley, J., and H. Tschofenig, "A Method for
              Signing HTTP Requests for OAuth", draft-ietf-oauth-signed-
              http-request-03 (work in progress), August 2016.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

Author's Address

   Annabelle Backman (editor)
   Amazon

   Email: richanna@amazon.com

















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