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Versions: 00 01 02 03

Network Working Group                                          M. Cavage
Internet-Draft                                                    Joyent
Intended status: Standards Track                               M. Sporny
Expires: November 5, 2013                                 Digital Bazaar
                                                             May 4, 2013


                            HTTP Signatures
                    draft-cavage-http-signatures-00

Abstract

   This document describes a way to add origin authentication, message
   integrity, and replay resistance to HTTP requests.  It is intended to
   be used over the HTTPS protocol.

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 5, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.







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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Signature Authentication Scheme . . . . . . . . . . . . . . . . 3
     2.1.  Authorization Header  . . . . . . . . . . . . . . . . . . . 3
       2.1.1.  Signature Parameters  . . . . . . . . . . . . . . . . . 4
       2.1.2.  Signature String Construction . . . . . . . . . . . . . 5
   3.  Appendix A: Security Considerations . . . . . . . . . . . . . . 6
     3.1.  Default Parameters  . . . . . . . . . . . . . . . . . . . . 6
     3.2.  Insecure Transports . . . . . . . . . . . . . . . . . . . . 7
     3.3.  Nonces  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     3.4.  Clock Skew  . . . . . . . . . . . . . . . . . . . . . . . . 7
     3.5.  Required Headers to Sign  . . . . . . . . . . . . . . . . . 7
   4.  Appendix B: Test Values . . . . . . . . . . . . . . . . . . . . 8
     4.1.  Default Test  . . . . . . . . . . . . . . . . . . . . . . . 8
     4.2.  All Headers Test  . . . . . . . . . . . . . . . . . . . . . 9
   5.  Normative References  . . . . . . . . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9

































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1.  Introduction

   This protocol is intended to provide a standard way for clients to
   sign HTTP requests.  RFC 2617 [RFC2617] (HTTP Authentication) defines
   Basic and Digest authentication mechanisms, and RFC 5246 [RFC5246]
   (TLS 1.2) defines client-auth, both of which are widely employed on
   the Internet today.  However, it is common place that the burdens of
   PKI prevent web service operators from deploying that methodoloy, and
   so many fall back to Basic authentication, which has poor security
   characteristics.

   Additionally, OAuth provides a fully-specified alternative for
   authorization of web service requests, but is not (always) ideal for
   machine to machine communication, as the key acquisition steps
   (generally) imply a fixed infrastructure that may not make sense to a
   service provider (e.g., symmetric keys).

   Several web service providers have invented their own schemes for
   signing HTTP requests, but to date, none have been placed in the
   public domain as a standard.  This document serves that purpose.
   There are no techniques in this proposal that are novel beyond
   previous art, however, this aims to be a simple mechanism for signing
   these requests.


2.  Signature Authentication Scheme

   The "signature" authentication scheme is based on the model that the
   client must authenticate itself with a digital signature produced by
   either a private asymmetric key (e.g., RSA) or a shared symmetric key
   (e.g., HMAC).  The scheme is parameterized enough such that it is not
   bound to any particular key type or signing algorithm.  However, it
   does explicitly assume that clients can send an HTTP `Date` header.

2.1.  Authorization Header

   The client is expected to send an Authorization header (as defined in
   RFC 2617) with the following parameterization:













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credentials := "Signature" SP params
params := keyId "," algorithm [", " headers] [", " ext] ", " signature

keyId := "keyId" "=" plain-string
algorithm := "algorithm" "=" DQUOTE ( rsa-sha1 / rsa-sha256 / rsa-sha512 /
                                      dsa-sha1 / hmac-sha1 / hmac-sha256 /
                                      hmac-sha512 )
                             DQUOTE
headers := "headers" "=" plain-string
ext := "ext" "=" plain-string
signature := "signature" "=" plain-string

plain-string   = DQUOTE *( %x20-21 / %x23-5B / %x5D-7E ) DQUOTE

2.1.1.  Signature Parameters

   The following section details the signature parameters of the
   Authorization Header.

2.1.1.1.  keyId

   REQUIRED.  The `keyId` field is an opaque string that the server can
   use to look up the component they need to validate the signature.  It
   could be an SSH key fingerprint, an LDAP DN, etc.  Management of keys
   and assignment of `keyId` is out of scope for this document.

2.1.1.2.  algorithm

   REQUIRED.  The `algorithm` parameter is used if the client and server
   agree on a non-standard digital signature algorithm.  The full list
   of supported signature mechanisms is listed below.

2.1.1.3.  headers

   OPTIONAL.  The `headers` parameter is used to specify the list of
   HTTP headers used to sign the request.  If specified, it should be a
   quoted list of HTTP header names, separated by a single space
   character.  By default, only one HTTP header is signed, which is the
   `Date` header.  Note that the list MUST be specified in the order the
   values are concatenated together during signing.  To include the HTTP
   request line in the signature calculation, use the special `request-
   line` value.  While this is overloading the definition of `headers`
   in HTTP linguism, the request-line is defined in RFC 2616 [RFC2616],
   and as the outlier from headers in useful signature calculation, it
   is deemed simpler to simply use `request-line` than to add a separate
   parameter for it.





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2.1.1.4.  extensions

   OPTIONAL.  The `extensions` parameter is used to include additional
   information which is covered by the request.  The content and format
   of the string is out of scope for this document, and expected to be
   specified by implementors.

2.1.1.5.  signature

   REQUIRED.  The `signature` parameter is a `Base64` encoded digital
   signature generated by the client.  The client uses the `algorithm`
   and `headers` request parameters to form a canonicalized `signing
   string`.  This `signing string` is then signed with the key
   associated with `keyId` and the algorithm corresponding to
   `algorithm`.  The `signature` parameter is then set to the `Base64`
   encoding of the signature.

2.1.2.  Signature String Construction

   In order to generate the string that is signed with a key, the client
   MUST take the values of each HTTP header specified by `headers` in
   the order they appear.

   1.  If the header name is not `request-line` then append the
       lowercased header name followed with an ASCII colon `:` and an
       ASCII space ` `.

   2.  If the header name is `request-line` then appened the HTTP
       request line, otherwise append the header value.

   3.  If value is not the last value then append an ASCII newline `\n`.
       The string MUST NOT include a trailing ASCII newline.

   The rest of this section uses the following HTTP request as an
   example.

   POST /foo HTTP/1.1
   Host: example.org
   Date: Tue, 07 Jun 2011 20:51:35 GMT
   Content-Type: application/json
   Content-MD5: lCMsW4/JJy9vc6HjbraPzw==
   Content-Length: 15

   {"bar": "baz"}

   The following sections also assume that the "rsa-key-1" keyId refers
   to a private key known to the client and a public key known to the
   server.  The "hmac-key-1" keyId refers to key known to the client and



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   server.

2.1.2.1.  RSA Example

   The authorization header and signature would be generated as:

Authorization: Signature keyId="rsa-key-1",algorithm="rsa-sha256",signature="Base64(RSA-SHA256(signing string))"

   The client would compose the signing string as:

   date: Tue, 07 Jun 2011 20:51:35 GMT

   For an RSA-based signature, the authorization header and signature
   would be generated as:

Authorization: Signature keyId="rsa-key-1",algorithm="rsa-sha256",headers="request-line date content-type content-md5",signature="Base64(RSA-SHA256(signing string))"

   The client would compose the signing string as (`+ "\n"` inserted for
   readability):

   POST /foo HTTP/1.1 + "\n"
   date: Tue, 07 Jun 2011 20:51:35 GMT + "\n"
   content-type: application/json + "\n"
   content-md5: lCMsW4/JJy9vc6HjbraPzw==

2.1.2.2.  HMAC Example

   For an HMAC-based signature without a list of headers specified, the
   authorization header and signature would be generated as:

Authorization: Signature keyId="hmac-key-1",algorithm="hmac-sha1",signature="Base64(HMAC-SHA1(signing string))"

   The client would compose the signing string as:

   date: Tue, 07 Jun 2011 20:51:35 GMT


3.  Appendix A: Security Considerations

   There are a number of security considerations to take into account
   when deploying HTTP Signatures.

3.1.  Default Parameters

   Note the default parameterization of the `Signature` scheme is only
   safe if all requests are carried over a secure transport (i.e., TLS).
   Sending the default scheme over a non-secure transport will leave the
   request vulnerable to spoofing, tampering, replay/repudiaton, and



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   integrity violations (if using the STRIDE threat-modeling
   methodology).

3.2.  Insecure Transports

   If sending the request over plain HTTP, service providers SHOULD
   require clients to sign ALL HTTP headers, and the `request-line`.
   Additionally, service providers SHOULD require `Content-MD5`
   calculations to be performed to ensure against any tampering from
   clients.

3.3.  Nonces

   Nonces are out of scope for this document simply because many service
   providers fail to implement them correctly, or do not adopt security
   specfiications because of the infrastructure complexity.  Given the
   `header` parameterization, a service provider is fully enabled to add
   nonce semantics into this scheme by using something like an
   `x-request-nonce` header, and ensuring it is signed with the `Date`
   header.

   ISSUE: This specification should probably explain exactly how to
   implement nonces for implementers that would like a fully vetted
   solution that protects against replay.  This would be useful for
   implementers implementing HTTP signatures in a clear channel
   environment.  Another consideration for nonces is the probability
   that multiple clients may share the same public key.  In this
   instance, due to clock skew issues, it is possible that some clients
   may accidentally trigger replay protection by sending a date in the
   past.  The balance that this spec attempts to achieve is a simple
   per-client, time-based counter.  Thus, the nonce would need to
   include something like a UUID-based client identifier, plus an
   incredibly accurate UTC datetime-based nonce as described in RFC 3339
   [RFC3339].  For example: "598ef3e8-98b0-435d-8ca3-fecefdd87568 2013-
   05-04 20:00:35.808785840+00:00"

3.4.  Clock Skew

   As the default scheme is to sign the `Date` header, service providers
   SHOULD protect against logged replay attacks by enforcing a clock
   skew.  The server SHOULD be synchronized with NTP, and the
   recommendation in this specification is to allow 300s of clock skew
   (in either direction).

3.5.  Required Headers to Sign

   It is out of scope for this document to dictate what headers a
   service provider will want to enforce, but service providers SHOULD



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   at minimum include the `Date` header.


4.  Appendix B: Test Values

   The following test data uses the following RSA 2048-bit keys, which
   we will refer to as `keyId=Test` in the following samples:

   -----BEGIN PUBLIC KEY-----
   MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDCFENGw33yGihy92pDjZQhl0C3
   6rPJj+CvfSC8+q28hxA161QFNUd13wuCTUcq0Qd2qsBe/2hFyc2DCJJg0h1L78+6
   Z4UMR7EOcpfdUE9Hf3m/hs+FUR45uBJeDK1HSFHD8bHKD6kv8FPGfJTotc+2xjJw
   oYi+1hqp1fIekaxsyQIDAQAB
   -----END PUBLIC KEY-----


   -----BEGIN RSA PRIVATE KEY-----
   MIICXgIBAAKBgQDCFENGw33yGihy92pDjZQhl0C36rPJj+CvfSC8+q28hxA161QF
   NUd13wuCTUcq0Qd2qsBe/2hFyc2DCJJg0h1L78+6Z4UMR7EOcpfdUE9Hf3m/hs+F
   UR45uBJeDK1HSFHD8bHKD6kv8FPGfJTotc+2xjJwoYi+1hqp1fIekaxsyQIDAQAB
   AoGBAJR8ZkCUvx5kzv+utdl7T5MnordT1TvoXXJGXK7ZZ+UuvMNUCdN2QPc4sBiA
   QWvLw1cSKt5DsKZ8UETpYPy8pPYnnDEz2dDYiaew9+xEpubyeW2oH4Zx71wqBtOK
   kqwrXa/pzdpiucRRjk6vE6YY7EBBs/g7uanVpGibOVAEsqH1AkEA7DkjVH28WDUg
   f1nqvfn2Kj6CT7nIcE3jGJsZZ7zlZmBmHFDONMLUrXR/Zm3pR5m0tCmBqa5RK95u
   412jt1dPIwJBANJT3v8pnkth48bQo/fKel6uEYyboRtA5/uHuHkZ6FQF7OUkGogc
   mSJluOdc5t6hI1VsLn0QZEjQZMEOWr+wKSMCQQCC4kXJEsHAve77oP6HtG/IiEn7
   kpyUXRNvFsDE0czpJJBvL/aRFUJxuRK91jhjC68sA7NsKMGg5OXb5I5Jj36xAkEA
   gIT7aFOYBFwGgQAQkWNKLvySgKbAZRTeLBacpHMuQdl1DfdntvAyqpAZ0lY0RKmW
   G6aFKaqQfOXKCyWoUiVknQJAXrlgySFci/2ueKlIE1QqIiLSZ8V8OlpFLRnb1pzI
   7U1yQXnTAEFYM560yJlzUpOb1V4cScGd365tiSMvxLOvTA==
   -----END RSA PRIVATE KEY-----

   And all examples use this request:

   POST /foo?param=value&pet=dog HTTP/1.1
   Host: example.com
   Date: Thu, 05 Jan 2012 21:31:40 GMT
   Content-Type: application/json
   Content-MD5: Sd/dVLAcvNLSq16eXua5uQ==
   Content-Length: 18

   {"hello": "world"}

4.1.  Default Test

   The string to sign would be:

   date: Thu, 05 Jan 2012 21:31:40 GMT



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   The Authorization header would be:

Authorization: Signature keyId="Test",algorithm="rsa-sha256",signature="JldXnt8W9t643M2Sce10gqCh/+E7QIYLiI+bSjnFBGCti7s+mPPvOjVb72sbd1FjeOUwPTDpKbrQQORrm+xBYfAwCxF3LBSSzORvyJ5nRFCFxfJ3nlQD6Kdxhw8wrVZX5nSem4A/W3C8qH5uhFTRwF4ruRjh+ENHWuovPgO/HGQ="

4.2.  All Headers Test

   Parameterized to include all headers, the string to sign would be (`+
   "\n"` inserted for readability):

   POST /foo?param=value&pet=dog HTTP/1.1 + "\n"
   host: example.com + "\n"
   date: Thu, 05 Jan 2012 21:31:40 GMT + "\n"
   content-type: application/json + "\n"
   content-md5: Sd/dVLAcvNLSq16eXua5uQ== + "\n"
   content-length: 18

   The Authorization header would be:

Authorization: Signature keyId="Test",algorithm="rsa-sha256",headers="request-line host date content-type content-md5 content-length",signature="Gm7W/r+e90REDpWytALMrft4MqZxCmslOTOvwJX17ViEBA5E65QqvWI0vIH3l/vSsGiaMVmuUgzYsJLYMLcm5dGrv1+a+0fCoUdVKPZWHyImQEqpLkopVwqEH67LVECFBqFTAKlQgBn676zrfXQbb+b/VebAsNUtvQMe6cTjnDY="


5.  Normative References

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

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [RFC3339]  Klyne, G., Ed. and C. Newman, "Date and Time on the
              Internet: Timestamps", RFC 3339, July 2002.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.











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Authors' Addresses

   Mark Cavage
   Joyent
   One Embarcadero Center
   9th Floor
   San Francisco, CA  94111
   US

   Phone: +1 ??? ??? ????
   Email: mark.cavage@joyent.com
   URI:   http://www.joyent.com/


   Manu Sporny
   Digital Bazaar
   1700 Kraft Drive
   Suite 2408
   Blacksburg, VA  24060
   US

   Phone: +1 540 961 4469
   Email: msporny@digitalbazaar.com
   URI:   http://manu.sporny.org/



























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