HTTP Signatures
draft-cavage-http-signatures-01

Network Working Group                                          M. Cavage
Internet-Draft                                                    Joyent
Intended status: Standards Track                               M. Sporny
Expires: August 5, 2014                                   Digital Bazaar
                                                        February 1, 2014

                            HTTP Signatures
                    draft-cavage-http-signatures-01

Abstract

   When communicating over the Internet using the HTTP protocol, it is
   often desirable to be able to securely verify the sender of a message
   as well as ensure that the message was not tampered with during
   transit.  This document describes a way to add origin authentication
   and message integrity to HTTP messages.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on August 5, 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
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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  . . . . . . . . . . . . .  7
   4.  Appendix B: Extensions . . . . . . . . . . . . . . . . . . . .  7
   5.  Appendix C: Test Values  . . . . . . . . . . . . . . . . . . .  7
     5.1.  Default Test . . . . . . . . . . . . . . . . . . . . . . .  8
     5.2.  Basic Test . . . . . . . . . . . . . . . . . . . . . . . .  8
     5.3.  All Headers Test . . . . . . . . . . . . . . . . . . . . .  9
   6.  Normative References . . . . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10

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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 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.  It is out of scope for this document to
   dictate what headers a service provider will want to enforce, but
   service providers SHOULD at minimum include the request line, Host,
   and Date headers.

   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 2014 20:51:35 GMT
   Content-Type: application/json
   Digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
   Content-Length: 18

   {"hello": "world"}

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   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
   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",
   headers="request-line host date digest content-length",
   signature="Base64(RSA-SHA256(signing string))"

   The client would compose the signing string as:

   POST /foo HTTP/1.1\n
   host: example.org\n
   date: Tue, 07 Jun 2014 20:51:35 GMT\n
   digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=\n
   content-length: 18

   Note that the '\n' symbols above are included to demonstrate where
   the new line character should be inserted.  There is no new line on
   the final line of the signing string.

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

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

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",
   headers="request-line host date digest content-length",
   signature="Base64(HMAC-SHA1(signing string))"

   The only difference between the RSA Example and the HMAC Example is
   the signature algorithm that is used.  The client would compose the
   signing string in the same way as the RSA Example above:

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   POST /foo HTTP/1.1\n
   host: example.org\n
   date: Tue, 07 Jun 2014 20:51:35 GMT\n
   digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=\n
   content-length: 18

3.  Appendix A: Security Considerations

   There are a number of security considerations to take into account
   when implementing or utilizing this specification.  A thorough
   security analysis of this protocol, including its strengths and
   weaknesses, can be found in Security Considerations for HTTP
   Signatures [1].

4.  Appendix B: Extensions

   This specification was designed to be simple, modular, and
   extensible.  There are a number of other specifications that build on
   this one.  For example, the HTTP Signature Nonces [2] specification
   details how to use HTTP Signatures over a non-secured channel like
   HTTP and the HTTP Signature Trailers [3] specification explains how
   to apply HTTP Signatures to streaming content.  Developers that
   desire more functionality than this specification provides are urged
   to ensure that an extension specification doesn't already exist
   before implementing a proprietary extension.

5.  Appendix C: 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-----

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   -----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-----

   All examples use this request:

   POST /foo?param=value&pet=dog HTTP/1.1
   Host: example.com
   Date: Thu, 05 Jan 2014 21:31:40 GMT
   Content-Type: application/json
   Digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
   Content-Length: 18

   {"hello": "world"}

5.1.  Default Test

   If a list of headers is not included, the date is the only header
   that is signed by default.  The string to sign would be:

   date: Thu, 05 Jan 2014 21:31:40 GMT

   The Authorization header would be:

   Authorization: Signature keyId="Test",algorithm="rsa-sha256",
   signature="ATp0r26dbMIxOopqw0OfABDT7CKMIoENumuruOtarj8n/97Q3htH
   FYpH8yOSQk3Z5zh8UxUym6FYTb5+A0Nz3NRsXJibnYi7brE/4tx5But9kkFGzG+
   xpUmimN4c3TMN7OFH//+r8hBf7BT9/GmHDUVZT2JzWGLZES2xDOUuMtA="

5.2.  Basic Test

   The minimum recommended data to sign is the request-line, host, and
   date.  In this case, the string to sign would be:

   POST /foo?param=value&pet=dog HTTP/1.1
   host: example.com

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   date: Thu, 05 Jan 2014 21:31:40 GMT

   The Authorization header would be:

   Authorization: Signature keyId="Test",algorithm="rsa-sha256",
   headers="request-line host date", signature="KcLSABBj/m3v2Dhxi
   CKJmzYJvnx74tDO1SaURD8Dr8XpugN5wpy8iBVJtpkHUIp4qBYpzx2QvD16t8X
   0BUMiKc53Age+baQFWwb2iYYJzvuUL+krrl/Q7H6fPBADBsHqEZ7IE8rR0Ys3l
   b7J5A6VB9J/4yVTRiBcxTypW/mpr5w="

5.3.  All Headers Test

   A strong signature including all of the headers and a digest of the
   body of the HTTP request would result in the following signing
   string:

   POST /foo?param=value&pet=dog HTTP/1.1
   host: example.com
   date: Thu, 05 Jan 2014 21:31:40 GMT
   content-type: application/json
   digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
   content-length: 18

   The Authorization header would be:

   Authorization: Signature keyId="Test",algorithm="rsa-sha256",
   headers="request-line host date content-type digest content-length",
   signature="jgSqYK0yKclIHfF9zdApVEbDp5eqj8C4i4X76pE+XHoxugXv7q
   nVrGR+30bmBgtpR39I4utq17s9ghz/2QFVxlnToYAvbSVZJ9ulLd1HQBugO0j
   Oyn9sXOtcN7uNHBjqNCqUsnt0sw/cJA6B6nJZpyNqNyAXKdxZZItOuhIs78w="

6.  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.

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

   [1]  <https://web-payments.org/specs/source/http-signatures-audit/>

   [2]  <https://web-payments.org/specs/source/http-signature-nonces/>

   [3]  <https://web-payments.org/specs/source/http-signature-trailers/>

Authors' Addresses

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

   Phone: +1 415 400 0626
   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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