atompub F. Chen Internet-Draft M. Hondo Expires: February 12, 2010 R. Salz IBM August 11, 2009 Advanced Security Processing for Atom and APP Documents draft-rsalz-atom-adv-sec-00.txt Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on February 12, 2010. Copyright Notice Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Chen, et al. Expires February 12, 2010 [Page 1] Internet-Draft ATOM ADVANCED SECURITY August 2009 Abstract The Atom and APP specifications specify simple uses of cryptography to sign and encrypt their documents. Each document is processed completely, and in isolation. This document specifies additional uses that enable selective protection or encryption of content, and allow a "trust path" to be created across "atom:link" elements. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Notational Conventions and Terminology . . . . . . . . . . 3 2. Using WS-Security . . . . . . . . . . . . . . . . . . . . . . 4 3. The "atomsec:credentials" element . . . . . . . . . . . . . . 6 4. Selectively Signing parts of an Atom document . . . . . . . . 8 5. Selectively Encrypting parts of an Atom document . . . . . . . 11 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 8. Normative References . . . . . . . . . . . . . . . . . . . . . 15 Appendix A. Crypto and Security Primer . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 Chen, et al. Expires February 12, 2010 [Page 2] Internet-Draft ATOM ADVANCED SECURITY August 2009 1. Introduction The Atom and APP specifications define how to use XML Digital Signature [W3C.REC-xmlenc-core-20021210], and XML Encryption [W3C.REC-xmlenc-core-20021210] to prevent the contents of a document from being modified or inadvertently disclosed. This specification profiles how to use WS-Security [oasis-wssec-v1.1] to provide selective protection and encryption of a document and allow a single document to be encrypted for multiple recipients. Linking is a key point of Atom and APP, and this document defines a new element that can be used to establish a chain of trust, from the document with the "atom:link" to the content being referred-to. 1.1. Notational Conventions and Terminology The conventions and terminology of both The Atom Syndication Format [RFC4287] and The Atom Publishing Protocol [RFC5023], known as Atom and APP respectively, are incorporated here by reference. Within this document, the phrase "Atom document" is used to refer to any document defined by either RFC. The following namespace prefixes are used in this document: +-------+-----------------------------------------------------------+ | Prefi | Namespace URI | | x | | +-------+-----------------------------------------------------------+ | atom | http://www.w3.org/2005/Atom | | | | | app | http://www.w3.org/2007/app | | | | | atoms | http://www.ibm.com/xmlns/stdwip/atomext/security | | e | | | c | | | | | | dsig | http://www.w3.org/2000/09/xmldsig# | | | | | xenc | http://www.w3.org/2001/04/xmlenc# | | | | | wsse | http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-w | | | ssecurity-secext-1.0.xsd | | | | | wsu | "http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss- | | | wssecurity-utility-1.0.xsd | +-------+-----------------------------------------------------------+ Chen, et al. Expires February 12, 2010 [Page 3] Internet-Draft ATOM ADVANCED SECURITY August 2009 2. Using WS-Security The "wsse:Security" element is part of a specification informally known as WS-Security. The element is defined as a container for security information, including security tokens, XML encryption keys, and/or XML digital signatures for SOAP message security. This specification uses the semantics of WS-Security processing to achieve the goals . An Atom or APP dcoument MUST NOT have more than one "wsse:Security" child element. While compatible with [oasis-wssec-v1.1] processing, the schema for the "wsse:Security" element is taken from [oasis-wssec-v1.0]. One feature of the WS-Security header is that it should be possible to process in a forward-streaming manner. That is, security tokens appear before they are used (such as in signatures), and encipherment keys appear before the encrypted data. Therefore, if present, the "wsse:Security" element SHOULD be the first child of the Atom document. The "wsse:SecurityTokenReference" element can be used to help enable streaming processing, and to reduce multiple occurrences of the same credentials. To do this, each credential is made the child of a "wsse:BinarySecurityToken" element, which in turn is a child of the "wsse:Security" element. For example: MII... . ... Note that [W3C.REC-xmlenc-core-20021210] specifies many ways to identify key material, including Distinguished Name, Issuer/ SerialNumber, etc. Any method other than embedding the entire certificate SHOULD NOT be used. In this document, anywhere a certificate is referenced, the content may instead be a "wsse:SecurityTokenReference" to a token in the "wsse:Security" element. For example, the following two document fragments are semantically equivalent: Chen, et al. Expires February 12, 2010 [Page 4] Internet-Draft ATOM ADVANCED SECURITY August 2009 MII... A reference other than a direct reference using the "wsse:Reference" element MUST NOT be used. Chen, et al. Expires February 12, 2010 [Page 5] Internet-Draft ATOM ADVANCED SECURITY August 2009 3. The "atomsec:credentials" element The "atomsec:credentials" element is a child element of an "atom: link" element. It specifies one or more security tokens that may be used to validate the provenance of the data being linked-to. The "use" attribute specifies how the credentials are to be used. Two values are specified, "content" and "transport". If the attribute is not present, it is equivalent to providing it with the value "content". atomSecCredentials = element atomsec:credentials { atomCommonAttributes*, attribute use { "content" | "transport" } ?, (extensionElement*) } The "transport" value specifies that the credentials can be used to validate the SSL certificate of the server containing the linked-to data. The "content" value specifies that the credentials can be used to validate any digital signatures on the linked-to data. An "atom:link" element can have no more than two "atom:credentials" elements, one for each of content and transport credentials. The child elements of the "atomsec:credentials" element SHOULD be "dsig:KeyInfo" elmenents used to locate X.509 certificate data. These certificates can be used by the relying party to verify the specified trust chain. A party that has out of band knowledge MAY ignore this element. Here is an example of an Atom document pointing to signed content: MII... Chen, et al. Expires February 12, 2010 [Page 6] Internet-Draft ATOM ADVANCED SECURITY August 2009 Here is another example, one that specifies the CA that issued the SSL/TLS certificate used by the server for the host www.example.com: MII... Chen, et al. Expires February 12, 2010 [Page 7] Internet-Draft ATOM ADVANCED SECURITY August 2009 4. Selectively Signing parts of an Atom document A "dsig:Signature" element in the "wsse:Security" element may be used to sign one or more elements of an Atom document. The signature should be detached, with one "dsig:Reference" for each item being signed. The processing rules are defined by sections 8.2 and 8.4 of [oasis-wssec-v1.1] with the following additions: o The SOAP message envelope is not used and the "wsse:Security" element MUST be the first element of the root document. o Each element being signed MUST have a unique "xml:id" attribute if not already present. o The enveloped-signature transform as defined by [W3C.REC-xmlenc-core-20021210] SHOULD be used to sign the root document. If there are additional signed elements, they MUST be signed first so that the root signature will include its descendant's signatures. Here is an example: XXXX-XX-XXT02:41:15Z XXXX-XX-XXT02:46:15Z MII... cHt... Chen, et al. Expires February 12, 2010 [Page 8] Internet-Draft ATOM ADVANCED SECURITY August 2009 Oj2... SWz... cRY... QAw... Example Feed 2003-12-13T18:30:02Z John Doe Chen, et al. Expires February 12, 2010 [Page 9] Internet-Draft ATOM ADVANCED SECURITY August 2009 urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6 Atom-Powered Robots Run Amok urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a 2003-12-13T18:30:02Z Some text.

[Update: The Atom draft is finished.]

 Chen, et al. Expires February 12, 2010 [Page 10] Internet-Draft ATOM ADVANCED SECURITY August 2009 5. Selectively Encrypting parts of an Atom document The processing rules for encrypting parts of an Atom document are defined by sections 9.4.1 and 9.4.2 of [oasis-wssec-v1.1] with the following additions: o The SOAP message envelope is not used and the "wsse:Security" element MUST be the first element of the root document. o Use WS-Security processing to encrypt the full document. If the encrypted result does not have to be valid according to the Atom schema's, then the [W3C.REC-xmlenc-core-20021210] standard SHOULD be used. Here is an example: YPArt... JG0... Example Feed 2003-12-13T18:30:02Z John Doe Chen, et al. Expires February 12, 2010 [Page 11] Internet-Draft ATOM ADVANCED SECURITY August 2009 urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6 Clm... Clm... Chen, et al. Expires February 12, 2010 [Page 12] Internet-Draft ATOM ADVANCED SECURITY August 2009 6. IANA Considerations None. Chen, et al. Expires February 12, 2010 [Page 13] Internet-Draft ATOM ADVANCED SECURITY August 2009 7. Security Considerations This entire document is about securing Atom documents. Authentication and authorization (e.g., to delete a update or delete a posting via APP) are not discussed here. Chen, et al. Expires February 12, 2010 [Page 14] Internet-Draft ATOM ADVANCED SECURITY August 2009 8. Normative References [RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom Syndication Format", RFC 4287, December 2005. [RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing Protocol", RFC 5023, October 2007. [W3C.REC-xmldsig-core-20080610] Hirsch, F., Roessler, T., Eastlake, D., Reagle, J., and D. Solo, "XML Signature Syntax and Processing (Second Edition)", World Wide Web Consortium Recommendation REC- xmldsig-core-20080610, June 2008, . [W3C.REC-xmlenc-core-20021210] Eastlake, D. and J. Reagle, "XML Encryption Syntax and Processing", World Wide Web Consortium Recommendation REC- xmlenc-core-20021210, December 2002, . [oasis-wssec-v1.0] Nadalin, A., Kaler, C., Hallam-Baker, P., and R. Monzillo, "Web Services Security: SOAP Message Security 1.0", OASIS Standard 200401, March 2004, . [oasis-wssec-v1.1] Nadalin, A., Kaler, C., Hallam-Baker, P., and R. Monzillo, "Web Services Security: SOAP Message Security 1.1", OASIS Standard (WS-Security 2004), February 2006, . Chen, et al. Expires February 12, 2010 [Page 15] Internet-Draft ATOM ADVANCED SECURITY August 2009 Appendix A. Crypto and Security Primer This section provides a very brief overview of common cryptographic techniques and how they are used. It is intended only to provide the smallest amount of information so that the rest of this document is understandable. It is not normative. Public-key cryptography is done using two numbers that are related to each other. One of these numbers is public and can be known or used by anyone, while the other is private and should only be known by its "owner." The numbers have two very important properties. First, anything encrypted with the public key can only be decrypted with the private key. This means that anyone can generate text that is only legible to the key's owner. The second is that anything that is encrypted with the private key can be decrypted by anyone who has the public key. This allows anyone receiving such an encrypted item to know that it came from the key holder. The most common public-key algorithms are RSA and Elliptic-Curve. A message digest, or hash takes an arbitrary sequence of bytes and returns a fixed-size identifier. The most important property is that it is statistically unlikely for two different streams to result in the same hash. The most useful hash algorithms are SHA-1 and SHA- 256. A message digest encrypted with a private key is a signature. Anyone with the original document can generate their own digest, decrypt the received one, and compare them. If the values do not match, then the document has been modified. The most common signature method is RSA/ SHA-n. In symmetric cryptography, the same key is used for encryption and decryption. This means that both sender and receiver have to have the same key. Common symmetric (or shared-secret) algorithms are AES and triple-DES. A common technique is to "wrap" a symmetric key by encyrpting it with the recipient's public key. The bulk of the data is then encrypted using the symmetric key. This allows multiple recipients to see the data by only encrypting the symmetric key multiple times, rather than the entire data. An X.509 certificate is a datum that contains a name and other identifying information, and a public key that can be associated with that name. The certificate also contains information such as its validity period, the ways in which the keys are to be used, and so on. For details see the IETF PKI Profile, RFC XXX. A certificate is signed by a CA, and common practice is for the entity receiving a Chen, et al. Expires February 12, 2010 [Page 16] Internet-Draft ATOM ADVANCED SECURITY August 2009 certificate to be configured to trust everything signed by the CA, or perhaps the CA's CA, or further up the chain. Chen, et al. Expires February 12, 2010 [Page 17] Internet-Draft ATOM ADVANCED SECURITY August 2009 Authors' Addresses Fred (Xiangfu) Chen IBM 1 Rogers Street Cambridge, MA 02142 USA Phone: +1 617-693-6313 Email: chenfr@us.ibm.com URI: http://www.ibm.com Maryann Hondo IBM 1 Rogers Street Cambridge, MA 02142 USA Phone: +1 617-693-1236 Email: mhondo@us.ibm.com URI: http://www.ibm.com Rich Salz IBM 1 Rogers Street Cambridge, MA 02142 USA Phone: +1 617-693-3808 Email: rsalz@us.ibm.com URI: https://www.ibm.com/developerworks/mydeveloperworks/blogs/soma/ Chen, et al. Expires February 12, 2010 [Page 18]