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</style><link href="http://www.w3.org/StyleSheets/TR/W3C-CR" rel="stylesheet" type="text/css" charset="utf-8"></head><body style="display: inherit; "><div class="head"><p><a href="http://www.w3.org/"><img width="72" height="48" src="http://www.w3.org/Icons/w3c_home" alt="W3C"></a></p><h1 class="title" id="title">XML Security Generic Hybrid Ciphers</h1><h2 id="w3c-candidate-recommendation-03-march-2011">W3C Candidate Recommendation 03 March 2011</h2><dl><dt>This version:</dt><dd><a href="http://www.w3.org/TR/2011/CR-xmlsec-generic-hybrid-20110303/">http://www.w3.org/TR/2011/CR-xmlsec-generic-hybrid-20110303/</a></dd><dt>Latest published version:</dt><dd><a href="http://www.w3.org/TR/xmlsec-generic-hybrid/">http://www.w3.org/TR/xmlsec-generic-hybrid/</a></dd><dt>Latest editor's draft:</dt><dd><a href="http://www.w3.org/2008/xmlsec/Drafts/generic-hybrid-ciphers/">http://www.w3.org/2008/xmlsec/Drafts/generic-hybrid-ciphers/</a></dd><dt>Previous version:</dt><dd><a href="http://www.w3.org/TR/2010/WD-xmlsec-generic-hybrid-20100513/">http://www.w3.org/TR/2010/WD-xmlsec-generic-hybrid-20100513/</a></dd><dt>Editors:</dt><dd><span>Magnus Nyström</span>, Microsoft Corporation</dd>
<dd><span>Frederick Hirsch</span>, Nokia</dd>
</dl><p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 2011 <a href="http://www.w3.org/"><acronym title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup> (<a href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute of Technology">MIT</acronym></a>, <a href="http://www.ercim.eu/"><acronym title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym></a>, <a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document use</a> rules apply.</p><hr></div>
    <div id="abstract" class="introductory section"><h2>Abstract</h2>
<p>Generic hybrid ciphers allow for a consistent treatment of asymmetric
ciphers when encrypting data and consist of a key encapsulation
algorithm with associated parameters and a data encapsulation
algorithm with associated parameters. Further, the key encapsulation
algorithms introduced in this specification have attractive security
properties.</p>
<p>
This document augments XML Encryption Version 1.1 [<cite><a class="bibref" rel="biblioentry" href="#bib-XMLENC-CORE1">XMLENC-CORE1</a></cite>] by
defining algorithms, XML types and elements
necessary to enable use of generic hybrid ciphers in XML Security
applications.
      </p>
    </div><div id="sotd" class="introductory section"><h2>Status of This Document</h2><p><em>This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the <a href="http://www.w3.org/TR/">W3C technical reports index</a> at http://www.w3.org/TR/.</em></p>
<p>There is no previous W3C Recommendation of XML Security Generic
  Hybrid Ciphers.
No substantive changes have been made to this specification since
  the previous Last Call Working Draft.
  Please
  review <a href="Overview_diff.html">differences between the previous
  Last Call Working Draft
  and this Candidate Recommendation</a>.</p>
  <p> Changes since the previous Last Call include updated
  References, editorial updates and corrections related to
  references to sections within referenced documents,
    example formatting and addition of acknowledgments.</p>

      <p>This document was published by the <a href="http://www.w3.org/2008/xmlsec/">XML Security Working Group</a> as a Candidate Recommendation. This document is intended to become a W3C Recommendation. If you wish to make comments regarding this document, please send them to <a href="mailto:public-xmlsec@w3.org">public-xmlsec@w3.org</a> (<a href="mailto:public-xmlsec-request@w3.org?subject=subscribe">subscribe</a>, <a href="http://lists.w3.org/Archives/Public/public-xmlsec/">archives</a>). W3C publishes a Candidate Recommendation to indicate that the document is believed to be stable and to encourage implementation by the developer community. This Candidate Recommendation is expected to advance to Proposed Recommendation no earlier than 01 June 2011. All feedback is welcome.</p><p>Publication as a Candidate Recommendation does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.</p><p>This document was produced by a group operating under the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent Policy</a>. W3C maintains a <a href="http://www.w3.org/2004/01/pp-impl/42458/status" rel="disclosure">public list of any patent disclosures</a> made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the W3C Patent Policy</a>.</p></div><div id="toc" class="section"><h2 class="introductory">Table of Contents</h2><ul class="toc"><li class="tocline"><a href="#sec-introduction" class="tocxref"><span class="secno">1. </span>Introduction</a><ul class="toc"><li class="tocline"><a href="#editorial" class="tocxref"><span class="secno">1.1 </span>Editorial</a></li></ul></li><li class="tocline"><a href="#sec-namespaces" class="tocxref"><span class="secno">2. </span>Versions, Namespaces and Identifiers</a></li><li class="tocline"><a href="#sec-background" class="tocxref"><span class="secno">3. </span>Generic Hybrid Ciphers Overview</a></li><li class="tocline"><a href="#sec-algorithms" class="tocxref"><span class="secno">4. </span>Algorithms</a><ul class="toc"><li class="tocline"><a href="#implementation-requirements" class="tocxref"><span class="secno">4.1 </span>Algorithm Identifiers and Implementation Requirements</a></li><li class="tocline"><a href="#sec-generic-hybrid-algorithms" class="tocxref"><span class="secno">4.2 </span>Generic Hybrid Encryption Algorithms</a><ul class="toc"><li class="tocline"><a href="#sec-generic-hybrid" class="tocxref"><span class="secno">4.2.1 </span>Generic-Hybrid</a></li></ul></li><li class="tocline"><a href="#sec-kem-algorithms" class="tocxref"><span class="secno">4.3 </span>Key Encapsulation Algorithms</a><ul class="toc"><li class="tocline"><a href="#sec-rsaes-kem" class="tocxref"><span class="secno">4.3.1 </span>RSAES-KEM</a></li><li class="tocline"><a href="#sec-ecies-kem" class="tocxref"><span class="secno">4.3.2 </span>ECIES-KEM</a></li></ul></li></ul></li><li class="tocline"><a href="#sec-key-transport-algorithms" class="tocxref"><span class="secno">5. </span>Using Key Encapsulation Algorithms for Key Transport</a></li><li class="tocline"><a href="#sec-examples" class="tocxref"><span class="secno">6. </span>Examples</a><ul class="toc"><li class="tocline"><a href="#sec-key-transport-example" class="tocxref"><span class="secno">6.1 </span>Key Transport Example</a></li></ul></li><li class="tocline"><a href="#sec-security-considerations" class="tocxref"><span class="secno">7. </span>Security Considerations</a></li><li class="tocline"><a href="#sec-conformance" class="tocxref"><span class="secno">8. </span>Conformance</a></li><li class="tocline"><a href="#sec-acknowledgements" class="tocxref"><span class="secno">9. </span>Acknowledgments</a></li><li class="tocline"><a href="#sec-schema" class="tocxref"><span class="secno">10. </span>Schema</a><ul class="toc"><li class="tocline"><a href="#sec-xsdSchema" class="tocxref"><span class="secno">10.1 </span>XSD Schema</a></li><li class="tocline"><a href="#sec-rngSchema" class="tocxref"><span class="secno">10.2 </span>RNG Schema</a></li></ul></li><li class="tocline"><a href="#references" class="tocxref"><span class="secno">A. </span>References</a><ul class="toc"><li class="tocline"><a href="#normative-references" class="tocxref"><span class="secno">A.1 </span>Normative references</a></li><li class="tocline"><a href="#informative-references" class="tocxref"><span class="secno">A.2 </span>Informative references</a></li></ul></li></ul></div>


    <div id="sec-introduction" class="section">
      <!--OddPage--><h2><span class="secno">1. </span>Introduction</h2>
      <p>
This document specifies an XML syntax and processing rules for
generic hybrid ciphers and key encapsulation mechanisms based on
[<cite><a class="bibref" rel="biblioentry" href="#bib-ISO18033-2">ISO18033-2</a></cite>]. The document augments XML Encryption
[<cite><a class="bibref" rel="biblioentry" href="#bib-XMLENC-CORE1">XMLENC-CORE1</a></cite>].
      </p>
      <p>
This document does not normatively specify when and how generic hybrid
ciphers and key encapsulation mechanisms are to be
used; rather it focuses on the basis for interoperability, namely the
fundamental data types required for use of these algorithms in
conjunction with XML Security applications and the meaning of those data types,
as well as identification of specific algorithms.
      </p>
<div id="editorial" class="section">
<h3><span class="secno">1.1 </span>Editorial</h3>
<p>
The key words "<em class="rfc2119" title="must">must</em>" and
"<em class="rfc2119" title="optional">optional</em>" in this specification are to be
interpreted as described in RFC2119 [<cite><a class="bibref" rel="biblioentry" href="#bib-RFC2119">RFC2119</a></cite>]:
</p>
<p>
</p><blockquote>
<p>"They <em class="rfc2119" title="must">must</em> only be used where it is actually required for
interoperation or to limit behavior which has potential for
causing harm (e.g., limiting retransmissions)"</p>
</blockquote>
<p></p>
<p>
Consequently, these capitalized keywords are used to unambiguously
specify requirements over protocol and application features and
behavior that affect the interoperability and security of
implementations. These key words are not used (capitalized) to
describe XML grammar; schema definitions unambiguously describe such
requirements. For instance, an XML attribute might be described as
being "optional."
</p>
<p>
Note also that this entire specification is <em class="rfc2119" title="optional">optional</em>; hence the
keywords apply only when compliance with this specification is
claimed.
</p>
</div>
    </div>
<div id="sec-namespaces" class="section">
      <!--OddPage--><h2><span class="secno">2. </span>Versions, Namespaces and Identifiers</h2>
<p>
No provision is made for an explicit version number in this syntax. If
a future version is needed, it will use a different namespace. The XML
namespace [<cite><a class="bibref" rel="biblioentry" href="#bib-XML-NAMES">XML-NAMES</a></cite>] URI that <em class="rfc2119" title="must">must</em> be used by
implementations of this (dated) specification is:</p>
<pre class="xml-example">xmlns ghc="http://www.w3.org/2010/xmlsec-ghc#"</pre>
<p>
While applications <em class="rfc2119" title="must">must</em> support XML and XML namespaces, the use of internal entities or the <code>ghc</code> XML namespace prefix is <em class="rfc2119" title="optional">optional</em>; we use these facilities to provide compact and readable examples.
</p>
<p>
This specification uses Uniform Resource Identifiers [<cite><a class="bibref" rel="biblioentry" href="#bib-URI">URI</a></cite>] to identify resources, algorithms, and semantics. Identifiers under the control of this specification are coined within the scope of the above namespace.
</p>
</div>
<div id="sec-background" class="section">
  <!--OddPage--><h2><span class="secno">3. </span>Generic Hybrid Ciphers Overview</h2>
  <p>
The term "generic hybrid cipher" is defined in [<cite><a class="bibref" rel="biblioentry" href="#bib-ISO18033-2">ISO18033-2</a></cite>] as an
asymmetric cipher that combines both
asymmetric and symmetric cryptographic techniques. Generic hybrid
ciphers that meet the requirements laid out in [<cite><a class="bibref" rel="biblioentry" href="#bib-ISO18033-2">ISO18033-2</a></cite>]  have attractive security properties. They are
introduced in this document to enable applications to use
cryptographic algorithms with tight security proofs.
</p>
<p>
Generic hybrid ciphers allow for a consistent treatment of asymmetric
ciphers when encrypting data and consists of a key encapsulation
algorithm with associated parameters and a data encapsulation
algorithm with associated parameters. The key encapsulation algorithm
results in an encapsulated shared key that is then used with the data
encapsulation algorithm, e.g. for encryption.
</p>
</div>
<div id="sec-algorithms" class="section">
  <!--OddPage--><h2><span class="secno">4. </span>Algorithms</h2>
  <p>
This section discusses and identifies algorithms to be used with this
specification. Entries contain the identifier to be used as the value
of the <code>Algorithm</code> attribute of the
<code>EncryptionMethod</code> element or other element representing
the role of the algorithm, a reference to the formal specification,
definitions for the representation of keys and the results of
cryptographic operations where applicable, and general applicability
comments.
  </p>
  <div id="implementation-requirements" class="section">
    <h3><span class="secno">4.1 </span>Algorithm Identifiers and Implementation Requirements</h3>
    <p>
This specification defines a set of algorithms, their URIs, and
requirements for implementation. Levels of requirement specified, such
as <em class="rfc2119" title="must">must</em> or <em class="rfc2119" title="optional">optional</em>, refer
to implementation, not use.
    </p>
<dl>
<dt>Generic Hybrid Encryption</dt>
<dd>
<ol>
<li> <em class="rfc2119" title="must">must</em> Generic-Hybrid <a href="http://www.w3.org/2010/xmlsec-ghc#generic-hybrid">http://www.w3.org/2010/xmlsec-ghc#generic-hybrid</a>
</li>
</ol>
</dd>
<dt>Key Encapsulation</dt>
<dd>
<ol>
<li><em class="rfc2119" title="must">must</em> RSAES-KEM
<a href="http://www.w3.org/2010/xmlsec-ghc#rsaes-kem">http://www.w3.org/2010/xmlsec-ghc#rsaes-kem</a>
</li>
<li>
          <em class="rfc2119" title="must">must</em> ECIES-KEM
<a href="http://www.w3.org/2010/xmlsec-ghc#ecies-kem">http://www.w3.org/2010/xmlsec-ghc#ecies-kem</a>
</li>
</ol>
</dd>
</dl>
    </div>
    <div id="sec-generic-hybrid-algorithms" class="section">
      <h3><span class="secno">4.2 </span>Generic Hybrid Encryption Algorithms</h3>
      <p>
Generic-hybrid encryption algorithms combine both asymmetric and
symmetric cryptographic techniques. Schema definition:
      </p>
<pre class="xml-dtd">  &lt;element name="GenericHybridCipherMethod" type="ghc:GenericHybridCipherMethodType"/&gt;
  &lt;complexType name="GenericHybridCipherMethodType"&gt;
    &lt;sequence&gt;
      &lt;element name="KeyEncapsulationMethod" type="ghc:KeyEncapsulationMethodType"/&gt;
      &lt;element name="DataEncapsulationMethod" type="xenc:EncryptionMethodType"/&gt;
    &lt;/sequence&gt;
  &lt;/complexType&gt;
</pre>
<p>
The <code>KeyEncapsulationMethod</code> element identifies the key
encapsulation method as well as provides values for its parameters.
</p>
<p>
The <code>DataEncapsulationMethod</code> element identifies the data
encapsulation (encryption) method as well as provides any parameters
associated with the data encapsulation method.
</p>
<div id="sec-generic-hybrid" class="section">
  <h4><span class="secno">4.2.1 </span>Generic-Hybrid</h4>
<dl>
<dt>Identifier:</dt>
<dd><a href="http://www.w3.org/2010/xmlsec-ghc#generic-hybrid">http://www.w3.org/2010/xmlsec-ghc#generic-hybrid</a> (<em class="rfc2119" title="required">required</em>)
</dd>
</dl>
<p>
The Generic-Hybrid encryption algorithm may be used for a variety of
purposes; in particular, when used with a key encapsulation mechanism
such as those specified in <a href="#sec-kem-algorithms" class="sectionRef">section 4.3 Key Encapsulation Algorithms</a>
and a suitable key wrap algorithm, it can be used for key transport
with tight security proofs.
</p>
<p>
The <code>GenericHybridCipherMethod</code> element shall appear
as a child element of the <code>xenc:EncryptionMethod</code> when
<code>generic-hybrid</code> is specified as the value of the <code>xenc:EncryptionMethod</code>
<code>Algorithm</code> attribute.
</p>
      </div>
    </div>
    <div id="sec-kem-algorithms" class="section">
      <h3><span class="secno">4.3 </span>Key Encapsulation Algorithms</h3>
<p>
This document specifies two key encapsulation algorithms, RSAES-KEM
and ECIES-KEM, for use with the Generic-Hybrid cipher in key
transport scenarios.
</p>
<pre class="xml-dtd">  &lt;complexType name="KeyEncapsulationMethodType"&gt;
    &lt;sequence&gt;
      &lt;element ref="xenc11:KeyDerivationMethod"/&gt;
      &lt;element name="KeyLen" type="positiveInteger"/&gt;
      &lt;any namespace="##other" minOccurs="0" maxOccurs="unbounded"/&gt;
    &lt;/sequence&gt;
    &lt;attribute name="Algorithm" type="anyURI" use="required"/&gt;
  &lt;/complexType&gt;
</pre>
<p>
The <code>xenc11:KeyDerivationMethod</code> element of the
<code>KeyEncapsulationMethodType</code> specifies a key derivation method
to use when deriving a key from key material generated in accordance
with the key encapsulation mechanism. The
<code>xenc11:KeyDerivationMethod</code> element is defined in
[<cite><a class="bibref" rel="biblioentry" href="#bib-XMLENC-CORE1">XMLENC-CORE1</a></cite>]. The <code>KeyLen</code> element
specifies length of the derived key. The
<code>Algorithm</code> attribute identifies the actual key
encapsulation method used.
</p>
<div id="sec-rsaes-kem" class="section">
  <h4><span class="secno">4.3.1 </span>RSAES-KEM</h4>
<dl>
<dt>Identifier</dt>
<dd><a href="http://www.w3.org/2010/xmlsec-ghc#rsaes-kem">http://www.w3.org/2010/xmlsec-ghc#rsaes-kem</a> (<em class="rfc2119" title="required">required</em>)
</dd>
</dl>
<p>
RSAES-KEM is a key encapsulation algorithm based on the RSA
encryption scheme.
</p>
<p>
Given a recipient's public RSA key (n, e) where n is the RSA modulus
and e is the public exponent, the following steps shall be taken to
encapsulate a symmetric key when the RSAES-KEM key encapsulation
algorithm is used (these are the same steps as specified in Section
11.5.3 of [<cite><a class="bibref" rel="biblioentry" href="#bib-ISO18033-2">ISO18033-2</a></cite>]):
</p>
<ol>
  <li>Generate a non-negative random number r less than the modulus n;
  </li>
  <li>Set R = I2OSP(r, len(n)) where I2OSP is the integer to octet
  string conversion specified in Section 4.1 of PKCS #1
[<cite><a class="bibref" rel="biblioentry" href="#bib-PKCS1">PKCS1</a></cite>] and len(n) is the length of the modulus
  n;
  </li>
  <li>Set c0 = RSAEP((n , e), r) where RSAEP is the RSA encryption
  primitive defined in Section 5.1.1 of PKCS #1 [<cite><a class="bibref" rel="biblioentry" href="#bib-PKCS1">PKCS1</a></cite>] (i.e. no padding);
  </li>
  <li>Set C0 = I2OSP(c0, len(n));
  </li>
  <li>Compute K = KDF(R, KeyLen, OtherInfo) where KDF is the key
  derivation function, KeyLen is the length of the encapsulated key
  and OtherInfo is optional other info (subject to the input parameters
  for the key derivation function, see [<cite><a class="bibref" rel="biblioentry" href="#bib-XMLENC-CORE1">XMLENC-CORE1</a></cite>]
  Section 5.4);
  </li>
  <li>Output the key K and ciphertext C0.
  </li>
</ol>
<p>
Given a recipient's private RSA key (n, d) where n is the RSA modulus
and d is the private exponent, the following steps shall be taken to
decrypt an encapsulated symmetric key from ciphertext C0 when the
RSAES-KEM key encapsulation algorithm is used (these are the same
steps as specified in Section 11.5.4 of [<cite><a class="bibref" rel="biblioentry" href="#bib-ISO18033-2">ISO18033-2</a></cite>]:
</p><ol>
<li> Set c0 =
OS2IP(C0) where OS2IP is the octet string to integer
  conversion specified in Section 4.2 of PKCS #1 [<cite><a class="bibref" rel="biblioentry" href="#bib-PKCS1">PKCS1</a></cite>].
  </li>
  <li>Set r = RSADP((n , d), c0) where RSADP is the RSA decryption
  primitive defined in Section 5.1.2 of PKCS #1 [<cite><a class="bibref" rel="biblioentry" href="#bib-PKCS1">PKCS1</a></cite>] (i.e. no padding);
  </li>
  <li>Set R = I2OSP(r, len(n));
  </li>
  <li>Compute K = KDF(R, KeyLen, OtherInfo) where KDF is the key
  derivation function, KeyLen is the length of the encapsulated key
  and OtherInfo is optional other info (subject to the input parameters
  for the key derivation function, see [<cite><a class="bibref" rel="biblioentry" href="#bib-XMLENC-CORE1">XMLENC-CORE1</a></cite>]
  Section 5.4);
  </li>
  <li>Output the secret key K.
  </li>
</ol>
<p>
For use of the RSAES-KEM key encapsulation algorithm with Key
Transport, see <a href="#sec-key-transport-algorithms" class="sectionRef">section 5. Using Key Encapsulation Algorithms for Key Transport</a>.
</p>
</div>
<div id="sec-ecies-kem" class="section">
  <h4><span class="secno">4.3.2 </span>ECIES-KEM</h4>
<dl>
<dt>Identifier</dt>
<dd><a href="http://www.w3.org/2010/xmlsec-ghc#ecies-kem">http://www.w3.org/2010/xmlsec-ghc#ecies-kem</a> (<em class="rfc2119" title="required">required</em>)
</dd>
</dl>
<p>
ECIES-KEM is a key encapsulation algorithm based on the Elliptic Curve
scheme.
</p>
<p>
Given a recipient's public EC key h and an elliptic curve E with base
point g and order (size) o, the following steps shall be taken to
encapsulate a symmetric key when the ECIES-KEM key encapsulation
algorithm is used (these are the same steps as specified in Section
10.2.3 of [<cite><a class="bibref" rel="biblioentry" href="#bib-ISO18033-2">ISO18033-2</a></cite>]):
</p>
<ol>
  <li>Generate a positive random number r less than o;
  </li>
  <li>Compute the elliptic curve point G = r * g where * denotes
  scalar multiplication;
  </li>
  <li>Compute the elliptic curve point H = r * h;
  </li>
  <li>Set C0 = ENCODE ( G ) where ENCODE is the encoding of the
  elliptic curve point G as specified in Section 4.4.2 of
[<cite><a class="bibref" rel="biblioentry" href="#bib-XMLDSIG-CORE1">XMLDSIG-CORE1</a></cite>].
  </li>
  <li>Set P = ENCODE ( H ) where ENCODE is the encoding of the
  elliptic curve point H; since H is a point on the curve the encoding shall
  again be as specified in Section 4.4.2 of
[<cite><a class="bibref" rel="biblioentry" href="#bib-XMLDSIG-CORE1">XMLDSIG-CORE1</a></cite>];
  </li>
  <li>Set K = KDF( C0 | P, KeyLen, OtherInfo ) where KDF is the key
  derivation function, KeyLen is the length of the derived key and
  OtherInfo is optional other info (subject to the input parameters
  for the key derivation function, see
[<cite><a class="bibref" rel="biblioentry" href="#bib-XMLDSIG-CORE1">XMLDSIG-CORE1</a></cite>];
  Section 5.4);
  </li>
  <li>Output the key K and ciphertext C0.
  </li>
</ol>
<p>
Given a recipient's private EC key x and an elliptic curve E with base
point g and order (size) o, the following steps shall be taken to
decrypt an encapsulated symmetric key from ciphertext C0 when the
ECIES-KEM key encapsulation algorithm is used (these are the same
steps as specified in Section 10.2.4 of
[<cite><a class="bibref" rel="biblioentry" href="#bib-ISO18033-2">ISO18033-2</a></cite>]):
</p>
<ol>
  <li>Set G = DECODE ( C0 ) where DECODE is the decoding function
  which is the reverse of the ENCODE function previously described;
  </li>
  <li>Compute the elliptic curve point H = x * G where * denotes
  scalar multiplication;
  </li>
  <li>If H = 0, then fail;
  </li>
  <li>Set P = ENCODE ( H ) where ENCODE is the encoding of the
  elliptic curve point H as specified in Section 4.4.2 of
[<cite><a class="bibref" rel="biblioentry" href="#bib-XMLDSIG-CORE1">XMLDSIG-CORE1</a></cite>].
  </li>
  <li>Set K = KDF( C0 | P, KeyLen, OtherInfo ) where KDF is the key
  derivation function, KeyLen is the length of the derived key and
  OtherInfo is optional other info (subject to the input parameters
  for the key derivation function, see
[<cite><a class="bibref" rel="biblioentry" href="#bib-XMLDSIG-CORE1">XMLDSIG-CORE1</a></cite>]
  Section 5.4);
  </li>
  <li>Output the secret key K.
  </li>
</ol>
<p>
For use of the ECIES-KEM key encapsulation algorithm with Key
Transport, see <a href="#sec-key-transport-algorithms" class="sectionRef">section 5. Using Key Encapsulation Algorithms for Key Transport</a>.
</p>
</div>
</div>
</div>
<div id="sec-key-transport-algorithms" class="section">
  <!--OddPage--><h2><span class="secno">5. </span>Using Key Encapsulation Algorithms for Key Transport</h2>
<p>
When using a Key Encapsulation algorithm such as RSAES-KEM or
ECIES-KEM for key transport, the key K which is one of the outputs of
the KEM algorithm (see <a href="#sec-rsaes-kem">RSAES-KEM</a> and <a href="#sec-ecies-kem">ECIES-KEM</a>) is now used as a wrapping key,
encrypting a data-encryption key DEK: C1 = WRAP(K, DEK). The combined
ciphertext C0 | C1 (where C0 is the other output of the KEM algorithm)
is then placed in the <code>xenc:CipherValue</code> element of
the <code>xenc:CipherData</code> child element of the
<code>xenc:EncryptedKey</code> (the
<code>ds:KeyInfo</code> element will identify the recipient's
public key).
</p>
</div>
<div id="sec-examples" class="informative section">
  <!--OddPage--><h2><span class="secno">6. </span>Examples</h2><p><em>This section is non-normative.</em></p>
<div id="sec-key-transport-example" class="section">
  <h3><span class="secno">6.1 </span>Key Transport Example</h3>
<p>
The following is a syntactically correct example of an
<code>xenc:EncryptedKey</code> element using the Generic-Hybrid
method together with the ECIES-KEM algorithm for key encapsulation and
AES-128 KeyWrap for wrapping the content key using the encapsulated
key (the example would look precisely the same when using the
RSAES-KEM algorithm except for the identification of the Key
Encapsulation Algorithm which instead would have the value
"http://www.w3.org/2010/xmlsec-ghc#rsaes-kem" and the identification
of an RSA public key instead of an ECC key in the
<code>ds:KeyInfo</code> element.)
</p>

<pre class="xml-example">&lt;xenc:EncryptedKey
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:xenc="http://www.w3.org/2001/04/xmlenc#"
  xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
  xmlns:dsig11="http://www.w3.org/2009/xmldsig11#"
  xmlns:xenc11="http://www.w3.org/2009/xmlenc11#"
  xmlns:ghc="http://www.w3.org/2010/xmlsec-ghc#"
  &lt;xenc:EncryptionMethod
    Algorithm="http://www.w3.org/2010/xmlsec-ghc#generic-hybrid"&gt;
    &lt;ghc:GenericHybridCipherMethod&gt;
      &lt;ghc:KeyEncapsulationMethod
        Algorithm="http://www.w3.org/2010/xmlsec-ghc#ecies-kem"&gt;
        &lt;xenc11:KeyDerivationMethod Algorithm="http://www.w3.org/2009/xmlenc11#ConcatKDF"&gt;
          &lt;xenc11:ConcatKDFParams AlgorithmID="0000" PartyUInfo="03D8" PartyVInfo=""&gt;
            &lt;ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/&gt;
          &lt;/xenc11:ConcatKDFParams&gt;
        &lt;ghc:KeyLen&gt;16&lt;/ghc:KeyLen&gt;
      &lt;/ghc:KeyEncapsulationMethod&gt;
      &lt;ghc:DataEncapsulationMethod
        Algorithm="http://www.w3.org/2001/04/xmlenc#kw-aes128"/&gt;
    &lt;/ghc:GenericHybridCipherMethod&gt;
  &lt;/xenc:EncryptionMethod&gt;
  &lt;ds:KeyInfo&gt;
    &lt;dsig11:ECKeyValue&gt;
      &lt;dsig11:NamedCurve URI="urn:oid:1.2.840.10045.3.1.7"/&gt;
      &lt;dsig11:PublicKey&gt;DEADBEEF&lt;/dsig11:PublicKey&gt;
    &lt;/dsig11:ECKeyValue&gt;
  &lt;/ds:KeyInfo&gt;
  &lt;xenc:CipherData&gt;
    &lt;xenc:CipherValue&gt;DEADBEEF&lt;/xenc:CipherValue&gt;
    &lt;!-- Is concatenation of originator's ephemeral key (expressed as
    an octet string) and the wrapped key --&gt;
  &lt;/xenc:CipherData&gt;
&lt;/xenc:EncryptedKey&gt;
</pre>
</div>
</div>
<div id="sec-security-considerations" class="section">
<!--OddPage--><h2><span class="secno">7. </span>Security Considerations</h2>
<p>
Generic hybrid ciphers with key encapsulation mechanisms as specified
in this document provides a high security level assuming key
derivation algorithms and other security parameters have been properly
chosen.  See further [<cite><a class="bibref" rel="biblioentry" href="#bib-ISO18033-2">ISO18033-2</a></cite>], Annex B for a deeper
security discussion on these constructions.
</p>
</div>
<div id="sec-conformance" class="section">
<!--OddPage--><h2><span class="secno">8. </span>Conformance</h2>
<p>
An implementation is conformant to this specification if it
successfully generates syntax according to the schema definitions and
satisfies any and all
<em class="rfc2119" title="must">must</em>/<em class="rfc2119" title="required">required</em>/<em class="rfc2119" title="shall">shall</em>
requirements.
</p>
The full normative grammar is defined by the XSD schema and the
normative text in this specification. The standalone XSD schema file
is authoritative in case there is any disagreement between it and the
XSD schema portions in this specification.
<p>

</p>
</div>
    <div id="sec-acknowledgements" class="informative section">
      <!--OddPage--><h2><span class="secno">9. </span>Acknowledgments</h2><p><em>This section is non-normative.</em></p>
      <p>
The contributions of the following Working Group members to this
specification are gratefully acknowledged in accordance with the
contributor policies and the active WG roster:
Scott Cantor, Pratik Datta,
Frederick Hirsch,
Meiko Jensen,
Brian LaMacchia,
Hal Lockhart,
Cynthia Martin,
Magnus Nyström,
Bruce Rich,
Thomas Roessler, and
Ed Simon.
      </p><p>
Additionally, we thank Burt Kaliski of EMC for his comments during and
subsequent to Last Call.
      </p>
    </div>

    <div id="sec-schema" class="section">
      <!--OddPage--><h2><span class="secno">10. </span>Schema</h2>
<div id="sec-xsdSchema" class="section">
      <h3><span class="secno">10.1 </span>XSD Schema</h3>
<dl>
<dt>XML Security Generic Hybrid Schema Instance</dt>
<dd><a href="xmlsec-ghc-schema.xsd">xmlsec-ghc-schema.xsd</a></dd>
<dd>Valid XML schema instance based on the XML Schema
            Second Edition [<cite><a class="bibref" rel="biblioentry" href="#bib-XMLSCHEMA-1">XMLSCHEMA-1</a></cite>], [<cite><a class="bibref" rel="biblioentry" href="#bib-XMLSCHEMA-2">XMLSCHEMA-2</a></cite>].</dd>
</dl>
</div>
<div id="sec-rngSchema" class="section">
<h3><span class="secno">10.2 </span>RNG Schema</h3>
<p>Non-normative RELAX NG schema [<cite><a class="bibref" rel="biblioentry" href="#bib-RELAXNG-SCHEMA">RELAXNG-SCHEMA</a></cite>]
 information is
  available in a separate document
[<cite><a class="bibref" rel="biblioentry" href="#bib-XMLSEC-RELAXNG">XMLSEC-RELAXNG</a></cite>].
</p>
</div>
    </div>


<div id="references" class="appendix section"><!--OddPage--><h2><span class="secno">A. </span>References</h2><p>Dated references below are to the latest known or appropriate edition of the referenced work.  The referenced works may be subject to revision, and conformant implementations may follow, and are encouraged to investigate the appropriateness of following, some or all more recent editions or replacements of the works cited. It is in each case implementation-defined which  editions are supported.</p><div id="normative-references" class="section"><h3><span class="secno">A.1 </span>Normative references</h3><dl class="bibliography"><dt id="bib-ISO18033-2">[ISO18033-2]</dt><dd><cite>Information technology -- Security techniques -- Encryption algorithms -- Part 2: Asymmetric ciphers</cite>, International Organization for Standardization.  18033-2:2006. May 2006. URL: <a href="http://www.iso.org/iso/home.htm">http://www.iso.org/iso/home.htm</a>.
</dd><dt id="bib-PKCS1">[PKCS1]</dt><dd>J. Jonsson and B. Kaliski. <a href="http://www.ietf.org/rfc/rfc3447.txt"><cite>Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications  Version 2.1.</cite></a> RFC 3447 (Informational), February  2003. URL: <a href="http://www.ietf.org/rfc/rfc3447.txt">http://www.ietf.org/rfc/rfc3447.txt</a>
</dd><dt id="bib-RFC2119">[RFC2119]</dt><dd>S. Bradner. <a href="http://www.ietf.org/rfc/rfc2119.txt"><cite>Key words for use in RFCs to Indicate Requirement Levels.</cite></a> March 1997. Internet RFC 2119.  URL: <a href="http://www.ietf.org/rfc/rfc2119.txt">http://www.ietf.org/rfc/rfc2119.txt</a>
</dd><dt id="bib-XML-NAMES">[XML-NAMES]</dt><dd>Richard Tobin; et al. <a href="http://www.w3.org/TR/2009/REC-xml-names-20091208/"><cite>Namespaces in XML 1.0 (Third Edition).</cite></a> 8 December 2009. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2009/REC-xml-names-20091208/">http://www.w3.org/TR/2009/REC-xml-names-20091208/</a>
</dd><dt id="bib-XMLDSIG-CORE1">[XMLDSIG-CORE1]</dt><dd>D. Eastlake, J. Reagle, D. Solo, F. Hirsch, T. Roessler, K. Yiu. <a href="http://www.w3.org/TR/2011/CR-xmldsig-core1-20110303/"><cite>XML Signature Syntax and Processing Version 1.1.</cite></a> 3 March 2011. W3C Candidate Recommendation. (Work in progress.) URL: <a href="http://www.w3.org/TR/2011/CR-xmldsig-core1-20110303/">http://www.w3.org/TR/2011/CR-xmldsig-core1-20110303/</a>
</dd><dt id="bib-XMLENC-CORE1">[XMLENC-CORE1]</dt><dd>J. Reagle; D. Eastlake, F. Hirsch, T. Roessler <a href="http://www.w3.org/TR/2011/CR-xmlenc-core1-20110303/"><cite>XML Encryption Syntax and Processing Version 1.1.</cite></a> 3 March 2011. W3C Candidate Recommendation. (Work in progress.) URL: <a href="http://www.w3.org/TR/2011/CR-xmlenc-core1-20110303/">http://www.w3.org/TR/2011/CR-xmlenc-core1-20110303/</a>
</dd></dl></div><div id="informative-references" class="section"><h3><span class="secno">A.2 </span>Informative references</h3><dl class="bibliography"><dt id="bib-RELAXNG-SCHEMA">[RELAXNG-SCHEMA]</dt><dd><a href="http://standards.iso.org/ittf/PubliclyAvailableStandards/c052348_ISO_IEC_19757-2_2008(E).zip"><cite>Information technology -- Document Schema Definition Language (DSDL) -- Part 2: Regular-grammar-based validation -- RELAX NG</cite></a>. ISO/IEC 19757-2:2008. URI: <a href="http://standards.iso.org/ittf/PubliclyAvailableStandards/c052348_ISO_IEC_19757-2_2008(E).zip">http://standards.iso.org/ittf/PubliclyAvailableStandards/c052348_ISO_IEC_19757-2_2008(E).zip</a>
</dd><dt id="bib-URI">[URI]</dt><dd>T. Berners-Lee; R. Fielding; L. Masinter. <a href="http://www.ietf.org/rfc/rfc3986.txt"><cite>Uniform Resource Identifiers (URI): generic syntax.</cite></a> January 2005. Internet RFC 3986. URL: <a href="http://www.ietf.org/rfc/rfc3986.txt">http://www.ietf.org/rfc/rfc3986.txt</a>
</dd><dt id="bib-XMLSCHEMA-1">[XMLSCHEMA-1]</dt><dd>Henry S. Thompson; et al. <a href="http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/"><cite>XML Schema Part 1: Structures Second Edition.</cite></a> 28 October 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/">http://www.w3.org/TR/2004/REC-xmlschema-1-20041028/</a>
</dd><dt id="bib-XMLSCHEMA-2">[XMLSCHEMA-2]</dt><dd>Paul V. Biron; Ashok Malhotra. <a href="http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/"><cite>XML Schema Part 2: Datatypes Second Edition.</cite></a> 28 October 2004. W3C Recommendation. URL: <a href="http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/">http://www.w3.org/TR/2004/REC-xmlschema-2-20041028/</a>
</dd><dt id="bib-XMLSEC-RELAXNG">[XMLSEC-RELAXNG]</dt><dd>Makoto Murata, Frederick Hirsch. <a href="http://www.w3.org/TR/2011/WD-xmlsec-rngschema-20110303/"><cite>XML Security RELAX NG Schemas.</cite></a> 3 March 2011. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2011/WD-xmlsec-rngschema-20110303/">http://www.w3.org/TR/2011/WD-xmlsec-rngschema-20110303/</a>
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