<?xml version='1.0' encoding='utf-8'?>
<rfc xmlns:xi="http://www.w3.org/2001/XInclude" version="3" ipr="trust200902" docName="draft-ietf-lamps-x509-alg-none-latest" category="std" consensus="true" submissionType="IETF" xml:lang="en" number="9925" updates="5280" tocInclude="true" sortRefs="true" symRefs="true" prepTime="2026-02-26T15:30:13" indexInclude="true" scripts="Common,Latin" tocDepth="3">
  <link href="https://datatracker.ietf.org/doc/draft-ietf-lamps-x509-alg-none-latest" rel="prev"/>
  <link href="https://dx.doi.org/10.17487/rfc9925" rel="alternate"/>
  <link href="urn:issn:2070-1721" rel="alternate"/>
  <front>
    <title>Unsigned X.509 Certificates</title>
    <seriesInfo name="RFC" value="9925" stream="IETF"/>
    <author initials="D." surname="Benjamin" fullname="David Benjamin">
      <organization showOnFrontPage="true">Google LLC</organization>
      <address>
        <email>davidben@google.com</email>
      </address>
    </author>
    <date month="02" year="2026"/>
    <area>SEC</area>
    <workgroup>lamps</workgroup>
    <keyword>self-signed certificate</keyword>
    <abstract pn="section-abstract">
      <t indent="0" pn="section-abstract-1">This document defines a placeholder X.509 signature algorithm that may be used
in contexts where the consumer of the certificate is not expected to verify the
signature. As part of this, it updates RFC 5280.</t>
    </abstract>
    <boilerplate>
      <section anchor="status-of-memo" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.1">
        <name slugifiedName="name-status-of-this-memo">Status of This Memo</name>
        <t indent="0" pn="section-boilerplate.1-1">
            This is an Internet Standards Track document.
        </t>
        <t indent="0" pn="section-boilerplate.1-2">
            This document is a product of the Internet Engineering Task Force
            (IETF).  It represents the consensus of the IETF community.  It has
            received public review and has been approved for publication by
            the Internet Engineering Steering Group (IESG).  Further
            information on Internet Standards is available in Section 2 of 
            RFC 7841.
        </t>
        <t indent="0" pn="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <eref target="https://www.rfc-editor.org/info/rfc9925" brackets="none"/>.
        </t>
      </section>
      <section anchor="copyright" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.2">
        <name slugifiedName="name-copyright-notice">Copyright Notice</name>
        <t indent="0" pn="section-boilerplate.2-1">
            Copyright (c) 2026 IETF Trust and the persons identified as the
            document authors. All rights reserved.
        </t>
        <t indent="0" pn="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<eref target="https://trustee.ietf.org/license-info" brackets="none"/>) 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 Revised BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Revised BSD License.
        </t>
      </section>
    </boilerplate>
    <toc>
      <section anchor="toc" numbered="false" removeInRFC="false" toc="exclude" pn="section-toc.1">
        <name slugifiedName="name-table-of-contents">Table of Contents</name>
        <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1">
          <li pn="section-toc.1-1.1">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.1.1"><xref derivedContent="1" format="counter" sectionFormat="of" target="section-1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-introduction">Introduction</xref></t>
          </li>
          <li pn="section-toc.1-1.2">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.2.1"><xref derivedContent="2" format="counter" sectionFormat="of" target="section-2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-requirements-language">Requirements Language</xref></t>
          </li>
          <li pn="section-toc.1-1.3">
            <t indent="0" pn="section-toc.1-1.3.1"><xref derivedContent="3" format="counter" sectionFormat="of" target="section-3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-constructing-unsigned-certi">Constructing Unsigned Certificates</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.3.2">
              <li pn="section-toc.1-1.3.2.1">
                <t indent="0" keepWithNext="true" pn="section-toc.1-1.3.2.1.1"><xref derivedContent="3.1" format="counter" sectionFormat="of" target="section-3.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-signature">Signature</xref></t>
              </li>
              <li pn="section-toc.1-1.3.2.2">
                <t indent="0" pn="section-toc.1-1.3.2.2.1"><xref derivedContent="3.2" format="counter" sectionFormat="of" target="section-3.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-issuer">Issuer</xref></t>
              </li>
              <li pn="section-toc.1-1.3.2.3">
                <t indent="0" pn="section-toc.1-1.3.2.3.1"><xref derivedContent="3.3" format="counter" sectionFormat="of" target="section-3.3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-extensions">Extensions</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.4">
            <t indent="0" pn="section-toc.1-1.4.1"><xref derivedContent="4" format="counter" sectionFormat="of" target="section-4"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-consuming-unsigned-certific">Consuming Unsigned Certificates</xref></t>
          </li>
          <li pn="section-toc.1-1.5">
            <t indent="0" pn="section-toc.1-1.5.1"><xref derivedContent="5" format="counter" sectionFormat="of" target="section-5"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-security-considerations">Security Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.6">
            <t indent="0" pn="section-toc.1-1.6.1"><xref derivedContent="6" format="counter" sectionFormat="of" target="section-6"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-iana-considerations">IANA Considerations</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.6.2">
              <li pn="section-toc.1-1.6.2.1">
                <t indent="0" pn="section-toc.1-1.6.2.1.1"><xref derivedContent="6.1" format="counter" sectionFormat="of" target="section-6.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-module-identifier">Module Identifier</xref></t>
              </li>
              <li pn="section-toc.1-1.6.2.2">
                <t indent="0" pn="section-toc.1-1.6.2.2.1"><xref derivedContent="6.2" format="counter" sectionFormat="of" target="section-6.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-algorithm">Algorithm</xref></t>
              </li>
              <li pn="section-toc.1-1.6.2.3">
                <t indent="0" pn="section-toc.1-1.6.2.3.1"><xref derivedContent="6.3" format="counter" sectionFormat="of" target="section-6.3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-relative-distinguished-name">Relative Distinguished Name Attribute</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.7">
            <t indent="0" pn="section-toc.1-1.7.1"><xref derivedContent="7" format="counter" sectionFormat="of" target="section-7"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-references">References</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.7.2">
              <li pn="section-toc.1-1.7.2.1">
                <t indent="0" pn="section-toc.1-1.7.2.1.1"><xref derivedContent="7.1" format="counter" sectionFormat="of" target="section-7.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-normative-references">Normative References</xref></t>
              </li>
              <li pn="section-toc.1-1.7.2.2">
                <t indent="0" pn="section-toc.1-1.7.2.2.1"><xref derivedContent="7.2" format="counter" sectionFormat="of" target="section-7.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-informative-references">Informative References</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.8">
            <t indent="0" pn="section-toc.1-1.8.1"><xref derivedContent="Appendix A" format="default" sectionFormat="of" target="section-appendix.a"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-asn1-module">ASN.1 Module</xref></t>
          </li>
          <li pn="section-toc.1-1.9">
            <t indent="0" pn="section-toc.1-1.9.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.b"/><xref derivedContent="" format="title" sectionFormat="of" target="name-acknowledgements">Acknowledgements</xref></t>
          </li>
          <li pn="section-toc.1-1.10">
            <t indent="0" pn="section-toc.1-1.10.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.c"/><xref derivedContent="" format="title" sectionFormat="of" target="name-authors-address">Author's Address</xref></t>
          </li>
        </ul>
      </section>
    </toc>
  </front>
  <middle>
    <section anchor="introduction" numbered="true" removeInRFC="false" toc="include" pn="section-1">
      <name slugifiedName="name-introduction">Introduction</name>
      <t indent="0" pn="section-1-1">An X.509 certificate <xref target="RFC5280" format="default" sectionFormat="of" derivedContent="RFC5280"/> relates two entities in the PKI: information
about a subject and a proof from an issuer. Viewing the PKI as a graph with
entities as nodes, as in <xref target="RFC4158" format="default" sectionFormat="of" derivedContent="RFC4158"/>, a certificate is an edge between the
subject and issuer.</t>
      <t indent="0" pn="section-1-2">In some contexts, an application needs standalone subject information instead of
a certificate. In the graph model, the application needs a node, not an edge.
For example, certification path validation (<xref section="6" sectionFormat="of" target="RFC5280" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5280#section-6" derivedContent="RFC5280"/>) begins at
a trust anchor, sometimes referred to as a root certification authority (root CA). The application
trusts this trust anchor information out-of-band and does not require an
issuer's signature.</t>
      <t indent="0" pn="section-1-3">X.509 does not define a structure for this scenario. Instead, X.509 trust
anchors are often represented with "self-signed" certificates, where the
subject's key signs over itself. Other formats, such as <xref target="RFC5914" format="default" sectionFormat="of" derivedContent="RFC5914"/>, exist to
convey trust anchors, but self-signed certificates remain widely used.</t>
      <t indent="0" pn="section-1-4">Additionally, some TLS <xref target="RFC8446" format="default" sectionFormat="of" derivedContent="RFC8446"/> server deployments use self-signed
end entity certificates when they do not intend to present a CA-issued
identity, instead expecting the relying party to authenticate the certificate
out-of-band, e.g., via a known fingerprint.</t>
      <t indent="0" pn="section-1-5">These self-signatures typically have no security value, aren't checked by
the receiver, and only serve as placeholders to meet syntactic requirements of
an X.509 certificate.</t>
      <t indent="0" pn="section-1-6">Computing signatures as placeholders has some drawbacks:</t>
      <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-1-7">
        <li pn="section-1-7.1">
          <t indent="0" pn="section-1-7.1.1">Post-quantum signature algorithms are large, so including a self-signature
significantly increases the size of the payload.</t>
        </li>
        <li pn="section-1-7.2">
          <t indent="0" pn="section-1-7.2.1">If the subject is an end entity, rather than a CA, computing an X.509
signature risks cross-protocol attacks with the intended use of the key.</t>
        </li>
        <li pn="section-1-7.3">
          <t indent="0" pn="section-1-7.3.1">It is ambiguous whether such a self-signature requires the CA bit in basic
constraints or keyCertSign in key usage. If the key is intended for a
non-X.509 use, asserting those capabilities is an unnecessary risk.</t>
        </li>
        <li pn="section-1-7.4">
          <t indent="0" pn="section-1-7.4.1">If the subject is an end entity, and the end entity's key is not a signing
key (e.g., a Key Encapsulation Mechanism (KEM) key), there is no valid signature algorithm to use with the key.</t>
        </li>
      </ul>
      <t indent="0" pn="section-1-8">This document defines a profile for unsigned X.509 certificates, which may be
used when the certificate is used as a container for subject information,
without any specific issuer.</t>
    </section>
    <section anchor="requirements-language" numbered="true" removeInRFC="false" toc="include" pn="section-2">
      <name slugifiedName="name-requirements-language">Requirements Language</name>
      <t indent="0" pn="section-2-1">
    The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
    "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>",
    "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
    "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to be
    interpreted as described in BCP 14 <xref target="RFC2119" format="default" sectionFormat="of" derivedContent="RFC2119"/> <xref target="RFC8174" format="default" sectionFormat="of" derivedContent="RFC8174"/> when, and only when, they appear in all capitals, as
    shown here.
      </t>
    </section>
    <section anchor="constructing-unsigned-certificates" numbered="true" removeInRFC="false" toc="include" pn="section-3">
      <name slugifiedName="name-constructing-unsigned-certi">Constructing Unsigned Certificates</name>
      <t indent="0" pn="section-3-1">This section describes how a sender constructs an unsigned certificate.</t>
      <section anchor="signature" numbered="true" removeInRFC="false" toc="include" pn="section-3.1">
        <name slugifiedName="name-signature">Signature</name>
        <t indent="0" pn="section-3.1-1">To construct an unsigned X.509 certificate, the sender <bcp14>MUST</bcp14> set the
Certificate's signatureAlgorithm and TBSCertificate's signature fields each to
an AlgorithmIdentifier with algorithm id-alg-unsigned, defined below:</t>
        <artwork align="left" pn="section-3.1-2">
  id-alg-unsigned OBJECT IDENTIFIER ::= {1 3 6 1 5 5 7 6 36}
</artwork>
        <t indent="0" pn="section-3.1-3">The parameters for id-alg-unsigned <bcp14>MUST</bcp14> be omitted. The Certificate's
signatureValue field <bcp14>MUST</bcp14> be a BIT STRING of length zero.</t>
      </section>
      <section anchor="issuer" numbered="true" removeInRFC="false" toc="include" pn="section-3.2">
        <name slugifiedName="name-issuer">Issuer</name>
        <t indent="0" pn="section-3.2-1">An unsigned certificate takes the place of a self-signed certificate in
scenarios where the application only requires subject information. It has no
issuer, so some requirements in the profile defined in <xref target="RFC5280" format="default" sectionFormat="of" derivedContent="RFC5280"/> cannot
meaningfully be applied. However, the application may have pre-existing
requirements derived from <xref target="X.509" format="default" sectionFormat="of" derivedContent="X.509"/> and <xref target="RFC5280" format="default" sectionFormat="of" derivedContent="RFC5280"/>, so senders <bcp14>MAY</bcp14> construct
the certificate as if it were a self-signed certificate, if needed for
interoperability.</t>
        <t indent="0" pn="section-3.2-2">In particular, the following fields describe a certificate's issuer:</t>
        <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-3.2-3">
          <li pn="section-3.2-3.1">
            <t indent="0" pn="section-3.2-3.1.1">issuer (<xref section="4.1.2.4" sectionFormat="of" target="RFC5280" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5280#section-4.1.2.4" derivedContent="RFC5280"/>)</t>
          </li>
          <li pn="section-3.2-3.2">
            <t indent="0" pn="section-3.2-3.2.1">issuerUniqueID (<xref section="4.1.2.8" sectionFormat="of" target="RFC5280" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5280#section-4.1.2.8" derivedContent="RFC5280"/>)</t>
          </li>
        </ul>
        <t indent="0" pn="section-3.2-4">The issuer field is not optional, and both <xref target="X.509" format="default" sectionFormat="of" derivedContent="X.509"/> and
<xref section="4.1.2.4" sectionFormat="of" target="RFC5280" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5280#section-4.1.2.4" derivedContent="RFC5280"/> forbid empty issuers, so such a value may not be
interoperable with existing applications.</t>
        <t indent="0" pn="section-3.2-5">If the subject is not empty, senders <bcp14>MAY</bcp14> set the issuer to the subject, similar
to how they would construct a self-signed certificate.
This may be useful in applications that, for example,
expect trust anchors to have a matching issuer and subject. This is, however, a
placeholder value. The unsigned certificate is not considered self-signed or
self-issued.</t>
        <t indent="0" pn="section-3.2-6">Senders <bcp14>MAY</bcp14> alternatively use a short placeholder issuer consisting of a single
relative distinguished name that has a single attribute with a type of id-rdna-unsigned
and value of a zero-length UTF8String. id-rdna-unsigned is defined as follows:</t>
        <artwork align="left" pn="section-3.2-7">
  id-rdna-unsigned OBJECT IDENTIFIER ::= {1 3 6 1 5 5 7 25 1}
</artwork>
        <t indent="0" pn="section-3.2-8">This placeholder name, in the string representation of <xref target="RFC4514" format="default" sectionFormat="of" derivedContent="RFC4514"/>, is:</t>
        <artwork align="left" pn="section-3.2-9">
  1.3.6.1.5.5.7.25.1=#0C00
</artwork>
        <t indent="0" pn="section-3.2-10">Senders <bcp14>MUST</bcp14> omit the issuerUniqueID field, as it is optional, not applicable,
and already forbidden by <xref section="4.1.2.8" sectionFormat="of" target="RFC5280" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5280#section-4.1.2.8" derivedContent="RFC5280"/>.</t>
      </section>
      <section anchor="extensions" numbered="true" removeInRFC="false" toc="include" pn="section-3.3">
        <name slugifiedName="name-extensions">Extensions</name>
        <t indent="0" pn="section-3.3-1">Some X.509 extensions also describe the certificate issuer and thus are not
meaningful for an unsigned certificate:</t>
        <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-3.3-2">
          <li pn="section-3.3-2.1">
            <t indent="0" pn="section-3.3-2.1.1">authority key identifier (<xref section="4.2.1.1" sectionFormat="of" target="RFC5280" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5280#section-4.2.1.1" derivedContent="RFC5280"/>)</t>
          </li>
          <li pn="section-3.3-2.2">
            <t indent="0" pn="section-3.3-2.2.1">issuer alternative name (<xref section="4.2.1.7" sectionFormat="of" target="RFC5280" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5280#section-4.2.1.7" derivedContent="RFC5280"/>)</t>
          </li>
        </ul>
        <t indent="0" pn="section-3.3-3">Senders <bcp14>SHOULD</bcp14> omit the authority key identifier and issuer alternative name
extensions. <xref section="4.2.1.1" sectionFormat="of" target="RFC5280" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5280#section-4.2.1.1" derivedContent="RFC5280"/> requires certificates to include
the authority key identifier, but it permits an exception for self-signed certificates
used when distributing a public key. This document updates <xref target="RFC5280" format="default" sectionFormat="of" derivedContent="RFC5280"/> to also
permit omitting the authority key identifier in unsigned certificates.</t>
        <t indent="0" pn="section-3.3-4">Some extensions reflect whether the subject is a CA or an end entity:</t>
        <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-3.3-5">
          <li pn="section-3.3-5.1">
            <t indent="0" pn="section-3.3-5.1.1">key usage (<xref section="4.2.1.3" sectionFormat="of" target="RFC5280" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5280#section-4.2.1.3" derivedContent="RFC5280"/>)</t>
          </li>
          <li pn="section-3.3-5.2">
            <t indent="0" pn="section-3.3-5.2.1">basic constraints (<xref section="4.2.1.9" sectionFormat="of" target="RFC5280" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5280#section-4.2.1.9" derivedContent="RFC5280"/>)</t>
          </li>
        </ul>
        <t indent="0" pn="section-3.3-6">Senders <bcp14>SHOULD</bcp14> fill in these values to reflect the subject. That is:</t>
        <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-3.3-7">
          <li pn="section-3.3-7.1">
            <t indent="0" pn="section-3.3-7.1.1">If the subject is a CA, it <bcp14>SHOULD</bcp14> assert the keyCertSign key usage bit and
<bcp14>SHOULD</bcp14> include a basic constraints extension that sets the cA boolean to TRUE.</t>
          </li>
          <li pn="section-3.3-7.2">
            <t indent="0" pn="section-3.3-7.2.1">If the subject is an end entity, it <bcp14>SHOULD NOT</bcp14> assert the keyCertSign key usage
bit, and it <bcp14>SHOULD</bcp14> either omit the basic constraints extension or set the cA
boolean to FALSE. Unlike a self-signed certificate, an unsigned certificate does
not issue itself, so there is no need to accommodate a self-signature in either
extension.</t>
          </li>
        </ul>
      </section>
    </section>
    <section anchor="consuming-unsigned-certificates" numbered="true" removeInRFC="false" toc="include" pn="section-4">
      <name slugifiedName="name-consuming-unsigned-certific">Consuming Unsigned Certificates</name>
      <t indent="0" pn="section-4-1">X.509 signatures of type id-alg-unsigned are always invalid:</t>
      <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-4-2">
        <li pn="section-4-2.1">
          <t indent="0" pn="section-4-2.1.1">When processing X.509 certificates without verifying signatures, receivers <bcp14>MAY</bcp14>
accept id-alg-unsigned.</t>
        </li>
        <li pn="section-4-2.2">
          <t indent="0" pn="section-4-2.2.1">When verifying X.509 signatures, receivers <bcp14>MUST</bcp14> reject id-alg-unsigned.</t>
        </li>
      </ul>
      <t indent="0" pn="section-4-3">In particular, X.509 validators <bcp14>MUST NOT</bcp14> accept id-alg-unsigned in the place of
a signature in the certification path.</t>
      <t indent="0" pn="section-4-4">It is expected that most unmodified X.509 applications will already be
compliant with this guidance. X.509 applications are thus <bcp14>RECOMMENDED</bcp14> to satisfy these
requirements by ignoring this document and instead treating id-alg-unsigned as
the same as an unrecognized signature algorithm. An unmodified X.509
validator will be unable to verify the signature (Step (a.1) of
<xref section="6.1.3" sectionFormat="of" target="RFC5280" format="default" derivedLink="https://rfc-editor.org/rfc/rfc5280#section-6.1.3" derivedContent="RFC5280"/>) and thus reject the certification path.
Conversely, in contexts where an X.509 application was ignoring the
self-signature, id-alg-unsigned will also be ignored but more efficiently.</t>
      <t indent="0" pn="section-4-5">In other contexts, an application may require modifications or limit itself to
particular forms of unsigned certificates. For example, an application might
check self-signedness to classify locally configured certificates as trust
anchors or untrusted intermediates. Such an application may need to modify its
configuration model or user interface before using an unsigned certificate as a
trust anchor.</t>
    </section>
    <section anchor="security-considerations" numbered="true" removeInRFC="false" toc="include" pn="section-5">
      <name slugifiedName="name-security-considerations">Security Considerations</name>
      <t indent="0" pn="section-5-1">It is best practice to limit cryptographic keys to a single purpose each. If a
key is reused across contexts, applications risk cross-protocol attacks when the
two uses collide. However, in applications that use self-signed end entity
certificates, the subject's key is necessarily used in two ways: the X.509
self-signature and the end entity protocol. Unsigned certificates fix this key
reuse by removing the X.509 self-signature.</t>
      <t indent="0" pn="section-5-2">If an application accepts id-alg-unsigned as part of a certification path, or
in any other context where it is necessary to verify the X.509 signature, the
signature check would be bypassed. Thus, <xref target="consuming-unsigned-certificates" format="default" sectionFormat="of" derivedContent="Section 4"/>
prohibits this and recommends that applications treat id-alg-unsigned the same
as any other previously unrecognized signature algorithm. Non-compliant
applications risk vulnerabilities analogous to those described in <xref target="JWT" format="default" sectionFormat="of" derivedContent="JWT"/> and
<xref section="1.1" sectionFormat="of" target="I-D.ietf-jose-deprecate-none-rsa15" format="default" derivedLink="https://datatracker.ietf.org/doc/html/draft-ietf-jose-deprecate-none-rsa15-03#section-1.1" derivedContent="JOSE"/>.</t>
      <t indent="0" pn="section-5-3">The signature in a self-signed certificate is self-derived and thus of limited
use to convey trust. However, some applications might, for example, use it as an integrity
check to guard against accidental storage corruption. An unsigned
certificate does not provide any integrity check. Applications checking
self-signature for integrity <bcp14>SHOULD</bcp14> instead use some other mechanism, such as an
external hash that is verified out-of-band.</t>
    </section>
    <section anchor="iana-considerations" numbered="true" removeInRFC="false" toc="include" pn="section-6">
      <name slugifiedName="name-iana-considerations">IANA Considerations</name>
      <section anchor="module-identifier" numbered="true" removeInRFC="false" toc="include" pn="section-6.1">
        <name slugifiedName="name-module-identifier">Module Identifier</name>
        <t indent="0" pn="section-6.1-1">IANA has added the following entry in the "SMI Security for PKIX
Module Identifier" registry, defined by <xref target="RFC7299" format="default" sectionFormat="of" derivedContent="RFC7299"/>:</t>
        <table align="center" pn="table-1">
          <thead>
            <tr>
              <th align="left" colspan="1" rowspan="1">Decimal</th>
              <th align="left" colspan="1" rowspan="1">Description</th>
              <th align="left" colspan="1" rowspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td align="left" colspan="1" rowspan="1">122</td>
              <td align="left" colspan="1" rowspan="1">id-mod-algUnsigned-2025</td>
              <td align="left" colspan="1" rowspan="1">RFC 9925</td>
            </tr>
          </tbody>
        </table>
      </section>
      <section anchor="algorithm" numbered="true" removeInRFC="false" toc="include" pn="section-6.2">
        <name slugifiedName="name-algorithm">Algorithm</name>
        <t indent="0" pn="section-6.2-1">IANA has added the following entry to the
"SMI Security for PKIX Algorithms" registry <xref target="RFC7299" format="default" sectionFormat="of" derivedContent="RFC7299"/>:</t>
        <table align="center" pn="table-2">
          <thead>
            <tr>
              <th align="left" colspan="1" rowspan="1">Decimal</th>
              <th align="left" colspan="1" rowspan="1">Description</th>
              <th align="left" colspan="1" rowspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td align="left" colspan="1" rowspan="1">36</td>
              <td align="left" colspan="1" rowspan="1">id-alg-unsigned</td>
              <td align="left" colspan="1" rowspan="1">RFC 9925</td>
            </tr>
          </tbody>
        </table>
      </section>
      <section anchor="relative-distinguished-name-attribute" numbered="true" removeInRFC="false" toc="include" pn="section-6.3">
        <name slugifiedName="name-relative-distinguished-name">Relative Distinguished Name Attribute</name>
        <t indent="0" pn="section-6.3-1">To allocate id-rdna-unsigned, this document introduces a new PKIX OID arc for
relative distinguished name attributes:</t>
        <t indent="0" pn="section-6.3-2">IANA has added the following entry to the "SMI Security for PKIX"
registry <xref target="RFC7299" format="default" sectionFormat="of" derivedContent="RFC7299"/>:</t>
        <table align="center" pn="table-3">
          <thead>
            <tr>
              <th align="left" colspan="1" rowspan="1">Decimal</th>
              <th align="left" colspan="1" rowspan="1">Description</th>
              <th align="left" colspan="1" rowspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td align="left" colspan="1" rowspan="1">25</td>
              <td align="left" colspan="1" rowspan="1">Relative Distinguished Name Attribute</td>
              <td align="left" colspan="1" rowspan="1">RFC 9925</td>
            </tr>
          </tbody>
        </table>
        <t indent="0" pn="section-6.3-4">IANA has created the "SMI Security for PKIX Relative Distinguished
Name Attribute" registry within the "Structure of Management Information (SMI)
Numbers (MIB Module Registrations)" registry group.</t>
        <t indent="0" pn="section-6.3-5">The new registry's description is
"iso.org.dod.internet.security.mechanisms.pkix.rdna (1.3.6.1.5.5.7.25)".</t>
        <t indent="0" pn="section-6.3-6">The new registry has three columns and is initialized with the following values:</t>
        <table align="center" pn="table-4">
          <thead>
            <tr>
              <th align="left" colspan="1" rowspan="1">Decimal</th>
              <th align="left" colspan="1" rowspan="1">Description</th>
              <th align="left" colspan="1" rowspan="1">Reference</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td align="left" colspan="1" rowspan="1">1</td>
              <td align="left" colspan="1" rowspan="1">id-rdna-unsigned</td>
              <td align="left" colspan="1" rowspan="1">RFC 9925</td>
            </tr>
          </tbody>
        </table>
        <t indent="0" pn="section-6.3-8">Future updates to this table are to be made according to the Specification
Required policy as defined in <xref target="RFC8126" format="default" sectionFormat="of" derivedContent="RFC8126"/>.</t>
      </section>
    </section>
  </middle>
  <back>
    <displayreference target="I-D.ietf-jose-deprecate-none-rsa15" to="JOSE"/>
    <references anchor="sec-combined-references" pn="section-7">
      <name slugifiedName="name-references">References</name>
      <references anchor="sec-normative-references" pn="section-7.1">
        <name slugifiedName="name-normative-references">Normative References</name>
        <reference anchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2119" quoteTitle="true" derivedAnchor="RFC2119">
          <front>
            <title>Key words for use in RFCs to Indicate Requirement Levels</title>
            <author fullname="S. Bradner" initials="S." surname="Bradner"/>
            <date month="March" year="1997"/>
            <abstract>
              <t indent="0">In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="2119"/>
          <seriesInfo name="DOI" value="10.17487/RFC2119"/>
        </reference>
        <reference anchor="RFC5280" target="https://www.rfc-editor.org/info/rfc5280" quoteTitle="true" derivedAnchor="RFC5280">
          <front>
            <title>Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile</title>
            <author fullname="D. Cooper" initials="D." surname="Cooper"/>
            <author fullname="S. Santesson" initials="S." surname="Santesson"/>
            <author fullname="S. Farrell" initials="S." surname="Farrell"/>
            <author fullname="S. Boeyen" initials="S." surname="Boeyen"/>
            <author fullname="R. Housley" initials="R." surname="Housley"/>
            <author fullname="W. Polk" initials="W." surname="Polk"/>
            <date month="May" year="2008"/>
            <abstract>
              <t indent="0">This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5280"/>
          <seriesInfo name="DOI" value="10.17487/RFC5280"/>
        </reference>
        <reference anchor="RFC5912" target="https://www.rfc-editor.org/info/rfc5912" quoteTitle="true" derivedAnchor="RFC5912">
          <front>
            <title>New ASN.1 Modules for the Public Key Infrastructure Using X.509 (PKIX)</title>
            <author fullname="P. Hoffman" initials="P." surname="Hoffman"/>
            <author fullname="J. Schaad" initials="J." surname="Schaad"/>
            <date month="June" year="2010"/>
            <abstract>
              <t indent="0">The Public Key Infrastructure using X.509 (PKIX) certificate format, and many associated formats, are expressed using ASN.1. The current ASN.1 modules conform to the 1988 version of ASN.1. This document updates those ASN.1 modules to conform to the 2002 version of ASN.1. There are no bits-on-the-wire changes to any of the formats; this is simply a change to the syntax. This document is not an Internet Standards Track specification; it is published for informational purposes.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5912"/>
          <seriesInfo name="DOI" value="10.17487/RFC5912"/>
        </reference>
        <reference anchor="RFC8126" target="https://www.rfc-editor.org/info/rfc8126" quoteTitle="true" derivedAnchor="RFC8126">
          <front>
            <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
            <author fullname="M. Cotton" initials="M." surname="Cotton"/>
            <author fullname="B. Leiba" initials="B." surname="Leiba"/>
            <author fullname="T. Narten" initials="T." surname="Narten"/>
            <date month="June" year="2017"/>
            <abstract>
              <t indent="0">Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA).</t>
              <t indent="0">To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry.</t>
              <t indent="0">This is the third edition of this document; it obsoletes RFC 5226.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="26"/>
          <seriesInfo name="RFC" value="8126"/>
          <seriesInfo name="DOI" value="10.17487/RFC8126"/>
        </reference>
        <reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8174" quoteTitle="true" derivedAnchor="RFC8174">
          <front>
            <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
            <author fullname="B. Leiba" initials="B." surname="Leiba"/>
            <date month="May" year="2017"/>
            <abstract>
              <t indent="0">RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="8174"/>
          <seriesInfo name="DOI" value="10.17487/RFC8174"/>
        </reference>
      </references>
      <references anchor="sec-informative-references" pn="section-7.2">
        <name slugifiedName="name-informative-references">Informative References</name>
        <reference anchor="I-D.ietf-jose-deprecate-none-rsa15" target="https://datatracker.ietf.org/doc/html/draft-ietf-jose-deprecate-none-rsa15-03" quoteTitle="true" derivedAnchor="JOSE">
          <front>
            <title>JOSE: Deprecate 'none' and 'RSA1_5'</title>
            <author fullname="Neil Madden" initials="N." surname="Madden">
              <organization showOnFrontPage="true">Hazelcast</organization>
            </author>
            <date day="19" month="September" year="2025"/>
            <abstract>
              <t indent="0">This document updates [RFC7518] to deprecate the JWS algorithm "none" and the JWE algorithm "RSA1_5". These algorithms have known security weaknesses. It also updates the Review Instructions for Designated Experts to establish baseline security requirements that future algorithm registrations should meet.</t>
            </abstract>
          </front>
          <seriesInfo name="Internet-Draft" value="draft-ietf-jose-deprecate-none-rsa15-03"/>
          <refcontent>Work in Progress</refcontent>
        </reference>
        <reference anchor="JWT" target="https://www.howmanydayssinceajwtalgnonevuln.com/" quoteTitle="true" derivedAnchor="JWT">
          <front>
            <title>How Many Days Has It Been Since a JWT alg:none Vulnerability?</title>
            <author initials="J." surname="Sanderson" fullname="James 'zofrex' Sanderson">
              <organization showOnFrontPage="true"/>
            </author>
            <date/>
          </front>
        </reference>
        <reference anchor="RFC4158" target="https://www.rfc-editor.org/info/rfc4158" quoteTitle="true" derivedAnchor="RFC4158">
          <front>
            <title>Internet X.509 Public Key Infrastructure: Certification Path Building</title>
            <author fullname="M. Cooper" initials="M." surname="Cooper"/>
            <author fullname="Y. Dzambasow" initials="Y." surname="Dzambasow"/>
            <author fullname="P. Hesse" initials="P." surname="Hesse"/>
            <author fullname="S. Joseph" initials="S." surname="Joseph"/>
            <author fullname="R. Nicholas" initials="R." surname="Nicholas"/>
            <date month="September" year="2005"/>
            <abstract>
              <t indent="0">This document provides guidance and recommendations to developers building X.509 public-key certification paths within their applications. By following the guidance and recommendations defined in this document, an application developer is more likely to develop a robust X.509 certificate-enabled application that can build valid certification paths across a wide range of PKI environments. This memo provides information for the Internet community.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="4158"/>
          <seriesInfo name="DOI" value="10.17487/RFC4158"/>
        </reference>
        <reference anchor="RFC4514" target="https://www.rfc-editor.org/info/rfc4514" quoteTitle="true" derivedAnchor="RFC4514">
          <front>
            <title>Lightweight Directory Access Protocol (LDAP): String Representation of Distinguished Names</title>
            <author fullname="K. Zeilenga" initials="K." role="editor" surname="Zeilenga"/>
            <date month="June" year="2006"/>
            <abstract>
              <t indent="0">The X.500 Directory uses distinguished names (DNs) as primary keys to entries in the directory. This document defines the string representation used in the Lightweight Directory Access Protocol (LDAP) to transfer distinguished names. The string representation is designed to give a clean representation of commonly used distinguished names, while being able to represent any distinguished name. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="4514"/>
          <seriesInfo name="DOI" value="10.17487/RFC4514"/>
        </reference>
        <reference anchor="RFC5914" target="https://www.rfc-editor.org/info/rfc5914" quoteTitle="true" derivedAnchor="RFC5914">
          <front>
            <title>Trust Anchor Format</title>
            <author fullname="R. Housley" initials="R." surname="Housley"/>
            <author fullname="S. Ashmore" initials="S." surname="Ashmore"/>
            <author fullname="C. Wallace" initials="C." surname="Wallace"/>
            <date month="June" year="2010"/>
            <abstract>
              <t indent="0">This document describes a structure for representing trust anchor information. A trust anchor is an authoritative entity represented by a public key and associated data. The public key is used to verify digital signatures, and the associated data is used to constrain the types of information or actions for which the trust anchor is authoritative. The structures defined in this document are intended to satisfy the format-related requirements defined in Trust Anchor Management Requirements. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5914"/>
          <seriesInfo name="DOI" value="10.17487/RFC5914"/>
        </reference>
        <reference anchor="RFC7299" target="https://www.rfc-editor.org/info/rfc7299" quoteTitle="true" derivedAnchor="RFC7299">
          <front>
            <title>Object Identifier Registry for the PKIX Working Group</title>
            <author fullname="R. Housley" initials="R." surname="Housley"/>
            <date month="July" year="2014"/>
            <abstract>
              <t indent="0">When the Public-Key Infrastructure using X.509 (PKIX) Working Group was chartered, an object identifier arc was allocated by IANA for use by that working group. This document describes the object identifiers that were assigned in that arc, returns control of that arc to IANA, and establishes IANA allocation policies for any future assignments within that arc.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7299"/>
          <seriesInfo name="DOI" value="10.17487/RFC7299"/>
        </reference>
        <reference anchor="RFC8446" target="https://www.rfc-editor.org/info/rfc8446" quoteTitle="true" derivedAnchor="RFC8446">
          <front>
            <title>The Transport Layer Security (TLS) Protocol Version 1.3</title>
            <author fullname="E. Rescorla" initials="E." surname="Rescorla"/>
            <date month="August" year="2018"/>
            <abstract>
              <t indent="0">This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery.</t>
              <t indent="0">This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8446"/>
          <seriesInfo name="DOI" value="10.17487/RFC8446"/>
        </reference>
        <reference anchor="X.509" target="https://www.itu.int/rec/t-rec-x.509/en" quoteTitle="true" derivedAnchor="X.509">
          <front>
            <title>Information technology - Open Systems Interconnection - The Directory: Public-key and attribute certificate frameworks</title>
            <author>
              <organization showOnFrontPage="true">ITU-T</organization>
            </author>
            <date year="2019" month="October"/>
          </front>
          <seriesInfo name="ITU-T Recommendation" value="X.509"/>
          <seriesInfo name="ISO/IEC" value="9594-8:2020"/>
        </reference>
      </references>
    </references>
    <section anchor="asn1-module" numbered="true" removeInRFC="false" toc="include" pn="section-appendix.a">
      <name slugifiedName="name-asn1-module">ASN.1 Module</name>
      <t indent="0" pn="section-appendix.a-1">This ASN.1 module uses the conventions established by <xref target="RFC5912" format="default" sectionFormat="of" derivedContent="RFC5912"/>.</t>
      <sourcecode type="asn.1" markers="false" pn="section-appendix.a-2">
SignatureAlgorithmNone
  { iso(1) identified-organization(3) dod(6) internet(1)
    security(5) mechanisms(5) pkix(7) id-mod(0)
    id-mod-algUnsigned-2025(122) }

DEFINITIONS IMPLICIT TAGS ::=
BEGIN

IMPORTS
  SIGNATURE-ALGORITHM
  FROM AlgorithmInformation-2009  -- in [RFC5912]
    { iso(1) identified-organization(3) dod(6) internet(1)
      security(5) mechanisms(5) pkix(7) id-mod(0)
      id-mod-algorithmInformation-02(58) }
  ATTRIBUTE
  FROM PKIX-CommonTypes-2009 -- in [RFC5912]
    { iso(1) identified-organization(3) dod(6) internet(1)
      security(5) mechanisms(5) pkix(7) id-mod(0)
      id-mod-pkixCommon-02(57) } ;

-- Unsigned Signature Algorithm

id-alg-unsigned OBJECT IDENTIFIER ::= { iso(1)
   identified-organization(3) dod(6) internet(1) security(5)
   mechanisms(5) pkix(7) alg(6) 36 }

sa-unsigned SIGNATURE-ALGORITHM ::= {
   IDENTIFIER id-alg-unsigned
   PARAMS ARE absent
}

id-rdna-unsigned OBJECT IDENTIFIER ::= { iso(1)
   identified-organization(3) dod(6) internet(1) security(5)
   mechanisms(5) pkix(7) rdna(25) 1 }

at-unsigned ATTRIBUTE ::= {
   TYPE UTF8String (SIZE (0))
   IDENTIFIED BY id-rdna-unsigned
}

END
</sourcecode>
    </section>
    <section numbered="false" anchor="acknowledgements" removeInRFC="false" toc="include" pn="section-appendix.b">
      <name slugifiedName="name-acknowledgements">Acknowledgements</name>
      <t indent="0" pn="section-appendix.b-1">Thanks to <contact fullname="Bob Beck"/>, <contact fullname="Nick Harper"/>, and <contact fullname="Sophie Schmieg"/> for reviewing an early
iteration of this document. Thanks to <contact fullname="Alex Gaynor"/> for providing a link to cite
for <xref target="JWT" format="default" sectionFormat="of" derivedContent="JWT"/>. Thanks to <contact fullname="Russ Housley"/> for additional input.</t>
    </section>
    <section anchor="authors-addresses" numbered="false" removeInRFC="false" toc="include" pn="section-appendix.c">
      <name slugifiedName="name-authors-address">Author's Address</name>
      <author initials="D." surname="Benjamin" fullname="David Benjamin">
        <organization showOnFrontPage="true">Google LLC</organization>
        <address>
          <email>davidben@google.com</email>
        </address>
      </author>
    </section>
  </back>
</rfc>
