From: Russ Housley <housley@vigilsec.com>
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Date: Wed, 8 Jul 2026 16:28:17 -0400
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To: suzanne wibada <suzannewibada01@gmail.com>
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CC: IETF LAMPS <spasm@ietf.org>
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Suzanne:

> 1. Simultaneous use of multiple certificates/keys
> The abstract mentions support for multi-key/certificate usage, but the =
current use cases seem to focus primarily on scenarios where one =
certificate acts as an alternative or backup to another.
>=20
> It may be interesting to introduce a Hybrid Certificate use case, =
where multiple certificates are used simultaneously to authenticate the =
same session.
>=20
> For example, during a post-quantum migration, both a classical =
certificate and a PQC certificate could contribute to the authentication =
of a connection. In a TLS context, this could potentially be achieved by =
introducing a second CertificateVerify message carrying an additional =
signature generated using the secondary certificate. In this model, both =
certificates would actively participate in establishing trust rather =
than serving merely as alternatives to one another.
>=20
We need to be careful here.  Some of this is not in scope for the LAMPS =
WG.  I think it would be fine for LAMPS to provide a mechanism for a =
relying party to discover that a subject has more than one valid =
certificate.  However, the use of one or more of those certificate in a =
security protocol needs to be handeled that the WG that specifies that =
security protocol.  The exception is S/MIME, as that security protocol =
is also part of LAMPS,  S/MIME already handles multiple signatures each =
validated with a separate certificate.

Russ


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<html aria-label="message body"><head><meta http-equiv="content-type" content="text/html; charset=us-ascii"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Suzanne:<div><br><div><blockquote type="cite"><b style="font-family: arial, sans-serif;">1. Simultaneous use of multiple certificates/keys</b><br><div><div dir="ltr"><p><font size="2"><span style="font-family:arial,sans-serif">The abstract 
mentions support for multi-key/certificate usage, but the current use 
cases seem to focus primarily on scenarios where one certificate acts as
 an alternative or backup to
 another. </span></font></p><p><font size="2"><span style="font-family:arial,sans-serif">It may be 
interesting to introduce a Hybrid Certificate use case, where multiple 
certificates are used simultaneously to authenticate the same session.</span></font></p><p><font size="2"><span style="font-family:arial,sans-serif">For example, 
during a post-quantum migration, both a classical certificate and a PQC 
certificate could contribute to the authentication of a connection. In a
 TLS context, this could
 potentially be achieved by introducing a second CertificateVerify 
message carrying an additional signature generated using the secondary 
certificate. In this model, both certificates would actively participate
 in establishing trust rather than serving merely
 as alternatives to one another.</span></font></p></div></div></blockquote>We need to be careful here. &nbsp;Some of this is not in scope for the LAMPS WG. &nbsp;I think it would be fine for LAMPS to provide a mechanism for a relying party to discover that a subject has more than one valid certificate. &nbsp;However, the use of one or more of those certificate in a security protocol needs to be handeled that the WG that specifies that security protocol. &nbsp;The exception is S/MIME, as that security protocol is also part of LAMPS, &nbsp;S/MIME already handles multiple signatures each validated with a separate certificate.</div><div><br></div><div>Russ</div><div><br></div></div></body></html>
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