CDNI Metadata for Delegated Credentials
draft-ietf-cdni-https-delegation-subcerts-06
| Document | Type | Active Internet-Draft (cdni WG) | |
|---|---|---|---|
| Authors | Frédéric Fieau , Stephan Emile , Guillaume Bichot , Christoph Neumann | ||
| Last updated | 2024-04-07 (Latest revision 2024-02-19) | ||
| Replaces | draft-cdni-https-delegation-subcerts | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Consensus: Waiting for Write-Up | |
| Associated WG milestone |
|
||
| Document shepherd | Kevin J. Ma | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | kevin.j.ma.ietf@gmail.com |
draft-ietf-cdni-https-delegation-subcerts-06
Network Working Group F. Fieau
Internet-Draft E. Stephan
Intended status: Standards Track Orange
Expires: 22 August 2024 G. Guillaume
C. Christoph
Broadpeak
19 February 2024
CDNI Metadata for Delegated Credentials
draft-ietf-cdni-https-delegation-subcerts-06
Abstract
The delivery of content over HTTPS involving multiple CDNs raises
credential management issues. This document defines metadata in the
CDNI Control and Metadata interface to setup HTTPS delegation using
delegated credentials from an Upstream CDN (uCDN) to a Downstream CDN
(dCDN).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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."
This Internet-Draft will expire on 22 August 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. CDNI Footprint and Capabilities Advertisement interface (FCI)
capabilities object for delegated credentials . . . . . . 3
3.1. FCI.DelegatedCredentials . . . . . . . . . . . . . . . . 4
3.2. Expected usage of the property number of supported
delegated credentials . . . . . . . . . . . . . . . . . . 5
4. CDNI Metadata interface (MI) metadata object for delegated
credentials . . . . . . . . . . . . . . . . . . . . . . . 5
5. Delegated credentials call flow . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6.1. CDNI MI DelegatedCredentials Payload Type . . . . . . . . 9
6.2. CDNI FCI DelegatedCredentials Payload Type . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Content delivery over HTTPS using one or more CDNs along the path
requires credential management. This specifically applies when an
entity delegates to another trusted entity delivery of content via
HTTPS.
This document defines the CDNI Metadata interface to setup HTTPS
delegation using delegated credentials (as defined by [RFC9345])
between an upstream CDN (uCDN) and downstream CDN (dCDN).
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here..
This document uses terminology from CDNI framework documents: CDNI
framework document [RFC7336], CDNI requirements [RFC7337] and CDNI
interface specifications documents: CDNI Metadata interface [RFC8006]
and CDNI Control interface / Triggers [RFC8007].
3. CDNI Footprint and Capabilities Advertisement interface (FCI)
capabilities object for delegated credentials
A dCDN should advertise its supported delegation methods using the
Footprint and Capabilities Advertisement interface (FCI) as defined
in [RFC8008]. The FCI.Metadata object allows a dCDN to advertise its
capabilities and the MI objects supported by the dCDN. Accordingly,
to announce the support for delegated credentials, the dCDN should
announce the support of MI.DelegatedCredentials as shown in the
example below.
{
"capabilities": [
{
"capability-type": "FCI.Metadata",
"capability-value": {
"metadata": [
"MI.DelegatedCredentials",
"... other supported MI objects ..."
]
},
"footprints": [
"Footprint objects"
]
}
]
}
This document also defines an object that announces to the delegating
entity how many delegated credentials the downstream supports such
that the delegating entity can provide corresponding number of
delegated credentials. For that purpose we introduce the FCI object
FCI.DelegationCredentials.
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3.1. FCI.DelegatedCredentials
The FCI.DelegationCredentials object enables advertising the maximum
number of delegated credentials supported by the dCDN. This number
is typically (but not necessarily) corresponding to the number of
servers designated by the dCDN to support delegated credentials.
The property PrivateKeyEncryptionKey contains a public key provided
by the dCDN that MUST be used by the uCDN to encrypt private keys
whenever such private keys are transmitted to the dCDN using
MI.DelegatedCredentials (see Section 4).
Property: number-delegated-certs-supported
Description: Number of delegated credentials supported by the
dCDN.
Type: integer
Mandatory-to-Specify: Yes
Property: PrivateKeyEncryptionKey
Description: Base64-encoded public key of the dCDN to be used by
the uCDN to encrypt private keys.
Type: string
Mandatory-to-Specify: No
The following is an example of the FCI.DelegatedCredentials.
{
"capabilities": [
{
"capability-type": "FCI.DelegatedCredentials",
"capability-value": {
"number-delegated-certs-supported": 10
}
"footprints": [
<Footprint objects>
]
}
]
}
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3.2. Expected usage of the property number of supported delegated
credentials
The dCDN uses the FCI.DelegatedCredentials object to announce the
number of servers that support delegated credentials
When the uCDN receives the FCI.DelegatedCredentials object it can
issue the supported number of delegated credentials to the dCDN.
When configuring the dCDN, the uCDN MAY decide to provide less than
the maximum supported delegated credentials to the dCDN. Note that,
within a dCDN, different deployment possibilities of the delegated
credentials on the endpoints exist. The dCDN may use one single
delegated credential and deploy it on multiple endpoints.
Alternatively, the dCDN may deploy a different delegated credential
for each endpoint (provided that the uCDN delivers enough different
delegated credentials). This choice is at the discretion of the dCDN
and depends on the number of delegated credentials provided by the
uCDN.
The FCI.DelegationCredentials object does not address expiry and
renewal of delegated credentials. Once the uCDN has provided
delegated credentials via the MI, uCDN SHOULD monitor the provided
credentials and their expiry times. The uCDN SHOULD timely refresh
dCDN credentials via the MI. If the delegated credential is not
renewed on time by the uCDN, the servers of the dCDN that only have
expired delegated credentials SHOULD refuse any new TLS connection
that requires an delegated credential that is up to date.
4. CDNI Metadata interface (MI) metadata object for delegated
credentials
As expressed in [RFC9345], when an uCDN has delgated to a dCDN, the
dCDN presents the "delegated_credential" during the TLS handshake
[RFC8446] to the User Agent, instead of its own certificate. This
implies that the dCDN is also in the possession of the private key
corresponding to the public key in DelegatedCredential.cred
[RFC9345]. This allows the User Agent to verify the signature in
CertificateVerify message sent and signed by the dCDN.
This section defines the MI.DelegatedCredentials object containing an
array of delegated credentials and optionally the corresponding
private keys. The CDNI Metadata Interface [RFC8006] describes the
CDNI metadata distribution mechanisms according to which a dCDN can
retrieve the MI.DelegatedCredentials object from the uCDN.
The properties of the MI.DelegatedCredentials object are as follows:
Property: delegated-credentials
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Description: Array of delegated credentials
Type: Array of DelegatedCredentialObject objects
Mandatory-to-Specify: Yes
The DelegatedCredentialObject object is composed of the following
properties:
Property: delegated-credential
Description: Base64-encoded version of a CertificateEntry as
defined in [RFC8446] Section 4.4.2. The CertificateEntry MUST
contain a DelegatedCredential structure (as defined in
[RFC9345]) using the extension in the CertificateEntry of its
end-entity certificate (see [RFC9345] section 4.1.1)
Type: string
Mandatory-to-Specify: Yes
Property: private-key
Description: Encrypted and base64-encoded private key
corresponding to the public key contained in the
DelegatedCredential
Type: string
Mandatory-to-Specify: No
The private-key property is not mandatory. If not specified, it is
assumed that the dCDN generated the public-private key pair for the
delegated credential itself and provided the public key information
with an out-of-band mechanism to the uCDN. As discussed in
Section 7, it is NOT RECOMMENDED to communicate private keys to the
dCDN using MI.
If the private-key property is used, the transported private key MUST
be encrypted using the PrivateKeyEncryptionKey specified in
FCI.DelegatedCredentials. The base64 envelope format for this
property MUST rely on JOSE/JWE [RFC7516], whereas the private key is
included as JWE Ciphertext in the JWE.
Below, please see an example MI.DelegatedCredential Object.
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{
"generic-metadata-type": "MI.DelegatedCredentials",
"generic-metadata-value": {
"delegated-credentials": [
{"delegated-credential":
"cBBfm8KK6pPz/tdgKyedwA...
iXCCIAmzMM0R8FLI3Ba0UQ=="},
{"delegated-credential":
"4pyIGtjFdys1+9y/4sS/Fg...
J+h9lnRY/xgmi65RLGKoRw=="},
{"delegated-credential":
"6PWFO0g2AXvUaULXLObcVA...
HXoldT/qaYCCNEyCc8JM2A=="}
]
}
}
5. Delegated credentials call flow
An example call-flow using delegated credentials is depicted in
Figure 1.
1. It is assumed that the uCDN has been provisioned and configured
with a certificate. Note that it is out of scope of CDNI and the
present document how and from where (e.g., CSP) the uCDN acquired its
certificate.
2. The uCDN generates a set of delegated credentials (here it is
assumed that public keys of the dCDN are known). Note, that the uCDN
may generate this material at different points in time, e.g., in
advance to have a pool of delegated credentials or on-demand when the
dCDN announces its maximum number of supported delegated crednetials.
3. Using the Footprint & Capabilities Advertisement interface
[RFC8008], the dCDN advertises MI.DelegatedCredentials capabilities
to the uCDN. The dCDN further uses FCI.DelegatedCredentials to
inform on the maximum number of supported delegated credentials.
4. Using the CDNI Metadata interface [RFC8006], the dCDN acquires
the MI.DelegatedCredentials, therefore retrieving an array of
delegated credentials.
5. The client establishes a TLS connection with an endpoint of the
dCDN according to [RFC9345] using the delegated credentials retrieved
in step 4.
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6. When some delegated credentials are about to expire, the uCDN
uses the CDNI MI [RFC8006] to provide new, valid delegated
credentials.
User-Agent dCDN uCDN
| | |
| | [1.uCDN acquires its certificate
| | out of scope of CDNI]
| | |
| | [2.generation of
| | delegated credentials]
| | |
| 3. CDNI FCI interface used to
| advertise support of MI.DelegatedCredentials
| and announce number of delegated credentials
| supported using FCI.DelegatedCredentials
| |-------------------->+
| | |
| 4. CDNI Metadata interface used to
| provide the MI.DelegatedCredential object
| |<--------------------+
| | |
.
.
.
[5. TLS handshake according |
to [I-D.ietf-tls-subcerts]] |
|<------------------->| |
| | |
.
.
.
| 6.Some delegated credentials about to expire.
| CDNI Metadata interface used to
| provide new MI.DelegatedCredential object
| |<--------------------+
| | |
Figure 1: Example call-flow of Delegated credentials in CDNI
6. IANA Considerations
This document requests IANA the registration of the following entries
under the "CDNI Payload Types" registry hosted by IANA regarding
"CDNI delegation":
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+--------------------------+---------------+
| Payload Type | Specification |
+--------------------------+---------------+
| MI.DelegatedCredentials | RFCthis |
+--------------------------+---------------+
| FCI.DelegatedCredentials | RFCthis |
+--------------------------+---------------+
Table 1
[RFC Editor: Please replace RFCthis with the published RFC number for
this document.]
6.1. CDNI MI DelegatedCredentials Payload Type
Purpose: The purpose of this Payload Type is to distinguish
delegated credentials MI Objects (and any associated capability
advertisement)
Interface: MI/FCI
Encoding: see Section 4
6.2. CDNI FCI DelegatedCredentials Payload Type
Purpose: The purpose of this Payload Type is to advertise the number
of delegated credentials needed (and any associated capability
advertisement)
Interface: FCI
Encoding: see Section 3.1
7. Security Considerations
The extensions defined enable providing delegated credentials to
dCDNs. A delegated credential can only be used by a dCDN if it is in
possession of the associated private key. Similarly, an attacker
requires access to the private key in order to exploit delegated
credential and impersonate dCDN nodes. Thus, leakage of only the
delegated credential without the private key represents a limited
security risk.
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Delegated credentials and associated private keys are short-lived
(per default the maximum validity period is set to 7 days in
[RFC9345]) and as such a single leaked delegated credential with its
private key represents a limited security risk. Still, it is NOT
RECOMMENDED to send private keys through the MI. Omitting the
private key further limits the possibility exploits by an attacker to
exploit the delegated credential.
If despite this recommendation, the private key is communicated via
the MI, the transported private key MUST be encrypted within a JOSE /
JWE envelope using the encryption key (PrivateKeyEncryptionKey)
provided within the FCI.DelegatedCredentials by the dCDN. Note that,
the specified encryption method does not offer forward secrecy. If
the dCDN's encryption key becomes compromised in the future, then all
encrypted JWEs will become compromised. Due to the short-lived
nature of delegated credentials, the imact is limited.
It is also important to ensure that an attacker is not able to
systematically retrieve a consecutive or consistent set of delegated
credentials and associated private keys. Such an attack would allow
the attacker to systematically impersonate dCDN nodes. The FCI and
MI objects defined in the present document are transferred via the
interfaces defined in CDNI [RFC8006]. [RFC8006] describes how to
secure these interfaces, protecting the integrity, confidentiality
and ensuring the authenticity of the dCDN and uCDN, which should
prevent an attacker to systematically retrieve delegated credential
and associated private keys.
8. Privacy Considerations
The information, FCI, and MI objects defined in the present document
do not contain any personally identifiable information (PII). As
such this document does not change or alter the Confidentiality and
Privacy Consideration outlined in the CDNI Metadata and Footprint and
Capabilities RFCs [RFC8006].
9. References
9.1. Normative References
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
RFC 7516, DOI 10.17487/RFC7516, May 2015,
<https://www.rfc-editor.org/info/rfc7516>.
[RFC8006] Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma,
"Content Delivery Network Interconnection (CDNI)
Metadata", RFC 8006, DOI 10.17487/RFC8006, December 2016,
<https://www.rfc-editor.org/info/rfc8006>.
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[RFC8007] Murray, R. and B. Niven-Jenkins, "Content Delivery Network
Interconnection (CDNI) Control Interface / Triggers",
RFC 8007, DOI 10.17487/RFC8007, December 2016,
<https://www.rfc-editor.org/info/rfc8007>.
[RFC8008] Seedorf, J., Peterson, J., Previdi, S., van Brandenburg,
R., and K. Ma, "Content Delivery Network Interconnection
(CDNI) Request Routing: Footprint and Capabilities
Semantics", RFC 8008, DOI 10.17487/RFC8008, December 2016,
<https://www.rfc-editor.org/info/rfc8008>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC9345] Barnes, R., Iyengar, S., Sullivan, N., and E. Rescorla,
"Delegated Credentials for TLS and DTLS", RFC 9345,
DOI 10.17487/RFC9345, July 2023,
<https://www.rfc-editor.org/info/rfc9345>.
9.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7336] Peterson, L., Davie, B., and R. van Brandenburg, Ed.,
"Framework for Content Distribution Network
Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336,
August 2014, <https://www.rfc-editor.org/info/rfc7336>.
[RFC7337] Leung, K., Ed. and Y. Lee, Ed., "Content Distribution
Network Interconnection (CDNI) Requirements", RFC 7337,
DOI 10.17487/RFC7337, August 2014,
<https://www.rfc-editor.org/info/rfc7337>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Authors' Addresses
Frederic Fieau
Orange
40-48, avenue de la Republique
92320 Chatillon
France
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Email: frederic.fieau@orange.com
Emile Stephan
Orange
2, avenue Pierre Marzin
22300 Lannion
France
Email: emile.stephan@orange.com
Guillaume Bichot
Broadpeak
15, rue Claude Chappe
35510 Cesson-Sevigne
France
Email: guillaume.bichot@broadpeak.tv
Christoph Neumann
Broadpeak
15, rue Claude Chappe
35510 Cesson-Sevigne
France
Email: christoph.neumann@broadpeak.tv
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