Network Working Group
Internet Engineering Task Force (IETF) F. Fieau
Internet-Draft
Request for Comments: 9677 E. Stephan
Intended status:
Category: Standards Track Orange
Expires: 9 March 2025
ISSN: 2070-1721 G. Guillaume Bichot
C. Christoph Neumann
Broadpeak
5 September
October 2024
CDNI
Content Delivery Network Interconnection (CDNI) Metadata for Delegated
Credentials
draft-ietf-cdni-https-delegation-subcerts-12
Abstract
The delivery of content over HTTPS involving multiple Content
Delivery Networks (CDNs) raises credential management issues. This
document defines metadata in the CDNI Content Delivery Network
Interconnection (CDNI) Control and Metadata interface to setup set up HTTPS
delegation using delegated credentials from an
Upstream upstream CDN (uCDN) to
a Downstream downstream CDN (dCDN).
Status of This Memo
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Internet-Drafts are draft documents valid the IETF community. It has
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This Internet-Draft will expire on 9 March 2025.
https://www.rfc-editor.org/info/rfc9677.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. CDNI Footprint and Capabilities Advertisement interface Interface (FCI)
capabilities object
Capabilities Object for delegated credentials . . . . . . 3 Delegated Credentials
3.1. FCI.DelegatedCredentials . . . . . . . . . . . . . . . . 4
3.2. Expected usage Usage of the property number Property Number of supported
delegated credentials . . . . . . . . . . . . . . . . . . 5 Supported
Delegated Credentials
4. CDNI Metadata interface Interface (MI) metadata object Metadata Object for delegated
credentials . . . . . . . . . . . . . . . . . . . . . . . 5 Delegated
Credentials
5. Delegated credentials call flow . . . . . . . . . . . . . . . 7 Credentials Call Flow
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6.1. CDNI MI DelegatedCredentials MI.DelegatedCredentials Payload Type . . . . . . . . 9
6.2. CDNI FCI DelegatedCredentials FCI.DelegatedCredentials Payload Type . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
Content delivery over HTTPS utilizing one or more Content Delivery
Networks (CDNs) along the delivery path necessitates the management
of credentials. This requirement is particularly pertinent when an
entity delegates the delivery of content via HTTPS to another trusted
entity.
This document specifies the CDNI Metadata interface for establishing
HTTPS delegation through the use of delegated credentials, as defined
in [RFC9345]) [RFC9345], between an upstream CDN (uCDN) and a downstream CDN
(dCDN).
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 the CDNI framework documents: specifications -- CDNI
framework document [RFC7336], CDNI requirements [RFC7337] [RFC7337], and CDNI
interface specifications documents: CDNI Metadata
interface [RFC8006].
3. CDNI Footprint and Capabilities Advertisement interface Interface (FCI)
capabilities object
Capabilities Object for delegated credentials 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 enables a dCDN to communicate
its capabilities and the Metadata Interface interface (MI) objects it supports.
To indicate support for delegated credentials, the dCDN should
announce the support for MI.DelegatedCredentials, as illustrated 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 informs the uCDN of the
number of delegated credentials supported by the dCDN, enabling the
uCDN to supply the appropriate number of delegated credentials. To
this end, the FCI object, FCI.DelegationCredentials, is introduced.
3.1. FCI.DelegatedCredentials
The FCI.DelegationCredentials object enables advertising the maximum
number of delegated credentials supported by the dCDN. This number
typically (but not necessarily) corresponds 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: Public key in JWK JSON Web Key (JWK) format ([RFC7517]) [RFC7517] 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>
]
}
]
}
3.2. Expected usage Usage of the property number Property Number of supported delegated
credentials Supported Delegated
Credentials
The dCDN uses the FCI.DelegatedCredentials object to announce the
number of servers that support delegated credentials credentials.
When the uCDN receives the FCI.DelegatedCredentials object 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 or
renewal of delegated credentials. Once the uCDN has provided
delegated credentials via the MI, the uCDN SHOULD monitor the
provided credentials and their expiry times and timely SHOULD refresh dCDN
credentials via the MI. MI in a timely manner. The uCDN may decide not
to monitor the validity period of delegated credentials and not to
refresh the credentials, for example example, in cases of short-term one shot one-shot
deployments or once it has decided to deprovision a dCDN. If the
delegated credential is not renewed on time by the uCDN, the servers
of the dCDN that only have expired delegated credentials MUST refuse
any new TLS connection that requires an up-to-date delegated
credential.
4. CDNI Metadata interface Interface (MI) metadata object Metadata Object for delegated
credentials Delegated
Credentials
As expressed in [RFC9345], when an uCDN has delegated to a dCDN, the
dCDN presents the "delegated_credential" (rather than its own
certificate) during the TLS handshake [RFC8446] to the User Agent, instead of its own certificate. Agent.
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 a
CertificateVerify message ([RFC8446] Section 4.4.3.) (Section 4.4.3 of [RFC8446]) 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 MI [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
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 (as defined in Section 4 of [RFC4648])
version of a CertificateEntry as defined in
[RFC8446] Section 4.4.2. 4.4.2 of
[RFC8446]. 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) Section 4.1.1 of [RFC9345]).
Type: string
Mandatory-to-Specify: Yes
Property: private-key
Description: Encrypted private key corresponding to the public key
contained in the DelegatedCredential. The envelope format for
this property is JWE JSON Web Encryption (JWE) [RFC7516] using the
base64 compact serialization (Section 7.1 of [RFC7516]).
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. See Section 7 for
constraints regarding the usage of the private key.
If the private-key property is used, the transported private key MUST
be encrypted using the PrivateKeyEncryptionKey specified in
FCI.DelegatedCredentials. The envelope format for this property MUST
use JWE [RFC7516] using the base64 compact serialization (Section 7.1
of [RFC7516]), whereas the private key is included as JWE Ciphertext
in the JWE. The JWE content-type field MAY be used to signal the
media type of the encrypted key.
Below, please see an example MI.DelegatedCredential Object. of an MI.DelegatedCredentials object.
{
"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 Credentials Call Flow
An example call-flow using delegated credentials is depicted in
Figure 1. The steps are as follows.
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) which Content Service
Provider) 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 on
demand when the dCDN announces its maximum number of supported
delegated credentials.
3. Using the CDNI FCI [RFC8008], the dCDN advertises
MI.DelegatedCredentials capabilities to the uCDN. The dCDN
further uses FCI.DelegatedCredentials to advertise the maximum
number of supported delegated credentials.
4. Using the CDNI MI [RFC8006], the dCDN acquires the
MI.DelegatedCredentials, 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.
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 [1. uCDN acquires its certificate
| | out of scope of CDNI]
| | |
| | [2.generation [2. generation of
| | delegated credentials]
| | |
| 3. CDNI FCI used to
| advertise support of MI.DelegatedCredentials
| and announce number of delegated credentials
| supported using FCI.DelegatedCredentials
| |-------------------->+
| | |
| 4. CDNI MI used to
| provide the MI.DelegatedCredential MI.DelegatedCredentials object
| |<--------------------+
| | |
.
.
.
[5. TLS handshake according |
to [RFC9345]] . |
|<------------------->| |
| | |
.
.
.
| 6.Some 6. Some delegated credentials about to expire.
| CDNI MI used to
| provide new MI.DelegatedCredential MI.DelegatedCredentials object
| |<--------------------+
| | |
Figure 1: Example call-flow Call Flow of Delegated credentials Credentials in CDNI
6. IANA Considerations
This document requests
IANA registration of has registered the following entries
under payload types in the "CDNI Payload
Types" registry hosted by IANA regarding
"CDNI delegation":
+--------------------------+---------------+ in the "Content Delivery Network Interconnection
(CDNI) Parameters" registry group.
+==========================+===========+
| Payload Type | Specification Reference |
+--------------------------+---------------+
+==========================+===========+
| MI.DelegatedCredentials | RFCthis RFC 9677 |
+--------------------------+---------------+
+--------------------------+-----------+
| FCI.DelegatedCredentials | RFCthis RFC 9677 |
+--------------------------+---------------+
+--------------------------+-----------+
Table 1
[RFC Editor: Please replace RFCthis with the published RFC number for
this document.]
The Section
Sections 6.1 and Section 6.2 below provide additional necessary information for the IANA
registration of those CDNI payload-types
parameters payload types (see [RFC7736] Section 2.2). 2.2 of
[RFC7736]).
6.1. CDNI MI DelegatedCredentials MI.DelegatedCredentials Payload Type
Purpose: The purpose of this Payload Type payload type is to distinguish
delegated credentials MI Objects objects.
Interface: MI/FCI
Encoding: see See Section 4 4.
6.2. CDNI FCI DelegatedCredentials FCI.DelegatedCredentials Payload Type
Purpose: The purpose of this Payload Type payload type is to advertise the number
of delegated credentials needed (and any associated capability
advertisement)
advertisement).
Interface: FCI
Encoding: see See Section 3.1 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 a delegated
credential and impersonate dCDN nodes. Thus, leakage of only the
delegated credential without the private key represents a limited
security risk.
Delegated credentials and associated private keys are short-lived
(per default 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 possible ways an attacker to exploit could
exploits the delegated credential.
If despite this recommendation, recommendation is not followed, i.e., the private key is
communicated via the MI, the transported private key MUST be
encrypted within a JWE envelope using the encryption key
(PrivateKeyEncryptionKey) provided within the
FCI.DelegatedCredentials by the dCDN. The JWE encryption key
(PrivateKeyEncryptionKey) MUST have a strength equal to or larger
than the private key it is encrypting for transport. 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 impact 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 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 integrity and
confidentiality, as well as ensuring the authenticity of the dCDN and
uCDN, which should prevent an attacker to from systematically retrieve retrieving
delegated credential credentials and associated private keys.
8. Privacy Considerations
The information, FCI, FCI and MI objects and the information defined in the present
document do not contain any personally identifiable information
(PII). As
such such, this document does not change or alter the Confidentiality
confidentiality and
Privacy Consideration privacy considerations outlined in the CDNI Metadata and Footprint Section 8.2 of
[RFC8006] and
Capabilities RFCs [RFC8006]. Section 7 of [RFC8008].
A single or systematic retrieval of delegated credentials and
associated private keys would allow the attacker to decrypt any data
sent by the end user intended for the end service, which may include
PII.
9. References
9.1. Normative 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>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[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>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<https://www.rfc-editor.org/info/rfc7517>.
[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>.
[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>.
[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>.
[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
[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>.
[RFC7736] Ma, K., "Content Delivery Network Interconnection (CDNI)
Media Type Registration", RFC 7736, DOI 10.17487/RFC7736,
December 2015, <https://www.rfc-editor.org/info/rfc7736>.
Authors' Addresses
Frederic
Frédéric Fieau
Orange
40-48, avenue de la Republique République
92320 Chatillon Châtillon
France
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
3771 Boulevard des Alliés
35510 Cesson-Sevigne Cesson-Sévigné
France
Email: guillaume.bichot@broadpeak.tv
Christoph Neumann
Broadpeak
15, rue Claude Chappe
3771 Boulevard des Alliés
35510 Cesson-Sevigne Cesson-Sévigné
France
Email: christoph.neumann@broadpeak.tv