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 working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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. Fieau, et al. Expires 22 August 2024 [Page 1] Internet-Draft RFC XML Examples February 2024 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). Fieau, et al. Expires 22 August 2024 [Page 2] Internet-Draft RFC XML Examples February 2024 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. Fieau, et al. Expires 22 August 2024 [Page 3] Internet-Draft RFC XML Examples February 2024 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": [ ] } ] } Fieau, et al. Expires 22 August 2024 [Page 4] Internet-Draft RFC XML Examples February 2024 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 Fieau, et al. Expires 22 August 2024 [Page 5] Internet-Draft RFC XML Examples February 2024 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. Fieau, et al. Expires 22 August 2024 [Page 6] Internet-Draft RFC XML Examples February 2024 { "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. Fieau, et al. Expires 22 August 2024 [Page 7] Internet-Draft RFC XML Examples February 2024 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": Fieau, et al. Expires 22 August 2024 [Page 8] Internet-Draft RFC XML Examples February 2024 +--------------------------+---------------+ | 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. Fieau, et al. Expires 22 August 2024 [Page 9] Internet-Draft RFC XML Examples February 2024 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, . [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, . Fieau, et al. Expires 22 August 2024 [Page 10] Internet-Draft RFC XML Examples February 2024 [RFC8007] Murray, R. and B. Niven-Jenkins, "Content Delivery Network Interconnection (CDNI) Control Interface / Triggers", RFC 8007, DOI 10.17487/RFC8007, December 2016, . [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, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . [RFC9345] Barnes, R., Iyengar, S., Sullivan, N., and E. Rescorla, "Delegated Credentials for TLS and DTLS", RFC 9345, DOI 10.17487/RFC9345, July 2023, . 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, . [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, . [RFC7337] Leung, K., Ed. and Y. Lee, Ed., "Content Distribution Network Interconnection (CDNI) Requirements", RFC 7337, DOI 10.17487/RFC7337, August 2014, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Authors' Addresses Frederic Fieau Orange 40-48, avenue de la Republique 92320 Chatillon France Fieau, et al. Expires 22 August 2024 [Page 11] Internet-Draft RFC XML Examples February 2024 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 Fieau, et al. Expires 22 August 2024 [Page 12]