Request for Comments: 6489
Category: Best Current Practice
Certification Authority (CA) Key Rollover in
the Resource Public Key Infrastructure (RPKI)
This document describes how a Certification Authority (CA) in the Resource Public Key Infrastructure (RPKI) performs a planned rollover of its key pair. This document also notes the implications of this key rollover procedure for relying parties (RPs). In general, RPs are expected to maintain a local cache of the objects that have been published in the RPKI repository, and thus the way in which a CA performs key rollover impacts RPs.
Status of This Memo
This memo documents an Internet Best Current Practice.
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 BCPs is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6489.
Copyright © 2012 IETF Trust and the persons identified as the document authors. All rights reserved.
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Table of Contents
1. Introduction ....................................................2 1.1. Terminology and Concepts ...................................2 2. CA Key Rollover Procedure .......................................3 3. Relying Party Requirements ......................................6 4. Reissuing Certificates and RPKI Signed Objects ..................7 4.1. CA Certificates ............................................7 4.2. RPKI Signed Objects ........................................7 5. Security Considerations .........................................8 6. Acknowledgements ................................................8 7. References ......................................................9 7.1. Normative References .......................................9 7.2. Informative References .....................................9
This document describes an algorithm to be employed by a Certification Authority (CA) in the Resource Public Key Infrastructure (RPKI) [RFC6480] to perform a rollover of its key pair.
This document defines a conservative procedure for such entities to follow when performing a key rollover. This procedure is "conservative" in that the CA's actions in key rollover are not intended to disrupt the normal operation of relying parties (RPs) in maintaining a local cached version of the RPKI distributed repository. Using this procedure, RPs are in a position to be able to validate all authentic objects in the RPKI using the validation procedure described in [RFC6480] at all times.
1.1. Terminology and Concepts
It is assumed that the reader is familiar with the terms and concepts described in "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile" [RFC5280], "X.509 Extensions for IP Addresses and AS Identifiers" [RFC3779], the profile for RPKI Certificates [RFC6487], and the RPKI repository structure [RFC6481] .
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
2. CA Key Rollover Procedure
A CA in the RPKI is an entity that issues CA and end-entity (EE) certificates and Certificate Revocation Lists (CRLs). A CA instance is associated with a single key pair [RFC6487], implying that if key rollover is a regularly scheduled event, then, over time, there will be many CA instances. The implication in the context of key rollover is that, strictly speaking, a CA does not perform a key rollover per se. In order to perform the equivalent of a key rollover, the CA creates a "new" instance of itself, with a new key pair, and then effectively substitutes this "new" CA instance into the RPKI hierarchy in place of the "old" CA instance.
Note that focus of this procedure is planned key rollover, not an emergency key rollover, e.g., promoted by a suspected or detected private key compromise. However, the procedure described here is applicable in emergency key rollover situations, with the exception of the "Staging Period" duration.
There are several considerations regarding this procedure that MUST be followed by a CA performing a key rollover operation. The critical consideration is that the RPKI has potential application in the area of control of routing integrity [RFC6480], and key rollover should not cause any transient hiatus in which an RP is led to incorrect conclusions regarding the authenticity of attestations made in the context of the RPKI. A CA cannot assume that all RPs will perform path validation and path discovery in the same fashion; therefore, the key rollover procedure MUST preserve the integrity of the CRL Distribution Points (CRLDP), Subject Information Access (SIA), and Authority Information Access (AIA) pointers in RPKI certificates.
In the procedure described here, the CA creates a "new" CA instance, and has the associated new public key published in the form of a "new" CA certificate. While the "current" and "new" CA instances share a single repository publication point, each CA has its own CRL and its own manifest. Initially, the "new" CA publishes an empty CRL and a manifest that contains a single entry for the CRL. The "current" CA also maintains its published CRL and manifest at this repository publication point.
The CA performing key rollover waits for a period of time to afford every RP an opportunity to discover and retrieve this "new" CA certificate, and store it in its local RPKI repository cache instance. This period of time is termed the Staging Period. During this period, the CA will have a "new" CA instance, with no subordinate products, and a "current" CA instance that has issued all subordinate products. At the expiration of the Staging Period, the
"new" CA instance MUST replace all (valid) subordinate products of the "current" CA instance, overwriting the "current" subordinate products in the CA's repository publication point. When this process is complete, the "current" CA instance is retired, and the "new" CA instance becomes the "current" CA.
During the transition of the "current" and "new" CA instances, the "new" CA instance MUST reissue all subordinate products of the "current" CA. The procedure described here requires that, with the exception of manifests and CRLs, the reissued subordinate products be published using the same repository publication point object names, effectively overwriting the old objects with these reissued objects. The intent of this overwriting operation is to ensure that the AIA pointers of subordinate products at lower tiers in the RPKI hierarchy remain correct, and that CA key rollover does not require any associated actions by any subordinate CA.
There are three CA states described here:
The CURRENT CA is the active CA instance used to accept and process certificate issuance and revocation requests. The starting point for this algorithm is that the key of the CURRENT CA is to be rolled over.
The NEW CA is the CA instance that is being created. The NEW CA is not active, and thus does not accept nor process certificate issuance and revocation requests. The NEW CA SHOULD issue a CRL and an EE certificate in association with its manifest to provide a trivial, complete, and consistent instance of a CA.
The CA instance is in the process of being removed. An OLD CA instance is unable to process any certificate issuance and revocation requests. An OLD CA instance will continue to issue regularly scheduled CRLs and issue an EE certificate as part of the process of updating its manifest to reflect the updated CRL.
To perform a key rollover operation, the CA MUST perform the following steps in the order given here. Unless specified otherwise each step SHOULD be performed without any intervening delay. The process MUST be run through to completion.
- Generate a new key pair for use by the NEW CA. Because the goal of this algorithm is key rollover, the key pair generated in this step MUST be different from the pair in use by the CURRENT CA.
- Generate a certificate request with this key pair and pass the request to the CA that issued the CURRENT CA certificate. This request MUST include the same SIA extension that is present in the CURRENT CA certificate. This request, when satisfied, will result in the publication of the NEW CA certificate. This (NEW) CA certificate will contain a subject name selected by the issuer, which MUST be distinct from the subject name used in the CURRENT CA certificate. The Certificate Practice Statement (CPS) for the issuer of the NEW CA certificate will indicate the time frame within which a certificate request is expected to be processed.
- Publish the NEW CA's CRL and manifest.
The steps involved here are:
- Wait for the issuer of the NEW CA to publish the NEW CA certificate.
- As quickly as possible following the publication of the NEW CA certificate, use the key pair associated with the NEW CA to generate an initially empty CRL, and publish this CRL in the NEW CA's repository publication point. It is RECOMMENDED that the CRL for the NEW CA have a nextUpdate value that will cause the CRL to be replaced at the end of the Staging Period (see in Step 4 below).
- Generate a new key pair, and generate an associated EE certificate request with an AIA value of the NEW CA's repository publication point. Pass this EE certificate request to the NEW CA, and use the returned (single-use) EE certificate as the NEW CA's manifest EE certificate.
- Generate a manifest containing the new CA's CRL as the only entry, and sign it with the private key associated with the manifest EE certificate. Publish the manifest at the NEW CA's repository publication point.
- Destroy the private key associated with the manifest EE certificate.
- The NEW CA enters a Staging Period. The duration of the Staging Period is determined by the CA, but it SHOULD be no less than 24 hours. The Staging Period is intended to afford an opportunity for all RPs to download the NEW CA certificate prior to publication of certificates, CRLs, and RPKI signed objects under the NEW CA. During the Staging Period, the NEW CA SHOULD reissue, but not publish, all of the products that were issued under the CURRENT CA. This includes all CA certificates, EE certificates, and RPKI signed objects. Section 4 describes how each reissued product relates to the product that it replaces. During the Staging Period, the CURRENT CA SHOULD continue to accept and process certificate issuance requests and MUST continue to accept and process certificate revocation requests. If any certificates are issued by the CURRENT CA during the Staging Period, they MUST be reissued under the NEW CA during this period. Any certificates that are revoked under the CURRENT CA MUST NOT be reissued under the NEW CA. As noted above, in the case of an emergency key rollover, a CA will decide whether the 24 hour minimal Staging Period interval is appropriate, or if a shorter Staging Period is needed. As the Staging Period imposes no additional burden on Relying Parties, there is no stipulated or recommended maximum Staging Period.
- Upon expiration of the Staging Period, the NEW CA MUST publish the signed products that have been reissued under the NEW CA, replacing the corresponding products issued under the CURRENT CA at the NEW CA's repository publication point. This replacement is implied by the file naming requirements imposed by [RFC6481] for these signed products. The trivial manifest for the NEW CA (which contained only one entry, for the NEW CA's CRL) is replaced by a manifest listing all of these reissued, signed products. At this point, the CURRENT CA becomes the OLD CA, and the NEW CA becomes the CURRENT CA. Use the OLD CA to issue a manifest that lists only the OLD CA's CRL. It is anticipated that this step is very brief, perhaps a few minutes in duration, because the CA has reissued all of the signed products during the Staging Period. Nonetheless, it is desirable that the activities performed in this step be viewed as atomic by RPs.
- Generate a certificate revocation request for the OLD CA certificate and submit it to the issuer of that certificate. When the OLD CA certificate is revoked, the CRL for the OLD CA is removed from the repository, along with the manifest for the OLD CA. The private key for the OLD CA is destroyed.
3. Relying Party Requirements
This procedure defines a Staging Period for CAs performing a key rollover operation. This period is defined as a period no shorter than 24 hours.
RPs who maintain a local cache of the distributed RPKI repository MUST perform a local cache synchronization operation against the distributed RPKI repository at regular intervals of no longer than 24 hours.
4. Reissuing Certificates and RPKI Signed Objects
This section provides rules a CA MUST use when it reissues subordinate certificates and RPKI signed objects [RFC6488] as part of the key rollover process. Note that CRLs and manifests are not reissued, per se. They are generated for each CA instance. A manifest catalogues the contents of a publication point relative to a CA instance. A CRL lists revoked certificates relative to a CA instance. Key rollover processing for CRLs and manifests is described above, in Section 3.
4.1. CA Certificates
When a CA, as part of the key rollover process, reissues a CA certificate, it copies all of the field and extension values from the old certificate into the new certificate. The only exceptions to this rule are that the notBefore value MAY be set to the current date and time, and the certificate serial number MAY change. Because the reissued CA certificate is issued by a different CA instance, it is not a requirement that the certificate serial number change in the reissued certificate. Nonetheless, the CA MUST ensure that each certificate issued under a specific CA instance (a distinct name and key) contains a unique serial number.
4.2. RPKI Signed Objects
An RPKI signed object is a Cryptographic Message Syntax (CMS) signed- data object, containing an EE certificate and a payload (content) [RFC6488]. When a key rollover occurs, the EE certificate for the RPKI signed object MUST be reissued, under the key of the NEW CA. A CA MAY choose to treat this EE certificate the same way that it deals with CA certificates, i.e., to copy over all fields and extensions, and MAY change only the notBefore date and the serial number. If the CA adopts this approach, then the new EE certificate is inserted into the CMS wrapper, but the signed context remains the same. (If the signing time or binary signing time values in the CMS wrapper are non-null, they MAY be updated to reflect the current time.) Alternatively, the CA MAY elect to generate a new key pair for this EE certificate. If it does so, the object content MUST be resigned under the private key corresponding to the EE certificate. In this case, the EE certificate MUST contain a new public key and a new notBefore value, and it MAY contain a new notAfter value, but all other field and extension values, other than those relating to the digital signature and its associated certificate validation path, remain unchanged. If the signing time or binary signing time values in the CMS wrapper are non-null, they MAY be updated to reflect the current time.
As noted in Sections 126.96.36.199.3 and 188.8.131.52.4 of [RFC6488], the presence or absence of the signing-time and/or the binary-signing- time attribute MUST NOT affect the validity of the RPKI signed object.
5. Security Considerations
No key should be used forever. The longer a key is in use, the greater the probability that it will have been compromised through carelessness, accident, espionage, or cryptanalysis. Infrequent key rollover increases the risk that the rollover procedures will not be followed to the appropriate level of precision, increasing the risk of operational failure of some form in the key rollover process. Regular scheduling of key rollover is generally considered to be a part of a prudent key management practice. However, key rollover does impose additional operational burdens on both the CA and the population of RPs.
These considerations imply that in choosing lifetimes for the keys it manages, a CA should balance security and operational impact (on RPs). A CA should perform key rollover at regularly scheduled intervals. These intervals should be frequent enough to minimize the risks associated with key compromise (noted above) and to maintain local operational proficiency with respect to the key rollover process. However, key lifetimes should be sufficiently long so that the (system-wide) load associated with key rollover events (across the entire RPKI) does not impose an excessive burden upon the population of RPs. RPs are encouraged to maintain an accurate local cache of the current state of the RPKI, which implies frequent queries to the RPKI repository system to detect changes. When a CA rekeys, it changes many signed objects, thus impacting all RPs.
The authors would like to acknowledge the review comments of Tim Bruijnzeels and Sean Turner in preparing this document.
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP Addresses and AS Identifiers", RFC 3779, June 2004. [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008. [RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support Secure Internet Routing", RFC 6480, February 2012. [RFC6481] Huston, G., Loomans, R., and G. Michaelson, "A Profile for Resource Certificate Repository Structure", RFC 6481, February 2012. [RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for X.509 PKIX Resource Certificates", RFC 6487, February 2012.
7.2. Informative References
EMail: firstname.lastname@example.org URI: http://www.apnic.net
EMail: email@example.com URI: http://www.apnic.net Stephen Kent BBN Technologies 10 Moulton St. Cambridge, MA 02138 USA