SIDR G. Huston
Internet-Draft G. Michaelson
Intended status: BCP APNIC
Expires: January 12, 2012 S. Kent
BBN
July 11, 2011
CA Key Rollover in the RPKI
draft-ietf-sidr-keyroll-08.txt
Abstract
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
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This Internet-Draft will expire on January 12, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology and Concepts . . . . . . . . . . . . . . . . . 3
2. CA Key Rollover Procedure . . . . . . . . . . . . . . . . . . 3
3. Relying Party Requirements . . . . . . . . . . . . . . . . . . 7
4. Re-issuing Certificates and RPKI Signed Objects . . . . . . . 7
4.1. CA Certificates . . . . . . . . . . . . . . . . . . . . . 8
4.2. RPKI Signed Objects . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
This document describes an algorithm to be employed by a
Certification Authority (CA) in the Resource Public Key
Infrastructure (RPKI) [ID.ietf-sidr-arch] 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 [ID.ietf-sidr-arch] 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 [ID.ietf-sidr-res-certs], and the RPKI
repository structure [ID.ietf-sidr-repos-struct] .
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 RFC 2119.
2. CA Key Rollover Procedure
A Certification Authority (CA) in the Resource Public Key
Infrastructure (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 ([ID.ietf-sidr-res-certs]),
implying that if key rollover is a regularly scheduled event then,
over time, there will be many instances of a CA. 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
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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 [ID.ietf-sidr-arch], and key
rollover should not cause any transient hiatus in which a Relying
Party (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, and 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 re-issue all subordinate products of the
"current" CA. The procedure described here requires that, with the
exception of manifests and CRLs, the re-issued subordinate products
be published using the same repository publication point object
names, effectively overwriting the old objects with these re-issued
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.
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There are three CA states described here:
CURRENT:
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.
NEW:
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, consistent instance of a CA.
OLD:
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.
1. 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.
2. 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.
3. Publish the NEW CA's CRL and manifest.
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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 initial, 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.
4. 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 re-issue, 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 re-issued 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 re-issued under the NEW CA during this period. Any
certificates that are revoked under the CURRENT CA MUST NOT be
re-issued 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
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imposes no additional burden on Relying Parties, there is no
stipulated or recommended maximum Staging Period.
5. Upon expiration of the Staging Period, the NEW CA MUST publish
the signed products that have been re-issued 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 [ID.ietf-sidr-repos-struct] 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 re-issued, 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 re-issued 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.
6. 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 synchronisation operation against the
distributed RPKI repository at regular intervals of no longer than 24
hours.
4. Re-issuing Certificates and RPKI Signed Objects
This section provides rules a CA MUST use when it re-issues
subordinate certificates and RPKI signed objects
[ID.ietf-sidr-signed-object] as part of the key rollover process.
Note that CRLs and manifests are not re-issued, 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
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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, re-issues 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
re-issued CA certificate is issued by a different CA instance, it is
not a requirement that the certificate serial number change in the
re-issued 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)
[ID.ietf-sidr-signed-object]. When a key rollover occurs, the EE
certificate for the RPKI signed object MUST be re-issued, 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 that
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 Section 2.1.6.4.3 and 2.1.6.4.4 of
[ID.ietf-sidr-signed-object], the presence or absence of the
SigningTime and/or the BinarySigningTime attribute MUST NOT affect
the validity of the RPKI signed object.
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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 upon
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.
6. IANA Considerations
[Note to RFC Editor, to be removed prior to publication: there are no
IANA considerations stated in this document.]
7. Acknowledgements
The authors would like to acknowledge the review comments of Tim
Bruijnzeels and Sean Turner in preparing this document.
8. References
8.1. Normative References
[ID.ietf-sidr-arch]
Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", draft-ietf-sidr-arch-12 (work in
progress), February 2011.
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[ID.ietf-sidr-repos-struct]
Huston, G., Loomans, R., and G. Michaelson, "A Profile for
Resource Certificate Repository Structure", Internet
Draft draft-ietf-sidr-repos-struct-07.txt, February 2010.
[ID.ietf-sidr-res-certs]
Huston, G., Michaelson, G., and R. Loomans, "A Profile for
X.509 PKIX Resource Certificates", Internet
Draft draft-ietf-sidr-res-certs-18.txt, May 2010.
[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.
8.2. Informative References
[ID.ietf-sidr-signed-object]
Lepinski, M., Chi, A., and S. Kent, "Signed Object
Template for the Resource Public Key Infrastructure",
draft-ietf-sidr-signed-object-03.txt (work in progress),
February 2011.
Authors' Addresses
Geoff Huston
Asia Pacific Network Information Centre
Email: gih@apnic.net
URI: http://www.apnic.net
George Michaelson
Email: ggm@apnic.net
URI: http://www.apnic.net
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Stephen Kent
BBN Technologies
10 Moulton St.
Cambridge, MA 02138
USA
Email: kent@bbn.com
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