INTERNET-DRAFT Rodney Thayer
26 May 1999 SSH
Expires: 31 November 1999 Charles A. Kunzinger
IBM
PKI Requirements for IP Security
draft-ietf-ipsec-pki-req-02.txt
Revision 02, 26 May 1999
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
The IP Security (IPsec) protocol set now being defined in the
IETF uses public key cryptography for authentication in its key
management protocol. This document defines the requirements that
IPsec has for Public Key Infrastructure (PKI) protocols, formats,
and services based on IETF PKIX (a/k/a X.509) certificate
schemes.
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Contents
Status of this Memo............................................1
Abstract.......................................................1
Contents.......................................................2
1. Introduction................................................4
1.1 Terminology................................................4
2. Environment.................................................6
2.1 PKI Environment Requirements...............................6
2.2 Authentication Topology Requirements.......................7
2.3 Certificate Usage Requirements.............................7
3. Processes...................................................8
3.1 Fulfillment................................................8
3.1.1 Certificate Request Creation.............................8
3.1.2 Certificate Delivery.....................................9
3.2 Retrieval.................................................10
3.3 Validation................................................11
3.4 Management................................................12
3.4.1 Certificate Issuance....................................12
3.4.2 Revocation of Certificate Validity......................12
3.4.3 IPsec validity checking.................................12
3.5 IKE Processing of Certificates............................13
4. Formats....................................................14
4.1 Certificate Format Component Details......................14
4.1.1 IPsec EKU Object Identifiers............................14
4.1.2 subjectAltName Name Format..............................14
4.1.3 Key Sizes...............................................15
4.1.4 Certificate Request and Certificate Formats.............15
4.1.5 Object Identifiers......................................15
4.2 Certificate Request.......................................15
4.3 IPsec Usage Certificate...................................16
4.4 Signing Certificates......................................16
4.4.1 Root Signing Certificate................................16
4.4.2 Intermediate Signing Certificate........................17
4.5 Certificate Revocation List...............................17
5. Samples....................................................18
5.1 Certificate Fulfilment Request............................18
5.2 IPsec Usage Certificate...................................18
5.3 Signing Certificate.......................................19
5.4 Certificate Revocation List...............................19
6. Acknowledgements...........................................19
7. Security Considerations....................................20
8. IANA Considerations........................................20
9.1 Authors' Addresses........................................21
9.2 About this document.......................................21
9.3 Change History............................................21
10. References................................................22
Appendix......................................................24
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A. Summary of Formats.........................................24
1. Names......................................................24
2. Object Identifiers for Signature Algorithms................24
3. Object Identifiers for Extended Key Usage..................24
B. PKIX Issues................................................25
C. IKE Issues.................................................27
D. Copyright Statement........................................28
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1. Introduction
This document describes the Public Key Infrastructure facilities
required to support IPsec [RFC-2401]. It is the intention of this
document to describe the mechanisms that are to be used today to
support certificate use in IPsec implementations, and to specify
how PKIX [PKIX-1, etc.] SHOULD be used in the future to support
IPsec.
The document discusses the (IPsec) environment in which
certificates will be used including the way certificates are
used, the processing involved, and the requirements for support
from a PKI.
The key words "MUST", "SHALL", "REQUIRED", "SHOULD",
"RECOMMENDED", and "MAY" in this document are to be interpreted
as described in RFC 2119.
Please send comments on this document to the ipsec@tis.com
mailing list.
1.1 Terminology
CA -- An organization that issues certificates signed by some
hierarchy.
CA Engine -- a machine or mechanism or software package used for
the process of signing certificates. This may be operated by an
organisation dedicated to this function (a "CA") or it may be
operated by a network management organisation within an Intranet.
commonName -- see [PKIX-1] for definition of this and other PKIX
data structure field names.
countryName -- see [PKIX-1] for definition of this and other PKIX
data structure field names.
CRL -- A Certificate Revocation List, in the PKIX sense of the
term.
EKU -- "Extended Key Usage" fields in certificate requests and
certificates.
End system -- a system that processes IPsec packets for use
within itself only.
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IKE -- IPsec Key Exchange protocol suite, a/k/a ISAKMP, Oakley,
and ISAKMP/Oakley resolution. See [RFC-2409]
Intermediate system -- a system that processes IPsec packets for
use within it and for forwarding, with or without IPsec
processing, to other systems.
Root Certificate -- A signing certificate that is self-signed. A
certificate representing a key pair used to sign Usage
Certificates, that is not in turn signed by other signing
certificates.
PKI service provider -- the software that issues certificates by
signing the public key and other information delivered to it in a
certificate request. A public ("retail") Certificate Authority
might operate this or also might be a private entity operating an
appropriate computer system ("certificate engine") within a local
Intranet.
PKIX -- IETF Working Group handling PKI issues. Note this work
references PKIX and NEVER references X.509, this is NOT based on
X.509. X.509 is NEVER the definitive reference, the PKIX draft
set is.
Signing Certificate -- a certificate containing the public key
portion of a key pair, where the certificate was used to sign
another certificate. In an exactly two-layer hierarchy there is a
("root") signing certificate and there are usage certificates.
This term is used because if there are hierarchies (e.g. root1 ->
root2 -> root3 -> usage certificate) then calling anything but
the top certificate a root is a misnomer.
subject -- see [PKIX-1] for definition of this and other PKIX
data structure field names.
subjectAltName -- see [PKIX-1] for definition of this and other
PKIX data structure field names.
Usage certificate -- a certificate issued to an IPsec-aware
device such as a router, gateway, VPN device, or end system. Note
these devices are not necessarily associated with a specific
person and therefore naming schemes such as email address are not
appropriate.
Validate -- to check a usage certificate in order to determine if
it is valid. This checking consists of recalculating digital
signatures from relevant signing certificates, checking
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certificate revocation and/or current status, and other field
checking as MAY be performed.
2. Environment
IPsec runs in both an End System and an Intermediate System
(Gateway) environment. These systems may or may not be attended
or associated with a person. IPsec devices may well represent a
site's only link to the outside world. Since these devices are
often initialised before they are ever connected to the network,
there is a requirement to support systems that are isolated from
real-time communications with a PKI service provider. Devices
that implement IPsec may or may not be connected to the public
Internet and cannot be assumed to have local mass storage or
removable media.
When IPsec uses a PKI it may be any combination of public and
private PKI Service Providers. This manifests itself as a
requirement to have available locally a copy of one or more
Signing Certificates for signature verification.
The PKI environment used by IPsec may provide a variety of
authorisation topologies; these are discussed in section 2.2.
2.1 PKI Environment Requirements
The relationship between an IPsec device and the PKI it uses is
one of a client and a service provider. In this case the client
is the IPsec device, and the service provider is the PKI Service
Provider. The IPsec device, by definition, is interacting with at
least one other IPsec device, and therefore there are a minimum
of two IPsec devices and a minimum of one PKI service provider.
At times, each IPsec device has it's own PKI service provider and
therefore the abstract minimum configuration has four parties,
the two IPsec parties and the two PKI parties. Therefore there is
a minimum of three and possibly four certificates involved _ the
two IPsec usage certificates and one or two signing certificates.
The IPsec device has it's own usage certificate, based on it's
own public and private key pair. The generation of the key pair
(i.e. was it generated inside or outside the IPsec device, is it
backed up, etc.) is outside of the scope of this document. In
order to establish this certificate, the PKI environment must
support the processes needed to support this. Sections 3.1 (PKI
Fulfilment) and 3.2 (PKI Retrieval) describe these processes.
These processes are used to get the IPsec the certificates it
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requires for processing by the IKE [RFC-2409] component. This
means the IPsec device requires this:
- A mechanism to request the issuance of a certificate and it's
revocation
- It's own certificate
- The signing certificate(s) that validate it's peer IPsec
component
- Validity checking information (e.g. CRL) to confirm validation
of it's peer's certificate
In order to provide a cryptographically sound environment, the
PKI SHOULD provide for the use of at least two public key
algorithms. The PKI must provide DSA [DSA] public key support and
SHOULD provide at least one other mechanism. The size of the keys
involved is specific to the algorithm.
2.2 Authentication Topology Requirements
The PKI Service Providers provide to the IPsec devices a
hierarchy of signing certificates, terminated at a root
certificate. There MUST be a minimum of one signing certificate.
The signing certificate(s) MUST be used to confirm that a usage
certificate designated for an IPsec peer is valid. A given IPsec
device MUST have available to it some set of trusted signing
certificates, which are used to validate usage certificates,
received from a peer IPsec device. This set of signing
certificates must be made available to the IPsec device in a
secure manner, e.g. manually loaded, because they are the basis
for the trust that is inherited by IPsec peers' usage
certificates.
IPsec devices MUST support a signing hierarchy containing at
least eight (8) signing certificates (i.e. an 8-layer root
topology.)
Each peer IPsec device MAY be associated with a different signing
hierarchy and therefore the IPsec device SHOULD support multiple
signing hierarchies. Also, each IPsec device MAY have multiple
usage certificates issued by different signing hierarchies.
It is outside the scope of this document to determine how an
IPsec device will determine which of its own usage certificates
to use or which signing hierarchies to check to validate a peer's
usage certificate.
2.3 Certificate Usage Requirements
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Determination of whether a given usage certificate will be for an
end system or an intermediate system, or both, or something else,
is outside the scope of this document. It is the responsibility
of the parties that produce the certificate request and the
resultant certificate to ensure that the key usage fields
properly represent the actual usage.
3. Processes
This section describes the processes that must be supported to
provide certificates and in general PKI support for IPsec
devices. Section 3.1 describes the processes to be supported to
request a certificate for an IPsec device, section 3.2 describes
the processes to be supported to retrieve certificates for use by
IPsec devices, section 3.3 describes the processes to be
supported to determine the validity of a given certificate,
section 3.4 describes the certificate management processes to be
supported.
3.1 Fulfillment
Note that some request formats may require external processing by
the CA (i.e., PKCS#10 does not support all PKIX/X509v3
extensions.) Use of those extensions may require the CA to
externally enter extension data into the certificate request.
Note that edge devices such as routers may use their network
management capabilities to facilitate this, e.g. the management
station may be the one to email the certificate fulfilment
request to the CA.
3.1.1 Certificate Request Creation
In order to initially establish a certificate for an IPsec device
there must be a certificate request generated by or on behalf of
the IPsec device and delivered to the some entity within the PKI
service provider. This involves these steps:
1. A public/private key pair is obtained
2. A certificate request data message is constructed
3. The certificate request is delivered to the PKI service
provider
The public private key pair is obtained through some mechanism
outside of this document.
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The certificate request can be constructed in one of two formats.
These are PKCS #10 [PKCS-10] or PKIX (Part 3) [PKIX-3.] PKCS
#10, although not an IETF document, is a format that already has
effective 'best current practice' status in the PKI community and
this format is available for implementers now and is known to
exist in current PKI service provider implementations.
The PKCS #10 certificate request format MUST be supported. When
this is used, the value to be placed in the subjectAltName and
the fact this certificate is to be used for IPsec must be
communicated to the PKI service provider in an out-of-band
manner.
The PKIX Part 3 Certificate Request format ('CertReqMsg' from
[CRMF]) SHOULD be used in the future to request a certificate for
IPsec usage. There MUST be an Extended Key Usage Extension
containing an iKEEnd or iKEIntermediate entry, and the
subjectAltName MUST be set to an appropriate value. See section
4.1.1 for a description of iKEEnd and iKEIntermediate.
In either case the certificate generated by the PKI service
provider MUST contain the subjectAltName specified and MAY NOT be
changed. If for whatever reason (policy, CPS, technical reasons,
etc.) the certificate request is not acceptable to the PKI
service provider, it MUST NOT issue a certificate for this
certificate request. In addition, the PKI service provider
SHOULD use the same subject as was supplied in the request and
SHOULD NOT change it. If the subject provided was not acceptable
to the PKI service provider, or if a change-of-name PKI policy is
not mutually acceptable, the certificate request SHOULD be
rejected. In other words, the IPsec Usage Certificate that comes
back should have a subject that is acceptable and expected.
3.1.2 Certificate Delivery
In order to deliver this certificate request to the PKI service
provider, there are several possible mechanisms. At this time,
best current practice does not include any automated mechanisms.
Therefore we must specify what delivery schemes are expected to
be used for an IPsec device.
In the case of a PKCS #10 request, the request itself MUST be
encoded as either DER or PEM format. It MAY be made available to
the PKI service provider as one of:
- text file suitable for email delivery
- disk file suitable for removable media transmission (e.g.
overnight shipment with documented receipt)
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- on-line delivery via ad hoc mechanism (e.g. web form, shared
disk directory, FTP, or email)
In the case of a PKIX request, the request itself is formatted
according to the rules of PKIX. A CertReqMsg is delivered through
one of the standard PKIX mechanisms, including offline and online
PKIX formats.
The offline (file based) PKCS #10 PEM formatted request mechanism
MUST be supported by the IPsec device and the PKI service
provider. It is outside the scope of this document to specify how
the IPsec device is to produce a file containing the request.
However it is assumed that IPsec devices will use their
associated network management facilities to produce such a file.
3.2 Retrieval
While a network is operating using IPsec the certificates
provided by the PKI are used for IKE identification purposes, and
thus are indirectly used for key exchange. The IPsec-aware
devices have a requirement to retrieve and to share device
identification certificates, signing certificates, and
certificate validity information.
IPsec devices MUST be able to retrieve their own fulfilled
certificates, signing certificates for other IPsec devices, and
identification certificates for other IPsec devices. An
identification certificate which identifies an IPsec device must
be loaded into that device in a secure manner.
A signing certificate which is used to validate other IPsec
devices' identification certificates must be loaded in a secure
manner. It should not be retrieved through an unsecured network
mechanism, for example, or accepted if received as an IKE
certificate payload. If a chain of certificates, i.e. a usage
certificate and associated signing certificates, must be
delivered over IKE certificate payloads, then the signing
certificate at the other end of the chain SHOULD NOT be delivered
over IKE, it should be loaded through some other (secure) manner.
It is necessary for at least one of the signing certificates in a
chain to be securely loaded, or else the entire chain can't be
trusted. Implementations MUST NOT allow loading of all signing
certificates for a usage certificate to be received in an
insecure manner (i.e. from the peer IPsec entity, for example.)
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Identification certificates received from IPsec devices through
IKE or through other means MUST be validated using signing
certificates and MAY be validated using other means to detect
revoked certificates, such as CRL's or online directories. IPsec
devices MUST be able to accept usage certificates sent through
IKE and they also MUST be able to accept certificates through
other mechanisms, such as manual loading, or some PKIX protocol.
These certificates which are received MAY be in PKCS #7 format,
DER or PEM encoded, unencrypted (see Section 4.3.1) or MAY be in
some standard PKIX format (see section 4.3.2).
3.3 Validation
Certificates as used for IPsec are validated using the signing
certificate(s) of the issuer in the certification hierarchy and
through other means.
After checking to ensure the certificate is not malformed, the
signature should be checked. (See Section 6 of [PKIX-part1] for a
brief tutorial on certification path validation.) In order for
signing certificate(s) to be used for verification, the
certificate(s) must be pre-loaded within the IPsec devices, or
retrieved in a secure manner.
After determining the signature is valid, the fields of the
certificate SHOULD be checked. If all these fields are not
checked, the IPsec implementation MUST document what checking is
done so that the level of security provided by the implementation
can be determined.
Certificate contents to be checked are:
1. Signature through chain as described above
2. Date. This SHOULD be year-2000 compliant by using GeneralTime
to provide four digit years.
3. ExtendedKeyUsage SHOULD be checked to ensure the certificate
is valid for the system in question, including the criticality
fields. This extension MUST be treated as critical.
4. subjectAltName validation checking (see below)
The subjectAltName field MAY be checked for consistency. For
ipAddress, the address MAY be checked to confirm it is valid for
the IKE negotiation in progress. For dNSName the name MAY be
retrieved from the DNS to validate it is valid for the IP address
which was the source of the certificate, if known, and for the
IKE negotiation in progress. For rFC822Name, the email address
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MAY be checked according to the style of SMTP to ensure email
name validity.
3.4 Management
The term "management" as used here means the processes used for
the creation, validity determination, and destruction of
certificates.
3.4.1 Certificate Issuance
Certificates SHOULD be issued only for certificate requests that
contain a valid Extended Key Usage extension in the certificate
request. The certificate that is issued SHOULD contain the same
Extended Key Usage object identifier as the request contained.
If the certificate request contains a subjectAltName extension
then the certificate MUST contain the same subjectAltName
extension. If the PKI service provider cannot meet these
requirements then it MUST NOT issue the certificate.
Certificate requests may be delivered to the PKI service provider
through either PKCS #7/10, CMC, or PKIX mechanisms and the
resultant certificate may be delivered through any of the
corresponding mechanisms. In all cases the certificate request
and resultant certificate SHOULD be delivered through an
appropriately secure mechanism.
3.4.2 Revocation of Certificate Validity
At any time the PKI service provider can revoke a usage or
signing certificate it has issued. The process of requesting
this revocation is outside of the scope of this document. Once
the certificate's status has changed from valid to invalid, IPsec
devices that use these certificates MUST NOT use these
certificates if they are aware they are no longer valid. The
process of determining whether a given certificate is valid is
outside the scope of this document. An IPsec device SHOULD use
some mechanism to determine if a certificate has had been
revoked before it is used. The IPsec device may use Certificate
Revocation Lists, on-line directory schemes, or other mechanisms.
These mechanism MUST be used in a secure manner, i.e. some scheme
MUST be used to secure the revocation information such as signing
certificate signatures on a CRL.
3.4.3 IPsec validity checking
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IKE implementations must check the certificate for validity at
the time it is used, e.g. at Main Mode initiation time. The
certificate MUST be checked for field validity and for semantic
validity. The fields that MUST be checked are:
1. NotBefore and notAfter times must be valid
2. "subjectAltName" MAY contain a relevant and valid value
3. "subject" SHOULD be non-empty
4. if extendedKeyUsage is present it must contain either
iKEIntermediate or iKEEnd. If additional EKU object
identifiers are present then their use is a locally defined
matter.
5. keyUsage MAY be checked for locally defined valid combinations
6. the signature of the certificate must be checked against
signing certificate hierarchy
IKE implementations MUST examine the not-after time in
conjunction with all relevant SA lifetimes (both IKE SA and IPsec
SA's) at the time the certificate is used to authenticate
creation of an SA. If the SA would definitely expire after the
end of the certificate lifetime then the one of two choices
SHOULD be selected: (1) the SA SHOULD NOT be created at all, or
(2) create an SA but reduce the lifetime to match the certificate
lifetime. If an IPsec device learns that a certificate used in
association with the creation of an IKE or an IPsec security
association becomes invalid for any reason the corresponding
security association MUST be deleted.
In addition, if a Certificate Revocation List or other PKIX-
defined mechanism is available to check the validity of the
certificate, it MUST be used.
3.5 IKE Processing of Certificates
[something about cert requests]
[something about 'signature' vs. digital encipherment"]
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4. Formats
This section describes the fields required in the various
certificate-related messages, as they are used for IPsec.
4.1 Certificate Format Component Details
4.1.1 IPsec EKU Object Identifiers
Two object identifiers are defined for declaring that a
certificate is used for IPsec. The OID "iKEIntermediate" SHOULD
be used if the distinction between end system and intermediate
system is not necessary.
The OID "iKEEnd"
(iso.org.dod.internet.security.ipsec.certificate.2, or
1.3.6.1.5.5.8.2.1) declares this certificate will be used for an
end-node with IPsec and IKE. An "end node" is defined to be an
IPsec device that does not offer IPsec services on behalf of
other devices such as a server or desktop system.
The OID "iKEIntermediate"
(iso.org.dod.internet.security.ipsec.certificate.2, or
1.3.6.1.5.5.8.2.2) declares this certificate will be used for an
intermediate node with IPsec and IKE. An "intermediate node" is
defined to be an IPsec device that offers IPsec services on
behalf of other devices e.g. using tunnel mode and IP forwarding.
4.1.2 subjectAltName Name Format
For IPsec devices the actual name of the subject is stored in the
subjectAltName field. This field SHOULD contain at most one of
each of these values:
- ipAddress
- dNSName
- rFC822Name
If the field contains an IP Address, this MUST be one single IPv4
address, expressed as four bytes in network order. Other uses of
this field such as Ipv6 or subnetwork address are not allowed.
Note the address SHOULD be checked for validity and not for
connectivity, that is, it is not necessary that there be a path
from the IPsec device to this address but rather that this IPsec
device make an explicit decision that this is a valid address.
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If the field contains a DNS name it SHOULD be a valid DNS name
that corresponds to a valid IP address as seen by the IPsec
device processing the certificate. The name SHOULD resolve to a
single IPv4 address and the name MUST NOT end in a trailing dot.
If the field contains an RFC 822 name it SHOULD be a valid email
address which the IPsec device may assume is accessible.
4.1.3 Key Sizes
1024 bit keys or equivalent MUST be supported.
4.1.4 Certificate Request and Certificate Formats
Certificate requests and certificates MAY be exchanged in either
raw binary ("DER") format or in encapsulated Base-64 format in
the style of PEM [RFC-1421]. Encapsulated Base-64 format means:
- first line SHOULD contain "-----BEGIN CERTIFICATE-----" or
"-----BEGIN CERTIFICATE REQUEST-----"
- Certificate or certificate request, encoded as per [RFC-1421]
(64 characters per line)
- Last line SHOULD contain "-----END CERTIFICATE-----" or
"-----END CERTIFICATE REQUEST-----"
The use of the begin and end delimiters is in the style of PEM
but uses the pre- and post-encapsulating boundaries first
developed by Netscape and now in common use [Weinstein.]
4.1.5 Object Identifiers
The object identifier used to identify RSA encryption with SHA-1
Hashing SHOULD be sha1WithRSAEncryption from [PKIX-1], i.e. the
(broken PKIX) RSA variant.
4.2 Certificate Request
A Certificate request is used to provide a public key and
associated naming information for an IPsec device to a PKI
service provider. The request itself MUST be a
'CertificationRequest' structure as defined in [RFC-2314]. This
MAY be encapsulated in a PKIX Enrolment Message [BAL-EMS] or
presented as a classic PKCS#10 Certificate Request.
The request SHOULD contain subjectAltName information, although
that may be provided out of band. If subjectAltName is provided
it is stored in the 'attributes' field of the
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CertificationRequest structure. The attributes are defined using
the "Extensions" format defined in [PKIX-1.] Alternatively and
for backward compatibility, the TIPEM/BCERT style of 'T-61
string' encoding MAY be used although this format should be
avoided if possible. [more clear wording awaiting response from
RSA...]
The request MUST contain some information in the subject field.
The exact contents of this field are not standardized. By
convention, a minimal subject contains countryName and
commonName.
4.3 IPsec Usage Certificate
A certificate that contains the public key component of a key
pair used to identify an IPsec device is called an "IPsec Usage
Certificate". This certificate is in the format described in
[PKIX-Part1] as a 'Certificate' containing a 'TBSCertificate'.
The 'extensions' field of the TBSCertificate SHOULD be present.
One of the EKU attributes MAY be present as an extension. One
subjectAltName attribute MAY be present. There SHOULD NOT be
more than one subjectAltName attribute present. A key pair that
corresponds to a Signing Certificate MUST sign an IPsec Usage
Certificate or another Signing Certificate and the Signing
Certificate MUST be available for other IPsec devices to validate
this signature.
4.4 Signing Certificates
This is a certificate that contains the public key component of
the key pair used to sign IPsec Usage Certificates. The only
relevant fields are the subject and the public key. IKE
implementations MUST use the subject of Signing Certificates to
match the issuerName of any certificate that is being checked.
Signing certificates MAY have EKU attributes identifying them for
use in signing IPsec certificates. The same two OID's are used
for signing certificates as for IPsec usage certificates.
Signing Certificates use the same format from [PKIX-1] as Usage
Certificates.
4.4.1 Root Signing Certificate
A 'Root' Signing Certificate is one in which the subject and
issuerName fields contain the same distinguished name.
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4.4.2 Intermediate Signing Certificate
This is a certificate used to sign other certificates. At this
time the only relevant fields are the subject and the public key.
IKE implementations MUST use the subject of the signing
certificate to match the issuerName of any certificate that is
being checked.
4.5 Certificate Revocation List
A CRL for IPsec looks just like a CRL as defined in PKIX.
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5. Samples
This section contains sample PKI objects for interoperability
testing. These are formatted in PEM or hex dumps of DER encoding.
5.1 Certificate Fulfilment Request
This is a request from commonName "10.0.0.1" with a 1024 bit key.
-----BEGIN CERTIFICATE REQUEST-----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-----END CERTIFICATE REQUEST-----
5.2 IPsec Usage Certificate
This is a certificate for commonName "10.0.8.1" signed by the
signing key in section 5.3. (to fit the lines in this document
'\' was inserted where lines were split.)
-----BEGIN CERTIFICATE-----
MIICQTCCAesCBQCYAvAMMA0GCSqGSIb3DQEBBAUAMIG2MQswCQYDVQQGEwJVUz\
ELMAkGA1UE
CBMCTUExDzANBgNVBAcTBk5ld3RvbjElMCMGA1UEChMcU2FibGUgVGVjaG5vbG\
9neSBDb3Jw
b3JhdGlvbjEsMCoGA1UECxMjU2VjdXJpdHkgSW5mcmFzdHJ1Y3R1cmUgRGlyZW\
N0b3JhdGUx
DzANBgNVBAMTBmRldi1jYTEjMCEGCSqGSIb3DQEJARYUcm9kbmV5QHNhYmxldG\
VjaC5jb20w
HhcNOTgwMjAzMDUwMDAwWhcNOTkwMjAzMDQ1OTU5WjBYMREwDwYDVQQDEwgxMC\
4wLjguMTEh
MB8GA1UEChMYVlBOZXQgVGVjaG5vbG9naWVzLCBJbmMuMRMwEQYDVQQIEwpDYW\
xpZm9ybmlh
MQswCQYDVQQGEwJVUzCBnzANBgkqhkiG9w0BAQEFAAOBjQAwgYkCgYEAsBktyH\
noHqADQ4IP
E3exE/kbPGDXCw+36CSruHOIpMvf0o1YBezL2G+MrhEwDbk0n0Kaqpf9jOc4+i2u9
Qlt\
4nck
sgoRdv7TiPp3EkJa3siwSjx+ikyo7oLUa6mWdLn0Wrnm9rVUf0yyQiYc3H6ul7\
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Pn9c7oNZ7G
KSZ1G4ILitkCAwEAATANBgkqhkiG9w0BAQQFAANBANveH7jw9U8yJPCcAmG7Lq\
h7f03ALEF/
SNfp5fHGo1UeeZiMFP7fNBS2oAlqNRDMCWJJnp+EXahaOjqDqTuqS9o=
-----END CERTIFICATE-----
5.3 Signing Certificate
-----BEGIN CERTIFICATE-----
MIICXDCCAgYCBQCYAvABMA0GCSqGSIb3DQEBBAUAMIG2MQswCQYDVQQGEwJVUz\
ELMAkGA1UE
CBMCTUExDzANBgNVBAcTBk5ld3RvbjElMCMGA1UEChMcU2FibGUgVGVjaG5vbG\
9neSBDb3Jw
b3JhdGlvbjEsMCoGA1UECxMjU2VjdXJpdHkgSW5mcmFzdHJ1Y3R1cmUgRGlyZW\
N0b3JhdGUx
DzANBgNVBAMTBmRldi1jYTEjMCEGCSqGSIb3DQEJARYUcm9kbmV5QHNhYmxldG\
VjaC5jb20w
HhcNOTgwMjAxMDUwMDAwWhcNOTgwNjAyMDQ1OTU5WjCBtjELMAkGA1UEBhMCVV\
MxCzAJBgNV
BAgTAk1BMQ8wDQYDVQQHEwZOZXd0b24xJTAjBgNVBAoTHFNhYmxlIFRlY2hub2\
xvZ3kgQ29y
cG9yYXRpb24xLDAqBgNVBAsTI1NlY3VyaXR5IEluZnJhc3RydWN0dXJlIERpcm\
VjdG9yYXRl
MQ8wDQYDVQQDEwZkZXYtY2ExIzAhBgkqhkiG9w0BCQEWFHJvZG5leUBzYWJsZX\
RlY2guY29t
MFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBAOv2J79yGQG6nb+KCFzNseNpWeFMD7\
d1NTeFtEqK
iYhiHbm3y/qoX5bMJDXp3c5EMhRF4akpl+51oAPzYoE4tZ0CAwEAATANBgkqhk\
iG9w0BAQQF
AANBAG3g34T44uP3lK1H1ngyXPN79hu50wF9eiknaSzZ6RNEBeM2flgjQYseC/\
WHlku01UFh
bg0WAvl/WWeesm4dHtc=
-----END CERTIFICATE-----
5.4 Certificate Revocation List
t.b.d.
6. Acknowledgements
This document was based on discussions with various IPsec
implementers and PKI service providers, as well as other members
of the IETF community. It also benefits from the spirit of
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interoperability exhibited by participants in the various IPsec
bakeoff events.
7. Security Considerations
Check the current literature for recent changes in the known
safety of the algorithms mentioned here, including MD5, SHA-1,
RSA, and DSA.
You have to store the private key(s) safely. If you use keys of
varying lengths, such as a 512-bit RSA root with 1024-bit usage
certificate, there may be implications as to the security of your
infrastructure.
Root or other Signing Certificates should be obtained in a secure
manner, probably NOT sent over the IKE exchange or from a
directory, in order to make sure you are not checking against a
spoofed root. The distinguished name in a signing certificate
cannot be assumed to be unique or correct.
Names in certificates, such as IP addresses or FQDN's should be
checked for consistency with other information about the security
associations being formed.
If you cross-sign signing certificates you run the risk of
leaking trust across hierarchies in unintended ways.
8. IANA Considerations
Two new object identifiers are added in this draft, which will be
submitted to IANA for inclusion in the SMI OID area, see
www.iana.org for more information.
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9. Colophon
9.1 Authors' Addresses
Rodney Thayer
SSH Communications Security, Inc.
4320 Stevens Creek Blvd, Suite 220
San Jose, CA 95129
Rodney@ipsec.com
Charles A. Kunzinger
IBM
kunzinge@us.ibm.com
9.2 About this document
Document edited with Word '98, printed to 'generic text only
printer' on Windows 95, post-processed to fix Carriage
Return/Line Feed issues with custom code. Spell checker
configured for UK English.
9.3 Change History
This is revision 02 of draft-ietf-ipsec-pki-req-<nn>.txt. The
section on chain delivery (3.2) was clarified. The object
identifiers iKEEnd and iKEIntermediate's values were corrected.
Text was altered per comments from the ANX group.
This is revision 01 of draft-ietf-ipsec-pki-req-<nn>.txt. This
version was spell-checked and certain other typographical errors
were corrected. The reference to key lengths all being the same
was removed. The last two paragraphs of the abstract were moved
to the introduction. The dates in the headers, footers, and
first and last page were updated. The text was changed so the
validation requirements on subjectAltName fields are listed as
"SHOULD" and "MAY" and not "MUST" operations. Chapter 3 was
changed significantly to reflect the existence of RFC2314 (IETF
version of PKCS#10) and to clarify some points about the
processes. The Security Considerations section has been updated
to reflect these various changes. Added and updated terms
section. Changed two-algorithm requirement to a SHOULD and made
it more clear.
This document was originally distributed in April 1998 under a
different name. There was a second version, distributed at the
September 1998 IPsec Bakeoff in Redmond at Microsoft.
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10. References
[PKCS #7] RSA PKCS specs
[DOI]
[DSA] dsa defn as specified in pkix, ietf doc or other?
Xxx
[BAL-EMS] LaMacchia, B. "Enrollment Message Syntax", unpublished
proposal discussed at IPsec Bake-off in Redmond, September 1998.
[DNS-TEST] Eastlake, D., "Reserved Top Level DNS Names", draft-
ietf-dnsind-test-tlds-11.txt, July 1998.
[PKIX-1] Housley, R. (SPYRUS), Ford, W. (VeriSign), Polk, W.
(NIST), Solo, D. (Citicorp), "Internet X.509 Public Key
Infrastructure, Certificate and CRL Profile", draft-ietf-pkix-
ipki-part1-11.txt.
[RFC-1421] Linn, J., "Privacy Enhancement for Internet Electronic
Mail: Part I: Message Encryption and Authentication Procedures",
RFC-1421, February 1993.
[RFC-2314] Kaliski, B., "PKCS #10: Certification Request Syntax
Version 1.5"
[RFC-2401] Atkinson, R. and Kent, S., "Security Architecture for
the Internet Protocol", November 1998.
[RFC-2409] Harkins, D. and Carrel, D., "The Internet Key
Exchange (IKE)", November 1998.
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[Weinstein] Weinstein, J., Private communication regarding "-----
BEGIN CERTIFICATE-----", September 1998.
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Appendix
A. Summary of Formats
1. Names
Distinguished Names SHOULD be no more than four (4)
attribute/value pairs each of which SHOULD be no more than 128
characters in length, or the length specified in [PKIX-1],
whatever is shorter.
2. Object Identifiers for Signature Algorithms
SHA-1 with RSA Signature should use the PKCS OID,
1.2.840.113549.1.1.5 [PKCS-1v1.5].
3. Object Identifiers for Extended Key Usage
The OID "iKEEnd"
(iso.org.dod.internet.security.ipsec.certificate.1, or
1.3.6.1.5.5.8.2.1) identifies an IPsec Usage Certificate for an
end system.
The OID "iKEIntermediate"
(iso.org.dod.internet.security.ipsec.certificate.2, or
1.3.6.1.5.5.8.2.2) identifies an IPsec Usage Certificate for an
intermediate system.
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B. PKIX Issues
This appendix describes differences between this document and
existing PKIX standards. It also lists items we need to alter
here to clarify the information presented.
1.
Our document actually has no definition of a "certificate".
For completeness, we should probably include one. Even the
PKIX documents didn't have an explicit definition. The best I
found was in "draft-ietf-pkix-ipki-part4-03.txt" , section
1.1, from which I extracted the following abbreviated : "A
public-key certificate binds a public-key value to a set of
information that identifies the entity (such as a person,
organization, account, or site) associated with the use of the
corresponding private key (this entity is known as the
"subject" of the certificate). The degree to which a
certificate user can trust the binding embodied in a
certificate depends on several factors [including] the
practices followed by the certification authority (CA) in
authenticating the subject."
2.
I'd like to use the definition of "Certification Authority"
from "draft-ietf-pkix-roadmap-00.txt", section 2, which is
more complete than the one in our document: "An authority
trusted by one or more users to create and assign
certificates. Optionally the certification authority may
create the user's [public/private] keys."
3.
The PKIX Roadmap also has a concise definition of a "root CA":
"A certification authority whose certificate is self-signed:
that is, the issuer [of the certificate} and the subject [of
the certificate] are the same entity." And then we could also
add Root certificate: "A self-signed certificate whose
associated private key is used by a certification authority to
sign the certificates that it issues." (Also, although this
isn't a direct definitoin in the PKIX documents, we might also
want to add that a rrot CA certificate will contain the
BasicCOnstraints extension with the cA value set to TRUE.)
4.
I found the definition of "Signing Certificate" a little hard
to follow. At first, I was thinking about the certificates
that IKE peers would use in creating the RSA signatures, for
example. But the text actually is talking about the CAs'
certificates, not the IKE peers' certificates. At least for
me, it might be clearer if we first defined the concept of a
certificate chain. I found some text in "draft-ietf-pkix-
part1-09.txt", section 3.2, that might be a good start. I
created the following definition by selectively using parts of
the first paragraph in that section: "Certification Paths --
If the user does already hold an assured copy of the public
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key of the CA that signed the certificate, then it might need
an additional certificate to obtain that public key. In
general, a chain of multiple certificates may be needed,
comprising a certificate of the public key owner signed by one
CA, and zero or more additional certificates of CAs signed by
other CAs. Such chains, called certification paths, are
required because a public key user is only initialized with a
limited number of assured public CA keys."
5.
Given this definition, we could then define "CA Certificate"
as follows: A certificate that carries the public key
associated with a certification authority. A CA Signing
Certificate will contain the basic constraints extension with
the "cA" value set to TRUE. The certification authority uses
the associated private key to sign the certificates that it
issues. In a certification chain, there will be only one root
CA: that is there will be only one self-signed signing
certificate. All other signing certificates in the chain will
have different values in the issuer and subject fields."
6.
The definition of usage certificates also seems somewhat
roundabout to me. Elsewhere in the draft, you refer to
"identification certificates", which are probably the same
thing. In the context of IPSec, could we use the term "IPSec
Identification Certificate". In PKIX terms, I think this is
probably what they call an "end entity certificate". A
possible definition could then be: " A certificate issued by a
certification authority to an IPSec-aware device that binds
the device's public key to a set of information that
identifies the device. IPSec Identification certificates are
not self-signed and do not include the BasicConstraints
extension. The public key contained in a given device's
IPSec Identification Certificate will be used by an IKE peer
during the Phase 1 IKE exchange in the process of
authenticating the given device.
7.
Having made use of the BasicConstraints extension in item 5,
we should probably also include a definition in our list for
clarity: "BasicConstraints Extension: a extension in a
certificate that identiifes whether the subject of the
certificate is a CA and how deep a certification path may
exist through that CA." (taken from section 4.2.1.10 of
"draft-ietf-pkix-ipki-part1-11.txt").
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C. IKE Issues
1.
Formats of payload contents_
2.
Cert Request is optional instead of mandatory
3.
Other...
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D. Copyright Statement
Copyright (C) The Internet Society 1999. All Rights Reserved.
This document and translations of it may be copied and furnished
to others, and derivative works that comment on or otherwise
explain it or assist in its implementation may be prepared,
copied, published and distributed, in whole or in part, without
restriction of any kind, provided that the above copyright notice
and this paragraph are included on all such copies and derivative
works. However, this document itself may not be modified in any
way, such as by removing the copyright notice or references to
the Internet Society or other Internet organisations, except as
needed for the purpose of developing Internet standards in which
case the procedures for copyrights defined in the Internet
Standards process shall be followed, or as required to translate
it into languages other than English.
The limited permissions granted above are perpetual and will not
be revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on
an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE
OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY
IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
PURPOSE.
This draft expires 31 November 1999.
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