Cisco IOS XE Security Configuration Guide: Secure Connectivity, Release 2

Configuring Authorization and Revocation of Certificates in a PKI

This module describes how to configure authorization and revocation of certificates in a public key infrastructure (PKI).

Finding Feature Information

For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Certificate Authorization and Revocation" section.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for Authorization and Revocation of Certificates

•Information About Authorization and Revocation of Certificates

•How to Configure Authorization and Revocation of Certificates for Your PKI

•Configuration Examples for Setting Up Authorization and Revocation of Certificates

•Additional References

•Feature Information for Certificate Authorization and Revocation

Prerequisites for Authorization and Revocation of Certificates

Plan Your PKI Strategy

Tip It is strongly recommended that you plan your entire PKI strategy before you begin to deploy actual certificates.

Authorization and revocation can occur only after you or a network administrator have completed the following tasks:

•Configured the certification authority (CA).

•Enrolled peer devices with the CA.

•Identified and configured the protocol (such as IP Security [IPsec] or secure socket layer [SSL]) that is to be used for peer-to-peer communication.

You should decide which authorization and revocation strategy you are going to configure before enrolling peer devices because the peer device certificates might have to contain authorization and revocation-specific information.

"crypto ca" to "crypto pki" CLI Change

All commands that begin as "crypto ca" have been changed to begin as "crypto pki." Although the router will still accept crypto ca commands, all output will be read back as crypto pki.

Information About Authorization and Revocation of Certificates

•PKI Authorization

•PKI and AAA Server Integration for Certificate Status

•CRLs or OCSP Server: Choosing a Certificate Revocation Mechanism

•When to Use Certificate-Based ACLs for Authorization or Revocation

•PKI Certificate Chain Validation

•PKI High Availability Support

PKI Authorization

PKI authentication does not provide authorization. Current solutions for authorization are specific to the router that is being configured, although a centrally managed solution is often required.

There is not a standard mechanism by which certificates are defined as authorized for some tasks and not for others. This authorization information can be captured in the certificate itself if the application is aware of the certificate-based authorization information. But this solution does not provide a simple mechanism for real-time updates to the authorization information and forces each application to be aware of the specific authorization information embedded in the certificate.

When the certificate-based ACL mechanism is configured as part of the trustpoint authentication, the application is no longer responsible for determining this authorization information, and it is no longer possible to specify for which application the certificate is authorized. In some cases, the certificate-based ACL on the router gets so large that it cannot be managed. Additionally, it is beneficial to retrieve certificate-based ACL indications from an external server. (For more information on using certificate-based ACLs for authentication, see the section "When to Use Certificate-Based ACLs for Authorization or Revocation.")

Current solutions to the real-time authorization problem involve specifying a new protocol and building a new server (with associated tasks, such as management and data distribution).

PKI and AAA Server Integration for Certificate Status

Integrating your PKI with an authentication, authorization, and accounting (AAA) server provides an alternative online certificate status solution that leverages the existing AAA infrastructure. Certificates can be listed in the AAA database with appropriate levels of authorization. For components that do not explicitly support PKI-AAA, a default label of "all" from the AAA server provides authorization. Likewise, a label of "none" from the AAA database indicates that the specified certificate is not valid. (The absence of any application label is equivalent, but "none" is included for completeness and clarity). If the application component does support PKI-AAA, the component may be specified directly; for example, the application component could be "ipsec," "ssl," or "osp." (ipsec=IP Security, ssl=Secure Sockets Layer, and osp=Open Settlement Protocol.)

Note•Currently, no application component supports specification of the application label.

•There may be a time delay when accessing the AAA server. If the AAA server is not available, the authorization fails.

RADIUS or TACACS+: Choosing a AAA Server Protocol

The AAA server can be configured to work with either the RADIUS or TACACS+ protocol. When you are configuring the AAA server for the PKI integration, you must set the RADIUS or TACACS attributes that are required for authorization.

If the RADIUS protocol is used, the password that is configured for the username in the AAA server should be set to "cisco," which is acceptable because the certificate validation provides authentication and the AAA database is only being used for authorization. When the TACACS protocol is used, the password that is configured for the username in the AAA server is irrelevant because TACACS supports authorization without requiring authentication (the password is used for authentication).

In addition, if you are using TACACS, you must add a PKI service to the AAA server. The custom attribute "cert-application=all" is added under the PKI service for the particular user or usergroup to authorize the specific username.

Attribute-Value Pairs for PKI and AAA Server Integration

Table 1 lists the attribute-value (AV) pairs that are to be used when setting up PKI integration with a AAA server. (Note the values shown in the table are possible values.) The AV pairs must match the client configuration. If they do not match, the peer certificate is not authorized.

Note Users can sometimes have AV pairs that are different from those of every other user. As a result, a unique username is required for each user. The all parameter (within the authorization username command) specifies that the entire subject name of the certificate will be used as the authorization username.

CRLs or OCSP Server: Choosing a Certificate Revocation Mechanism

After a certificate is validated as a properly signed certificate, a certificate revocation method is performed to ensure that the certificate has not been revoked by the issuing CA. Cisco IOS XE software supports two revocation mechanisms—certificate revocation lists (CRLs) and Online Certificate Status Protocol (OCSP). (Cisco IOS XE software also supports AAA integration for certificate checking; however, additional authorization functionality is included. For more information on PKI and AAA certificate authorization and status check, see the section "PKI and AAA Server Integration for Certificate Status.")

The following sections explain how each revocation mechanism works:

•What Is a CRL?

•What Is OCSP?

What Is a CRL?

A certificate revocation list (CRL) is a list of revoked certificates. The CRL is created and digitally signed by the CA that originally issued the certificates. The CRL contains dates for when each certificate was issued and when it expires.

CAs publish new CRLs periodically or when a certificate for which the CA is responsible has been revoked. By default, a new CRL will be downloaded after the currently cached CRL expires. An administrator may also configure the duration for which CRLs are cached in router memory or disable CRL caching completely. The CRL caching configuration will apply to all CRLs associated with a trustpoint.

When the CRL expires, the router deletes it from its cache. A new CRL is downloaded when a certificate is presented for verification; however, if a newer version of the CRL that lists the certificate under examination is on the server but the router is still using the CRL in its cache, the router will not know that the certificate has been revoked. The certificate will pass the revocation check even though it should have been denied.

When a CA issues a certificate, the CA can include in the certificate the CRL distribution point (CDP) for that certificate. Cisco IOS XE client devices use CDPs to locate and load the correct CRL. The Cisco IOS XE client supports multiple CDPs, but the Cisco IOS XE CA currently supports only one CDP; however, third-party vendor CAs may support multiple CDPs or different CDPs per certificate. If a CDP is not specified in the certificate, the client device will use the default Simple Certificate Enrollment Protocol (SCEP) method to retrieve the CRL. (The CDP location can be specified via the cdp-url command.)

When implementing CRLs, you should consider the following design considerations:

•CRL lifetimes and the security association (SA) and Internet Key Exchange (IKE) lifetimes

The CRL lifetime determines the length of time between CA-issued updates to the CRL. (The default CRL lifetime value, which is 168 hours [1 week], can be changed via the lifetime crl command.)

•The method and location of the CDP

–The method determines how the CRL is retrieved; some possible choices include HTTP, Lightweight Directory Access Protocol (LDAP), SCEP, or TFTP.

HTTP, TFTP, and LDAP are the most commonly used methods. Although Cisco IOS XE software defaults to SCEP, an HTTP CDP is recommended for large installations using CRLs because HTTP can be made highly scalable.

–The location determines from where the CRL is retrieved; for example, you can specify the server and file path from which to retrieve the CRL.

Querying All CDPs During Revocation Check

When a CDP server does not respond to a request, the Cisco IOS XE software reports an error, which may result in the peer's certificate being rejected. To prevent a possible certificate rejection and if there are multiple CDPs in a certificate, the Cisco IOS XE software will attempt to use the CDPs in the order in which they appear in the certificate. The router will attempt to retrieve a CRL using each CDP URL or directory specification. If an error occurs using a CDP, an attempt will be made using the next CDP.

Tip Although the Cisco IOS XE software will make every attempt to obtain the CRL from one of the indicated CDPs, it is recommended that you use an HTTP CDP server with high-speed redundant HTTP servers to avoid application timeouts because of slow CDP responses.

What Is OCSP?

OCSP is an online mechanism that is used to determine certificate validity and provides the following flexibility as a revocation mechanism:

•OCSP can provide real-time certificate status checking.

•OCSP allows the network administrator to specify a central OCSP server, which can service all devices within a network.

•OCSP also allows the network administrator the flexibility to specify multiple OCSP servers, either per client certificate or per group of client certificates.

•OCSP server validation is usually based on the root CA certificate or a valid subordinate CA certificate, but may also be configured so that external CA certificates or self-signed certificates may be used. Using external CA certificates or self-signed certificates allows the OCSP servers certificate to be issued and validated from an alternative PKI hierarchy.

A network administrator can configure an OCSP server to collect and update CRLs from different CA servers. The devices within the network can rely on the OCSP server to check the certificate status without retrieving and caching each CRL for every peer. When peers have to check the revocation status of a certificate, they send a query to the OCSP server that includes the serial number of the certificate in question and an optional unique identifier for the OCSP request, or a nonce. The OCSP server holds a copy of the CRL to determine if the CA has listed the certificate as being revoked; the server then responds to the peer including the nonce. If the nonce in the response from the OCSP server does not match the original nonce sent by the peer, the response is considered invalid and certificate verification fails. The dialog between the OCSP server and the peer consumes less bandwidth than most CRL downloads.

If the OCSP server is using a CRL, CRL time limitations will be applicable; that is, a CRL that is still valid might be used by the OCSP server although a new CRL has been issued by the CRL containing additional certificate revocation information. Because fewer devices are downloading the CRL information on a regular basis, you can decrease the CRL lifetime value or configure the OCSP server not to cache the CRL. For more information, check your OCSP server documentation.

When to Use an OCSP Server

OCSP may be more appropriate than CRLs if your PKI has any of the following characteristics:

•Real-time certificate revocation status is necessary. CRLs are updated only periodically and the latest CRL may not always be cached by the client device. For example, if a client does not yet have the latest CRL cached and a newly revoked certificate is being checked, that revoked certificate will successfully pass the revocation check.

•There are a large number of revoked certificates or multiple CRLs. Caching a large CRL consumes large portions of Cisco IOS XE memory and may reduce resources available to other processes.

•CRLs expire frequently, causing the CDP to handle a larger load of CRLs.

Note An administrator may configure CRL caching, either by disabling CRL caching completely or setting a maximum lifetime for a cached CRL per trustpoint.

When to Use Certificate-Based ACLs for Authorization or Revocation

Certificates contain several fields that are used to determine whether a device or user is authorized to perform a specified action.

Because certificate-based ACLs are configured on the device, they do not scale well for large numbers of ACLs; however, certificate-based ACLs do provide very granular control of specific device behavior. Certificate-based ACLs are also leveraged by additional features to help determine when PKI components such as revocation, authorization, or a trustpoint should be used. They provide a general mechanism allowing users to select a specific certificate or a group of certificates that are being validated for either authorization or additional processing.

Certificate-based ACLs specify one or more fields within the certificate and an acceptable value for each specified field. You can specify which fields within a certificate should be checked and which values those fields may or may not have.

There are six logical tests for comparing the field with the value—equal, not equal, contains, does not contain, less than, and greater than or equal. If more than one field is specified within a single certificate-based ACL, the tests of all of the fields within the ACL must succeed to match the ACL. The same field may be specified multiple times within the same ACL. More than one ACL may be specified, and ACL will be processed in turn until a match is found or all of the ACLs have been processed.

Ignore Revocation Checks Using a Certificate-Based ACL

Certificate-based ACLs can be configured to instruct your router to ignore the revocation check and expired certificates of a valid peer. Thus, a certificate that meets the specified criteria can be accepted regardless of the validity period of the certificate, or if the certificate meets the specified criteria, revocation checking does not have to be performed. You can also use a certificate-based ACL to ignore the revocation check when the communication with a AAA server is protected with a certificate.

Ignoring Revocation Lists

To allow a trustpoint to enforce CRLs except for specific certificates, enter the match certificate command with the skip revocation-check keyword. This type of enforcement is most useful in a hub-and-spoke configuration in which you also want to allow direct spoke-to-spoke connections. In pure hub-and-spoke configurations, all spokes connect only to the hub, so CRL checking is necessary only on the hub. For one spoke to communicate directly with another spoke, the match certificate command with the skip revocation-check keyword can be used for neighboring peer certificates instead of requiring a CRL on each spoke.

Ignoring Expired Certificates

To configure your router to ignore expired certificates, enter the match certificate command with the allow expired-certificate keyword. This command has the following purposes:

•If the certificate of a peer has expired, this command may be used to "allow" the expired certificate until the peer can obtain a new certificate.

•If your router clock has not yet been set to the correct time, the certificate of a peer will appear to be not yet valid until the clock is set. This command may be used to allow the certificate of the peer even though your router clock is not set.

Note•If Network Time Protocol (NTP) is available only via the IPSec connection (usually via the hub in a hub-and-spoke configuration), the router clock can never be set. The tunnel to the hub cannot be "brought up" because the certificate of the hub is not yet valid.

•"Expired" is a generic term for a certificate that is expired or that is not yet valid. The certificate has a start and end time. An expired certificate, for purposes of the ACL, is one for which the current time of the router is outside the start and end times specified in the certificate.

Skipping the AAA Check of the Certificate

If the communication with an AAA server is protected with a certificate, and you want to skip the AAA check of the certificate, use the match certificate command with the skip authorization-check keyword. For example, if a virtual private network (VPN) tunnel is configured so that all AAA traffic goes over that tunnel, and the tunnel is protected with a certificate, you can use the match certificate command with the skip authorization-check keyword to skip the certificate check so that the tunnel can be established.

The match certificate command and the skip authorization-check keyword should be configured after PKI integration with an AAA server is configured.

Note If the AAA server is available only via an IPSec connection, the AAA server cannot be contacted until after the IPSec connection is established. The IPSec connection cannot be "brought up" because the certificate of the AAA server is not yet valid.

PKI Certificate Chain Validation

A certificate chain establishes a sequence of trusted certificates —from a peer certificate to the root CA certificate. Within a PKI hierarchy, all enrolled peers can validate the certificate of one another if the peers share a trusted root CA certificate or a common subordinate CA. Each CA corresponds to a trustpoint.

When a certificate chain is received from a peer, the default processing of a certificate chain path continues until the first trusted certificate, or trustpoint, is reached. In Cisco IOS XE Release 2.1 and later releases, an administrator may configure the level to which a certificate chain is processed on all certificates including subordinate CA certificates.

Configuring the level to which a certificate chain is processed allows for the reauthentication of trusted certificates, the extension of a trusted certificate chain, and the completion of a certificate chain that contains a gap.

Reauthentication of Trusted Certificates

The default behavior is for the router to remove any trusted certificates from the certificate chain sent by the peer before the chain is validated. An administrator may configure certificate chain path processing so that the router does not remove CA certificates that are already trusted before chain validation, so that all certificates in the chain are re-authenticated for the current session.

Extending the Trusted Certificate Chain

The default behavior is for the router to use its trusted certificates to extend the certificate chain if there are any missing certificates in the certificate chain sent by the peer. The router will validate only certificates in the chain sent by the peer. An administrator may configure certificate chain path processing so that the certificates in the peer's certificate chain and the router's trusted certificates are validated to a specified point.

Completing Gaps in a Certificate Chain

An administrator may configure certificate chain processing so that if there is a gap in the configured Cisco IOS XE trustpoint hierarchy, certificates sent by the peer can be used to complete the set of certificates to be validated.

Note If the trustpoint is configured to require parent validation and the peer does not provide the full certificate chain, the gap cannot be completed and the certificate chain is rejected and invalid.

Note It is a configuration error if the trustpoint is configured to require parent validation and there is no parent trustpoint configured. The resulting certificate chain gap cannot be completed and the subordinate CA certificate cannot be validated. The certificate chain is invalid.

PKI High Availability Support

High Availability (HA) support is provided for the client-side PKI only. There is no CA server support. Route processor to route processor redundancy and Stateful Switchover (SSO) are supported.

In Service Software Upgrade (ISSU) and box-to-box HA are not supported.

How to Configure Authorization and Revocation of Certificates for Your PKI

This section contains the following procedures:

•Configuring PKI Integration with a AAA Server

•Configuring a Revocation Mechanism for PKI Certificate Status Checking

•Configuring Certificate Authorization and Revocation Settings

•Configuring Certificate Chain Validation

Configuring PKI Integration with a AAA Server

Perform this task to generate a AAA username from the certificate presented by the peer and specify which fields within a certificate should be used to build the AAA database username.

Restrictions When Using the Entire Subject Name for PKI Authorization

The following restrictions should be considered when using the all keyword as the subject name for the authorization username command:

•Some AAA servers limit the length of the username (for example, to 64 characters). As a result, the entire certificate subject name cannot be longer than the limitation of the server.

•Some AAA servers limit the available character set that may be used for the username (for example, a space [ ] and an equal sign [=] may not be acceptable). You cannot use the all keyword for a AAA server having such a character-set limitation.

•The subject-name command in the trustpoint configuration may not always be the final AAA subject name. If the fully qualified domain name (FQDN), serial number, or IP address of the router are included in a certificate request, the subject name field of the issued certificate will also have these components. To turn off the components, use the fqdn, serial-number, and ip-address commands with the none keyword.

•CA servers sometimes change the requested subject name field when they issue a certificate. For example, CA servers of some vendors switch the relative distinguished names (RDNs) in the requested subject names to the following order: CN, OU, O, L, ST, and C. However, another CA server might append the configured LDAP directory root (for example, O=cisco.com) to the end of the requested subject name.

•Depending on the tools you choose for displaying a certificate, the printed order of the RDNs in the subject name could be different. Cisco IOS XE software always displays the least significant RDN first, but other software, such as Open Source Secure Socket Layer (OpenSSL), does the opposite. Therefore, if you are configuring a AAA server with a full distinguished name (DN) (subject name) as the corresponding username, ensure that the Cisco IOS XE software style (that is, with the least significant RDN first) is used.

SUMMARY STEPS

1. enable

2. configure terminal

3. aaa new-model

4. aaa authorization network listname [method]

5. crypto pki trustpoint name

6. enrollment url url

7. revocation-check method

8. exit

9. authorization username subjectname subjectname

10. authorization list listname

11. tacacs-server host hostname [key string]

       or

       radius-server host hostname [key string]

DETAILED STEPS

Troubleshooting Tips

To display debug messages for the trace of interaction (message type) between the CA and the router, use the debug crypto pki transactions command. (See the sample output, which shows a successful PKI integration with AAA server exchange and a failed PKI integration with AAA server exchange.)

Successful Exchange

Router# debug crypto pki transactions

Apr 22 23:15:03.695: CRYPTO_PKI: Found a issuer match

Apr 22 23:15:03.955: CRYPTO_PKI: cert revocation status unknown.

Apr 22 23:15:03.955: CRYPTO_PKI: Certificate validated without revocation check

Each line that shows "CRYPTO_PKI_AAA" indicates the state of the AAA authorization checks. Each of the AAA AV pairs is indicated, and then the results of the authorization check are shown.

Apr 22 23:15:04.019: CRYPTO_PKI_AAA: checking AAA authorization (ipsecca_script_aaalist, 
PKIAAA-L, <all>)

Apr 22 23:15:04.503: CRYPTO_PKI_AAA: reply attribute ("cert-application" = "all")

Apr 22 23:15:04.503: CRYPTO_PKI_AAA: reply attribute ("cert-trustpoint" = "CA1")

Apr 22 23:15:04.503: CRYPTO_PKI_AAA: reply attribute ("cert-serial" = "15DE")

Apr 22 23:15:04.503: CRYPTO_PKI_AAA: authorization passed

Apr 22 23:12:30.327: CRYPTO_PKI: Found a issuer match

Failed Exchange

Router# debug crypto pki transactions

Apr 22 23:11:13.703: CRYPTO_PKI_AAA: checking AAA authorization =

Apr 22 23:11:14.203: CRYPTO_PKI_AAA: reply attribute ("cert-application" = "all")

Apr 22 23:11:14.203: CRYPTO_PKI_AAA: reply attribute ("cert-trustpoint"= "CA1")

Apr 22 23:11:14.203: CRYPTO_PKI_AAA: reply attribute ("cert-serial" = "233D")

Apr 22 23:11:14.203: CRYPTO_PKI_AAA: parsed cert-lifetime-end as: 21:30:00

Apr 22 23:11:14.203: CRYPTO_PKI_AAA: timezone specific extended

Apr 22 23:11:14.203: CRYPTO_PKI_AAA: cert-lifetime-end is expired

Apr 22 23:11:14.203: CRYPTO_PKI_AAA: cert-lifetime-end check failed.

Apr 22 23:11:14.203: CRYPTO_PKI_AAA: authorization failed

In the above failed exchange, the certificate has expired.

Configuring a Revocation Mechanism for PKI Certificate Status Checking

Perform this task to set up a CRL as the certificate revocation mechanism—CRLs or OCSP—that is used to check the status of certificates in a PKI.

The revocation-check Command

Use the revocation-check command to specify at least one method (OCSP, CRL, or skip the revocation check) that is to be used to ensure that the certificate of a peer has not been revoked. For multiple methods, the order in which the methods are applied is determined by the order specified via this command.

If your router does not have the applicable CRL and is unable to obtain one or if the OCSP server returns an error, your router will reject the peer's certificate—unless you include the none keyword in your configuration. If the none keyword is configured, a revocation check will not be performed and the certificate will always be accepted.

Nonces and Peer Communications with OCSP Servers

When using OCSP, nonces, unique identifiers for OCSP requests, are sent by default during peer communications with your OCSP server. The use of nonces offers a more secure and reliable communication channel between the peer and OCSP server.

If your OCSP server does not support nonces, you may disable the sending of nonces. For more information, check your OCSP server documentation.

Prerequisites

•Before issuing any client certificates, the appropriate settings on the server (such as setting the CDP) should be configured.

•When configuring an OCSP server to return the revocation status for a CA server, the OCSP server must be configured with an OCSP response signing certificate that is issued by that CA server. Ensure that the signing certificate is in the correct format, or the router will not accept the OCSP response. See your OCSP manual for additional information.

Restrictions

•OCSP transports messages over HTTP, so there may be a time delay when you access the OCSP server.

•If the OCSP server depends on normal CRL processing to check revocation status, the same time delay that affects CRLs will also apply to OCSP.

SUMMARY STEPS

1. enable

2. configure terminal

3. crypto pki trustpoint name

4. ocsp url url

5. revocation-check method1 [method2 [method3]]

6. ocsp disable-nonce

7. exit

8. exit

9. show crypto pki certificates

10. show crypto pki trustpoints [status | label [status]]

DETAILED STEPS

Configuring Certificate Authorization and Revocation Settings

Perform this task to specify a certificate-based ACL, to ignore revocation checks or expired certificates, to manually override the default CDP location, to manually override the OCSP server setting, to configure CRL caching, or to set session acceptance or rejection based on a certificate serial number, as appropriate.

Configuring Certificate-Based ACLs to Ignore Revocation Checks

To configure your router to use certificate-based ACLs to ignore revocation checks and expired certificates, perform the following steps:

•Identify an existing trustpoint or create a new trustpoint to be used when verifying the certificate of the peer. Authenticate the trustpoint if it has not already been authenticated. The router may enroll with this trustpoint if you want. Do not set optional CRLs for the trustpoint if you plan to use the match certificate command and skip revocation-check keyword.

•Determine the unique characteristics of the certificates that should not have their CRL checked and of the expired certificates that should be allowed.

•Define a certificate map to match the characteristics identified in the prior step.

•You can add the match certificate command and skip revocation-check keyword and the match certificate command and allow expired-certificate keyword to the trustpoint that was created or identified in the first step.

Note Certificate maps are checked even if the peer's public key is cached. For example, when the public key is cached by the peer, and a certificate map is added to the trustpoint to ban a certificate, the certificate map is effective. This prevents a client with the banned certificate, which was once connected in the past, from reconnecting.

Manually Overriding CDPs in a Certificate

Users can override the CDPs in a certificate with a manually configured CDP. Manually overriding the CDPs in a certificate can be advantageous when a particular server is unavailable for an extended period of time. The certificate's CDPs can be replaced with a URL or directory specification without reissuing all of the certificates that contain the original CDP.

Manually Overriding the OCSP Server Setting in a Certificate

Administrators can override the OCSP server setting specified in the Authority Information Access (AIA) field of the client certificate or set by the issuing the ocsp url command. One or more OCSP servers may be manually specified, either per client certificate or per group of client certificates by the match certificate override ocsp command. The match certificate override ocsp command overrides the client certificate AIA field or the ocsp url command setting if a client certificate is successfully matched to a certificate map during the revocation check.

Note Only one OCSP server can be specified per client certificate.

Configuring CRL Cache Control

By default, a new CRL will be downloaded after the currently cached CRL expires. Administrators can either configure the maximum amount of time in minutes a CRL remains in the cache by issuing the crl cache delete-after command or disable CRL caching by issuing the crl cache none command. Only the crl-cache delete-after command or the crl-cache none command may be specified. If both commands are entered for a trustpoint, the last command executed will take effect and a message will be displayed.

Neither the crl-cache none command nor the crl-cache delete-after command affects the currently cached CRL. If you configure the crl-cache none command, all CRLs downloaded after this command is issued will not be cached. If you configure the crl-cache delete-after command, the configured lifetime will only affect CRLs downloaded after this command is issued.

This functionality is useful is when a CA issues CRLs with no expiration date or with expiration dates days or weeks ahead.

Configuring Certificate Serial Number Session Control

A certificate serial number can be specified to allow a certificate validation request to be accepted or rejected by the trustpoint for a session. A session may be rejected, depending on certificate serial number session control, even if a certificate is still valid. Certificate serial number session control may be configured by using either a certificate map with the serial-number field or an AAA attribute, with the cert-serial-not command.

Using certificate maps for session control allows an administrator to specify a single certificate serial number. Using the AAA attribute allows an administrator to specify one or more certificate serial numbers for session control.

Prerequisites

•The trustpoint should be defined and authenticated before attaching certificate maps to the trustpoint.

•The certificate map must be configured before the CDP override feature can be enabled or the serial-number command is issued.

•The PKI and AAA server integration must be successfully completed to use AAA attributes as described in "PKI and AAA Server Integration for Certificate Status."

SUMMARY STEPS

1. enable

2. configure terminal

3. crypto pki certificate map label sequence-number

4. field-name match-criteria match-value

5. exit

6. crypto pki trustpoint name

7. crl-cache none

or

crl-cache delete-after time

8. match certificate certificate-map-label [allow expired-certificate | skip revocation-check | skip authorization-check]

9. match certificate certificate-map-label override cdp {url | directory} string

10. match certificate certificate-map-label override ocsp [trustpoint trustpoint-label] sequence-number url ocsp-url

11. exit

12. aaa new-model

13. aaa attribute list list-name

14. attribute type name label

15. exit

16. exit

17. show crypto pki certificates

DETAILED STEPS

Examples

The following is a sample certificate. The OCSP-related extensions are shown using exclamation points.

Certificate:

        Data:

            Version: v3

            Serial Number:0x14

            Signature Algorithm:MD5withRSA - 1.2.840.113549.1.1.4

            Issuer:CN=CA server,OU=PKI,O=Cisco Systems

            Validity:

                Not Before:Thursday, August 8, 2002 4:38:05 PM PST

                Not After:Tuesday, August 7, 2003 4:38:05 PM PST

            Subject:CN=OCSP server,OU=PKI,O=Cisco Systems

            Subject Public Key Info:

                Algorithm:RSA - 1.2.840.113549.1.1.1

                Public Key:

                    Exponent:65537

                    Public Key Modulus:(1024 bits) :

                        <snip>

            Extensions:

                Identifier:Subject Key Identifier - 2.5.29.14

                    Critical:no 

                    Key Identifier:

                        <snip>

                Identifier:Authority Key Identifier - 2.5.29.35

                    Critical:no 

                    Key Identifier:

                        <snip>

!                Identifier:OCSP NoCheck:- 1.3.6.1.5.5.7.48.1.5

                     Critical:no 

                Identifier:Extended Key Usage:- 2.5.29.37

                     Critical:no 

                     Extended Key Usage:

                     OCSPSigning

!

                Identifier:CRL Distribution Points - 2.5.29.31

                    Critical:no 

                    Number of Points:1

                    Point 0

                        Distribution Point:

[URIName:ldap://CA-server/CN=CA server,OU=PKI,O=Cisco Systems]

        Signature:

            Algorithm:MD5withRSA - 1.2.840.113549.1.1.4

            Signature:

            <snip>

The following example shows an excerpt of the running configuration output when adding a match certificate override ocsp command to the beginning of an existing sequence:

match certificate map3 override ocsp 5 url http://192.0.2.3/

show running-configuration 

.

.

.

        match certificate map3 override ocsp 5 url http://192.0.2.3/ 

        match certificate map1 override ocsp 10 url http://192.0.2.1/ 

        match certificate map2 override ocsp 15 url http://192.0.2.2/

The following example shows an excerpt of the running configuration output when an existing match certificate override ocsp command is replaced and a trustpoint is specified to use an alternative PKI hierarchy:

match certificate map4 override ocsp trustpoint tp4 10 url http://192.0.2.4/newvalue

show running-configuration

.

.

.

        match certificate map3 override ocsp trustpoint tp3 5 url http://192.0.2.3/ 

        match certificate map1 override ocsp trustpoint tp1 10 url http://192.0.2.1/ 

        match certificate map4 override ocsp trustpoint tp4 10 url 
              http://192.0.2.4/newvalue 

        match certificate map2 override ocsp trustpoint tp2 15 url http://192.0.2.2/ 

Troubleshooting Tips

If you ignored revocation check or expired certificates, you should carefully check your configuration. Verify that the certificate map properly matches either the certificate or certificates that should be allowed or the AAA checks that should be skipped. In a controlled environment, try modifying the certificate map and determine what is not working as expected.

Configuring Certificate Chain Validation

Perform this task to configure the processing level for the certificate chain path of your peer certificates.

Prerequisites

•The device must be enrolled in your PKI hierarchy.

•The appropriate key pair must be associated with the certificate.

Restrictions

•A trustpoint associated with the root CA cannot be configured to be validated to the next level.

The chain-validation command is configured with the continue keyword for the trustpoint associated with the root CA, an error message will be displayed and the chain validation will revert to the default chain-validation command setting.

SUMMARY STEPS

1. enable

2. configure terminal

3. crypto pki trustpoint name

4. chain-validation [{stop | continue} [parent-trustpoint]]

5. exit

DETAILED STEPS

Configuration Examples for Setting Up Authorization and Revocation of Certificates

•Examples: Configuring and Verifying PKI AAA Authorization

•Examples: Configuring a Revocation Mechanism

•Example: Configuring a Hub Router at a Central Site for Certificate Revocation Checks

•Examples: Configuring Certificate Authorization and Revocation Settings

•Examples: Configuring Certificate Chain Validation

Examples: Configuring and Verifying PKI AAA Authorization

•Example: Router Configuration

•Example: Debug of a Successful PKI AAA Authorization

•Example: Debugs of a Failed PKI AAA Authorization

Example: Router Configuration

The following show running-config command output shows the working configuration of a router that is set up to authorize VPN connections using the PKI Integration with AAA Server feature:

Router# show running-config 

Building configuration...

!

version 12.3

!

hostname router7200router7200

!

aaa new-model

!

!

aaa authentication login default group tacacs+

aaa authentication login no_tacacs enable

aaa authentication ppp default group tacacs+

aaa authorization exec ACSLab group tacacs+

aaa authorization network ACSLab group tacacs+

aaa accounting exec ACSLab start-stop group tacacs+

aaa accounting network default start-stop group ACSLab

aaa session-id common

!

ip domain name example.com

!

crypto pki trustpoint EM-CERT-SERV

 enrollment url http://192.0.2.33:80

 serial-number

 crl optional

 rsakeypair STOREVPN 1024

 auto-enroll

 authorization list ACSLab

!

crypto pki certificate chain EM-CERT-SERV

 certificate 04

  30820214 3082017D A0030201 02020104 300D0609 2A864886 F70D0101 04050030

  17311530 13060355 0403130C 454D2D43 4552542D 53455256 301E170D 30343031

  31393232 30323535 5A170D30 35303131 38323230 3235355A 3030312E 300E0603

  55040513 07314437 45424434 301C0609 2A864886 F70D0109 02160F37 3230302D

  312E6772 696C2E63 6F6D3081 9F300D06 092A8648 86F70D01 01010500 03818D00

  30818902 818100BD F3B837AA D925F391 2B64DA14 9C2EA031 5A7203C4 92F8D6A8

  7D2357A6 BCC8596F A38A9B10 47435626 D59A8F2A 123195BB BE5A1E74 B1AA5AE0

  5CA162FF 8C3ACA4F B3EE9F27 8B031642 B618AE1B 40F2E3B4 F996BEFE 382C7283

  3792A369 236F8561 8748AA3F BC41F012 B859BD9C DB4F75EE 3CEE2829 704BD68F

  FD904043 0F555702 03010001 A3573055 30250603 551D1F04 1E301C30 1AA018A0

  16861468 7474703A 2F2F3633 2E323437 2E313037 2E393330 0B060355 1D0F0404

  030205A0 301F0603 551D2304 18301680 1420FC4B CF0B1C56 F5BD4C06 0AFD4E67

  341AE612 D1300D06 092A8648 86F70D01 01040500 03818100 79E97018 FB955108

  12F42A56 2A6384BC AC8E22FE F1D6187F DA5D6737 C0E241AC AAAEC75D 3C743F59

  08DEEFF2 0E813A73 D79E0FA9 D62DC20D 8E2798CD 2C1DC3EC 3B2505A1 3897330C

  15A60D5A 8A13F06D 51043D37 E56E45DF A65F43D7 4E836093 9689784D C45FD61D

  EC1F160C 1ABC8D03 49FB11B1 DA0BED6C 463E1090 F34C59E4

  quit

 certificate ca 01

  30820207 30820170 A0030201 02020101 300D0609 2A864886 F70D0101 04050030

  17311530 13060355 0403130C 454D2D43 4552542D 53455256 301E170D 30333132

  31363231 34373432 5A170D30 36313231 35323134 3734325A 30173115 30130603

  55040313 0C454D2D 43455254 2D534552 5630819F 300D0609 2A864886 F70D0101

  01050003 818D0030 81890281 8100C14D 833641CF D784F516 DA6B50C0 7B3CB3C9

  589223AB 99A7DC14 04F74EF2 AAEEE8F5 E3BFAE97 F2F980F7 D889E6A1 2C726C69

  54A29870 7E7363FF 3CD1F991 F5A37CFF 3FFDD3D0 9E486C44 A2E34595 C2D078BB

  E9DE981E B733B868 AA8916C0 A8048607 D34B83C0 64BDC101 161FC103 13C06500

  22D6EE75 7D6CF133 7F1B515F 32830203 010001A3 63306130 0F060355 1D130101

  FF040530 030101FF 300E0603 551D0F01 01FF0404 03020186 301D0603 551D0E04

  16041420 FC4BCF0B 1C56F5BD 4C060AFD 4E67341A E612D130 1F060355 1D230418

  30168014 20FC4BCF 0B1C56F5 BD4C060A FD4E6734 1AE612D1 300D0609 2A864886

  F70D0101 04050003 81810085 D2E386F5 4107116B AD3AC990 CBE84063 5FB2A6B5

  BD572026 528E92ED 02F3A0AE 1803F2AE AA4C0ED2 0F59F18D 7B50264F 30442C41

  0AF19C4E 70BD3CB5 0ADD8DE8 8EF636BD 24410DF4 DB62DAFC 67DA6E58 3879AA3E

  12AFB1C3 2E27CB27 EC74E1FC AEE2F5CF AA80B439 615AA8D5 6D6DEDC3 7F9C2C79

  3963E363 F2989FB9 795BA8

  quit

!

!

crypto isakmp policy 10

 encr 3des

 group 2

!

!

crypto ipsec transform-set ISC_TS_1 esp-3des esp-sha-hmac

!

crypto ipsec profile ISC_IPSEC_PROFILE_2

 set security-association lifetime kilobytes 530000000

 set security-association lifetime seconds 14400

 set transform-set ISC_TS_1

!

!

controller ISA 1/1

!

!

interface Tunnel0

 description MGRE Interface provisioned by ISC

 bandwidth 10000

 ip address 192.0.2.172 255.255.255.0

 no ip redirects

 ip mtu 1408

 ip nhrp map multicast dynamic

 ip nhrp network-id 101

 ip nhrp holdtime 500

 ip nhrp server-only

 no ip split-horizon eigrp 101

 tunnel source FastEthernet2/1

 tunnel mode gre multipoint

 tunnel key 101

 tunnel protection ipsec profile ISC_IPSEC_PROFILE_2

!

interface FastEthernet2/0

 ip address 192.0.2.1 255.255.255.0

 duplex auto

 speed auto

!

interface FastEthernet2/1

 ip address 192.0.2.2 255.255.255.0

 duplex auto

 speed auto

!

!

tacacs-server host 192.0.2.55 single-connection

tacacs-server directed-request

tacacs-server key company lab

!

ntp master 1

!

end

Example: Debug of a Successful PKI AAA Authorization

The following show debugging command output shows a successful authorization using the PKI Integration with AAA Server feature:

Router# show debugging

General OS:

  TACACS access control debugging is on

  AAA Authentication debugging is on

  AAA Authorization debugging is on

Cryptographic Subsystem:

Crypto PKI Trans debugging is on

Router#

May 28 19:36:11.117: CRYPTO_PKI: Trust-Point EM-CERT-SERV picked up

May 28 19:36:12.789: CRYPTO_PKI: Found a issuer match

May 28 19:36:12.805: CRYPTO_PKI: cert revocation status unknown.

May 28 19:36:12.805: CRYPTO_PKI: Certificate validated without revocation check

May 28 19:36:12.813: CRYPTO_PKI_AAA: checking AAA authorization (ACSLab, POD5.example.com, 
<all>)

May 28 19:36:12.813: AAA/BIND(00000042): Bind i/f  

May 28 19:36:12.813: AAA/AUTHOR (0x42): Pick method list 'ACSLab'

May 28 19:36:12.813: TPLUS: Queuing AAA Authorization request 66 for processing

May 28 19:36:12.813: TPLUS: processing authorization request id 66

May 28 19:36:12.813: TPLUS: Protocol set to None .....Skipping

May 28 19:36:12.813: TPLUS: Sending AV service=pki

May 28 19:36:12.813: TPLUS: Authorization request created for 66(POD5.example.com)

May 28 19:36:12.813: TPLUS: Using server 192.0.2.55

May 28 19:36:12.813: TPLUS(00000042)/0/NB_WAIT/203A4628: Started 5 sec timeout

May 28 19:36:12.813: TPLUS(00000042)/0/NB_WAIT: wrote entire 46 bytes request

May 28 19:36:12.813: TPLUS: Would block while reading pak header

May 28 19:36:12.817: TPLUS(00000042)/0/READ: read entire 12 header bytes (expect 27 bytes)

May 28 19:36:12.817: TPLUS(00000042)/0/READ: read entire 39 bytes response

May 28 19:36:12.817: TPLUS(00000042)/0/203A4628: Processing the reply packet

May 28 19:36:12.817: TPLUS: Processed AV cert-application=all

May 28 19:36:12.817: TPLUS: received authorization response for 66: PASS

May 28 19:36:12.817: CRYPTO_PKI_AAA: reply attribute ("cert-application" = "all")

May 28 19:36:12.817: CRYPTO_PKI_AAA: authorization passed

Router#

Router#

May 28 19:36:18.681: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 101: Neighbor 192.0.2.171 (Tunnel0) is 
up: new adjacency

Router#

Router# show crypto isakmp sa

dst             src             state          conn-id slot

192.0.2.22   	 192.0.2.102   QM_IDLE             84    0

Example: Debugs of a Failed PKI AAA Authorization

The following show debugging command output shows that the router is not authorized to connect using VPN. The messages are typical of those that you might see in such a situation.

In this example, the peer username was configured as not authorized, by moving the username to a Cisco Secure ACS group called VPN_Router_Disabled in Cisco Secure ACS. The router, router7200.example.com, has been configured to check with a Cisco Secure ACS AAA server prior to establishing a VPN connection to any peer.

Router# show debugging

General OS:

  TACACS access control debugging is on

  AAA Authentication debugging is on

  AAA Authorization debugging is on

Cryptographic Subsystem:

  Crypto PKI Trans debugging is on

Router#

May 28 19:48:29.837: CRYPTO_PKI: Trust-Point EM-CERT-SERV picked up

May 28 19:48:31.509: CRYPTO_PKI: Found a issuer match

May 28 19:48:31.525: CRYPTO_PKI: cert revocation status unknown.

May 28 19:48:31.525: CRYPTO_PKI: Certificate validated without revocation check

May 28 19:48:31.533: CRYPTO_PKI_AAA: checking AAA authorization (ACSLab, POD5.example.com, 
<all>)

May 28 19:48:31.533: AAA/BIND(00000044): Bind i/f  

May 28 19:48:31.533: AAA/AUTHOR (0x44): Pick method list 'ACSLab'

May 28 19:48:31.533: TPLUS: Queuing AAA Authorization request 68 for processing

May 28 19:48:31.533: TPLUS: processing authorization request id 68

May 28 19:48:31.533: TPLUS: Protocol set to None .....Skipping

May 28 19:48:31.533: TPLUS: Sending AV service=pki

May 28 19:48:31.533: TPLUS: Authorization request created for 68(POD5.example.com)

May 28 19:48:31.533: TPLUS: Using server 192.0.2.55

May 28 19:48:31.533: TPLUS(00000044)/0/NB_WAIT/203A4C50: Started 5 sec timeout

May 28 19:48:31.533: TPLUS(00000044)/0/NB_WAIT: wrote entire 46 bytes request

May 28 19:48:31.533: TPLUS: Would block while reading pak header

May 28 19:48:31.537: TPLUS(00000044)/0/READ: read entire 12 header bytes (expect 6 bytes)

May 28 19:48:31.537: TPLUS(00000044)/0/READ: read entire 18 bytes response

May 28 19:48:31.537: TPLUS(00000044)/0/203A4C50: Processing the reply packet

May 28 19:48:31.537: TPLUS: received authorization response for 68: FAIL

May 28 19:48:31.537: CRYPTO_PKI_AAA: authorization declined by AAA, or AAA server not 
found.

May 28 19:48:31.537: CRYPTO_PKI_AAA: No cert-application attribute found. Failing.

May 28 19:48:31.537: CRYPTO_PKI_AAA: authorization failed

May 28 19:48:31.537: CRYPTO_PKI: AAA authorization for list 'ACSLab', and user 
'POD5.example.com' failed.

May 28 19:48:31.537: %CRYPTO-5-IKMP_INVAL_CERT: Certificate received from 192.0.2.162 is 
bad: certificate invalid

May 28 19:48:39.821: CRYPTO_PKI: Trust-Point EM-CERT-SERV picked up

May 28 19:48:41.481: CRYPTO_PKI: Found a issuer match

May 28 19:48:41.501: CRYPTO_PKI: cert revocation status unknown.

May 28 19:48:41.501: CRYPTO_PKI: Certificate validated without revocation check

May 28 19:48:41.505: CRYPTO_PKI_AAA: checking AAA authorization (ACSLab, POD5.example.com, 
<all>)

May 28 19:48:41.505: AAA/BIND(00000045): Bind i/f  

May 28 19:48:41.505: AAA/AUTHOR (0x45): Pick method list 'ACSLab'

May 28 19:48:41.505: TPLUS: Queuing AAA Authorization request 69 for processing

May 28 19:48:41.505: TPLUS: processing authorization request id 69

May 28 19:48:41.505: TPLUS: Protocol set to None .....Skipping

May 28 19:48:41.505: TPLUS: Sending AV service=pki

May 28 19:48:41.505: TPLUS: Authorization request created for 69(POD5.example.com)

May 28 19:48:41.505: TPLUS: Using server 198.168.244.55

May 28 19:48:41.509: TPLUS(00000045)/0/IDLE/63B22834: got immediate connect on new 0

May 28 19:48:41.509: TPLUS(00000045)/0/WRITE/63B22834: Started 5 sec timeout

May 28 19:48:41.509: TPLUS(00000045)/0/WRITE: wrote entire 46 bytes request

May 28 19:48:41.509: TPLUS(00000045)/0/READ: read entire 12 header bytes (expect 6 bytes)

May 28 19:48:41.509: TPLUS(00000045)/0/READ: read entire 18 bytes response

May 28 19:48:41.509: TPLUS(00000045)/0/63B22834: Processing the reply packet

May 28 19:48:41.509: TPLUS: received authorization response for 69: FAIL

May 28 19:48:41.509: CRYPTO_PKI_AAA: authorization declined by AAA, or AAA server not 
found.

May 28 19:48:41.509: CRYPTO_PKI_AAA: No cert-application attribute found. Failing.

May 28 19:48:41.509: CRYPTO_PKI_AAA: authorization failed

May 28 19:48:41.509: CRYPTO_PKI: AAA authorization for list 'ACSLab', and user 
'POD5.example.com' failed.

May 28 19:48:41.509: %CRYPTO-5-IKMP_INVAL_CERT: Certificate received from 192.0.2.162 is 
bad: certificate invalid

Router#

Router# show crypto iskmp sa

dst             src             state          conn-id slot

192.0.2.2 	      192.0.2.102   MM_KEY_EXCH         95    0

Examples: Configuring a Revocation Mechanism

•Example: Configuring an OCSP Server

•Example: Specifying a CRL and Then an OCSP Server

•Example: Specifying an OCSP Server

•Example: Disabling Nonces in Communications with the OCSP Server

Example: Configuring an OCSP Server

The following example shows how to configure the router to use the OCSP server that is specified in the AIA extension of the certificate:

Router(config)# crypto pki trustpoint mytp

Router(ca-trustpoint)# revocation-check ocsp

Example: Specifying a CRL and Then an OCSP Server

The following example shows how to configure the router to download the CRL from the CDP. If the CRL is unavailable, the OCSP server that is specified in the AIA extension of the certificate will be used. If both options fail, certificate verification will also fail.

Router(config)# crypto pki trustpoint mytp

Router(ca-trustpoint)# revocation-check crl ocsp

Example: Specifying an OCSP Server

The following example shows how to configure your router to use the OCSP server at the HTTP URL "http://myocspserver:81." If the server is down, the revocation check will be ignored.

Router(config)# crypto pki trustpoint mytp

Router(ca-trustpoint)# ocsp url http://myocspserver:81

Router(ca-trustpoint)# revocation-check ocsp none

Example: Disabling Nonces in Communications with the OCSP Server

The following example shows communications when a nonce, or a unique identifier for the OCSP request, is disabled for communications with the OCSP server:

Router(config)# crypto pki trustpoint mytp 

Router(ca-trustpoint)# ocsp url http://myocspserver:81 

Router(ca-trustpoint)# revocation-check ocsp none 

Router(ca-trustpoint)# ocsp disable-nonce

Example: Configuring a Hub Router at a Central Site for Certificate Revocation Checks

The following example shows a hub router at a central site that is providing connectivity for several branch offices to the central site.

The branch offices are also able to communicate directly with each other using additional IPSec tunnels between the branch offices.

The CA publishes CRLs on an HTTP server at the central site. The central site checks CRLs for each peer when setting up an IPSec tunnel with that peer.

The example does not show the IPSec configuration—only the PKI-related configuration is shown.

Home Office Hub Configuration

crypto pki trustpoint VPN-GW

 enrollment url http://ca.home-office.com:80/certsrv/mscep/mscep.dll

 serial-number none

 fqdn none

 ip-address none

 subject-name o=Home Office Inc,cn=Central VPN Gateway

 revocation-check crl

Central Site Hub Router

Router# show crypto ca certificate

Certificate

  Status: Available

  Certificate Serial Number: 2F62BE14000000000CA0

  Certificate Usage: General Purpose

  Issuer: 

    cn=Central Certificate Authority

    o=Home Office Inc

  Subject:

    Name: Central VPN Gateway

    cn=Central VPN Gateway

    o=Home Office Inc

  CRL Distribution Points: 

    http://ca.home-office.com/CertEnroll/home-office.crl

  Validity Date: 

    start date: 00:43:26 GMT Sep 26 2003

    end   date: 00:53:26 GMT Sep 26 2004

    renew date: 00:00:00 GMT Jan 1 1970

  Associated Trustpoints: VPN-GW

CA Certificate

  Status: Available

  Certificate Serial Number: 1244325DE0369880465F977A18F61CA8

  Certificate Usage: Signature

  Issuer: 

    cn=Central Certificate Authority

    o=Home Office Inc

  Subject: 

    cn=Central Certificate Authority

    o=Home Office Inc

  CRL Distribution Points: 

    http://ca.home-office.com/CertEnroll/home-office.crl

  Validity Date: 

    start date: 22:19:29 GMT Oct 31 2002

    end   date: 22:27:27 GMT Oct 31 2017

  Associated Trustpoints: VPN-GW

Trustpoint on the Branch Office Router

crypto pki trustpoint home-office

 enrollment url http://ca.home-office.com:80/certsrv/mscep/mscep.dll

 serial-number none

 fqdn none

ip-address none

 subject-name o=Home Office Inc,cn=Branch 1

 revocation-check crl

A certificate map is entered on the branch office router.

Router# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z.

branch1(config)# crypto pki certificate map central-site 10

branch1(ca-certificate-map)#

The output from the show certificate command on the central site hub router shows that the certificate was issued by the following:

cn=Central Certificate Authority

o=Home Office Inc

These two lines are combined into one line using a comma (,) to separate them, and the original lines are added as the first criteria for a match.

Router (ca-certificate-map)# issuer-name co cn=Central Certificate Authority, ou=Home 
Office Inc

!The above line wrapped but should be shown on one line with the line above it.

The same combination is done for the subject name from the certificate on the central site router (note that the line that begins with "Name:" is not part of the subject name and must be ignored when creating the certificate map criteria). This is the subject name to be used in the certificate map.

cn=Central VPN Gateway

o=Home Office Inc

Router (ca-certificate-map)# subject-name eq cn=central vpn gateway, o=home office inc

Now the certificate map is added to the trustpoint that was configured earlier.

Router (ca-certificate-map)# crypto pki trustpoint home-office

Router (ca-trustpoint)# match certificate central-site skip revocation-check

Router (ca-trustpoint)# exit

Router (config)# exit

The configuration is checked (most of configuration is not shown).

Router# write term

!Many lines left out

.

.

.

crypto pki trustpoint home-office

 enrollment url http://ca.home-office.com:80/certsrv/mscep/mscep.dll

 serial-number none

 fqdn none

 ip-address none

 subject-name o=Home Office Inc,cn=Branch 1

 revocation-check crl

 match certificate central-site skip revocation-check

!

!

crypto pki certificate map central-site 10

 issuer-name co cn = Central Certificate Authority, ou = Home Office Inc

 subject-name eq cn = central vpn gateway, o = home office inc

!many lines left out

Note that the issuer-name and subject-name lines have been reformatted to make them consistent for later matching with the certificate of the peer.

If the branch office is checking the AAA, the trustpoint will have lines similar to the following:

crypto pki trustpoint home-office

 auth list allow_list

 auth user subj commonname

After the certificate map has been defined as was done above, the following command is added to the trustpoint to skip AAA checking for the central site hub.

match certificate central-site skip authorization-check

In both cases, the branch site router has to establish an IPSec tunnel to the central site to check CRLs or to contact the AAA server. However, without the match certificate command and central-site skip authorization-check (argument and keyword), the branch office cannot establish the tunnel until it has checked the CRL or the AAA server. (The tunnel will not be established unless the match certificate command and central-site skip authorization-check argument and keyword are used.)

The match certificate command and allow expired-certificate keyword would be used at the central site if the router at a branch site had an expired certificate and it had to establish a tunnel to the central site to renew its certificate.

Trustpoint on the Central Site Router

crypto pki trustpoint VPN-GW

 enrollment url http://ca.home-office.com:80/certsrv/mscep/mscep.dll

 serial-number none

 fqdn none

 ip-address none

 subject-name o=Home Office Inc,cn=Central VPN Gateway

 revocation-check crl

Trustpoint on the Branch 1 Site Router

Router# show crypto ca certificate

Certificate

  Status: Available

  Certificate Serial Number: 2F62BE14000000000CA0

  Certificate Usage: General Purpose

  Issuer: 

    cn=Central Certificate Authority

    o=Home Office Inc

  Subject:

    Name: Branch 1 Site

    cn=Branch 1 Site

    o=Home Office Inc

  CRL Distribution Points: 

    http://ca.home-office.com/CertEnroll/home-office.crl

  Validity Date: 

    start date: 00:43:26 GMT Sep 26 2003

    end   date: 00:53:26 GMT Oct 3 2003

    renew date: 00:00:00 GMT Jan 1 1970

  Associated Trustpoints: home-office 

CA Certificate

  Status: Available

  Certificate Serial Number: 1244325DE0369880465F977A18F61CA8

  Certificate Usage: Signature

  Issuer: 

    cn=Central Certificate Authority

    o=Home Office Inc

  Subject: 

    cn=Central Certificate Authority

    o=Home Office Inc

  CRL Distribution Points: 

    http://ca.home-office.com/CertEnroll/home-office.crl

  Validity Date: 

    start date: 22:19:29 GMT Oct 31 2002

    end   date: 22:27:27 GMT Oct 31 2017

  Associated Trustpoints: home-office

A certificate map is entered on the central site router.

Router# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Router (config)# crypto pki certificate map branch1 10

Router (ca-certificate-map)# issuer-name co cn=Central Certificate Authority, ou=Home 
Office Inc

!The above line wrapped but should be part of the line above it.

Router (ca-certificate-map)# subject-name eq cn=Brahcn 1 Site,o=home office inc

The certificate map is added to the trustpoint.

Router (ca-certificate-map)# crypto pki trustpoint VPN-GW

Router (ca-trustpoint)# match certificate branch1 allow expired-certificate

Router (ca-trustpoint)# exit

Router (config) #exit

The configuration should be checked (most of the configuration is not shown).

Router# write term

!many lines left out

crypto pki trustpoint VPN-GW

 enrollment url http://ca.home-office.com:80/certsrv/mscep/mscep.dll

 serial-number none

 fqdn none

 ip-address none

 subject-name o=Home Office Inc,cn=Central VPN Gateway

 revocation-check crl

 match certificate branch1 allow expired-certificate

!

!

crypto pki certificate map central-site 10

 issuer-name co cn = Central Certificate Authority, ou = Home Office Inc

 subject-name eq cn = central vpn gateway, o = home office inc

! many lines left out

The match certificate command and branch1 allow expired-certificate (argument and keyword) and the certificate map should be removed as soon as the branch router has a new certificate.

Examples: Configuring Certificate Authorization and Revocation Settings

•Example: Configuring CRL Cache Control

•Example: Configuring Certificate Serial Number Session Control

Example: Configuring CRL Cache Control

The following example shows how to disable CRL caching for all CRLs associated with the CA1 trustpoint:

crypto pki trustpoint CA1

 enrollment url http://CA1:80

 ip-address FastEthernet0/0

 crl query ldap://ldap_CA1

 revocation-check crl

 crl-cache none 

The current CRL is still cached immediately after executing the example configuration shown above:

Router# show crypto pki crls

CRL Issuer Name: 

    cn=name Cert Manager,ou=pki,o=example.com,c=US

    LastUpdate: 18:57:42 GMT Nov 26 2005

    NextUpdate: 22:57:42 GMT Nov 26 2005

    Retrieved from CRL Distribution Point: 

      ldap://ldap.example.com/CN=name Cert Manager,O=example.com

When the current CRL expires, a new CRL is then downloaded to the router at the next update. The crl-cache none command takes effect and all CRLs for the trustpoint are no longer cached; caching is disabled. You can verify that no CRL is cached by executing the show crypto pki crls command. No output will be shown because there are no CRLs cached.

The following example shows how to configure the maximum lifetime of 2 minutes for all CRLs associated with the CA1 trustpoint:

crypto pki trustpoint CA1

 enrollment url http://CA1:80

 ip-address FastEthernet0/0

 crl query ldap://ldap_CA1

 revocation-check crl

 crl-cache delete-after 2

The current CRL is still cached immediately after executing the example configuration above for setting the maximum lifetime of a CRL:

Router# show crypto pki crls

CRL Issuer Name: 

    cn=name Cert Manager,ou=pki,o=example.com,c=US

    LastUpdate: 18:57:42 GMT Nov 26 2005

    NextUpdate: 22:57:42 GMT Nov 26 2005

    Retrieved from CRL Distribution Point: 

      ldap://ldap.example.com/CN=name Cert Manager,O=example.com

When the current CRL expires, a new CRL is downloaded to the router at the next update and 
the crl-cache delete-after command takes effect. This newly cached CRL and all subsequent 
CRLs will be deleted after a maximum lifetime of 2 minutes.

You can verify that the CRL will be cached for 2 minutes by executing the show crypto pki 
crls command. Note that the NextUpdate time is 2 minutes after the LastUpdate time.

Router# show crypto pki crls

CRL Issuer Name: 

    cn=name Cert Manager,ou=pki,o=example.com,c=US

    LastUpdate: 22:57:42 GMT Nov 26 2005

    NextUpdate: 22:59:42 GMT Nov 26 2005

    Retrieved from CRL Distribution Point: 

ldap://ldap.example.com/CN=name Cert Manager,O=example.com

Example: Configuring Certificate Serial Number Session Control

The following example shows the configuration of certificate serial number session control using a certificate map for the CA1 trustpoint:

crypto pki trustpoint CA1

 enrollment url http://CA1

 chain-validation stop

 crl query ldap://ldap_server

 revocation-check crl

 match certificate crl

!

crypto pki certificate map crl 10

 serial-number co 279d

Note If the match-criteria value is set to eq (equal) instead of co (contains), the serial number must match the certificate map serial number exactly, including any spaces.

The following example shows the configuration of certificate serial number session control using AAA attributes. In this case, all valid certificates will be accepted if the certificate does not have the serial number "4ACA."

crypto pki trustpoint CA1

 enrollment url http://CA1

 ip-address FastEthernet0/0

 crl query ldap://ldap_CA1

 revocation-check crl

 aaa new-model

!

aaa attribute list crl

attribute-type aaa-cert-serial-not 4ACA

The server log shows that the certificate with the serial number "4ACA" was rejected. The certificate rejection is shown using exclamation points.

.

.

.

Dec 3 04:24:39.051: CRYPTO_PKI: Trust-Point CA1 picked up

Dec 3 04:24:39.051: CRYPTO_PKI: locked trustpoint CA1, refcount is 1

Dec 3 04:24:39.051: CRYPTO_PKI: unlocked trustpoint CA1, refcount is 0

Dec 3 04:24:39.051: CRYPTO_PKI: locked trustpoint CA1, refcount is 1

Dec 3 04:24:39.135: CRYPTO_PKI: validation path has 1 certs

Dec 3 04:24:39.135: CRYPTO_PKI: Found a issuer match

Dec 3 04:24:39.135: CRYPTO_PKI: Using CA1 to validate certificate

Dec 3 04:24:39.135: CRYPTO_PKI: Certificate validated without revocation check

Dec 3 04:24:39.135: CRYPTO_PKI: Selected AAA username: 'PKIAAA'

Dec 3 04:24:39.135: CRYPTO_PKI: Anticipate checking AAA list:'CRL'

Dec 3 04:24:39.135: CRYPTO_PKI_AAA: checking AAA authorization (CRL, PKIAAA-L1, <all>)

Dec 3 04:24:39.135: CRYPTO_PKI_AAA: pre-authorization chain validation status (0x4)

Dec 3 04:24:39.135: AAA/BIND(00000021): Bind i/f

Dec 3 04:24:39.135: AAA/AUTHOR (0x21): Pick method list 'CRL'

.

.

.

Dec 3 04:24:39.175: CRYPTO_PKI_AAA: reply attribute ("cert-application" = "all")

Dec 3 04:24:39.175: CRYPTO_PKI_AAA: reply attribute ("cert-trustpoint" = "CA1")

!

Dec 3 04:24:39.175: CRYPTO_PKI_AAA: reply attribute ("cert-serial-not" = "4ACA")

Dec 3 04:24:39.175: CRYPTO_PKI_AAA: cert-serial doesn't match ("4ACA" != "4ACA")

!

Dec 3 04:24:39.175: CRYPTO_PKI_AAA: post-authorization chain validation status (0x7)

!

Dec 3 04:24:39.175: CRYPTO_PKI: AAA authorization for list 'CRL', and user 'PKIAAA' 
failed.

Dec 3 04:24:39.175: CRYPTO_PKI: chain cert was anchored to trustpoint CA1, and chain 
validation result was: CRYPTO_PKI_CERT_NOT_AUTHORIZED

!

Dec 3 04:24:39.175: %CRYPTO-5-IKMP_INVAL_CERT: Certificate received from 192.0.2.43 is 
bad: certificate invalid

Dec 3 04:24:39.175: %CRYPTO-6-IKMP_MODE_FAILURE: Processing of Main mode failed with peer 
at 192.0.2.43

.

.

.

Examples: Configuring Certificate Chain Validation

•Example: Configuring Certificate Chain Validation from Peer to Root CA

•Example: Configuring Certificate Chain Validation from Peer to Subordinate CA

•Example: Configuring Certificate Chain Validation Through a Gap

Example: Configuring Certificate Chain Validation from Peer to Root CA

In the following configuration example, all of the certificates will be validated—the peer, SubCA11, SubCA1, and RootCA certificates.

crypto pki trustpoint RootCA

 enrollment terminal

 chain-validation stop

 revocation-check none

 rsakeypair RootCA

crypto pki trustpoint SubCA1

 enrollment terminal

 chain-validation continue RootCA

 revocation-check none

 rsakeypair SubCA1

crypto pki trustpoint SubCA11

 enrollment terminal

 chain-validation continue SubCA1

 revocation-check none

 rsakeypair SubCA11

Example: Configuring Certificate Chain Validation from Peer to Subordinate CA

In the following configuration example, the following certificates will be validated—the peer and SubCA1 certificates.

crypto pki trustpoint RootCA

 enrollment terminal

 chain-validation stop

 revocation-check none

 rsakeypair RootCA

crypto pki trustpoint SubCA1

 enrollment terminal

 chain-validation continue RootCA

 revocation-check none

 rsakeypair SubCA1

crypto pki trustpoint SubCA11

 enrollment terminal

 chain-validation continue SubCA1

 revocation-check none

 rsakeypair SubCA11

Example: Configuring Certificate Chain Validation Through a Gap

In the following configuration example, SubCA1 is not in the configured Cisco IOS XE hierarchy but is expected to have been supplied in the certificate chain presented by the peer.

If the peer supplies the SubCA1 certificate in the presented certificate chain, the following certificates will be validated—the peer, SubCA11, and SubCA1 certificates.

If the peer does not supply the SubCA1 certificate in the presented certificate chain, the chain validation will fail.

crypto pki trustpoint RootCA

 enrollment terminal

 chain-validation stop

 revocation-check none

 rsakeypair RootCA

crypto pki trustpoint SubCA11

 enrollment terminal

 chain-validation continue RootCA

 revocation-check none

 rsakeypair SubCA11

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Certificate Authorization and Revocation

Table 2 lists the features in this module and provides links to specific configuration information.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 2 lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

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