Home > Articles > Security > Network Security

This chapter is from the book

This chapter is from the book

Digital Certificates for IPSec VPNs

You have learned from Chapter 2, "IPSec Overview," that pre-shared keys and digital certificates are two primary authentication methods in IKE that can be used in the context of IPSec VPN deployments. You also saw that pre-shared keys with IKE Main Mode cannot be used for remote access scenarios in which the responder does not know the source IP address of the initiator in advance. Although Aggressive Mode can alleviate this issue, given that Aggressive Mode does not offer any form of ID protection, such a solution may not be acceptable. You also saw XAUTH provide an additional level of authentication for Aggressive Mode with pre-shared keys. Another solution for such a scenario is the use of digital certificates instead of pre-shared keys.

In addition to solving the authentication issue for remote access users, digital certificate–based authentication is also becoming increasingly popular for large IPSec VPN site-to-site deployments because it is more scalable than pre-shared keys. Without digital signatures, users must either manually exchange public keys or secrets between each pair of devices that use IPSec to protect communications. This is cumbersome because when a new device is added to the network, users are required to make configuration changes on every other device it securely communicates with. By using digital certificates, users simply enroll each new device with a Certificate Authority, and none of the other devices need modification. When the new device attempts an IPSec connection, IKE automatically exchanges certificates with the peer and the devices authenticate each other, thus making a large-scale IPSec VPN deployment very scalable using digital certificates. An entire book can be written on digital certificates and PKI. You will be introduced to some of the components of PKI in the remainder of this chapter.

Digital Certificates

Digital certificates provide a means to digitally authenticate devices and individual users. These certificates act kind of like an online passport—they are tamper proof and cannot be forged. An individual that wishes to send encrypted data obtains a digital certificate from a Certificate Authority (CA). The CA issues an encrypted digital certificate containing the applicant's public key and a variety of other identification information. The CA makes its own public key readily available. The recipient of the encrypted message uses the CA's public key to decode the digital certificate attached to the message, verifies it as issued by the CA, and then obtains the sender's public key and identification information held within the certificate. With this information, the recipient can send an encrypted reply. Public key infrastructure (PKI) is the enabler for managing digital certificates for IPSec VPN deployment. The most widely used format for digital certificates is X.509, which is supported by Cisco IOS.

Certificate Authority—Enrollment

The Certificate Authority is the entity that issues the digital certificate. Enrollment is the process of obtaining a new certificate from a certificate authority. The IOS command crypto ca trustpoint is used to declare the specific CA that the router should use for enrollment.

As PKI is deployed on larger networks, enrollment becomes a big problem if it requires manual enrollment. The Cisco auto-enroll feature will be useful for this situation. With this feature, an IOS router can be configured to periodically contact the CA and request a new certificate. Auto enrollment may be configured to generate new encryption keys or to continue to use existing keys. Routers can initially auto-enroll with CA and when the certificate lifetime expires, the router re-enrolls automatically. Example 4-11 shows the configuration snippet for enrolling a Cisco router to a CA as well as the auto-enrollment command.

Example 4-11. Cisco IOS Configuration for Enrolling with CA

crypto ca trustpoint Public_CA
 enrollment url http://100.1.1.5:80
subject-name OU=Engineering., O=ABC

 auto-enroll 95 regenerate                                                            

    password cisco                                                                       
 rsakeypair public-ca

Auto enrollment makes sure that the router re-enrolls with the CA after the certificate lifetime expires. However, while re-enrollment is occurring, new incoming IKE connections cannot be established because the existing certificate and key pairs are deleted immediately after the new key is generated, and the new key does not have a certificate to match it until the enrollment is complete. A simple workaround is to have the router re-enroll to the CA before the certificate lifetime expires, using the IOS command auto enroll < percent > regenerate."

It's possible that a router may be required to enroll with multiple certificate servers. Each CA server has an independent policy and may have different requirements as to general versus special purpose certificates or key length. Also, although it does not substantially affect the security of the system, VPN providers would like to use different key pairs for each VPN. Using the same key pair gives the impression of lower security, which is detrimental to end-user satisfaction. Example 4-12 shows an example of enrollment to multiple CAs using multiple key pairs.

Example 4-12. Enrollment with Multiple CAs Using Multiple Key Pairs

vpn-gw1-east#show running-config
!
crypto ca trustpoint Public_CA
 enrollment url http://100.1.1.5:80
 revocation-check crl
 rsakeypair public-ca                                                                 
 match certificate engg
!
crypto ca trustpoint IOS_CA
 enrollment url http://100.1.1.179:80
 revocation-check none
 rsakeypair ios-ca                                                                    
!

vpn-gw1-east#show cry ca trustpoints
Trustpoint Public_CA:                                                                 
    Subject Name:
    cn=Certificate Manager
    ou=nsite-rtp
    o=cisco-rtp
    l=rtp
    st=nc
    c=US
          Serial Number: 01
    Certificate configured.
    CEP URL: http://100.1.1.5

Trustpoint IOS_CA:                                                                    
    Subject Name:
    cn=Certmanager O\=cisco OU\=nsite
          Serial Number: 01
    Certificate configured.
    CEP URL: http://100.1.1.179

Certificate Revocation

Situations may arise in which the certificate issued by a CA may need to be revoked before the lifetime of the certificate expires. One such situation would be if the certificate itself is known to have been compromised. Yet another more common situation in the context of IPSec VPNs is when temporary access to a VPN is desired. For example, assume that a user that belongs to Company A may want temporary access to Company B's VPN, and is granted a certificate for access. The access would need to be revoked after a short time in order to maintain integrity of the network.

Another precaution maintained prevents users whose certificate has been revoked from being granted access to a VPN. To achieve this, a list of certificates that have been revoked, known as a Certificate Revocation List (CRL), is sent periodically from the CA to the IPSec gateway. When an incoming IKE session is initiated for a user whose certificate is revoked, the CRL will be checked to see if the certificate is valid; if the certificate is revoked, IKE will fail and access to the VPN will be denied. Example 4-13 shows Cisco IOS configuration to check for a revoked certificate in the CRL.

Example 4-13. Cisco IOS Configuration for Checking Certificate Status Using CRL

crypto ca trustpoint Public_CA
 enrollment url http://100.1.1.5:80
 revocation-check crl                                                                 
 rsakeypair public-ca
 match certificate eng

Once the CRL is obtained by the VPN endpoint from the CA, it will maintain it until the Certificate Revocation timer expires or if the endpoint reloads.

An alternate mechanism for checking the validity of a certificate is the use of the Online Certificate Status Protocol (OCSP). Unlike CRLs, which provide only periodic certificate status checks, OCSP can provide timely information regarding the status of a certificate. Example 4-14 shows the configuration to enable OCSP to check certificate status.

Example 4-14. Cisco IOS Configuration for Checking Certificate Status Using OCSP

crypto ca trustpoint Public_CA
 enrollment url http://100.1.1.5:80
 revocation-check ocsp
 rsakeypair public-ca
 match certificate eng

If the deployment needs more granular control over the permission to connect users (even those with valid certificates), certificate-based ACLs may be used. For example, there may be situations in which you wish to allow only a subset of users with a valid certificate to connect to the VPN. The configuration in Example 4-15 allows only users whose certificates contain "Engineering" in the subject name.

Example 4-15. Cisco IOS Configuration for Certificate-Based ACLs

crypto ca certificate map eng 10                                                      

    subject-name co Engineering                                                          

crypto ca trustpoint Public_CA
match certificate eng
 enrollment url http://100.1.1.5:80
 auto-enroll 95 regenerate
 password cisco
 rsakeypair public-ca

Digital certificates as an authentication method for large-scale IPSec VPNs is becoming increasingly popular for both remote access and site-to-site deployments. You learned in this section that the use of digital certificates requires some form of PKI infrastructure such as a CA server. Network administrators should be aware that managing the PKI infrastructure and digital certificates can be much more complicated than username-based password management. The benefits to be gained by the additional work by network administration should be carefully considered before using digital certificates.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020