Selected ASDM VPN Configuration Procedures for the Cisco ASA 5500 Series, Version 5.2
Enrolling for Digital Certificates
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Enrolling for Digital Certificates

Table Of Contents

Enrolling for Digital Certificates

Overview of Configuration Procedure

Understanding Key Pairs

Generating an RSA Key Pair

Creating the Trustpoint

Obtaining Certificates with SCEP

Enrolling with the Certificate Authority

Managing Certificates


Enrolling for Digital Certificates


This chapter describes how to enroll for a digital certificate using ASDM. Once enrolled, you can use the certificate to authenticate VPN LAN-to-LAN tunnels and remote access tunnels. If you intend to use only preshared keys to authenticate, you do not need to read this chapter.

This chapter includes the following sections:

Overview of Configuration Procedure

Understanding Key Pairs

Generating an RSA Key Pair

Creating the Trustpoint

Obtaining Certificates with SCEP

Enrolling with the Certificate Authority

Managing Certificates


Note As you following the instructions in this chapter, click Help for more information about the attributes shown in the ASDM windows.


Overview of Configuration Procedure

To enroll with a CA and get an identity certificate for authenticating tunnels, complete the following tasks.


Note This example shows automatic (SCEP) enrollment.


1. Create a key pair for the identity certificate. The key pair are RSA keys. The instructions in the sections that follow show how to generate an RSA key pair.

2. Create a trustpoint. The name of the trustpoint in this example is newmsroot.

3. Configure an enrollment URL. The URL this example uses is http://10.20.30.40/certsrv/mscep/mscep.dll.

4. Authenticate the CA.

5. Enroll with the CA, which gets an identity certificate onto the ASA.

Understanding Key Pairs

Each peer has a key pair containing both a public and a private key. These keys act as complements; any communication encrypted with one can be decrypted with the other.

Key pairs are RSA keys.

The maximum key modulus is 2048 The default size is 1024 bits.

For signature operations, the maximum key size is 4096 bits.

You can generate a general purpose RSA key pair used for both signing and encryption, or usage RSA key pairs separated for each respective purpose, thus requiring two certificates for the corresponding identity. The default setting is general purpose.

To configure a key pair for a certificate, you specify the labels to identify the key pair to be generated. The following sections show how to generate an RSA key pair with a specified label using ASDM, and use the default settings for the other parameters.

Generating an RSA Key Pair

To generate an RSA key pair, perform the following steps.


Step 1 In the Configuration > Properties > Certificate > Key Pair window, click Add.

Step 2 Configure the information in the Add Key Pair dialog box:

a. Name—Click to use the default name, or type a name for the key pair(s). This example uses the default RSA key, but you could, instead, enter a name such as key1.

b. Size list—For an RSA key pair, the Size list displays the options: 512, 768, 1024, or 2048. The default size is 1024. This example accepts the default setting.

c. Usage options— The options are General Purpose (one pair for both signing and encryption) and Special (one pair for each respective function). For this example, accept the default setting (General Purpose).

Step 3 Click Generate Now.

Step 4 To view the key pair generated, click Show Details. ASDM displays information about the key pair. Figure 1-1 shows sample output.


Figure 1-1 Key-pair Details Display

Creating the Trustpoint

A trustpoint represents a CA/identity pair and contains the identity of the CA, CA-specific configuration parameters, and an association with one enrolled identity certificate. Refer to the section that names the interface you want to use to create a trustpoint.

To create a trustpoint, perform the following steps.


Step 1 In the Configuration > Properties > Certificate > Trustpoint > Configuration window, click Add.

Step 2 Configure the basic information in the Add Trustpoint Configuration dialog box. For all other parameters, accept the default values.

a. Trustpoint Name field—Type the trustpoint name in the Trustpoint Name field. For this example, the name is newmsroot.

b. Enrollment URL field—In the Enrollment Settings window, under the Enrollment Mode area, click the Use automatic enrollment option. Then type the enrollment URL in the field. For this example, type 10.20.30.40/certsrv/mscep/mscep.dll.

Step 3 Configure the subject name using the common name (CN) and the name of the organizational unit (OU):

a. In the Enrollment Settings window, select the key pair you configured for this trustpoint in the Key Pair list. For this example, the key pair is key1.

b. In the Enrollment Settings window, click Certificate Parameters.

c. To add subject distinguished (X.500) name values, click Edit in the Certificate Parameters dialog box.

d. In the Edit DN area under DN Attribute to be Added, select an attribute in the Attribute list and type a value in the Value field. Then click Add. After entering the DN information, click OK.

For this example, first select Common Name (CN), type Pat in the Value field, and click Add; then select Department (OU) and type Techpubs in the Value field. Figure 1-2 shows what you have entered in the Edit DN dialog box.

Figure 1-2 Subject Name Attributes and Values

Step 4 After reviewing the dialog box, click OK, then click OK in the remaining two dialog boxes.


Obtaining Certificates with SCEP

This section shows how to configure certificates using SCEP. Repeat the instructions for each trustpoint you configure for automatic enrollment. As you complete the instructions for each trustpoint, the security appliance receives a CA certificate for the trustpoint and one or two certificates for signing and encryption purposes. If you do not follow these procedures, the security appliance prompts you to paste the base-64 formatted CA certificate into the text box.

If you use general-purpose RSA keys, the certificate received is for signing and encryption. If you use separate RSA keys for signing and encryption, the security appliance receives separate certificates for each purpose.

To obtain certificates, perform the following steps.


Step 1 Select the Configuration > Properties > Certificate > Authentication window.

Step 2 In the Trustpoint Name list, select the name of the trustpoint. For this example, select newmsroot.

Step 3 Click Authenticate.

Step 4 Click Apply. When ASDM displays the Authentication Successful dialog, click OK.


Enrolling with the Certificate Authority

After you configure the trustpoint and authenticate with it, you can enroll for an identity certificate by performing the following steps.


Step 1 In the Configuration > Properties > Certificate > Enrollment window, select the trustpoint in the Trustpoint Name list. For this example, you would select newmsroot.

Step 2 Click Enroll.


Managing Certificates

To manage certificates, use the Configuration > Properties > Certificate > Manage Certificates window.

You can use this window to add a new certificate and delete a certificate.

This pane displays the following information:

Subject—Identifies the owner of the certificate.

Type—CA, RA general, RA encryption, RA signature, identity.

Status—Available or pending

Available means that the CA has accepted the enrollment request and has issued an identity certificate.

Pending means that the enrollment request is still in process and that the CA has not yet issued the identity certificate.

Usage—identifies how the certificate is used: signature, general purpose, or encryption.

You can also display information about a certificate by clicking Show Details. The Certificate Details dialog displays three tables: General, Subject, and Issuer.

General—Displays the values for type, serial number, status, usage, CRL distribution point, the time within which the certificate is valid, and associated trustpoints. This applies to both available and pending status.

Subject— Displays the X.500 fields of the subject DN or certificate owner and their values. This applies only to available status.

Issuer—Displays the X.500 fields of the entity that granted the certificate. This applies only to available status.