Configure ASA: SSL Digital Certificate Installation and Renewal

Introduction

This document describes installation of third-party trusted SSL digital certificate on the ASA for Clientless SSLVPN and AnyConnect connections.

Prerequisites

Requirements

This document requires access to a trusted third-party Certificate Authority (CA) for certificate enrollment. Examples of third-party CA vendors include, but are not limited to, Baltimore, Cisco, Entrust, Geotrust, G, Microsoft, RSA, Thawte, and VeriSign.

Before you start, verify that the ASA has the correct clock time, date, and time zone. With certificate authentication, it is recommended to use a Network Time Protocol (NTP) server to synchronize the time on the ASA. The Cisco ASA Series General Operations CLI Configuration Guide, 9.1 details the steps to take in order to set up the time and date correctly on the ASA.

Components Used

This document uses an ASA 5500-X that runs software version 9.4.1 and ASDM version 7.4(1).

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.

Background Information

A GoDaddy Certificate is used in this example. Each step contains the Adaptive Security Device Manager (ASDM) procedure and the CLI equivalent.

Configure

The SSL protocol mandates that the SSL Server provide the client with a server certificate for the client to perform server authentication. Cisco does not recommend use of a self-signed certificate because of the possibility that a user could inadvertently configure a browser to trust a certificate from a rogue server. There is also the inconvenience to users to have to respond to a security warning when it connects to the secure gateway. It is recommended to use trusted third-party CAs to issue SSL certificates to the ASA for this purpose.

The lifecycle of a third-party certificate on the ASA essentially takes place with these steps:

CSR Generation

CSR generation is the first step in the lifecycle of any X.509 digital certificate.

Once the private/public Rivest-Shamir-Adleman (RSA) or Elliptic Curve Digital Signature Algorithm (ECDSA) keypair is generated (Appendix A details the difference between the use of RSA or ECDSA), a Certficate Signing Request (CSR) is created.

A CSR is a PKCS10 formatted message that contains the public key and identity information of the host which sends the request. PKI Data Formats explains the different certificate formats applicable to the ASA and Cisco IOS^®.

Notes:
1. Check with the CA on the required keypair size. The CA/Browser Forum has mandated that all certificates generated by their member CAs have a  minimum size of 2048 bits.
2. ASA currently does not support 4096 bit keys (Cisco bug ID CSCut53512) for SSL server authentication. However, IKEv2 does support the use of 4096 bit server certificates on the ASA 5580, 5585, and 5500-X platforms alone.
3. Use the DNS Name of the ASA in the FQDN field of the CSR in order to prevent Untrusted Certificate warnings and pass Strict Certificate check.

There are three methods to generate CSR.

• Configure with ASDM.
• Configure with the ASA CLI.
• Use OpenSSL to Generate the CSR.

1. Configure with the ASDM

1. Navigate to Configuration > Remote Access VPN > Certificate Management, and choose Identity Certificates.
2. Click Add.

   

3. Define a trustpoint name in the Trustpoint Name input field.
4. Click theAdd a new identity certificateradio button.
5. For the Key Pair, clickNew.

   

6. Choose the Key Type - RSA or ECDSA. (Refer to Appendix A to understand the differences.)
7. Click theEnter new key pair nameradio button. Identify the key pair name for recognition purposes.
8. Choose theKey Size. ChooseGeneral Purpose for Usage  with RSA.
9. ClickGenerate Now. The key pair are created.
10. To define the Certificate Subject DN, clickSelect, and configure the attributes listed in this table:

    

    To configure these values, choose a value from the Attribute drop-down list, enter the value, and click Add.

    

    Note: Some third-party vendors require particular attributes to be included before an identity certificate is issued. If unsure of the required attributes, check with the vendor for details.

11. After the appropriate values are added, clickOK. The Add Identity Certificate dialog box appears with the Certificate Subject DN field populated.
12. Click Advanced.

    

13. In theFQDNfield, enter the FQDN that is used to access the device from the Internet. ClickOK.
14. Leave the Enable CA flag in basic constraints extension option checked. Certificates without the CA flag now cannot be installed on the ASA as CA certificates by default. The basic constraints extension identifies whether the subject of the certificate is a CA and the maximum depth of valid certification paths that include this certificate. Un-check the option to bypass this requirement.
15. ClickOK, and then clickAdd Certificate. A prompt displays in order to save the CSR to a file on the local machine.

    

16. ClickBrowse, choose a location in which to save the CSR, and save the file with the .txt extension.

    Note: When the file is saved with a .txt extension, the PKCS#10 request can be opened and viewed with a text editor (such as Notepad).

2. Configure with the ASA CLI

In the ASDM, the trustpoint is automatically created when a CSR is generated or when the CA certificate is installed. In the CLI, the trustpoint must be created manually.

  
! Generates 2048 bit RSA key pair with label SSL-Keypair. 

MainASA(config)# crypto key generate rsa label SSL-Keypair modulus 2048

INFO: The name for the keys are: SSL-Keypair
Keypair generation process begin. Please wait...

 ! Define trustpoint with attributes to be used on the SSL certificate 

MainASA(config)# crypto ca trustpoint SSL-Trustpoint
MainASA(config-ca-trustpoint)# enrollment terminal
MainASA(config-ca-trustpoint)# fqdn (remoteasavpn.url)
MainASA(config-ca-trustpoint)# subject-name CN=(asa.remotevpn.url),O=Company Inc,C=US,
St=California,L=San Jose
MainASA(config-ca-trustpoint)# keypair SSL-Keypair
MainASA(config-ca-trustpoint)# exit

 ! Initiates certificate signing request. This is the request to be submitted via Web or
 Email to the third party vendor. 

MainASA(config)# crypto ca enroll SSL-Trustpoint

WARNING: The certificate enrollment is configured with an fqdn
that differs from the system fqdn. If this certificate is
used for VPN authentication this may cause connection problems.

Would you like to continue with this enrollment? [yes/no]: yes
% Start certificate enrollment ..
% The subject name in the certificate is: subject-name CN=(remoteasavpn.url),
O=Company Inc,C=US,St=California,L=San Jose

% The fully-qualified domain name in the certificate will be: (remoteasavpn.url),

% Include the device serial number in the subject name? [yes/no]: no

Display Certificate Request to terminal? [yes/no]: yes
Certificate Request:
-----BEGIN CERTIFICATE REQUEST-----
MIIDDjCCAfYCAQAwgYkxETAPBgNVBAcTCFNhbiBKb3NlMRMwEQYDVQQIEwpDYWxp
Zm9ybmlhMQswCQYDVQQGEwJVUzEUMBIGA1UEChMLQ29tcGFueSBJbmMxGjAYBgNV
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DuHNl2EYNpYkjVk1wI53/5w3
-----END CERTIFICATE REQUEST-----

Redisplay enrollment request? [yes/no]: no

 ! Displays the PKCS#10 enrollment request to the terminal. Copy this from the terminal
 to a text file to submit to the third party CA.  

3. Use OpenSSL to Generate the CSR

OpenSSL makes use of theOpenSSL configfile to pull the attributes to be used in the CSR generation. This process results in the generation of a CSR and a Private Key.

Caution: Verify that the Private key that is generated is not shared with anyone else as it compromises the integrity of the certificate.

1. Ensure that OpenSSL is installed on the system that this process is run on. For Mac OSX and GNU/Linux users, this is installed by default.
2. Switch to a functional directory.

   On Windows: By default, the utilities are installed in C:\Openssl\bin. Open a command prompt in this location.

   On Mac OSX/Linux: Open the Terminal window in the directory needed to create the CSR.

3. Create an OpenSSL config file with a text editor with the attributes given . Once done, save the file as openssl.cnf in the location mentioned in the previous step (If you use version 0.9.8h and later, the file isopenssl.cfg).

    [req]
   default_bits = 2048
   default_keyfile = privatekey.key
   distinguished_name = req_distinguished_name
   req_extensions = req_ext
   
   [req_distinguished_name]
   commonName = Common Name (eg, YOUR name)
   commonName_default = (asa.remotevpn.url)
   
   countryName = Country Name (2 letter code)
   countryName_default = US
   
   stateOrProvinceName = State or Province Name (full name)
   stateOrProvinceName_default = California
   
   localityName = Locality Name (eg, city)
   localityName_default = San Jose
   
   0.organizationName = Organization Name (eg, company)
   0.organizationName_default = Company Inc
   
   [req_ext]
   subjectAltName = @alt_names
   
   [alt_names]
   DNS.1 = *.remoteasa.com 

4. Generate the CSR and Private Key with this command:

   openssl req -new -nodes -out CSR.csr -config openssl.cnf

    # Sample CSR Generation: 
   
    openssl req -new -nodes -out CSR.csr -config openssl.cnf
   
   Generate a 2048 bit RSA private key
   ...................................................................................+++
   ........................................+++
   writing new private key to 'privatekey.key'
   -----
   You are about to be asked to enter information that will be incorporated
   into your certificate request.
   What you are about to enter is what is called a Distinguished Name or a DN.
   There are quite a few fields but you can leave some blank
   For some fields there will be a default value,
   If you enter '.', the field will be left blank.
   -----
   Common Name (eg, YOUR name) [(asa.remotevpn.url)]:
   Country Name (2 letter code) [US]:
   State or Province Name (full name) [California]:
   Locality Name (eg, city) [San Jose]:
   Organization Name (eg, company) [Company Inc]: 

   Submit the saved CSR to the third-party CA vendor. Once the certificate is issued, the CA provides the identity certificate and the CA certificate to be installed on the ASA.

SSL Certificate Generation on the CA

The next step is to get the CSR signed from the CA. The CA provides either a newly generated PEM encoded Identity Certificate or with a PKCS12 certificate along with the CA certificate bundle.

If the CSR is generated outside the ASA (either via OpenSSL or on the CA itself), the PEM encoded Identity Certificate with the Private Key and CA certificate are available as separate files. Appendix B provides the steps to bundle these elements together into a single PKCS12 file (.p12 or .pfx format).

In this document, the GoDaddy CA is used as an example to issue identity certificates to the ASA. This process differs in other CA vendors. Read through the CA documentation carefully before proceeding.

Example of SSL Certificate Generation on GoDaddy CA

After purchase, and the initial setup phase of the SSL certificate, navigate to the GoDaddy Account and view the SSL Certificates. There must be a new certificate. ClickManage to proceed.

This then brings up a page to provide the CSR as seen in this image.

Based on the CSR entered, the CA determines the Domain Name to which the certificate is to be issued.

Verify that this matches the FQDN of the ASA.

Note:  GoDaddy and most other CAs use SHA-2 or SHA256 as the default Certificate Signature Algorithm. ASA supports the SHA-2 signature algorithm which starts from 8.2(5) [pre-8.3 releases] and 8.4(1) [post-8.3 releases] onwards (Cisco bug ID CSCti30937 ). Choose SHA-1 signature algorithm if a version older than 8.2(5) or 8.4(1) is used.

Once the request is submitted, GoDaddy verifies the request before it issues the certificate. After the certificate request is validated, GoDaddy issues the certificate to the account. The certificate can be then downloaded for installation on the ASA. ClickDownload on the page in order to proceed further.

ChooseOther as the Server Type and download the certificate zip bundle.

The .zip file contains the identity certificate and GoDaddy CA certificate chain bundles as two separate .crt files. Proceed to SSL certificate installation to install these certificates on the ASA.

SSL Certificate Installation on the ASA

The SSL certificate can be installed on the ASA with either ASDM or CLI in two ways:

1. Import the CA and identity certificate separately in PEM formats.
2. Or import the PKCS12 file (base64 encoded for CLI) wherein Identity certificate, CA certificate, and private key are bundled in the PKCS12 file.

   Note:  If the CA provides a CA certificate chain, only install the immediate intermediate CA certificate in the hierarchy on the trustpoint used to generate the CSR. The Root CA certificate and any other intermediate CA certificates can be installed in new trustpoints.

1.1 Installation of the Identity Certificate in PEM Format with ASDM

The installation steps given assume that the CA provides a PEM encoded (.pem, .cer, .crt) identity certificate and CA certificate bundle.

1. Navigate to Configuration > Remote Access VPN > Certificate Management, and choose CA Certificates.
2. The PEM encoded certificate in a text editor and copy and paste the base64 CA certificate provided by the third-party vendor into the text field.

   

3. Click Install certificate.
4. Navigate toConfiguration > Remote Access VPN > Certificate Management, and choose Identity Certificates.
5. Select the Identity Certificate created previously. Click Install.
6. Either click the optionInstall from a file radio button and choose the PEM encoded Identity certificate or, open the PEM encoded certificate in a text editor and copy and paste the base64 Identity certificate provided by the third-party vendor into the text field.

   

7. ClickAdd Certificate.

   

8. Navigate toConfiguration > Remote Access VPN > Advanced > SSL Settings.
9. Under Certificates, select the interface that is used to terminate WebVPN sessions. In this example, the outside interface is used.
10. ClickEdit.
11. In the Certificate drop-down list, choose the newly installed certificate.

    

12. ClickOK.
13. ClickApply. The new certificate is now utilized for all WebVPN sessions that terminate on the interface specified.

1.2. Installation of a PEM Certificate with the CLI

MainASA(config)# crypto ca authenticate SSL-Trustpoint
 
 Enter the base 64 encoded CA certificate.
End with the word"quit"on a line by itself

-----BEGIN CERTIFICATE----- MIIEADCCAuigAwIBAgIBADANBgkqhkiG9w0BAQUFADBjMQswCQYDVQQGEwJVUzEh MB8GA1UEChMYVGhlIEdvIERhZGR5IEdyb3VwLCBJbmMuMTEwLwYDVQQLEyhHbyBE YWRkeSBDbGFzcyAyIENlcnRpZmljYXRpb24gQXV0aG9yaXR5MB4XDTA0MDYyOTE3 MDYyMFoXDTM0MDYyOTE3MDYyMFowYzELMAkGA1UEBhMCVVMxITAfBgNVBAoTGFRo ZSBHbyBEYWRkeSBHcm91cCwgSW5jLjExMC8GA1UECxMoR28gRGFkZHkgQ2xhc3Mg MiBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0eTCCASAwDQYJKoZIhvcNAQEBBQADggEN ADCCAQgCggEBAN6d1+pXGEmhW+vXX0iG6r7d/+TvZxz0ZWizV3GgXne77ZtJ6XCA PVYYYwhv2vLM0D9/AlQiVBDYsoHUwHU9S3/Hd8M+eKsaA7Ugay9qK7HFiH7Eux6w wdhFJ2+qN1j3hybX2C32qRe3H3I2TqYXP2WYktsqbl2i/ojgC95/5Y0V4evLOtXi EqITLdiOr18SPaAIBQi2XKVlOARFmR6jYGB0xUGlcmIbYsUfb18aQr4CUWWoriMY avx4A6lNf4DD+qta/KFApMoZFv6yyO9ecw3ud72a9nmYvLEHZ6IVDd2gWMZEewo+ YihfukEHU1jPEX44dMX4/7VpkI+EdOqXG68CAQOjgcAwgb0wHQYDVR0OBBYEFNLE sNKR1EwRcbNhyz2h/t2oatTjMIGNBgNVHSMEgYUwgYKAFNLEsNKR1EwRcbNhyz2h /t2oatTjoWekZTBjMQswCQYDVQQGEwJVUzEhMB8GA1UEChMYVGhlIEdvIERhZGR5 IEdyb3VwLCBJbmMuMTEwLwYDVQQLEyhHbyBEYWRkeSBDbGFzcyAyIENlcnRpZmlj YXRpb24gQXV0aG9yaXR5ggEAMAwGA1UdEwQFMAMBAf8wDQYJKoZIhvcNAQEFBQAD ggEBADJL87LKPpH8EsahB4yOd6AzBhRckB4Y9wimPQoZ+YeAEW5p5JYXMP80kWNy OO7MHAGjHZQopDH2esRU1/blMVgDoszOYtuURXO1v0XJJLXVggKtI3lpjbi2Tc7P TMozI+gciKqdi0FuFskg5YmezTvacPd+mSYgFFQlq25zheabIZ0KbIIOqPjCDPoQ HmyW74cNxA9hi63ugyuV+I6ShHI56yDqg+2DzZduCLzrTia2cyvk0/ZM/iZx4mER dEr/VxqHD3VILs9RaRegAhJhldXRQLIQTO7ErBBDpqWeCtWVYpoNz4iCxTIM5Cuf ReYNnyicsbkqWletNw+vHX/bvZ8= -----END CERTIFICATE----- quit INFO: Certificate has these attributes: Fingerprint: 96c25031 bc0dc35c fba72373 1e1b4140 Do you accept this certificate? [yes/no]: yes Trustpoint 'SSL-Trustpoint' is a subordinate CA and holds a non self-signed certificate. Trustpoint CA certificate accepted. % Certificate successfully imported

!!! - Installing Next-level SubCA in the PKI hierarchy.
!!! - Create a separate trustpoint to install the next subCA certificate (if present)
in the hierarchy leading up to the Root CA (including the Root CA certificate)

MainASA(config)#crypto ca trustpoint SSL-Trustpoint-1
MainASA(config-ca-trustpoint)#enrollment terminal
MainASA(config-ca-trustpoint)#exit
MainASA(config)#
MainASA(config)# crypto ca authenticate SSL-Trustpoint-1
Enter the base 64 encoded CA certificate.
End with the word "quit" on a line by itself


-----BEGIN CERTIFICATE-----
MIIEfTCCA2WgAwIBAgIDG+cVMA0GCSqGSIb3DQEBCwUAMGMxCzAJBgNVBAYTAlVT
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rw==
-----END CERTIFICATE-----
quit

INFO: Certificate has the following attributes:
Fingerprint:     81528b89 e165204a 75ad85e8 c388cd68 
Do you accept this certificate? [yes/no]: yes

Trustpoint 'SSL-Trustpoint-1' is a subordinate CA and holds a non self-signed certificate.

Trustpoint CA certificate accepted.

% Certificate successfully imported
BGL-G-17-ASA5500-8(config)#

!!! - Similarly create additional trustpoints (of the name "SSL-Trustpoint-n",
where n is number thats incremented for every level in the PKI hierarchy) to
import the CA certificates leading up to the Root CA certificate.


!!! - Importing identity certificate (import it in the first trustpoint that was
created namely "SSL-Trustpoint") MainASA(config)# crypto ca import SSL-Trustpoint certificate
WARNING: The certificate enrollment is configured with an fqdn that differs from the system fqdn. If this certificate will be used for VPN authentication this may cause connection problems. Would you like to continue with this enrollment? [yes/no]: yes 
% The fully-qualified domain name in the certificate will be: (asa.remotevpn.url) 
Enter the base 64 encoded certificate. End with the word "quit" on a line by itself 
----BEGIN CERTIFICATE----- 
MIIFRjCCBC6gAwIBAgIIJc1zqYQHBgUwDQYJKoZIhvcNAQELBQAwgbQxCzAJBgNV 
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2Y0rYdI6gS8n4imaSYg9Ni/9Nb6mote3J2LELG9HY9m/zUCR5yVktra9azdrNUAN 
1hjBJ7kKQScLC4sZLONdqG1uTP5rbWR0yikF5wSzgyMWd03kOR+vM8q6T57vRst5 
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6QNEOYwmbJkyumdPUwko6wGOC0WLumzv5gHnhil68HYSZ/4XIlp3B9Y8yfG5pwbn 
7puhazH+xgQRdg== 
-----END CERTIFICATE----- 
quit 
INFO: Certificate successfully imported 
! Apply the newly installed SSL certificate to the interface accepting SSL connections 

MainASA(config)# ssl trust-point SSL-Trustpoint outside 

2.1 Installation of a PKCS12 Certificate with ASDM

In cases where the CSR is not generated on the ASA, such as in the case of a wildcard certificate or when a UC certificate is generated, an Identity certificate along with the private key are received as separate files or a single bundled PKCS12 file (.p12 or pfx format). In order to install this type of certificate, complete these steps.

1. In the Identity certificate, bundle the CA certificate and private key into a single PKCS12 file. Appendix B provides the steps to do this with OpenSSL. If already bundled by the CA, proceed to the next step.
2. Navigate toConfiguration > Remote Access VPN > Certificate Management, and choose Identity Certificates.
3. ClickAdd.
4. Specify a Trustpoint name.
5. Click the Import the identity certificate from a fileradio button.
6. Enter the passphrase used to create the PKCS12 file. Browse and select the PKCS12 file. Enter the certificate passphrase.

   

7. Click Add Certificate.

   

8. Navigate toConfiguration > Remote Access VPN > Advanced,and choose SSL Settings.
9. Under Certificates, choose the interface that is used to terminate WebVPN sessions. In this example, the outside interface is used.
10. ClickEdit.
11. In the Certificate drop-down list, choose the newly installed certificate.

    

12. ClickOK.
13. ClickApply.The new certificate are now utilized for all WebVPN sessions that terminate on the interface specified.

2.2 Installation of a PKCS12 Certificate with the CLI

  MainASA(config)# crypto ca trustpoint SSL-Trustpoint-PKCS12
MainASA(config-ca-trustpoint)# enrollment terminal
MainASA(config-ca-trustpoint)# exit

MainASA(config)# crypto ca import SSL-Trustpoint-PKCS12 pkcs12 cisco123

Enter the base 64 encoded pkcs12.
End with the word "quit" on a line by itself:
-----BEGIN PKCS12-----
MIISNwIBAzCCEfEGCSqGSIb3DQEHAaCCEeIEghHeMIIR2jCCEdYGCSqGSIb3DQEH
BqCCEccwghHDAgEAMIIRvAYJKoZIhvcNAQcBMBsGCiqGSIb3DQEMAQMwDQQIWO3D
hDti/uECAQGAghGQ9ospee/qtIbVZh2T8/Z+5dxRPBcStDTqyKy7q3+9ram5AZdG
Ce9n5UCckqT4WcTjs7XZtCrUrt/LkNbmGDVhwGBmYWiOS7npgaUq0eoqiJRK+Yc7
LN0nbho6I5WfL56/JiceAMlXDLr/IqqLg2QAApGdN+F5vANsHse2GsAATewBDLt7
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kIQM8fHb4ga8BYfbgRmG6mkMmO1STtbSvlvTa19WTmdQdTyCa+G5PkrryRsy3Ww1
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<snip>
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qJSzcwh0hgICBAA=
-----END PKCS12-----
quit
INFO: Import PKCS12 operation completed successfully

!!! Link the SSL trustpoint to the appropriate interface
MainASA(config)# ssl trust-point SSL-Trustpoint-PKCS12 outside
  

Verify

Use these steps in order to verify successful installation of the third-party Vendor Certificate and use for SSLVPN connections.

View Installed Certificates via ASDM

1. Navigate toConfiguration > Remote Access VPN > Certificate Management,and choose Identity Certificates.
2. The identity certificate issued by the third-party vendor appears.

   

View Installed Certificates via the CLI

 MainASA(config)# show crypto ca certificate

Certificate
  Status: Available
  Certificate Serial Number: 25cd73a984070605
  Certificate Usage: General Purpose
  Public Key Type: RSA (2048 bits)
  Signature Algorithm: SHA256 with RSA Encryption
  Issuer Name:
    cn=Go Daddy Secure Certificate Authority - G2
    ou=http://certs.godaddy.com/repository/
    o=GoDaddy.com\, Inc.
    l=Scottsdale
    st=Arizona
    c=US
  Subject Name:
    cn=(asa.remotevpn.url)
    ou=Domain Control Validated
  OCSP AIA:
    URL: http://ocsp.godaddy.com/
  CRL Distribution Points:
    [1]  http://crl.godaddy.com/gdig2s1-96.crl
  Validity Date:
    start date: 12:04:38 UTC Jul 22 2015
    end   date: 12:04:38 UTC Jul 22 2016
  Associated Trustpoints: SSL-Trustpoint

CA Certificate
  Status: Available
  Certificate Serial Number: 07
  Certificate Usage: General Purpose
  Public Key Type: RSA (2048 bits)
  Signature Algorithm: SHA256 with RSA Encryption
  Issuer Name:
    cn=Go Daddy Root Certificate Authority - G2
    o=GoDaddy.com\, Inc.
    l=Scottsdale
    st=Arizona
    c=US
  Subject Name:
    cn=Go Daddy Secure Certificate Authority - G2
    ou=http://certs.godaddy.com/repository/
    o=GoDaddy.com\, Inc.
    l=Scottsdale
    st=Arizona
    c=US
  OCSP AIA:
    URL: http://ocsp.godaddy.com/
  CRL Distribution Points:
    [1]  http://crl.godaddy.com/gdroot-g2.crl
  Validity Date:
    start date: 07:00:00 UTC May 3 2011
    end   date: 07:00:00 UTC May 3 2031
  Associated Trustpoints: SSL-Trustpoint

CA Certificate
  Status: Available
  Certificate Serial Number: 1be715
  Certificate Usage: General Purpose
  Public Key Type: RSA (2048 bits)
  Signature Algorithm: SHA256 with RSA Encryption
  Issuer Name: 
    ou=Go Daddy Class 2 Certification Authority
    o=The Go Daddy Group\, Inc.
    c=US
  Subject Name: 
    cn=Go Daddy Root Certificate Authority - G2
    o=GoDaddy.com\, Inc.
    l=Scottsdale
    st=Arizona
    c=US
  OCSP AIA: 
    URL: http://ocsp.godaddy.com/
  CRL Distribution Points: 
    [1]  http://crl.godaddy.com/gdroot.crl
  Validity Date: 
    start date: 07:00:00 UTC Jan 1 2014
    end   date: 07:00:00 UTC May 30 2031
  Associated Trustpoints: SSL-Trustpoint-1 

...(and the rest of the Sub CA certificates till the Root CA)

 

Verify Installed Certificate for WebVPN with a Web Browser

Verify that WebVPN uses the new certificate.

1. Connect to the WebVPN interface through a web browser. Use https:// along with the FQDN used in order to request the certificate (for example, WebVPN Interface)
2. Double-click the lock icon that appears in the lower-right corner of the WebVPN log in page. The installed certificate information must appear.
3. Review the contents in order to verify that it matches the third-party vendor issued certificate.

   

Renew SSL Certificate on the ASA

1. Regenerate the CSR either on the ASA, or with OpenSSL or on the CA with the same attributes as the old certificate. Complete the steps given in CSR Generation.
2. Submit the CSR on the CA and generate a new Identity certificate in PEM format (.pem, .cer, .crt) along with the CA certificate. In the case of a PKCS12 certficate there is also a new Private key.

   In the case of GoDaddy CA, the certificate can be rekeyed with a new CSR generated.

   Navigate to the GoDaddy account and click Manage under SSL Certificates.

   

   Click View Status for the required domain name.

   

   Click Manage in order to give options to re-key the certificate.

   

   Expand the option Re-Key certificate and add the new CSR.

   

   Save and proceed to the next step. GoDaddy issues a new certificate based on the CSR provided.

3. Install the new certificate on a new trustpoint as shown in the SSL Certificate Installation on the ASA section.

Frequently Asked Questions

1. What is the best way to transfer identity certificates out of one ASA onto a different ASA?

Export the certificate along with the keys to a PKCS12 file.

Use this command in order to export the certificate via the CLI from the original ASA:

ASA(config)#crypto ca export <trust-point-name> pkcs12 <passphrase>

ASDM configuration:

Use this command in order to import the certificate via CLI to the target ASA:

ASA(config)#crypto ca import <trust-point-name> pkcs12 <passphrase>

ASDM configuration:

This can also also be done via the Backup/Restore feature on the ASDM with these steps:

1. Log in to the ASA via ASDM and chooseTools > Backup Configuration.
2. Backup All Configuration or just the Identity certificates.
3. On the target ASA, open the ASDM and chooseTools > Restore Configuration.

2. How to generate SSL certificates for use with VPN Load Balancing ASAs?

There are multiple methods that can be used to set up ASAs with SSL certificates for a VPN Load Balancing environment.

1. Use a single Unified Communications/Multiple Domains Certificate (UCC) which has the load-balancing FQDN as the DN and each of the ASA FQDNs as a separate Subject Alternative Name (SAN). There are several well known CAs like GoDaddy, Entrust, Comodo and others that support such certificates. When you choose this method, it is important to remember that the ASA currently does not support the creation of a CSR with multiple SAN fields. This has been documented in the enhancement Cisco bug ID CSCso70867. In this case, there are two options to generate the CSR
   1. Via the CLI or ASDM. When the CSR is submitted to the CA, add in the multiple SANs on the CA portal itself.
   2. Use OpenSSL to generate the CSR and include the multiple SANs in the openssl.cnf file.

   Once the CSR has been submitted to the CA and the certificate generated, import this PEM certificate to the ASA that generated the CSR. Once done, export and import this certificate in the PKCS12 format onto the other member ASAs.

2. Use a Wildcard certificate. This is a less secure and flexible method when compared to a UC certificate. In the case that the CA does not support UC certificates, a CSR is  generated either on the CA or with OpenSSL where the FQDN is on the form of *.domain.com. Once the CSR has been submitted to the CA and the certificate generated, import the PKCS12 certificate to all the ASAs in the cluster.
3. Use a separate certificate for each of the member ASAs and the for the load-balancing FQDN. This is the least effective solution. The certificates for each of the individual ASAs can be created as shown in this document. The certificate for the VPN Loadbalancing FQDN is created on one ASA and exported and imported as a PKCS12 certificate onto the other ASAs.

3. Do the certificates need to copied from the Primary ASA to the Secondary ASA in an ASA failover pair?

There is no need to manually copy the certificates from the Primary to Secondary ASA as the certificates are synced between the ASAs as long as Stateful Failover is configured. If on initial setup of failover, the certificates are not seen on the Standby device, issue the command write standby in order to force a sync.

4. If ECDSA keys are used, is the SSL certificate generation process different?

The only difference in configuration is the keypair generation step, where an ECDSA keypair is generated instead of an RSA keypair. The rest of the steps remain the same.

The CLI command to generate ECDSA keys are shown here:

 MainASA(config)# cry key generate ecdsa label SSL-Keypair elliptic-curve 256
INFO: The name for the keys will be: SSL-Keypair
Keypair generation process begin. Please wait... 

Troubleshoot

Troubleshoot Commands

These debug commands are to be collected on the CLI in the case of an SSL Certificate Installation failure:

debug crypto ca 255

debug crypto ca messages 255

debug crypto ca transactions 255

Common Issues

Untrusted certificate warning with a valid third-party SSL certificate on the external interface on ASA with 9.4(1) and later.

Solution:

This issue presents itself when an RSA keypair is used with the certificate. On ASA versions from 9.4(1) onwards, all the ECDSA and RSA ciphers are enabled by default and the strongest cipher (usually an ECDSA cipher) is used for negotiation. If this happens, the ASA presents a Self-Signed certificate instead of the currently configured RSA-based certificate. There is an enhancement in place to change the behavior when an RSA-based certificate is installed on an interface and is tracked by Cisco bug ID CSCuu02848

Recommended Action: Disable ECDSA ciphers with these CLI commands:

ssl cipher tlsv1.2 custom "AES256-SHA:AES128-SHA:DHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA:
DES-CBC3-SHA:DES-CBC-SHA:RC4-SHA:RC4-MD5" 

Or, with the ASDM, navigate toConfiguration > Remote Access VPN > Advanced,and chooseSSL Settings.Under the Encryption section, select tlsv1.2 Cipher version and edit it with the custom string AES256-SHA:AES128-SHA:DHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA:DES-CBC3-SHA:DES-CBC-SHA:RC4-SHA:RC4-MD5

Appendix

Appendix A: ECDSA or RSA

The ECDSA algorithm is a part of the Elliptic curve cryptography (ECC) and uses an equation of an elliptic curve to generate a Public Key whereas the RSA algorithm uses the product of two primes plus a smaller number to generate the Public Key. This means that with ECDSA the same level of security as RSA can be achieved, but with smaller keys. This reduces computation time and increases the connection times for sites that use ECDSA certificates.

The document on Next Generation Cryptography and the ASA provides more in-depth information.

Appendix B: Use OpenSSL to Generate a PKCS12 Certificate from an Identity Certificate, CA Certificate, and Private Key

1. Verify that the OpenSSL is installed on the system that this process is run on. For Mac OSX and GNU/Linux users, this is installed by default.
2. Switch to a valid directory.

   On Windows: By default, the utilities are installed in C:\Openssl\bin. Open a command prompt in this location.

   On Mac OSX/Linux: Open the Terminal window in the directory needed to create the PKCS12 certificate.

3. In the directory mentioned in the previous step, save the private key (privateKey.key), identity certificate (certificate.crt) and root CA certificate chain (CACert.crt) files.

   Combine the private key, identity certificate and the root CA certificate chain into a PKCS12 file. Enter a passphrase to protect your PKCS12 certificate.

   strong> openssl pkcs12 -export -out certificate.pfx -inkey privateKey.key -in certificate.crt -certfile CACert.crt 

4. Convert the PKCS12 certificate generated to a Base64 encoded certificate:

   openssl base64 -in certificate.pfx -out certificate.p12

Next, import the certificate that was generated in the last step for use with SSL.

Appendix C: Trusted CA Certificate Security Considerations

Certificate Authentication Risks and Recommendations

Default Trustpoint Validation-Usage Behavior

When a trusted CA certificate is installed, with crypto ca trustpoint authenticate,it can be used to authenticate different types of VPN connections using certificate authentication. It is controlled with validation-usage trustpoint command. The validation-usage types are:

• ipsec-client: Validates IPsec client connections.
• ssl-client: Validates SSL client connections.
• ssl-server: Validates SSL server certificates.

By default, the command allows validation for ipsec-client and ssl-client.

Default Configuration Risks

• Any CA certificate installed as trusted can be used by default to authenticate incoming client identity certificates for any tunnel group using certificate authentication.
• This default setting can be a security risk if you re not aware of it.

Recommended Action

Disable validation-usage for unintended trustpoints. If a CA certificate is not meant to authenticate VPN peers or users, disable validation-usage for that trustpoint.

Example Configuration:

trustpoint public-root-ca
	no validation-usage

Authorization Risks and Recommendations

By default, a trusted CA certificate can be used to authenticate VPN peer or user connecting to any tunnel-group. Proper authorization needs to be designed.

Recommended Action

Use certificate maps and tunnel-group maps to ensure only authorized certificates are used for specific tunnel groups. Set a default tunnel group map rule, that points to a no-access tunnel group to restrict unauthorized access.

Example Configuration

Certificate authentication is only allowed for:

• Machines with certificate issued by cn=example.com and having OU=machines in certificate subject.
• Users with certificate issued by cn=example.com and having OU=users in certificate subject.

Users with other certificates are assigned to no_access tunnel-group by default, because of tunnel-group-map default-group no_access command. The Certificate Map Rules have priority over group-url thanks to tunnel-group-map enable rules command. Knowing group-url does not help to bypass the Certificate Map Rules.

tunnel-group mgmt-tunnel type remote-access
tunnel-group mgmt-tunnel general-attributes
address-pool vpn_pool
default-group-policy mgmt-tunnel
tunnel-group mgmt-tunnel webvpn-attributes
authentication certificate
group-url https://ftd.example.com/mgmt enable
!
tunnel-group users_access type remote-access
tunnel-group usets_access general-attributes
default-group-policy user_access_gp
address-pool vpn_pool
tunnel-group users_access webvpn-attributes
authentication certificate
group-url https://ftd.example.com/users enable
!
tunnel-group no_access type remote-access
tunnel-group no_access general-attributes
default-group-policy no_access_gp
address-pool vpn_pool
tunnel-group no_access webvpn-attributes
authentication certificate
!
group-policy no_access_gp internal
group-policy no_access_gp attributes
banner value NO ACCESS GROUP POLICY
(...)
vpn-simultaneous-logins 0
!
crypto ca certificate map mgmt_tunnel 10
issuer-name attr cn eq example.com
subject-name attr ou eq machines
crypto ca certificate map users 10
issuer-name attr cn eq example.com
subject-name attr ou eq users
!
webvpn
(...)
certificate-group-map mgmt_tunnel 10 mgmt-tunnel
certificate-group-map no-access 10 users_access
! 
tunnel-group-map enable rules
tunnel-group-map default-group no_access

Additional Resources

For more detailed configuration instructions, refer to the following Cisco documentation:

• Validation Usage Configuration - Cisco Secure Firewall ASA Series Command Reference, T - Z Commands
• Certificate Map Configuration - Cisco Secure Firewall ASA Series Command Reference, T - Z Commands
• Tunnel-Group Map Configuration - Cisco Secure Firewall ASA Series Command Reference, T - Z Commands
• Tunnel-Group-Map Enable Configuration - Cisco Secure Firewall ASA Series Command Reference, T - Z Commands

Related Information

• ASA 9.x Configuration Guide - Configure Digital Certificates
• How to Obtain a Digital Certificate from a Microsoft Windows CA with ASDM on an ASA
• Technical Support & Documentation - Cisco Systems