Troubleshooting certificates

There are times when there are problems with certificates — a certificate is seen as expired when its not, or it can’t be found. Often the problem is with a third party web site, and not FortiOS. However, some problems can be traced back to FortiOS such as DNS or routing issues.

Certificate is reported as expired when it is not

Certificates often are issued for a set period of time such as a day or a month, depending on their intended use. This ensures everyone is using up-to-date certificates. It is also more difficult for hackers to steal and use old certificates.

Reasons a certificate may be reported as expired include:

• It really has expired based on the “best before” date in the certificate l The FortiGate unit clock is not properly set. If the FortiGate clock is fast, it will see a certificate as expired before the expiry date is really here.
• The requesting server clock is not properly set. A valid example is if your certificate is 2 hours from expiring, a server more than two time zones away would see the certificate as expired. Otherwise, if the server’s clock is set wrongly it will also have the same effect.
• The certificate was revoked by the issuer before the expiry date. This may happen if the issuer believes a certificate was either stolen or misused. Its possible it is due to reasons on the issuer’s side, such as a system change or such. In either case it is best to contact the certificate issuer to determine what is happening and why.

A secure connection cannot be completed (Certificate cannot be found)

Everyone who uses a browser has encountered a message such as This connection is untrusted. Normally when you try to connect securely to a web site, that web site will present its valid certificate to prove their identity is valid. When the web site’s certificate cannot be verified as valid, the message appears stating This connection is untrusted or something similar. If you usually connect to this web site without problems, this error could mean that someone is trying to impersonate or hijack the web site, and best practices dictates you not continue.

Reasons a web site’s certificate cannot be validated include:

• The web site uses an unrecognized self-signed certificate. These are not secure because anyone can sign them. If you accept self-signed certificates you do so at your own risk. Best practices dictate that you must confirm the ID of the web site using some other method before you accept the certificate.
• The certificate is valid for a different domain. A certificate is valid for a specific location, domain, or sub-section of a domain such as one certificate for example.com that is not valid for marketing.example.com. If you encounter this problem, contact the webmaster for the web site to inform them of the problem.
• There is a DNS or routing problem. If the web site’s certificate cannot be verified, it will not be accepted. Generally to be verified, your system checks with the third party certificate signing authority to verify the certificate is valid. If you cannot reach that third party due to some DNS or routing error, the certificate will not be verified.
• Firewall is blocking required ports. Ensure that any firewalls between the requesting computer and the web site allow the secure traffic through the firewall. Otherwise a hole must be opened to allow it through. This includes ports such as 443 (HTTPS) and 22 (SSH).

Online updates to certificates and CRLs

If you obtained your local or CA certificate using SCEP, you can configure online renewal of the certificate before it expires. Similarly, you can receive online updates to CRLs.

Local certificates

In the config vpn certificate local command, you can specify automatic certificate renewal. The relevant fields are:

Troubleshooting

scep-url <URL_str>	The URL of the SCEP server. This can be HTTP or HTTPS. The following options appear after you add the <URL_str>.
scep-password <password_str>	The password for the SCEP server.
auto-regenerate-days <days_ int>	How many days before expiry the FortiGate unit requests an updated local certificate. The default is 0, no auto-update.
auto-regenerate-days-warning <days_int>	How many days before local certificate expiry the FortiGate generates a warning message. The default is 0, no warning.

In this example, an updated certificate is requested three days before it expires.

config vpn certificate local edit mycert set scep-url http://scep.example.com/scep set scep-server-password my_pass_123 set auto-regenerate-days 3 set auto-regenerate-days-warning 2

end

CA certificates

In the config vpn certificate ca command, you can specify automatic certificate renewal. The relevant fields are:

Variable	Description
scep-url <URL_str>	The URL of the SCEP server. This can be HTTP or HTTPS.
auto-update-days <days_int>	How many days before expiry the FortiGate unit requests an updated CA certificate. The default is 0, no auto-update.
auto-update-days-warning <days_int>	How many days before CA certificate expiry the FortiGate generates a warning message. The default is 0,no warning.

In this example, an updated certificate is requested three days before it expires.

config vpn certificate ca edit mycert set scep-url http://scep.example.com/scep set auto-update-days 3 set auto-update-days-warning 2

end

Certificate Revocation Lists

If you obtained your CRL using SCEP, you can configure online updates to the CRL using the config vpn certificate crl command. The relevant fields are:

Troubleshooting

Variable	Description
http-url <http_url>	URL of the server used for automatic CRL certificate updates. This can be HTTP or HTTPS.
scep-cert <scep_certificate>	Local certificate used for SCEP communication for CRL autoupdate.
scep-url <scep_url>	URL of the SCEP CA server used for automatic CRL certificate updates. This can be HTTP or HTTPS.
update-interval <seconds>	How frequently, in seconds, the FortiGate unit checks for an updated CRL. Enter 0 to update the CRL only when it expires. Not available for http URLs.
update-vdom <update_vdom>	VDOM used to communicate with remote SCEP server for CRL auto-update.

In this example, an updated CRL is requested only when it expires.

config vpn certificate crl edit cert_crl set http-url http://scep.example.com/scep set scep-cert my-scep-cert

set scep-url http://scep.ca.example.com/scep set update-interval 0 set update-vdom root

end

Backing up and restoring local certificates

The FortiGate unit provides a way to export and import a server certificate and the FortiGate unit’s personal key through the CLI. If required (to restore the FortiGate unit configuration), you can import the exported file through the System > Certificates page of the web-based manager.

As an alternative, you can back up and restore the entire FortiGate configuration through the System Information widget on the Dashboard of the web-based manager. Look for [Backup] and [Restore] in the System Configuration row. The backup file is created in a FortiGate-proprietary format.

To export a server certificate and private key – CLI:

This procedure exports a server (local) certificate and private key together as a password protected PKCS12 file. The export file is created through a customer-supplied TFTP server. Ensure that your TFTP server is running and accessible to the FortiGate unit before you enter the command.

1. Connect to the FortiGate unit through the CLI.
2. Type the following command:

execute vpn certificate local export tftp <cert_name> <exp_filename> <tftp_ip>

<password>

where:

Configuring certificate-based authentication

• <cert_name> is the name of the server certificate; typing ? displays a list of installed server certificates.
• <exp_filename> is a name for the output file.
• <tftp_ip> is the IP address assigned to the TFTP server host interface.

3. Move the output file from the TFTP server location to the management computer for future reference.

To import a server certificate and private key – web-based manager:

1. Go to System > Certificates and select Import.
2. In Type, select PKCS12 Certificate.
3. Select Browse. Browse to the location on the management computer where the exported file has been saved, select the file, and then select Open.
4. In the Password field, type the password needed to upload the exported file.
5. Select OK, and then select Return.

To import a server certificate and private key – CLI:

1. Connect to the FortiGate unit through the CLI.
2. Type the following command:

execute vpn certificate local import tftp <file_name> <tftp_ip_address> <file_type> <Enter for ‘cer’>|<password for ‘p12’> For example:

execute vpn certificate local import tftp FGTF-extern.p12 10.1.100.253 p12 123456

To import separate server certificate and private key files – web-based manager

Use the following procedure to import a server certificate and the associated private key file when the server certificate request and private key were not generated by the FortiGate unit. The two files to import must be available on the management computer.

1. Go to System > Certificates and select Import.
2. In Type, select Certificate.
3. Select the Browse button beside the Certificate file Browse to the location on the management computer where the certificate file has been saved, select the file, and then select Open.
4. Select the Browse button beside the Key file Browse to the location on the management computer where the key file has been saved, select the file, and then select Open.
5. If required, in the Password field, type the associated password, and then select OK.
6. Select Return.

Configuring certificate-based authentication

You can configure certificate-based authentication for FortiGate administrators, SSL VPN users, and IPsec VPN users.

In Microsoft Windows 7, you can use the certificate manager to keep track of all the different certificates on your local computer. To access certificate manager, in Windows 7 press the Windows key, enter “certmgr.msc” at the Configuring certificate-based authentication

search prompt, and select the displayed match. Remember that in addition to these system certificates, many applications require you to register certificates with them directly.

To see FortiClient certificates, open the FortiClient Console, and select VPN. The VPN menu has options for My Certificates (local or client) and CA Certificates (root or intermediary certificate authorities). Use Import on those screens to import certificate files from other sources.

Authenticating administrators with security certificates

You can install a certificate on the management computer to support strong authentication for administrators. When a personal certificate is installed on the management computer, the FortiGate unit processes the certificate after the administrator supplies a username and password.

To enable strong administrative authentication:

• Obtain a signed personal certificate for the administrator from a CA and load the signed personal certificate into the web browser on the management computer according to the browser documentation.
• Install the root certificate and the CRL from the issuing CA on the FortiGate unit (see Installing a CA root certificate and CRL to authenticate remote clients on page 115 ).
• Create a PKI user account for the administrator.
• Add the PKI user account to a firewall user group dedicated to PKI-authenticated administrators.
• In the administrator account configuration, select PKI as the account Type and select the User Group to which the administrator belongs.

Authenticating SSL VPN users with security certificates

While the default self-signed certificates can be used for HTTPS connections, it is preferable to use the X.509 server certificate to avoid the redirection as it can be misinterpreted as possible session hijacking. However, the server certificate method is more complex than self-signed security certificates. Also the warning message is typically displayed for the initial connection, and future connections will not generate these messages.

X.509 certificates can be used to authenticate IPsec VPN peers or clients, or SSL VPN clients. When configured to authenticate a VPN peer or client, the FortiGate unit prompts the VPN peer or client to authenticate itself using the X.509 certificate. The certificate supplied by the VPN peer or client must be verifiable using the root CA certificate installed on the FortiGate unit in order for a VPN tunnel to be established.

To enable certificate authentication for an SSL VPN user group:

1. Install a signed server certificate on the FortiGate unit and install the corresponding root certificate (and CRL) from the issuing CA on the remote peer or client.
2. Obtain a signed group certificate from a CA and load the signed group certificate into the web browser used by each user. Follow the browser documentation to load the certificates.
3. Install the root certificate and the CRL from the issuing CA on the FortiGate unit (see Installing a CA root certificate and CRL to authenticate remote clients on page 115).
4. Create a PKI user for each SSL VPN user. For each user, specify the text string that appears in the Subject field of the user’s certificate and then select the corresponding CA certificate.
5. Use the config user peergrp CLI command to create a peer user group. Add to this group all of the SSL VPN users who are authenticated by certificate.
6. Go to Policy & Objects > IPv4 Policy.
7. Edit the SSL-VPN security policy.

Support for per-VDOM certificates

8. Select the user group created earlier in the Source User(s)
9. Select OK.

Authenticating IPsec VPN users with security certificates

To require VPN peers to authenticate by means of a certificate, the FortiGate unit must offer a certificate to authenticate itself to the peer.

To enable the FortiGate unit to authenticate itself with a certificate:

1. Install a signed server certificate on the FortiGate unit.

See To install or import the signed server certificate – web-based manager on page 115.

2. Install the corresponding CA root certificate on the remote peer or client. If the remote peer is a FortiGate unit, see To install a CA root certificate on page 115.
3. Install the certificate revocation list (CRL) from the issuing CA on the remote peer or client. If the remote peer is a FortiGate unit, see To import a certificate revocation list on page 115.
4. In the VPN phase 1 configuration, set Authentication Method to Signature and from the Certificate Name list select the certificate that you installed in Step 1.

To authenticate a VPN peer using a certificate, you must install a signed server certificate on the peer. Then, on the FortiGate unit, the configuration depends on whether there is only one VPN peer or if this is a dialup VPN that can be multiple peers.

To configure certificate authentication of a single peer

1. Install the CA root certificate and CRL.
2. Create a PKI user to represent the peer. Specify the text string that appears in the Subject field of the user’s certificate and then select the corresponding CA certificate.
3. In the VPN phase 1 Peer Options, select peer certificate for Accept Types field and select the PKI user that you created in the Peer certificate

To configure certificate authentication of multiple peers (dialup VPN)

1. Install the corresponding CA root certificate and CRL.
2. Create a PKI user for each remote VPN peer. For each user, specify the text string that appears in the Subject field of the user’s certificate and then select the corresponding CA certificate.
3. Use the config user peergrp CLI command to create a peer user group. Add to this group all of the PKI users who will use the IPsec VPN.

In the VPN phase 1 Peer Options, select peer certificate group for Accept Types field and select the PKI user group that you created in the Peer certificate group field.

Support for per-VDOM certificates

The CA and local certificate configuration is available per-VDOM. When an admin uploads a certificate to a VDOM, it will only be accessible inside that VDOM. When an admin uploads a certificate to global, it will be accessible to all VDOMs and global.

There are factory default certificates such as Fortinet_CA_SSL, Fortinet_SSL, Fortinet_Wifi, and Fortinet_ Factory. These certificates are moved to per-VDOM and automatically generated when a new VDOM is created.

CLI Changes

Two new attributes range and source have been added:

range can be global or per-VDOM, if the certificate file is imported from global, it is a global certificate. If the certificate file is imported from a VDOM, it is VDOM certificate. source can be either factory, user, or fortiguard:

• factory: The factory certificate file with FortiOS version, this includes: Fortinet_CA_SSL, Fortinet_SSL, PositiveSSL_CA, Fortinet_Wifi, Fortinet_Factory.
• user: Certificate file imported by the user.
• fortiguard: Certificate file imported from FortiGuard.

config certificate local edit Fortinet_Factory set range {global | vdom} set source {factory | user | fortiguard}

end

end

GUI Changes

Global and new VDOMs have the following factory default certificates:

These certificates are created automatically when a new VDOM is created, with every VDOM having its own versions of these certificates.

Example — Generate a CSR on the FortiGate unit

This example follows all the steps required to create and install a local certificate on the FortiGate unit, without using CA software.

Example — Generate and Import CA certificate with private key pair on

The FortiGate unit is called myFortiGate60, and is located at 10.11.101.101 (a private IP address) and http://myfortigate.example.com. Mr. John Smith (john.smith@myfortigate.example.com) is the IT administrator for this FortiGate unit, and the unit belongs to the Sales department located in Greenwich, London, England.

To generate a certificate request on the FortiGate unit – web-based manager:

1. Go to System > Certificates.
2. Select Generate.
3. In the Certificate Name field, enter myFortiGate60.

Since the IP address is private, we will use the FQDN instead.

4. Select Domain Name, and enter http://myfortigate.example.com.
5. Enter values in the Optional Information area to further identify the FortiGate unit.

Organization Unit	Sales
Organization	Example.com
Locality (City)	Greenwich
State/Province	London
Country	England
e-mail	john.smith@myfortigate.example.com

6. From the Key Type list, select RSA or Elliptic Curve.
7. If RSA is selected, from the Key Size list, select 2048 Bit. If Elliptic Curve is selected,from the Curve Name list, select secp256r1.
8. In Enrollment Method, select File Based to generate the certificate request
9. Select OK.

The request is generated and displayed in the Local Certificates list with a status of PENDING.

10. Select the Download button to download the request to the management computer.
11. In the File Download dialog box, select Save and save the Certificate Signing Request on the local file system of the management computer.
12. Name the file and save it on the local file system of the management computer.