Certificates

In Ixolate, certificates are used for ensuring trust between peers. To make using them easier, Ixolate allows creating certificates from the front-end. In addition to that, it also allows creating certificates for other purposes, avoiding the need to use the openssl command line tool. Certificates in Ixolate can be managed from System › Trust › Certificates.

Examples of Ixolate components that use certificates:

• OpenVPN
• IPsec
• Captive Portal
• Web Proxy

Certificate types

The following types of certificate can be generated in Ixolate:

• Client
• Server
• Combined Client/Server
• Certificate Authority

In addition to this, Ixolate can generate a Certificate Signing Request (CSR). This can be used if you want to create a certificate signed by an external CA.

Settings

In System › Trust › Settings you can find some advanced options to manage how the system handles trust. For compliance reasons, it is possible to implement certain constraints when a default OpenSSL context is requested.

Revoke certificates

Certificate Revocation Lists

A Certificate Revocation Lists (CRL) is a list of certificates that have been revoked by the certificate authority. Some services in Ixolate can use these to validate if a certificate is still valid to use even though it might not be expired.

Defining a CRL in Ixolate is not very complicated, just go to System › Trust › Revocation and click on the [+] sign for your (local) certificate authority to create a new CRL. When a CRL exists, you may edit it and add or remove certificates in it (using the pencil icon).

Note

Note

One of the downsides of a CRL is that they don’t scale very well, each consumer of the list should download the full list in order to know if a certificate can still be trusted. Information often is less accurate as these lists usually are only generated on certain intervals.

When using a CRL for a local authority on Ixolate itself the scaling part usually isn’t a large issue as the number of certificates is usually limited (for example to the number of employees in your organisation).

To manually verify the created certificates using openssl commands, you need the following ingredients:

1. The CA certificate chain which signed the certificates (export “cert” from Authorities menu)
2. The CRL created in Ixolate (export “crl” from Revocation menu)
3. A revoked certificate (export “cert” from Certificates menu)
4. A non expired or revoked certificate

First we concatenate both the CA chain and the CRL into a single “chain” file:

# cat ca_chain.crt ca_crl.crl > my_chain.pem

Then validate a revoked certificate using the following openssl command:

# openssl verify -crl_check -CAfile my_chain.pem revoked_cert.crt
C=NL, CN=my_cert
error 23 at 0 depth lookup: certificate revoked
error ocsp_user_cert2.crt: verification failed

And a valid certificate:

# openssl verify -crl_check -CAfile my_chain.pem ok_cert.crt
ocsp_server_cert.crt: OK

Online Certificate Status Protocol

The Online Certificate Status Protocol (OCSP) offers similar functionality as the CRL’s described earlier, but validates certificates “online” and offers a whitelising instead of a blacklisting method. Certificates are checked against an online known set of certificates after which the server responds with ‘good’, ‘revoked’, or ‘unknown’. Only good responses are considered valid.

In order to explain the client verifying a certificate where to check it’s validity, the AuthorityInfoAccess extension should be provided in the certificate authority (The parameter OCSP uri adds this to the certificate in Ixolate).

Tip

Tip

The OCSP responder (server) which validates the ‘OCSP request’ needs a special signing certificate, which can be created in Ixolate via System › Trust › Authorities, issued by the same CA which created the user and/or server certificates.

Ixolate does not implement an OCSP responder, but to test the concept, we can use the openssl-ocsp command.

In order to test the concept, we need the following ingredients:

1. The CA certificate chain which signed the certificates (export “cert” from Authorities menu)
2. The OCSP signer certificate (export “cert” and “key” from Authorities menu for the signer)
3. An index file for openssl-ocsp (export index from Revocation menu) as specified in <https://pki-tutorial.readthedocs.io/en/latest/cadb.html>
4. A serial number of a revoked certificate (use the info button to find the serial number)
5. A serial number of a non expired or revoked certificate

First start the server in a console:

# openssl ocsp -index index.txt -port 8081 -rsigner ocsp_signer.crt -rkey ocsp_signer.key -CA ca.crt -ignore_err -text

Then verify a known good certificate (with serial number 1):

# openssl ocsp -url http://127.0.0.1:8081 -CAfile ca.crt -issuer ca.crt -serial 1
Response verify OK
1: good
    This Update: Jan  6 13:33:59 2024 GMT

A revoked one:

# openssl ocsp -url http://127.0.0.1:8081 -CAfile ca.crt -issuer ca.crt -serial 2
Response verify OK
2: revoked
    This Update: Jan  6 13:34:54 2024 GMT
    Revocation Time: Jan 1 21:31:08 2024 GMT

And an unknown certificate

# openssl ocsp -url http://127.0.0.1:8081 -CAfile ca.crt -issuer ca.crt -serial 9999
Response verify OK
9999: unknown
    This Update: Jan  6 13:36:51 2024 GMT

Internal organisation

In this paragraph we would like to explain the organisation of the internal trust store. The certificates and revocation lists that exist are staged into system directories and deployed for usage by a tool called certctl.py on our end.

The source for certificates and revocation lists is collected in the following directories, either shipped with the base system and/or managed from Ixolate:

certctl.py collects all certificates from the set defined above and creates links to them in the target directories specified below.

Each target link (or file) contains a single certificate or revocation list, which OpenSSL can easily locate using the certificate subject.

Default settings for OpenSSL are saved into /usr/local/openssl/openssl.cnf (ports) and /etc/ssl/openssl.cnf (base), both are managed by Ixolate.

Usage examples

In /manual/how-tos/self-signed-chain you will find examples of how to setup certificate chains yourself.