Requirements for certificates used with Windows 7¶

The Windows 7 Beta release was liberal in accepting certificates, but already the Release Candidate added several new requirements for the VPN gateway certificate.

Required fields¶

Your gateway certificate must have:

• An Extended Key Usage flag explicitly allowing the certificate to be used for authentication purposes. The serverAuth EKU having the OID 1.3.6.1.5.5.7.3.1 (often called TLS Web server authentication) will do that. If you are using OpenSSL to generate your certificates then include the option
  

  extendedKeyUsage = serverAuth
  

  For the ipsec pki tool add the following argument
  

  --flag serverAuth
  

  In addition to serverAuth the "IP Security IKE Intermediate" EKU with OID 1.3.6.1.5.5.8.2.2 does not hurt either and will allow you to use the certificate with older Mac OS X releases too.
  So, this will work too:

  extendedKeyUsage = serverAuth, 1.3.6.1.5.5.8.2.2
  

  --flag serverAuth --flag ikeIntermediate
  

• The hostname of the VPN gateway entered in the clients connection properties MUST be contained either in the subjectDistinguishedName of the server certificate

  C=CH, O=strongSwan Project, CN=vpn.strongswan.org
  

  or in a subjectAltName extension that can be added with the OpenSSL option

  subjectAltName = DNS:vpn.strongswan.org
  

  or the ipsec pki issue argument

  --san vpn.strongswan.org
  

  For optimal compatibility with other client implementations it is recommended to include the hostname as subjectAltName, as matching only parts of the distinguished name is not compliant with RFC 4945.

Disabling extended certificate checks¶

Alternatively, you may disable these extended certificate checks on the client.

This is potentially dangerous, as any certificate holder assured by your CA may act as the VPN gateway.

To disable the extended checks, add a DWORD called DisableIKENameEkuCheck to

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\RasMan\Parameters\

in the client's registry.

Further information¶

For more details about the requirements and other ways to disable the certificate checks, have a look to this knowledge base article.

This blog entry also provides detailed information about the Windows 7 certificate requirements.