I was recently speaking with someone about their infrastructure and an issue they were addressing. Their infrastructure is based around Active Directory. It is a standard implementation that uses AD to identify end entities, grant privilege and to push policy. The issue is that they are faced with an Advanced Persistent Threat against this existing AD implementation. The question becomes how does one move from this existing infrastructure to a new one while ensuring that they can safely port the existing end entity population (machines and persons) and to ensure that they implement a strategy that mitigates the risk of the ongoing and future APTs.
It seemed to me that the initial strategy has to be one around the segregation of the authentication infrastructure. In a traditional layered security approach we speak of separation of duty, roles and in some cases networks but infrequently do I see people look at the authentication infrastructure as a separate element – it normally is imbedded into some other element – usually preceded by comments like “well Microsoft gives me a CA imbedded in AD”. no knock against Microsoft but we need to be careful of architectural implementations.
The authentication infrastructure is a key component of usability but also of defense. Knowing who is accessing a resource is critical and in the case of an APT even more so as the traditional ways to protect a resource may already be compromised. There was a very good example of this within the last year when a major technology/defense firm had their AD compromised. In the process of that compromise the attacker was able to act as a administrator for the certificate authority that was part of the AD implementation and was able to issue credentials that allowed broader access and possibly to a wider audience.
It is becoming critical in light of these persistent attacks that additional precautions be taken. Layering the authentication infrastructure is one element of this that allows for migration of the core elements with less impact on end entity credentials. Similarly if the authentication infrastructure becomes compromised, such as the RSA breach, then you can also take a layered approach to credential replacement. Although this is more challenging if you do not know how deep the attack became after the credential breach but this is another reason to stress the importance of the authentication infrastructure. One step beyond that would be to look at layers of credentials within your infrastructure that would allow levels of access to resources based upon risk and type of credential presented …. but that is another topic.