A software-defined perimeter (SDP), also called a "black cloud", is an approach to computer security which evolved from the work done at the Defense Information Systems Agency (DISA) under the Global Information Grid (GIG) Black Core Network initiative around 2007. Software-defined perimeter (SDP) framework was developed by the Cloud Security Alliance (CSA) to control access to resources based on identity. Connectivity in a Software Defined Perimeter is based on a need-to-know model, in which device posture and identity are verified before access to application infrastructure is granted. Application infrastructure is effectively “black” (a DoD term meaning the infrastructure cannot be detected), without visible DNS information or IP addresses. The inventors of these systems claim that a Software Defined Perimeter mitigates the most common network-based attacks, including: server scanning, denial of service, SQL injection, operating system and application vulnerability exploits, man-in-the-middle, pass-the-hash, pass-the-ticket, and other attacks by unauthorized users. Background The premise of the traditional enterprise network architecture is to create an internal network separated from the outside world by a fixed perimeter that consists of a series of firewall functions that block external users from coming in, but allows internal users to get out. Traditional fixed perimeters help protect internal services from external threats via simple techniques for blocking visibility and accessibility from outside the perimeter to internal applications and infrastructure. But the weaknesses of this traditional fixed perimeter model are becoming ever more problematic because of the popularity of user-managed devices and phishing attacks, providing untrusted access inside the perimeter, and SaaS and IaaS extending the perimeter into the internet. Software defined perimeters address these issues by giving application owners the ability to deploy perimeters that retain the traditional model's value of invisibility and inaccessibility to outsiders, but can be deployed anywhere – on the internet, in the cloud, at a hosting center, on the private corporate network, or across some or all of these locations. Authorization Techniques There are several techniques for delivering a software-defined perimeter (SDP). This includes: Single Packet Authorization: A single packet is sent by a client to an SDP gateway which listens for SPA packets. The contents of the packet will be decrypted for further inspection. If verified, the gateway adds a rule to the firewall so that a mutual TLS connection to the intended service can be established. Once this connection is established, the firewall rules are removed making the service invisible to