Zero trust is a security model and framework originally described by John Kindervag in 2010. Around that time, as a result of the Operation Aurora breach, Google also began developing BeyondCorp which shared similar ideas.

Zero trust improves on perimeter security's shortcomings, namely:

• Insider threat is not properly addressed; 28% of breaches are by internal actors.
• Impenetrable fortress in theory; multiple entry points (like VPNs), lots of firewall rules in practice.
• The perimeter's scope has expanded. Enterprises today support heterogeneous mix of cloud, on-premise, cloud, and multi-cloud environments.

• Do not trust the network. Network location does not impart trust.
• There are always internal and external threats. Act like you are already breached, because your probably are.
• Every device, user, and application communication should be authenticated, authorized, and encrypted.
• Policy should be dynamic, and built from multiple sources.

These tools implement some of the concepts of Zero Trust:

• ZeroTier - ZeroTier delivers the capabilities of VPNs, SDN, and SD-WAN with a single system. Manage all your connected resources across both local and wide area networks as if the whole world is a single data center.
• Pomerium - Pomerium is a context and identity aware access proxy.
• Pritunl Zero - Free and open source BeyondCorp server providing zero trust security for privileged access to ssh and web applications
• Transcend - BeyondCorp-inspired Access Proxy. Secure internal services outside your VPN/perimeter network during a zero-trust transition.
• kilo - Kilo is a multi-cloud network overlay built on WireGuard and designed for Kubernetes (k8s + wg = kg)
• wg-dynamic - wg-dynamic is a tool designed officially by WireGuard developing team. This new utility will provide a convenient way of configuring networks dynamically, where mesh network being one of the them.
• WireHub - Decentralized, peer-to-peer and secure overlay networks
• ztncui - ztncui is a web user interface for a standalone ZeroTier network controller.

• Zero Trust Networks by Gilman and Barth

• Forrester Build Security Into Your Network’s DNA: The Zero Trust Network Architecture
• Google BeyondCorp 1 An overview: “A New Approach to Enterprise Security”
• Google BeyondCorp 2 How Google did it: “Design to Deployment at Google”
• Google BeyondCorp 3 Google’s front-end infrastructure: “The Access Proxy”
• Google BeyondCorp 4 Migrating to BeyondCorp: Maintaining Productivity While Improving Security
• Google BeyondCorp 5 The human element: “The User Experience”
• Google BeyondCorp 6 Secure your endpoints: "Building a Healthy Fleet"

• Google How Google adopted BeyondCorp
• Google Securing your business and securing your fleet the BeyondCorp way
• Google Preparing for a BeyondCorp world: Understanding your device inventory
• Google How BeyondCorp can help businesses be more productive
• Google How to use BeyondCorp to ditch your VPN, improve security and go to the cloud
• Cloudflare Introducing Cloudflare Access: Like BeyondCorp, But You Don’t Have To Be A Google Employee To Use It
• Duo BeyondCorp For The Rest Of Us
• Microsoft Building Zero Trust networks with Microsoft 365
• Wall Street Journal Google Moves Its Corporate Applications to the Internet

• USENIX Enigma 2016 - NSA TAO Chief on Disrupting Nation State Hackers
• What, Why, and How of Zero Trust Networking by Armon Dadgar, Hashicorp
• O'Reilly Security 2017 NYC Beyondcorp: Beyond Fortress Security by Neal Muller, Google
• Be Ready for BeyondCorp: enterprise identity, perimeters and your application by Jason Kent