What is the goal of the security architecture and design phase, and what are its steps?

Make sure the architecture fulfils the relevant security quality attributes and that the security controls are designed properly in detail.

The Architect is responsible. Inputs are the high-level system architecture, the product security requirements and the threat model.

1. Security quality attributes: decide which properties matter (confidentiality of patient data, availability of the controller, updatability).
2. Derive requirements from them for the architecture.
3. Security architecture: place the controls, such as zones, authentication and crypto boundaries.
4. Design decisions and trade-offs: security against cost, performance and usability, with the decision recorded.
5. Architecture and design review.

Deliverables are the quality attributes, a high-level security architecture, a detailed security design and the review. The phase sits after threat modelling and before sourcing. It is where mitigations from the threat model become concrete structure.

Go deeper:

• Defense in depth (Wikipedia) — the layering principle behind most security architectures
• Secure by design (Wikipedia) — design principles such as least privilege and fail-secure