A Secure Software Development Lifecycle (SSDLC) is a systematic process designed to integrate security at every phase of the software development process. The SSDLC is an enhancement over the traditional Software Development Lifecycle (SDLC) models by explicitly incorporating security steps and considerations to ensure the application is secure by design. 

The goal of SSDLC is to help organizations create more secure software by reducing vulnerabilities, improving resistance to attacks, and ensuring compliance with security policies and regulations.

Phases of a Secure Software Development Lifecycle:

1. Requirements Analysis:

Security Requirements: Define specific security requirements along with functional requirements. This includes identifying data protection needs, regulatory compliance, and privacy requirements. 

Risk Assessment: Perform an initial risk assessment to understand potential threats and impacts, helping guide the security posture throughout the lifecycle.

2. Design: 

Threat Modeling: Conduct threat modeling to identify, categorize, and prioritize potential threats to the system.

Secure Architecture Design: Design the architecture of the software with security in mind, ensuring that the system is resilient to attacks. Use security frameworks and guidelines to aid in creating a secure architecture.

3. Implementation (Coding): 

Secure Coding Practices: Adhere to secure coding standards and guidelines to prevent common security flaws such as SQL injection, cross-site scripting (XSS), and buffer overflow. 

Code Review: Perform regular and thorough code reviews to identify security vulnerabilities. Use both manual and automated tools to detect issues.

4. Testing: 

Security Testing: Implement rigorous security testing practices, including static application security testing (SAST), dynamic application security testing (DAST), penetration testing, and vulnerability assessments. 

Remediation: Fix security issues found during testing promptly and retest to ensure they are resolved.

5. Deployment:

Secure Deployment Processes: Ensure that the deployment process itself is secure. This includes using secure protocols, checking for vulnerabilities in the deployment environment, and conducting pre-deployment security assessments. 

Change Management: Use a secure change management process that includes security impact analysis for any changes to the system.

6. Maintenance and Update:

Patch Management: Develop and implement a process for ongoing patch management to address newly discovered vulnerabilities in the software.

Incident Response: Have a well-defined incident response plan in place that can be quickly enacted in case of a security breach.

7. Retirement:

Secure Decommissioning: When software is to be retired, ensure that data is securely wiped or migrated, and that the software is decommissioned in a manner that does not expose the organization to additional risks.

Benefits of Implementing SSDLC:

Proactive Security Posture: By integrating security from the start, organizations can adopt a more proactive approach to security, rather than a reactive one.

Cost Efficiency: Addressing security early in the development process significantly reduces costs related to fixing security flaws post-deployment.

Enhanced Compliance: Ensures that the software complies with all relevant security standards and regulations, reducing legal and compliance risks.

Improved Trust and Reliability: Secure applications enhance the trust of users and customers, and provide a competitive edge in the market.

The SSDLC transforms the approach to software development by treating security as a fundamental, integral component throughout the software development process, rather than an afterthought. This shift not only improves the security of the software produced but also aligns with a broader organizational culture that values and prioritizes security.