Cryptographic Signing

Definition of Cryptographic Signing and Its Role in Software Supply Chain Security

Cryptographic signing is the application of public-key cryptography to create digital signatures that verify the authenticity and integrity of software artifacts, commits, and attestations throughout the development lifecycle. For DevSecOps leaders and security directors managing enterprise software development, understanding cryptographic signing becomes critical to maintaining trust and security in modern software supply chains. This fundamental security mechanism enables organizations to prove that code, containers, and other digital assets originated from trusted sources and haven't been tampered with during transit or storage.

The practice of cryptographic signing has evolved from a nice-to-have security measure into a mandatory component of secure software development. Organizations across industries now face mounting pressure from compliance frameworks, customer demands, and regulatory requirements to implement robust signing practices. Digital signatures created through cryptographic signing provide mathematical proof of origin and integrity that traditional security measures simply cannot match.

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What is Cryptographic Signing in Software Development?

Cryptographic signing in software development contexts involves using asymmetric cryptography to generate unique digital signatures for code, binaries, container images, and other artifacts produced during the software development lifecycle. The process relies on a pair of mathematically related keys: a private key kept secret by the signer, and a public key distributed to anyone who needs to verify signatures.

When a developer or automated system signs a software artifact, the signing process creates a unique fingerprint of that artifact using a cryptographic hash function. This hash gets encrypted with the private key, producing a digital signature that accompanies the artifact. Anyone with access to the corresponding public key can verify that signature, confirming two critical facts: the artifact came from whoever holds the private key, and the artifact hasn't changed since signing.

The mathematics behind public-key cryptography makes it computationally infeasible to forge signatures without access to the private key. This property distinguishes cryptographic signing from simple checksums or passwords, which can be replicated if compromised. The asymmetric nature of the key pair means that verification doesn't require sharing secrets, making public distribution of verification capabilities safe and practical.

Core Components of Cryptographic Signing Systems

Understanding the building blocks of cryptographic signing helps security teams implement and maintain effective signing practices. Several components work together to create a complete signing infrastructure:

• Private Keys: Secret cryptographic keys used to create signatures, requiring protection through hardware security modules, key management systems, or secure key storage solutions
• Public Keys: Corresponding keys distributed openly to enable signature verification without compromising security
• Hash Functions: Algorithms like SHA-256 or SHA-512 that create unique fixed-size fingerprints of artifacts regardless of their size
• Signature Algorithms: Cryptographic schemes such as RSA, ECDSA, or EdDSA that perform the actual signing and verification operations
• Certificate Authorities: Trusted third parties that bind public keys to identities through digital certificates in many enterprise implementations
• Verification Tools: Software utilities that validate signatures against public keys to confirm authenticity and integrity

How Cryptographic Signing Differs from Other Security Measures

Cryptographic signing provides specific security guarantees that complement but don't replace other security controls. Unlike encryption, which protects confidentiality, signing focuses on authenticity and integrity. A signed artifact might be publicly readable, but tampering becomes immediately detectable. Unlike access controls, which prevent unauthorized actions, signing creates an audit trail proving who performed actions and whether results remain unmodified.

The non-repudiation property of cryptographic signatures distinguishes them from shared secrets or passwords. When properly implemented with secure key management, a valid signature proves that someone with access to a specific private key signed an artifact. This property supports compliance requirements and incident investigation by creating verifiable records of who produced which artifacts.

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Explanation of Cryptographic Signing in the Software Supply Chain

The software supply chain encompasses every step from writing code to deploying applications in production. Each step introduces opportunities for compromise, whether through malicious insiders, compromised developer accounts, or attacks on build infrastructure. Cryptographic signing addresses these risks by creating verifiable checkpoints throughout the supply chain.

Modern software rarely consists of code written entirely in-house. Dependencies, libraries, base images, and third-party components make up significant portions of most applications. Each component represents a potential attack vector if an adversary can substitute malicious versions. Cryptographic signing enables verification that each component comes from its claimed source and hasn't been modified.

The 2020 SolarWinds breach demonstrated how attackers can compromise build systems to inject malicious code into legitimate software updates. Organizations that verified cryptographic signatures on their software components gained protection against such supply chain attacks. This incident accelerated adoption of signing practices across the industry, transforming cryptographic signing from a recommended practice to a security essential.

Code Commit Signing and Developer Identity

Git and other version control systems support commit signing, allowing developers to cryptographically sign their commits. This practice creates a verifiable record of who authored each code change, protecting against account compromise and impersonation. When developers sign commits with their personal private keys, teams gain confidence that code attributed to a developer actually came from them.

Code commit signing addresses several attack scenarios. If an attacker gains access to a developer's account credentials, they might push malicious code under that developer's identity. Without commit signing, distinguishing legitimate commits from malicious ones becomes difficult. With signing enabled, unsigned commits or commits with invalid signatures raise immediate red flags for investigation.

Organizations implementing commit signing need policies governing key generation, distribution, and revocation. Developers require training on protecting their private keys and understanding the security properties that signing provides. Teams also need processes for verifying signatures during code review and blocking unsigned commits from critical branches.

Artifact Signing in Build Pipelines

Build systems compile source code into executable artifacts like binaries, container images, and packages. Signing these artifacts creates cryptographic proof that they originated from your build pipeline and haven't been tampered with. The build process produces artifacts that teams deploy to staging, testing, and production environments, making artifact integrity crucial for operational security.

Container image signing has become particularly important as organizations adopt Kubernetes and containerized deployments. Images pulled from registries might be compromised if registries get breached or network traffic gets intercepted. Signing container images and requiring signature verification before deployment prevents execution of tampered or malicious containers.

Build pipeline signing often integrates with continuous integration and continuous delivery systems. Automated signing occurs after successful builds, with private keys stored in secure vaults or hardware security modules. The automation ensures consistent signing without requiring manual intervention, while secure key storage prevents compromise of signing keys.

Attestation Signing and Metadata Verification

Beyond signing the artifacts themselves, organizations increasingly sign attestations about the build process. These attestations document which source code versions, build tools, and dependencies went into creating an artifact. Signing attestations creates tamper-evident records of the complete build provenance.

The in-toto framework and SLSA (Supply chain Levels for Software Artifacts) specifications define standards for creating and verifying signed attestations. These frameworks enable organizations to verify not just that an artifact came from a trusted source, but that it was built using approved processes and materials. This deeper verification protects against compromised build environments and malicious dependencies.

Attestation verification happens at deployment time or during security audits. Teams can require that deployed artifacts include valid attestations proving they were built from reviewed source code using trusted build systems. This requirement prevents deployment of artifacts that bypass security controls or originate from unknown sources.

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How to Implement Cryptographic Signing in Your Organization

Implementing cryptographic signing requires planning around key management, tool selection, and integration with existing development workflows. Organizations need to balance security requirements with developer experience, ensuring that signing doesn't create friction that teams might bypass.

Starting with a pilot project allows teams to learn signing practices before rolling out organization-wide. Choosing a single application or team to implement signing first provides valuable lessons about tool integration, key management challenges, and training needs. Success with the pilot builds momentum for broader adoption.

Key Management Infrastructure

Secure key management forms the foundation of effective cryptographic signing. Private keys require protection equivalent to the assets they secure. If signing keys protect production deployments, their compromise could enable attackers to deploy malicious code across your infrastructure.

Hardware security modules provide high-assurance key storage that prevents extraction of private keys even by administrators. Cloud key management services offer similar security properties with easier integration into cloud-native workflows. For development signing, developer workstations might store keys with operating system keychain protection.

Key rotation policies determine how often signing keys get replaced and old keys get revoked. More frequent rotation limits the impact of key compromise but requires updating all verification configurations. Organizations need to balance rotation frequency against operational complexity and the risk profile of different signing use cases.

Tool Selection and Integration

Multiple tools support cryptographic signing across different parts of the software supply chain. Sigstore provides open-source signing tools including Cosign for container images and Gitsign for Git commits. GPG remains widely used for file and package signing. Cloud provider tools offer integrated signing services for their platforms.

Tool selection should consider existing infrastructure, team skills, and compliance requirements. Organizations already using specific version control or CI/CD systems might prioritize tools with native integrations. Teams with limited cryptography expertise might prefer managed services that handle key management complexity.

Integration points span the entire development lifecycle. Version control systems need configuration to require signed commits. Build systems need access to signing keys and integration with signing tools. Deployment systems need verification capabilities to check signatures before deploying artifacts. Runtime systems might verify signatures when loading libraries or executing code.

Developer Training and Change Management

Technical implementation alone doesn't ensure successful adoption. Developers need to understand why signing matters, how to sign their work, and what to do when verification fails. Training programs should cover both the practical steps for signing and the security principles underlying the practice.

Change management addresses the workflow modifications that signing introduces. Developers might need to generate and register keys, configure their development tools, and adjust their commit processes. Teams need clear documentation, troubleshooting guides, and support channels for addressing issues.

Gradual rollout reduces disruption and allows teams to adapt. Starting with warnings for unsigned commits before enforcing requirements gives developers time to adopt new practices. Monitoring signature verification rates helps identify teams needing additional support or training.

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Benefits of Cryptographic Signing for Enterprise Security

Organizations implementing cryptographic signing gain multiple security and operational benefits. These advantages justify the investment in infrastructure and process changes required for effective signing programs.

Supply Chain Attack Prevention

Cryptographic signing provides strong defense against supply chain attacks where adversaries compromise dependencies or build systems. Verification of signatures before using external packages or deploying internally-built artifacts prevents execution of tampered code. This protection extends beyond your own infrastructure to encompass third-party libraries and open-source components.

The verification process detects both sophisticated attacks and simple errors. Whether an artifact gets modified by malicious actors or corrupted during storage or transit, signature verification identifies the integrity violation. This reliability makes signing more dependable than trusting checksums that attackers might modify alongside compromised files.

Compliance and Audit Requirements

Regulatory frameworks increasingly require organizations to demonstrate software provenance and integrity. Cryptographic signing provides auditable evidence that satisfies compliance requirements. Signed artifacts and attestations create tamper-evident records showing what code was deployed, who built it, and when.

Audit processes benefit from the non-repudiation property of digital signatures. When investigating security incidents or compliance violations, signed artifacts prove which versions were deployed and who authorized them. This evidence supports forensic analysis and accountability in ways that log files alone cannot match.

Trust and Transparency

Customers and partners increasingly request evidence of secure development practices. Publishing public keys and documenting signing practices demonstrates security commitment. Some organizations sign publicly-distributed software to enable customer verification, building trust through transparency.

Internal trust also improves when teams can verify the provenance of artifacts they depend on. Development teams using libraries from other internal teams can verify signatures to confirm they're using approved versions. This internal verification supports secure collaboration in large organizations with multiple development teams.

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Challenges and Considerations in Cryptographic Signing

While cryptographic signing provides significant security benefits, implementation presents challenges that organizations need to address. Understanding these challenges helps teams plan realistic deployments and avoid common pitfalls.

Key Management Complexity

Managing cryptographic keys at scale introduces operational complexity. Organizations might need hundreds or thousands of keys for different developers, teams, and automated systems. Each key requires secure generation, storage, backup, rotation, and eventual revocation.

Key compromise scenarios need planned responses. If a developer's signing key gets compromised, teams must revoke the key, re-sign any artifacts signed with it, and update verification configurations. The blast radius of key compromise depends on what that key protected, making key segmentation important for limiting impact.

Backup and recovery procedures for signing keys require careful design. Backups must remain secure to prevent compromise, but accessibility during disaster recovery can't be so restricted that recovery becomes impossible. Many organizations use threshold cryptography or split keys across multiple secure locations to balance these concerns.

Performance and Scalability

Signing and verification operations consume computational resources. High-throughput build systems might generate thousands of artifacts per day, each requiring signing. Large artifacts like container images might take significant time to hash and sign. Organizations need to plan infrastructure capacity for signing workloads.

Verification at scale presents similar challenges. Deploying a microservices application might require verifying signatures on dozens of container images. Each verification involves cryptographic operations and potentially network calls to retrieve public keys or check revocation status. Caching strategies and optimized verification workflows help maintain performance.

Developer Experience Impact

Additional steps in developer workflows can create friction that reduces productivity or encourages workarounds. If signing processes are too cumbersome, developers might resist adoption or find ways to bypass requirements. Balancing security needs with developer experience requires careful design and iteration.

Tool integration that fits naturally into existing workflows reduces friction. Automatic signing during git commits or build processes requires less manual intervention than separate signing steps. Clear error messages when verification fails help developers troubleshoot issues without security team intervention.

The learning curve for cryptographic concepts shouldn't block developers from their primary work. Providing good defaults, clear documentation, and responsive support helps teams adopt signing practices without becoming cryptography experts. Abstracting complexity where possible while maintaining security properties requires thoughtful design.

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Cryptographic Signing Standards and Frameworks

Industry standards and frameworks guide implementation of cryptographic signing across organizations. These standards promote interoperability, define security requirements, and codify best practices learned from collective experience.

SLSA Framework

Supply chain Levels for Software Artifacts defines progressive requirements for supply chain security, with cryptographic signing playing a central role. The SLSA levels describe increasingly stringent controls, from basic provenance documentation to comprehensive integrity guarantees throughout the build process.

Organizations adopt SLSA levels incrementally, starting with basic signing and progressing toward higher levels as capabilities mature. Each level requires specific attestations about the build process, all protected by cryptographic signatures. This progressive approach makes SLSA accessible to organizations at different security maturity stages.

in-toto Framework

The in-toto framework provides tools and specifications for creating cryptographically verifiable records of the entire software supply chain. Supply chain steps each produce signed attestations documenting inputs, outputs, and the operations performed. Consumers verify that artifacts passed through required steps executed by authorized parties.

in-toto layouts define allowed supply chain workflows, specifying which steps must occur and who can perform them. This policy-based approach enables organizations to enforce process requirements through cryptographic verification rather than relying solely on access controls or procedural compliance.

Sigstore Project

Sigstore addresses practical challenges in signing adoption by providing free, easy-to-use signing services and tools. The project includes Cosign for container signing, Fulcio for certificate issuance, and Rekor for transparency logging. These tools reduce barriers to signing adoption by handling key management complexity and providing verifiable public signing records.

The transparency log maintained by Rekor creates a public record of signatures, enabling detection of misissuance or compromise. This transparency builds on lessons from certificate transparency in web PKI, applying similar principles to software artifact signing. Organizations can operate their own Sigstore infrastructure or use the public instance.

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Integrating Cryptographic Signing with Security Tools

Cryptographic signing works alongside other security tools to create defense in depth. Integration with vulnerability scanning, policy enforcement, and monitoring systems amplifies the value of each component.

Vulnerability scanners can verify signatures before scanning artifacts, ensuring they analyze genuine artifacts rather than potentially compromised versions. Some scanners sign their scan results, creating verifiable records of which vulnerabilities were identified in which artifact versions. This signing creates an audit trail connecting artifacts to their security assessments.

Policy enforcement systems use signature verification to make deployment decisions. Admission controllers in Kubernetes can require valid signatures before allowing pod creation. These enforcement points prevent deployment of unsigned or invalidly signed artifacts, regardless of how they entered the environment. The combination of signing and policy enforcement creates robust controls that are difficult to bypass.

Runtime verification provides defense against attacks that might bypass build-time controls. Systems can verify signatures when loading libraries or modules, ensuring that even if malicious code reaches production systems, it won't execute. This runtime verification creates a final security checkpoint protecting production environments.

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Future Directions in Cryptographic Signing

Cryptographic signing continues evolving as threats advance and technology capabilities expand. Several trends shape the future of signing practices in software development.

Post-Quantum Cryptography

Quantum computers threaten current public-key cryptography algorithms. Organizations need to plan transitions to quantum-resistant algorithms before quantum computers become powerful enough to break existing signatures. Standards bodies are developing and evaluating post-quantum signature schemes that remain secure against quantum attacks.

Migration to post-quantum algorithms will require updating signing tools, key management systems, and verification infrastructure. Organizations should track standardization efforts and plan migration timelines that ensure security before quantum threats materialize. The transition will likely involve supporting multiple algorithms during a migration period.

Automated Trust Decisions

Machine learning and policy automation increasingly drive trust decisions based on signatures and associated metadata. Systems might automatically approve deployment of artifacts signed by specific keys, built from approved repositories, and scanned without critical vulnerabilities. This automation speeds deployment while maintaining security controls.

Risk scoring systems can incorporate signature verification results alongside other security signals. An artifact with valid signatures from known keys might receive lower risk scores than unsigned artifacts from unknown sources. These scores inform automated decisions and help security teams prioritize manual review efforts.

Hardware Root of Trust

Hardware security features in processors and specialized security chips provide stronger protection for signing keys. Trusted Platform Modules, secure enclaves, and confidential computing environments create isolated execution contexts where keys never exist in unprotected memory. These hardware roots of trust raise the bar for attackers attempting to steal signing keys.

Cloud providers increasingly offer signing services backed by hardware security modules, making high-assurance signing accessible without hardware procurement. These managed services handle key generation, storage, and signing operations while preventing key extraction. Organizations gain security benefits without managing complex hardware infrastructure.

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Strengthen Your Software Supply Chain with Kusari

Implementing comprehensive cryptographic signing across your software supply chain requires specialized expertise and purpose-built tools. Kusari provides end-to-end supply chain security solutions that integrate cryptographic signing with policy enforcement, attestation verification, and compliance reporting. Our platform helps DevSecOps teams implement SLSA requirements, verify artifact integrity, and enforce signing policies across development and deployment pipelines.

If you're ready to strengthen your software supply chain security through cryptographic signing and attestation verification, schedule a demo with Kusari to see how our platform can help your organization achieve supply chain security goals.

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What are the Main Benefits of Implementing Cryptographic Signing?

The main benefits of implementing cryptographic signing span security, compliance, and operational domains. Cryptographic signing provides verifiable proof of artifact origin and integrity, preventing attackers from substituting malicious code for legitimate software components. This protection extends throughout the software supply chain, from source code commits through deployment in production environments.

Organizations gain compliance advantages through the audit trails that cryptographic signing creates. Signed artifacts and attestations provide tamper-evident records satisfying regulatory requirements for software provenance and change tracking. These records support incident investigation by proving which code versions were deployed and who authorized them.

Operational benefits include faster incident response and more confident deployment processes. When teams trust that artifacts haven't been tampered with, they can deploy with confidence knowing signatures verify integrity. Detection of signature verification failures provides early warning of potential compromises or system errors, enabling teams to investigate before problems escalate.

Trust between teams improves when signatures enable verification of artifact sources. Development teams using components from other internal teams can verify signatures rather than relying on assumed trustworthiness. This verifiable trust supports secure collaboration in large organizations with complex software ecosystems.

How Does Cryptographic Signing Differ from Code Encryption?

Cryptographic signing and code encryption serve different security objectives and provide distinct protections. Cryptographic signing focuses on authenticity and integrity, proving who created an artifact and detecting any modifications. Encryption focuses on confidentiality, preventing unauthorized parties from reading protected information. These complementary techniques address different threats in comprehensive security strategies.

Signed artifacts can be publicly readable while still providing security value. The signature proves origin and integrity without hiding content. This property makes signing suitable for open-source software and publicly distributed applications where hiding code isn't possible or desired. Encryption, by contrast, renders content unreadable to parties without decryption keys.

The key management requirements differ between signing and encryption. Cryptographic signing uses public-private key pairs where public keys can be freely distributed for verification. Anyone can verify a signature without compromising security. Encryption requires protecting both encryption and decryption keys, with key distribution presenting challenges when many parties need access to encrypted data.

Organizations often use both signing and encryption together. Development teams might encrypt sensitive source code in storage while signing commits to verify authorship. Build systems might encrypt artifacts in transit while signing them to enable integrity verification. The techniques complement rather than replace each other in defense-in-depth strategies.

What Tools and Technologies Support Cryptographic Signing?

Multiple tools and technologies enable cryptographic signing across different parts of the software development lifecycle. Version control systems like Git include built-in support for commit signing using GPG keys. Developers configure their Git clients with signing keys and enable commit signing through configuration options. Platforms like GitHub and GitLab display verification status for signed commits, making signature verification visible during code review.

Container signing tools address the specific needs of containerized applications. Cosign from the Sigstore project provides straightforward container image signing and verification. Docker Content Trust implements signing using Notary, while cloud provider registries offer integrated signing capabilities. These tools integrate with container registries and Kubernetes deployments to enable comprehensive container signature verification.

Build pipeline signing requires integration with CI/CD platforms. Jenkins, GitLab CI, GitHub Actions, and other pipeline tools support signing through plugins or custom steps. Organizations might use dedicated signing services or integrate with key management systems to access signing keys securely during automated builds. The signing process becomes a standard build step that executes after successful compilation.

Package managers and distribution systems include signing capabilities for software packages. NPM, Maven, PyPI, and other package repositories support signed packages that users can verify before installation. Operating system package managers like apt and yum require signatures on packages, preventing installation of tampered software through verification requirements.

Key management systems from cloud providers and security vendors provide infrastructure for managing signing keys at scale. AWS KMS, Azure Key Vault, Google Cloud KMS, and HashiCorp Vault offer secure key storage with APIs for signing operations. These systems prevent key extraction while enabling automated signing through API calls, balancing security with operational needs.

How Can Organizations Get Started with Cryptographic Signing?

Organizations beginning their cryptographic signing journey should start with clear objectives and realistic scope. Identifying high-value use cases helps focus initial efforts where signing provides maximum security benefit. Production deployment pipelines, customer-facing applications, and privileged access tools typically represent good starting points because compromise would have serious consequences.

Building foundational key management infrastructure should precede broad signing adoption. Teams need secure methods for generating, storing, and accessing signing keys before rolling out signing requirements. Starting with cloud key management services or existing PKI infrastructure reduces initial complexity compared to building custom key management systems. The key management approach should scale to support eventual organization-wide adoption.

Pilot projects allow teams to learn signing practices with limited scope and risk. Choosing a single application or development team for initial implementation provides valuable lessons about tool integration, training needs, and process changes. Success with the pilot demonstrates value and builds organizational knowledge that supports broader rollout.

Developer training must accompany technical implementation to ensure successful adoption. Training should cover both practical steps for signing commits and artifacts, and the security principles underlying signing requirements. Hands-on workshops where developers configure their tools and sign their first commits build confidence and identify common challenges that documentation should address.

Gradual enforcement prevents disruption while encouraging adoption. Starting with visibility into signature status without blocking unsigned artifacts allows teams to adapt their workflows. Monitoring signature verification rates helps identify teams needing additional support. Tightening requirements over time through warning periods before enforcement gives developers opportunity to adjust without blocking their work.

Integration with existing security tools maximizes value from signing investments. Connecting signature verification to vulnerability scanners, policy engines, and monitoring systems creates comprehensive security that's greater than the sum of individual components. These integrations help justify signing investments by demonstrating clear security improvements.

Building Trust Through Verified Software Integrity

Cryptographic signing transforms software development from trust-based processes to verification-based security. Rather than assuming that artifacts originated from trusted sources and haven't been modified, teams can cryptographically verify these properties. This shift from trust to verification represents a fundamental improvement in software supply chain security that addresses increasingly sophisticated threats.

The journey to comprehensive signing practices takes time and requires organizational commitment. Technical infrastructure, process changes, and cultural shifts all contribute to successful implementation. Organizations that invest in signing capabilities build competitive advantages through demonstrably more secure software development practices that satisfy customers, regulators, and their own risk management requirements.

As supply chain attacks continue affecting organizations across industries, cryptographic signing moves from optional best practice to essential security control. The mathematical properties of public-key cryptography provide security guarantees that procedural controls simply cannot match. Teams implementing signing today position themselves ahead of eventual regulatory requirements while protecting against current threats.

Starting the cryptographic signing journey begins with understanding the concepts, evaluating tools, and planning infrastructure. Organizations that take these first steps gain immediate security benefits while building foundations for mature supply chain security practices. The investment in cryptographic signing pays dividends through reduced risk, improved compliance posture, and stronger trust in software integrity throughout the development lifecycle and beyond.