Cosign

Cosign is designed to ensure the integrity and authenticity of container images in cloud-native environments. At its core, Cosign leverages the Sigstore project, which includes Fulcio, a certificate authority, and Rekor, a transparency log, to provide keyless signing and verification.

Technically, Cosign supports multiple signing mechanisms, including keyless signing with Fulcio and Rekor, hardware and KMS signing, and signing with encrypted private/public keypairs. It integrates with OCI registries, allowing for the signing, verification, and storage of container images. The tool also supports bring-your-own PKI, providing flexibility in security configurations.

Operationally, Cosign can be integrated into CI/CD pipelines using GitHub Actions, such as the cosign-installer action, which verifies the integrity of the Cosign release during installation. This ensures that the signing process is automated and secure. For example, in a GitHub workflow, you can use the cosign-installer action to install Cosign and then sign images using GitHub OIDC tokens.

Key operational considerations include the need for proper authentication via OIDC, which prompts users to sign in with their email addresses to obtain a code signing certificate. The certificate and signature are then stored in the Rekor transparency log and uploaded to the OCI registry. Verification involves passing the expected certificate subject and issuer via specific flags, ensuring that only authenticated and valid images are deployed.

From a technical details perspective, Cosign uses sub-minute granularity for signing and verification operations, and it supports regex patterns for certificate identity and issuer verification. However, it is important to note that while Cosign provides robust security features, it may introduce additional complexity in terms of key management and log retention, particularly in multi-account setups.