The correct answer is Azure Policy.

Azure Policy lets you create rules that evaluate resource properties and enforce allowed configurations across a scope such as a subscription or resource group. You can write or assign a policy that checks Key Vault key properties and denies or modifies requests that do not match the required algorithm or key length, so it is the right tool to enforce cryptographic algorithms and key sizes for keys placed in a vault.

Secret versioning is not correct because that feature manages different versions of stored secrets and does not control cryptographic algorithm or key length for keys.

Access policies are used to grant or restrict who can perform operations on Key Vault secrets keys and certificates and they do not enforce the cryptographic algorithm or key length constraints when keys are created or updated.

Azure Blueprints is not the best choice because blueprints orchestrate the deployment of resources and can include policy assignments but they are a packaging and deployment mechanism rather than the primary enforcement tool for ongoing configuration rules.

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