Synthèse
Understanding how the Machine DPAPI store becomes populated requires examining how ADFS persists its token-signing key material. During initial deployment, automatic certificate rollover, or manual certificate rotation, ADFS persists its RSA private key material in the machine-scoped CAPI key store at C:\ProgramData\Microsoft\Crypto\RSA\MachineKeys\, protected using machine DPAPI context rather than a user-bound DPAPI context. SharpDPAPI /machine enumeration in the assessed environment confirmed
Understanding how the Machine DPAPI store becomes populated requires examining how ADFS persists its token-signing key material. During initial deployment, automatic certificate rollover, or manual certificate rotation, ADFS persists its RSA private key material in the machine-scoped CAPI key store at C:\ProgramData\Microsoft\Crypto\RSA\MachineKeys\, protected using machine DPAPI context rather than a user-bound DPAPI context. SharpDPAPI /machine enumeration in the assessed environment confirmed that the active machine key material resided under this path, while the CNG Crypto\Keys store was not observed in use in the assessed environment. The protection chain relies on the DPAPI_SYSTEM LSA secret together with machine masterkeys associated with the S-1-5-18 security context, stored in C:\Windows\System32\Microsoft\Protect\S-1-5-18\ as DPAPI-protected key material—both components ultimately resolvable only within highly privileged SYSTEM-level contexts on the host. The corresponding certificate is enrolled into the LocalMachine\My certificate store, from which ADFS retrieves the associated private key during token-signing operations.
The architectural rationale for machine-scoped key storage is operational resilience. A machine-scoped key remains usable across service account password changes, gMSA rotations, system reboots, and service restarts without requiring key reprovisioning or dependency on a specific interactive logon session. This design ensures that the ADFS service can consistently access the signing key regardless of changes to the underlying service account credentials. However, this same design choice has important security implications. Because the private key is protected using Machine DPAPI rather than a user-bound DPAPI context, a sufficiently privileged local process capable of accessing the machine key store and associated DPAPI artifacts may be able to recover the key material independently of the original service logon session.