Expected flow, which begins with a device that has already been
provisioned with Prov 4 stage 1:
1. OEMCrypto_InstallOEMPrivateKey()
2. OEMCrypto_GenerateCertificateKeyPair() -> wrapped_csr_priv
3. OEMCrypto_LoadDRMPrivateKey(wrapped_csr_priv)
4. OEMCrypto_PrepAndSignProvisioningRequest() to create a Prov 4
provisioning request message type with a CAST request in the
message body
5. Server sends a Prov 2 response. Server side derivation uses CSR keys
to derive session key, mac keys, and encryption keys.
6. OEMCrypto_DeriveKeysFromSessionKey(), same derivation as server side
7. OEMCrypto_LoadProvisioning(), use derived keys to verify + decrypt
The OEMCrypto_LoadDRMPrivateKey() step can happen before or after the
PrepAndSignProvisioningRequest() call.
Test: tests fail
Bug: 259452440
Merged from https://widevine-internal-review.googlesource.com/172310
Change-Id: Id5e6737b187339ec93e3d0d03c28e2b379d60747
27421a9161