RPMC Commands

RPMC Support Using eSPI OOB (eRPMC)

Architecture Specification

ID	Date	Version	Classification
739180	06/01/2025		Public

RPMC Command Codes:

Command	Command OpCode	OpCode Value	OP1 CmdType	Response
Write Root Key Register	OP1	9Bh	00h	RPMC Device, Counter Addr & Status
Update HMAC Key Register	OP1	9Bh	01h	RPMC Device, Counter Addr & Status
Increment Monotonic Counter	OP1	9Bh	02h	RPMC Device, Counter Addr & Status
Request Monotonic Counter	OP1	9Bh	03h	RPMC Device, Counter Addr, Status and Counter Data
Read RPMC Parameters	N/A	9Fh (Note)	N/A	RPMC Parameters

Note:This is not a standard RPMC command and therefore 9Fh is not an RPMC defined OpCode.

All individual fields are Byte wide fields. For a multi-byte field, Most Significant Byte is issued first; Last Significant Byte is issued last. Within a Byte, Most Significant Bit is issued first; Least Significant Bit is issued last.

When an OP1 command is received, the EC device responds a shown in the “RPMC Command Codes” table above when the command completes.

Note:All commands defined below use SHA-256. SHA-384 is left for a future update.