rpmb · shipping · also Replay Protected Memory Block

RPMB (Replay Protected Memory Block)

RPMB is a dedicated storage area and authenticated access mechanism in eMMC and UFS that uses freshness checks to resist unauthorized modification and replay.

An authenticated write incorporates a write counter; once an accepted write advances that counter, an old authenticated write cannot simply be reused as a current one. This protects a protocol operation, not every copy of an application's data. [1]

RPMB authentication is not encryption. OP-TEE uses distinct authentication and storage-encryption keys, while mmc-utils permits reading RPMB blocks without supplying the optional verification key. Receiving bytes without checking authenticity is not a trusted read. [2] [3]

The eMMC authentication key is programmed once for the device lifetime, making secure provisioning and platform integration important. [2] Hesela's architectural inference: rollback policy still needs trusted software, and replay resistance does not provide a backup if the device fails. [5]

The fTPM paper distinguishes nonce-bound authenticated reads from counter-bound writes; it uses a separate shadow-block commit mechanism for multi-write atomicity. Replay protection alone is not a transaction protocol. [4]

Relations

related

emmc, ufs, replay-attack, rollback-protection, authenticated-encryption

Citations

1. KIOXIA: Introducing Replay Protected Memory Block within the e-MMC and UFS Specifications, November 2022, Rev. 1.1 (accessed 2026-10-17)
2. OP-TEE documentation: Secure storage, RPMB device access and security considerations (accessed 2026-10-17)
3. Linux mmc-utils: RPMB read-block help, pinned commit c6692d5 (accessed 2026-10-17)
4. Raj et al.: fTPM: A Software-Only Implementation of a TPM Chip, USENIX Security 2016, sections 6.1.1 and 9.1 (accessed 2026-10-17)
5. Hesela: eMMC, UFS and RPMB: interface, boot and security boundaries (accessed 2026-10-17)

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