Modern security features on many platforms leverage the eMMC CID to bind encrypted data to a specific piece of hardware. For example, a device might use the CID as a seed to generate a unique encryption key for full-disk encryption. In more advanced security models, the CID is used to derive keys for the Replay Protected Memory Block (RPMB). The RPMB stores sensitive data like secure boot counters and key material. If the eMMC is physically removed and placed in another device, the RPMB will fail to authenticate because the CID—and thus the derived key—won't match, protecting the data from extraction.
| Byte | Val | Field | Decoded | |------|-----|-------|---------| | 15 | 0x15 | MID | Samsung | | 14 | 0x01 | CBX | BGA | | 13-12 | 0x00 0x4D | OID | 0x004D (undefined) | | 11-8 | 0x34 0x47 0x42 0x55 | PNM | "4GBU" ("4GB" class device) | | 7 | 0x01 | PRV | v0.1 (BCD 0x01) | | 6-4 | 0x5A 0x1A 0xC0 | PSN | 5903040 (decimal) | | 3-2 | 0xE8 0x01 | MDT | Aug 2018 (0xE8=year 18, 0x01=Jan? see note ) | emmc cid decoder
Or
# Product Revision (PRV) prv = cid_bytes[9] rev_major = (prv >> 4) & 0x0F rev_minor = prv & 0x0F print(f"Product Revision (PRV): rev_major.rev_minor (BCD)") Modern security features on many platforms leverage the
The CID register is a data field located on the eMMC device. It is accessed by the host processor using the CMD2 command, which forces the eMMC to output the CID data as part of the identification phase. The official JEDEC eMMC standard breaks down this 16-byte (128-bit) block into several distinct fields that together paint a complete picture of the device. The RPMB stores sensitive data like secure boot