The NXP Data Co-Processor (DCP) is a built-in hardware module for specific NXP SoCs¹ that implements a dedicated AES cryptographic engine for encryption/decryption operations.
A device specific random 256-bit OTPMK key is fused in each SoC at manufacturing time, this key is unreadable and can only be used by the DCP for AES encryption/decryption of user data, through the Secure Non-Volatile Storage (SNVS) companion block.
This directory contains a Linux kernel driver for the DCP, with the specific functionality of encrypting/decrypting a data blob (typically an encryption key) with the OTPMK made available by the SNVS.
The module allows DCP supported symmetric ciphers and hash functions to be used
through the Linux Crypto API, available algorithms are listed in
/proc/crypto.
The driver is a customized version of the mainline Linux kernel mxs-dcp driver, patched to allow use of the OTPMK released by the SNVS.
Ensure the CONFIG_CRYPTO_DEV_MXS_DCP option is not built-in in your kernel.
¹i.MX23, i.MX28, i.MX6SL, i.MX6SLL, i.MX6ULL, i.MX6ULZ
Marek Vasut (original driver)
marex@denx.de
Andrea Barisani (OTP key support and userspace tool)
andrea.barisani@withsecure.com | andrea@inversepath.com
The following instructions assume compilation on a native armv7 architecture,
when cross compiling adjust ARCH and CROSS_COMPILE variables accordingly.
# the Makefile attempts to locate your Linux kernel source tree, if this fails
# it can be passed with a Makefile variable (e.g. `make KERNEL_SRC=path`)
git clone https://github.com/usbarmory/mxs-dcp
cd mxs-dcp
make
make modules_install
Once installed the resulting module can be loaded in the traditional manner:
modprobe mxs_dcp
The probing of the driver depends on the DCP Device Tree (dts) inclusion in the running Linux kernel, on modern kernel dts files this should already be the case for SoCs that support it (e.g. i.MX6ULL).
IMPORTANT: the unique OTPMK internal key is available only when Secure Boot (HAB) is enabled, otherwise a Non-volatile Test Key (NVTK), identical for each SoC, is used. The secure operation of the DCP and SNVS, in production deployments, should always be paired with Secure Boot activation.
The mxs_dcp module, when not in Trusted or Secure State, issues the
following warning at load time:
mxs_dcp: WARNING - not in Trusted or Secure State, Non-volatile Test Key in effect
When in Trusted or Secure State the module issues a corresponding log message at load time:
mxs_dcp: Trusted State detected
The driver exposes hardware accelerated symmetric ciphers AES-128-ECB
(ecb-aes-dcp) and AES-128-CBC (cbc-aes-dcp). When a key of length 0 is set
through ALG_SET_KEY then the OTPMK derived hardware key (UNIQUE KEY) is
selected, otherwise the passed key is used.
Additionally the driver also exposes hardware accelerated hash functions SHA1
(sha1-dcp) and SHA256 (sha256-dcp).
The INTERLOCK file encryption front-end supports the DCP through this driver, providing a Go userspace implementation reference.
A standalone Go tool, for encryption and decryption, is also available in the dcp_tool.go file.
NXP Data Co-Processor (DCP) - Linux driver https://github.com/usbarmory/mxs-dcp
Copyright (c) WithSecure Corporation
Copyright (c) 2013 Marek Vasut marex@denx.de
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation under version 3 of the License.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
See accompanying LICENSE file for full details.