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NXP Data Co-Processor (DCP) - Linux driver

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 disabled in your kernel.

¹i.MX23, i.MX28, i.MX6SL, i.MX6SLL, i.MX6ULL, i.MX6ULZ

Authors

Marek Vasut (original driver)
marex@denx.de

Andrea Barisani (OTP key support and userspace tool)
andrea.barisani@withsecure.com | andrea@inversepath.com

Compiling

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).

Operation

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.

The included dcp_aes_kdf utility provides a reference implementation for data blob encryption/decryption, it can be built like any Go executable or with make dcp_aes_kdf.

License

NXP Data Co-Processor (DCP) - Linux driver https://github.com/usbarmory/mxs-dcp

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.