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38 lines
3.0 KiB
Markdown
38 lines
3.0 KiB
Markdown
# Guidelines for porting Cryptocell to Mbed OS
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Cryptocell (CC) 310 is a hardware accelerator you can port to boards that have CC 310 embedded in their hardware.
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The CC 310 driver consists of three libraries:
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* A common core library (`libcc_core.a`).
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* A platform-specific TRNG library containing TRNG-related information for sampling sufficient entropy on the specific platform (`libcc_trng.a`).
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* A platform-specific library containing extra information, such as the CC register's base addresses on the specific board (`libcc_ext.a`).
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Library version information:
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* The CC 310 libraries were built from version `arm_sw-cc310-1.1.0.1285`.
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* The `IAR` libraries were built using `IAR ANSI C/C++ Compiler V7.80.1.11864/W32 for ARM` with `--cpu Cortex-M4f`.
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* The `ARM` libraries were built using `ARM Compiler 5.06 update 4 (build 422)` with `--cpu cortex-m4`.
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* The `GCC_ARM` libraries were built using `arm-none-eabi-gcc 6.3.1 20170620 (release)` with `-mcpu=cortex-m4`.
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To port your CC 310 driver to Mbed OS on your specific target:
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1. In `targets.json`, add the following to your target:
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* `MBEDTLS_CONFIG_HW_SUPPORT` to `macros_add` key. This instructs Mbed TLS to look for an alternative cryptographic implementation.
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* `CRYPTOCELL310` to `feature`. Use this in your common code that you need to remove from compilation in case CC exists in your board. Use `#if !defined(FEATURE_CRYPTOCELL310)` and `#if defined(FEATURE_CRYPTOCELL310)`.
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1. In `objects.h`, include `objects_cryptocell.h`. You can use the `FEATURE_CRYPTOCELL310` precompilation check as defined above.
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1. In `features/cryptocell/FEATURE_CRYPTOCELL310/TARGET_<target name>`, add your platform-specific libraries for all toolchains in `TOOLCHAIN_ARM`, `TOOLCHAIN_GCC_ARM` and `TOOLCHAIN_IAR` respectively.
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1. Add your CC setup code:
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* Implement `crypto_platform_setup()` and `crypto_platform_terminate()` to enable CC on your platform, in case you have board-specific setup functionality, required for CC setup. You MUST call `SaSi_LibInit()` and `SaSi_LibFini()` in these functions.
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* Define `crypto_platform_ctx` in `crypto_device_platform.h` in a way that suits your implementation.
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## Enabling optional alternative drivers
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Three additional modules that are not enabled by default have alternative implementation support. This allows backward compatibility because these modules don't have full functionality and returns `MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED` for some features. The modules are:
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* `AES`, which only supports 128 bit key size, as opposed to previous support for all key sizes.
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* `CMAC`, which only supports AES 128 bit key size, as opposed to previous support for DES and all key sizes.
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* `SHA512`, which only supports SHA512, as opposed to previous support for SHA384, as well.
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To enable these modules, define `MBEDTLS_AES_ALT`, `MBEDTLS_CMAC_ALT` and `MBEDTLS_SHA512_ALT`, either in `mbed_app.json` or in your `MBEDTLS_USER_CONFIG_FILE`, to have hardware accelerated module with reduced RAM size, on the expense of full functionality.
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