File platform.h

This file contains the definitions and functions of the Mbed TLS platform abstraction layer.

The platform abstraction layer removes the need for the library to directly link to standard C library functions or operating system services, making the library easier to port and embed. Application developers and users of the library can provide their own implementations of these functions, or implementations specific to their platform, which can be statically linked to the library or dynamically configured at runtime.

When all compilation options related to platform abstraction are disabled, this header just defines mbedtls_xxx function names as aliases to the standard xxx function.

Most modules in the library and example programs are expected to include this header.

Defines

mbedtls_free

mbedtls_calloc

MBEDTLS_EXIT_SUCCESS

MBEDTLS_EXIT_FAILURE

MBEDTLS_PLATFORM_HAVE_DEV_RANDOM

Functions

int mbedtls_platform_set_fprintf(int (*fprintf_func)(FILE *stream, const char*, ...))

This function dynamically configures the fprintf function that is called when the mbedtls_fprintf() function is invoked by the library.

Parameters:: fprintf_func – The fprintf function implementation.
Returns:: 0.

int mbedtls_platform_set_printf(int (*printf_func)(const char*, ...))

This function dynamically configures the snprintf function that is called when the mbedtls_snprintf() function is invoked by the library.

Note

The snprintf implementation should conform to C99:

it must always correctly zero-terminate the buffer (except when n == 0, then it must leave the buffer untouched)
however it is acceptable to return -1 instead of the required length when the destination buffer is too short.
It must support common modifiers in formats, including "zu" for a size_t parameter and "lld" for a long long parameter.
Floating point support is not required.

Parameters:: printf_func – The printf function implementation.
Returns:: 0 on success.

int mbedtls_platform_set_snprintf(int (*snprintf_func)(char *s, size_t n, const char *format, ...))

This function allows configuring a custom snprintf function pointer.

Parameters:: snprintf_func – The snprintf function implementation.
Returns:: 0 on success.

int mbedtls_platform_set_vsnprintf(int (*vsnprintf_func)(char *s, size_t n, const char *format, va_list arg))

Set your own snprintf function pointer.

Parameters:: vsnprintf_func – The vsnprintf function implementation
Returns:: 0

int mbedtls_platform_set_setbuf(void (*setbuf_func)(FILE *stream, char *buf))

Dynamically configure the function that is called when the mbedtls_setbuf() function is called by the library.

Parameters:: setbuf_func – The setbuf function implementation
Returns:: 0

int mbedtls_platform_set_exit(void (*exit_func)(int status))

This function dynamically configures the exit function that is called when the mbedtls_exit() function is invoked by the library.

Parameters:: exit_func – The exit function implementation.
Returns:: 0 on success.

int mbedtls_platform_set_nv_seed(int (*nv_seed_read_func)(unsigned char *buf, size_t buf_len), int (*nv_seed_write_func)(unsigned char *buf, size_t buf_len))

This function allows configuring custom seed file writing and reading functions.

Parameters:

nv_seed_read_func – The seed reading function implementation.
nv_seed_write_func – The seed writing function implementation.

Returns:

0 on success.

int mbedtls_platform_get_entropy(psa_driver_get_entropy_flags_t flags, size_t *estimate_bits, unsigned char *output, size_t output_size)

User defined callback function that is used from the entropy module to gather entropy data from some hardware device.

Note

This function is not meant to be called by application code, and it is not guaranteed that this function will exist or will behave in the same way in future versions of the library. Applications should call psa_generate_random() to obtain random data.

Warning

For the time being TF-PSA-Crypto only supports implementations that return a maximum entropy output on each call, i.e. estimate_bits = 8 * output_size. Returning a smaller entropy content is the same as returning PSA_ERROR_INSUFFICIENT_ENTROPY so the hardware polling will fail. In the future TF-PSA-Crypto will be smarter and capable to cope with entropy sources with lower entropy content (i.e. 0 < estimate_bits < 8 * output_size) by calling the callback function in loop.

Parameters:

flags – A mask of PSA_DRIVER_GET_ENTROPY_xxx flags. As of TF-PSA-Crypto 1.0, this is always 0.
estimate_bits – [out] Measure of the entropy content (in bits) of the data written in the output buffer.
output – [out] Output buffer where the entropy data will be stored.
output_size – Size of the output buffer in bytes.

Return values:

0 – Success.
PSA_ERROR_INSUFFICIENT_ENTROPY – The entropy source failed.
PSA_ERROR_NOT_SUPPORTED – The value of flags is not supported.

int mbedtls_platform_setup(mbedtls_platform_context *ctx)

This function performs any platform-specific initialization operations.

Note

This function should be called before any other library functions.

    Its implementation is platform-specific, and unless
    platform-specific code is provided, it does nothing.

Note

The usage and necessity of this function is dependent on the platform.

Parameters:: ctx – The platform context.
Returns:: 0 on success.

void mbedtls_platform_teardown(mbedtls_platform_context *ctx)

This function performs any platform teardown operations.

Its implementation is platform-specific, and unless platform-specific code is provided, it does nothing.

Note

This function should be called after every other Mbed TLS module has been correctly freed using the appropriate free function.

Note

The usage and necessity of this function is dependent on the platform.

Parameters:: ctx – The platform context.

Variables

int (*mbedtls_fprintf)(FILE *stream, const char *format, ...)

int (*mbedtls_printf)(const char *format, ...)

int (*mbedtls_snprintf)(char *s, size_t n, const char *format, ...)

int (*mbedtls_vsnprintf)(char *s, size_t n, const char *format, va_list arg)

void (*mbedtls_setbuf)(FILE *stream, char *buf)

Function pointer to call for setbuf() functionality (changing the internal buffering on stdio calls).

The library always calls this function with buf equal to NULL.

Note

The library calls this function to disable buffering when reading or writing sensitive data, to avoid having extra copies of sensitive data remaining in stdio buffers after the file is closed. If this is not a concern, for example if your platform’s stdio doesn’t have any buffering, you can set mbedtls_setbuf to a function that does nothing.

void (*mbedtls_exit)(int status)

const char *mbedtls_platform_dev_random

Path to a special file that returns cryptographic-quality random bytes when read.

The default value is MBEDTLS_PLATFORM_DEV_RANDOM. See the documentation of this option for guidance.

int (*mbedtls_nv_seed_read)(unsigned char *buf, size_t buf_len)

int (*mbedtls_nv_seed_write)(unsigned char *buf, size_t buf_len)