Merge pull request #4110 from gilles-peskine-arm/psa-external-random-in-mbedtls

Expose the PSA RNG in mbedtls

include/mbedtls/psa_util.h

@@ -419,4 +419,90 @@ static inline int mbedtls_psa_tls_ecpoint_to_psa_ec( unsigned char const *src,
 
 #endif /* MBEDTLS_USE_PSA_CRYPTO */
 
+/* Expose whatever RNG the PSA subsystem uses to applications using the
+ * mbedtls_xxx API. The declarations and definitions here need to be
+ * consistent with the implementation in library/psa_crypto_random_impl.h.
+ * See that file for implementation documentation. */
+#if defined(MBEDTLS_PSA_CRYPTO_C)
+
+/* The type of a `f_rng` random generator function that many library functions
+ * take.
+ *
+ * This type name is not part of the Mbed TLS stable API. It may be renamed
+ * or moved without warning.
+ */
+typedef int mbedtls_f_rng_t( void *p_rng, unsigned char *output, size_t output_size );
+
+#if defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG)
+
+/** The random generator function for the PSA subsystem.
+ *
+ * This function is suitable as the `f_rng` random generator function
+ * parameter of many `mbedtls_xxx` functions. Use #MBEDTLS_PSA_RANDOM_STATE
+ * to obtain the \p p_rng parameter.
+ *
+ * The implementation of this function depends on the configuration of the
+ * library.
+ *
+ * \note Depending on the configuration, this may be a function or
+ *       a pointer to a function.
+ *
+ * \note This function may only be used if the PSA crypto subsystem is active.
+ *       This means that you must call psa_crypto_init() before any call to
+ *       this function, and you must not call this function after calling
+ *       mbedtls_psa_crypto_free().
+ *
+ * \param p_rng         The random generator context. This must be
+ *                      #MBEDTLS_PSA_RANDOM_STATE. No other state is
+ *                      supported.
+ * \param output        The buffer to fill. It must have room for
+ *                      \c output_size bytes.
+ * \param output_size   The number of bytes to write to \p output.
+ *                      This function may fail if \p output_size is too
+ *                      large. It is guaranteed to accept any output size
+ *                      requested by Mbed TLS library functions. The
+ *                      maximum request size depends on the library
+ *                      configuration.
+ *
+ * \return              \c 0 on success.
+ * \return              An `MBEDTLS_ERR_ENTROPY_xxx`,
+ *                      `MBEDTLS_ERR_PLATFORM_xxx,
+ *                      `MBEDTLS_ERR_CTR_DRBG_xxx` or
+ *                      `MBEDTLS_ERR_HMAC_DRBG_xxx` on error.
+ */
+int mbedtls_psa_get_random( void *p_rng,
+                            unsigned char *output,
+                            size_t output_size );
+
+/** The random generator state for the PSA subsystem.
+ *
+ * This macro expands to an expression which is suitable as the `p_rng`
+ * random generator state parameter of many `mbedtls_xxx` functions.
+ * It must be used in combination with the random generator function
+ * mbedtls_psa_get_random().
+ *
+ * The implementation of this macro depends on the configuration of the
+ * library. Do not make any assumption on its nature.
+ */
+#define MBEDTLS_PSA_RANDOM_STATE NULL
+
+#else /* !defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG) */
+
+#if defined(MBEDTLS_CTR_DRBG_C)
+#include "mbedtls/ctr_drbg.h"
+typedef mbedtls_ctr_drbg_context mbedtls_psa_drbg_context_t;
+static mbedtls_f_rng_t *const mbedtls_psa_get_random = mbedtls_ctr_drbg_random;
+#elif defined(MBEDTLS_HMAC_DRBG_C)
+#include "mbedtls/hmac_drbg.h"
+typedef mbedtls_hmac_drbg_context mbedtls_psa_drbg_context_t;
+static mbedtls_f_rng_t *const mbedtls_psa_get_random = mbedtls_hmac_drbg_random;
+#endif
+extern mbedtls_psa_drbg_context_t *const mbedtls_psa_random_state;
+
+#define MBEDTLS_PSA_RANDOM_STATE mbedtls_psa_random_state
+
+#endif /* !defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG) */
+
+#endif /* MBEDTLS_PSA_CRYPTO_C */
+
 #endif /* MBEDTLS_PSA_UTIL_H */