psa: move mbedtls_psa_get_random() to psa_util.c
Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/psa_util.c b/library/psa_util.c
index 125b173..eda6ca8 100644
--- a/library/psa_util.c
+++ b/library/psa_util.c
@@ -338,6 +338,39 @@
}
#endif /* PSA_WANT_KEY_TYPE_ECC_PUBLIC_KEY */
+/* Wrapper function allowing the classic API to use the PSA RNG.
+ *
+ * `mbedtls_psa_get_random(MBEDTLS_PSA_RANDOM_STATE, ...)` calls
+ * `psa_generate_random(...)`. The state parameter is ignored since the
+ * PSA API doesn't support passing an explicit state.
+ *
+ * In the non-external case, psa_generate_random() calls an
+ * `mbedtls_xxx_drbg_random` function which has exactly the same signature
+ * and semantics as mbedtls_psa_get_random(). As an optimization,
+ * instead of doing this back-and-forth between the PSA API and the
+ * classic API, psa_crypto_random_impl.h defines `mbedtls_psa_get_random`
+ * as a constant function pointer to `mbedtls_xxx_drbg_random`.
+ */
+#if defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG)
+int mbedtls_psa_get_random(void *p_rng,
+ unsigned char *output,
+ size_t output_size)
+{
+ /* This function takes a pointer to the RNG state because that's what
+ * classic mbedtls functions using an RNG expect. The PSA RNG manages
+ * its own state internally and doesn't let the caller access that state.
+ * So we just ignore the state parameter, and in practice we'll pass
+ * NULL. */
+ (void) p_rng;
+ psa_status_t status = psa_generate_random(output, output_size);
+ if (status == PSA_SUCCESS) {
+ return 0;
+ } else {
+ return MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
+ }
+}
+#endif /* MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
+
#endif /* MBEDTLS_PSA_CRYPTO_C */
#if defined(MBEDTLS_PSA_UTIL_HAVE_ECDSA)