diff --git a/library/psa_crypto_random.h b/library/psa_crypto_random.h
index c90891d..95974d9 100644
--- a/library/psa_crypto_random.h
+++ b/library/psa_crypto_random.h
@@ -22,5 +22,109 @@
 #ifndef PSA_CRYPTO_RANDOM_H
 #define PSA_CRYPTO_RANDOM_H
 
+/* Currently, the only supported RNG is Mbed TLS's CTR_DRBG seeded with
+ * mbedtls_entropy_func(). */
+
+#include "mbedtls/ctr_drbg.h"
+#include "mbedtls/entropy.h"
+
+/** The type of the PSA DRBG context.
+ */
+typedef mbedtls_ctr_drbg_context mbedtls_psa_drbg_context_t;
+
+/** Initialize the PSA DRBG.
+ *
+ * \param p_rng        Pointer to the Mbed TLS DRBG state.
+ */
+static inline void mbedtls_psa_drbg_init( mbedtls_psa_drbg_context_t *p_rng )
+{
+    mbedtls_ctr_drbg_init( p_rng );
+}
+
+/** Deinitialize the PSA DRBG.
+ *
+ * \param p_rng        Pointer to the Mbed TLS DRBG state.
+ */
+static inline void mbedtls_psa_drbg_free( mbedtls_psa_drbg_context_t *p_rng )
+{
+    mbedtls_ctr_drbg_free( p_rng );
+}
+
+/** The type of the PSA random generator context.
+ *
+ * The random generator context is composed of an entropy context and
+ * a DRBG context.
+ */
+typedef struct
+{
+    void (* entropy_init )( mbedtls_entropy_context *ctx );
+    void (* entropy_free )( mbedtls_entropy_context *ctx );
+    mbedtls_entropy_context entropy;
+    mbedtls_psa_drbg_context_t drbg;
+} mbedtls_psa_random_context_t;
+
+/** Return random data.
+ *
+ * This function is suitable as the \p f_rng parameter to Mbed TLS functions
+ * that require a random generator. Use mbedtls_psa_random_state() to
+ * obtain the \p p_rng parameter.
+ *
+ * \param p_rng         The CTR_DRBG context. This must be
+ *                      mbedtls_psa_random_state( \c rng )
+ *                      where \c rng is a pointer to a
+ *                      ::mbedtls_psa_random_context_t structure.
+ * \param output        The buffer to fill.
+ * \param output_len    The length of the buffer in bytes.
+ *                      It must be at most #MBEDTLS_PSA_RANDOM_MAX_REQUEST.
+ *
+ * \return              \c 0 on success.
+ * \return              #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
+ *                      #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
+ */
+static inline int mbedtls_psa_get_random( void *p_rng,
+                                          unsigned char *output,
+                                          size_t output_len )
+{
+    return( mbedtls_ctr_drbg_random( p_rng, output, output_len ) );
+}
+
+/** The maximum number of bytes that mbedtls_psa_get_random() is expected to
+ * return.
+ */
+#define MBEDTLS_PSA_RANDOM_MAX_REQUEST MBEDTLS_CTR_DRBG_MAX_REQUEST
+
+/** Retrieve the DRBG state from the PSA RNG state.
+ *
+ * \param rng           Pointer to the PSA random generator state.
+ *
+ * \return              The DRBG state (\c p_rng argument ).
+ */
+static inline mbedtls_psa_drbg_context_t *mbedtls_psa_random_state(
+    mbedtls_psa_random_context_t *rng )
+{
+    return( &rng->drbg );
+}
+
+
+/** Seed the PSA DRBG.
+ *
+ * \param rng           DRBG context to be seeded.
+ * \param custom        The personalization string.
+ *                      This can be \c NULL, in which case the personalization
+ *                      string is empty regardless of the value of \p len.
+ * \param len           The length of the personalization string.
+ *
+ * \return              \c 0 on success.
+ * \return              An Mbed TLS error code (\c MBEDTLS_ERR_xxx) on failure.
+ */
+static inline int mbedtls_psa_drbg_seed(
+    mbedtls_psa_random_context_t *rng,
+    const unsigned char *custom, size_t len )
+{
+    return( mbedtls_ctr_drbg_seed( mbedtls_psa_random_state( rng ),
+                                   mbedtls_entropy_func,
+                                   &rng->entropy,
+                                   custom, len ) );
+}
 
 #endif /* PSA_CRYPTO_RANDOM_H */