PSA: support HMAC_DRBG
Support using HMAC_DRBG instead of CTR_DRBG in the PSA subsystem.
Use HMAC_DRBG if CTR_DRBG is available. Choose between SHA-256 and
SHA-512 based on availability.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/psa_crypto_random.h b/library/psa_crypto_random.h
index 2e7f94d..0f13c13 100644
--- a/library/psa_crypto_random.h
+++ b/library/psa_crypto_random.h
@@ -50,15 +50,48 @@
#else /* MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
-/* Currently, the only supported RNG is Mbed TLS's CTR_DRBG seeded with
- * mbedtls_entropy_func(). */
+/* Choose a DRBG based on configuration and availability */
+#if defined(MBEDTLS_PSA_HMAC_DRBG_MD_TYPE)
+
+#include "mbedtls/hmac_drbg.h"
+
+#elif defined(MBEDTLS_CTR_DRBG_C)
#include "mbedtls/ctr_drbg.h"
+
+#elif defined(MBEDTLS_HMAC_DRBG_C)
+
+#include "mbedtls/hmac_drbg.h"
+#if defined(MBEDTLS_SHA512_C) && defined(MBEDTLS_SHA256_C)
+#include <limits.h>
+#if SIZE_MAX > 0xffffffff
+/* Looks like a 64-bit system, so prefer SHA-512. */
+#define MBEDTLS_PSA_HMAC_DRBG_MD_TYPE MBEDTLS_MD_SHA512
+#else
+/* Looks like a 32-bit system, so prefer SHA-256. */
+#define MBEDTLS_PSA_HMAC_DRBG_MD_TYPE MBEDTLS_MD_SHA256
+#endif
+#elif defined(MBEDTLS_SHA512_C)
+#define MBEDTLS_PSA_HMAC_DRBG_MD_TYPE MBEDTLS_MD_SHA512
+#elif defined(MBEDTLS_SHA256_C)
+#define MBEDTLS_PSA_HMAC_DRBG_MD_TYPE MBEDTLS_MD_SHA256
+#else
+#error "No hash algorithm available for HMAC_DBRG."
+#endif
+
+#else
+#error "No DRBG module available for the psa_crypto module."
+#endif
+
#include "mbedtls/entropy.h"
/** The type of the PSA DRBG context.
*/
+#if defined(MBEDTLS_CTR_DRBG_C)
typedef mbedtls_ctr_drbg_context mbedtls_psa_drbg_context_t;
+#elif defined(MBEDTLS_HMAC_DRBG_C)
+typedef mbedtls_hmac_drbg_context mbedtls_psa_drbg_context_t;
+#endif
/** Initialize the PSA DRBG.
*
@@ -66,7 +99,11 @@
*/
static inline void mbedtls_psa_drbg_init( mbedtls_psa_drbg_context_t *p_rng )
{
+#if defined(MBEDTLS_CTR_DRBG_C)
mbedtls_ctr_drbg_init( p_rng );
+#elif defined(MBEDTLS_HMAC_DRBG_C)
+ mbedtls_hmac_drbg_init( p_rng );
+#endif
}
/** Deinitialize the PSA DRBG.
@@ -75,7 +112,11 @@
*/
static inline void mbedtls_psa_drbg_free( mbedtls_psa_drbg_context_t *p_rng )
{
+#if defined(MBEDTLS_CTR_DRBG_C)
mbedtls_ctr_drbg_free( p_rng );
+#elif defined(MBEDTLS_HMAC_DRBG_C)
+ mbedtls_hmac_drbg_free( p_rng );
+#endif
}
/** The type of the PSA random generator context.
@@ -97,7 +138,7 @@
* 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
+ * \param p_rng The 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.
@@ -105,21 +146,29 @@
* \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.
+ * \retval \c 0 on success.
+ * \return \c MBEDTLS_ERR_xxx_DRBG_xxx or
+ * \c MBEDTLS_ERR_PLATFORM_xxx on failure.
*/
static inline int mbedtls_psa_get_random( void *p_rng,
unsigned char *output,
size_t output_len )
{
+#if defined(MBEDTLS_CTR_DRBG_C)
return( mbedtls_ctr_drbg_random( p_rng, output, output_len ) );
+#elif defined(MBEDTLS_HMAC_DRBG_C)
+ return( mbedtls_hmac_drbg_random( p_rng, output, output_len ) );
+#endif
}
/** The maximum number of bytes that mbedtls_psa_get_random() is expected to
* return.
*/
+#if defined(MBEDTLS_CTR_DRBG_C)
#define MBEDTLS_PSA_RANDOM_MAX_REQUEST MBEDTLS_CTR_DRBG_MAX_REQUEST
+#elif defined(MBEDTLS_HMAC_DRBG_C)
+#define MBEDTLS_PSA_RANDOM_MAX_REQUEST MBEDTLS_HMAC_DRBG_MAX_REQUEST
+#endif
/** Retrieve the DRBG state from the PSA RNG state.
*
@@ -133,7 +182,6 @@
return( &rng->drbg );
}
-
/** Seed the PSA DRBG.
*
* \param rng DRBG context to be seeded.
@@ -149,10 +197,20 @@
mbedtls_psa_random_context_t *rng,
const unsigned char *custom, size_t len )
{
+#if defined(MBEDTLS_CTR_DRBG_C)
return( mbedtls_ctr_drbg_seed( mbedtls_psa_random_state( rng ),
mbedtls_entropy_func,
&rng->entropy,
custom, len ) );
+#elif defined(MBEDTLS_HMAC_DRBG_C)
+ const mbedtls_md_info_t *md_info =
+ mbedtls_md_info_from_type( MBEDTLS_PSA_HMAC_DRBG_MD_TYPE );
+ return( mbedtls_hmac_drbg_seed( mbedtls_psa_random_state( rng ),
+ md_info,
+ mbedtls_entropy_func,
+ &rng->entropy,
+ custom, len ) );
+#endif
}
#endif /* MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */