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>

include/mbedtls/check_config.h

@@ -573,7 +573,7 @@
 #endif
 
 #if defined(MBEDTLS_PSA_CRYPTO_C) &&                                    \
-    !( ( defined(MBEDTLS_CTR_DRBG_C) &&                                 \
+    !( ( ( defined(MBEDTLS_CTR_DRBG_C) || defined(MBEDTLS_HMAC_DRBG_C) ) && \
          defined(MBEDTLS_ENTROPY_C) ) ||                                \
        defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG) )
 #error "MBEDTLS_PSA_CRYPTO_C defined, but not all prerequisites (missing RNG)"

include/mbedtls/config.h

@@ -3146,6 +3146,7 @@
  * Module:  library/psa_crypto.c
  *
  * Requires: either MBEDTLS_CTR_DRBG_C and MBEDTLS_ENTROPY_C,
+ *           or MBEDTLS_HMAC_DRBG_C and MBEDTLS_ENTROPY_C,
  *           or MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG.
  *
  */

library/psa_crypto.c

@@ -63,7 +63,6 @@
 #include "mbedtls/cipher.h"
 #include "mbedtls/ccm.h"
 #include "mbedtls/cmac.h"
-#include "mbedtls/ctr_drbg.h"
 #include "mbedtls/des.h"
 #include "mbedtls/ecdh.h"
 #include "mbedtls/ecp.h"
@@ -214,6 +213,8 @@ psa_status_t mbedtls_to_psa_error( int ret )
         case MBEDTLS_ERR_CMAC_HW_ACCEL_FAILED:
             return( PSA_ERROR_HARDWARE_FAILURE );
 
+#if !( defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG) ||      \
+       defined(MBEDTLS_PSA_HMAC_DRBG_MD_TYPE) )
         case MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED:
             return( PSA_ERROR_INSUFFICIENT_ENTROPY );
         case MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG:
@@ -221,6 +222,7 @@ psa_status_t mbedtls_to_psa_error( int ret )
             return( PSA_ERROR_NOT_SUPPORTED );
         case MBEDTLS_ERR_CTR_DRBG_FILE_IO_ERROR:
             return( PSA_ERROR_INSUFFICIENT_ENTROPY );
+#endif
 
         case MBEDTLS_ERR_DES_INVALID_INPUT_LENGTH:
             return( PSA_ERROR_NOT_SUPPORTED );
@@ -239,6 +241,17 @@ psa_status_t mbedtls_to_psa_error( int ret )
         case MBEDTLS_ERR_GCM_HW_ACCEL_FAILED:
             return( PSA_ERROR_HARDWARE_FAILURE );
 
+#if !defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG) &&        \
+    defined(MBEDTLS_PSA_HMAC_DRBG_MD_TYPE)
+        case MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED:
+            return( PSA_ERROR_INSUFFICIENT_ENTROPY );
+        case MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG:
+        case MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG:
+            return( PSA_ERROR_NOT_SUPPORTED );
+        case MBEDTLS_ERR_HMAC_DRBG_FILE_IO_ERROR:
+            return( PSA_ERROR_INSUFFICIENT_ENTROPY );
+#endif
+
         case MBEDTLS_ERR_MD2_HW_ACCEL_FAILED:
         case MBEDTLS_ERR_MD4_HW_ACCEL_FAILED:
         case MBEDTLS_ERR_MD5_HW_ACCEL_FAILED:

library/psa_crypto_random.h

@@ -50,15 +50,48 @@ static inline void *mbedtls_psa_random_state( mbedtls_psa_random_context_t *rng
 
 #else /* MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
 
-/* Currently, the only supported RNG is Mbed TLS's CTR_DRBG seeded with
+/* Choose a DRBG based on configuration and availability */
- * mbedtls_entropy_func(). */
+#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 @@ typedef mbedtls_ctr_drbg_context mbedtls_psa_drbg_context_t;
  */
 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_init( mbedtls_psa_drbg_context_t *p_rng )
  */
 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 @@ typedef struct
  * 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 @@ typedef struct
  * \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.
+ * \retval              \c 0 on success.
- * \return              #MBEDTLS_ERR_CTR_DRBG_ENTROPY_SOURCE_FAILED or
+ * \return              \c MBEDTLS_ERR_xxx_DRBG_xxx or
- *                      #MBEDTLS_ERR_CTR_DRBG_REQUEST_TOO_BIG on failure.
+ *                      \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 @@ static inline mbedtls_psa_drbg_context_t *mbedtls_psa_random_state(
     return( &rng->drbg );
 }
 
-
 /** Seed the PSA DRBG.
  *
  * \param rng           DRBG context to be seeded.
@@ -149,10 +197,20 @@ static inline int mbedtls_psa_drbg_seed(
     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 */

tests/scripts/all.sh

@@ -915,10 +915,6 @@ component_test_no_ctr_drbg () {
     msg "build: Full minus CTR_DRBG"
     scripts/config.py full
     scripts/config.py unset MBEDTLS_CTR_DRBG_C
-    scripts/config.py unset MBEDTLS_PSA_CRYPTO_C # requires CTR_DRBG
-    scripts/config.py unset MBEDTLS_PSA_CRYPTO_STORAGE_C # requires PSA Crypto
-    scripts/config.py unset MBEDTLS_PSA_CRYPTO_SE_C # requires PSA Crypto
-    scripts/config.py unset MBEDTLS_USE_PSA_CRYPTO # requires PSA Crypto
 
     CC=gcc cmake -D CMAKE_BUILD_TYPE:String=Asan .
     make

tests/suites/test_suite_psa_crypto_init.function

@@ -11,11 +11,21 @@
 #define ENTROPY_MIN_NV_SEED_SIZE                                        \
     MAX(MBEDTLS_ENTROPY_MIN_PLATFORM, MBEDTLS_ENTROPY_BLOCK_SIZE)
 
+#include "psa_crypto_random.h"
+#if defined(MBEDTLS_PSA_HMAC_DRBG_MD_TYPE)
+/* PSA crypto uses the HMAC_DRBG module. It reads from the entropy source twice:
+ * once for the initial entropy and once for a nonce. The nonce length is
+ * half the entropy length. For SHA-256, SHA-384 or SHA-512, the
+ * entropy length is 256 per the documentation of mbedtls_hmac_drbg_seed(),
+ * and PSA crypto doesn't support other hashes for HMAC_DRBG. */
+#define ENTROPY_NONCE_LEN ( 256 / 2 )
+#else
 /* PSA crypto uses the CTR_DRBG module. In some configurations, it needs
  * to read from the entropy source twice: once for the initial entropy
  * and once for a nonce. */
 #include "mbedtls/ctr_drbg.h"
 #define ENTROPY_NONCE_LEN MBEDTLS_CTR_DRBG_ENTROPY_NONCE_LEN
+#endif
 
 #if !defined(MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG)