commit 4353b698ed10851dcd97c1064119c6f65eedaa29
author Andrzej Kurek <andrzej.kurek@arm.com> Sun Jul 19 04:58:58 2020 -0400
committer Andrzej Kurek <andrzej.kurek@arm.com> Sun Jul 19 09:00:18 2020 -0400
tree c9db375bd8b7d242556c42d68b1035a6b3aa7ca8
parent f6265441b04dacb7c88e1a8133a13eca9ea245bc

hmac_drbg: make no reseeding behaviour explicit

Add a flag to the hmac_drbg context that will signal that reseeding is not required.
Change tests and one ecdsa call to not use reseeding, as was the previous case.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>

library/hmac_drbg.c

diff --git a/library/hmac_drbg.c b/library/hmac_drbg.c
index fc7aea9..d8669c3 100644
--- a/library/hmac_drbg.c
+++ b/library/hmac_drbg.c
@@ -63,6 +63,7 @@
     memset( ctx, 0, sizeof( mbedtls_hmac_drbg_context ) );
 
     ctx->prediction_resistance = MBEDTLS_HMAC_DRBG_PR_OFF;
+    ctx->reseed_flag = MBEDTLS_HMAC_DRBG_RESEED;
 #if defined(MBEDTLS_THREADING_C)
     mbedtls_mutex_init( &ctx->mutex );
 #endif
@@ -389,6 +390,15 @@
 }
 
 /*
+ * Set the reseeding flag
+ */
+void mbedtls_hmac_drbg_set_reseeding( mbedtls_hmac_drbg_context *ctx,
+                                      int reseed_flag )
+{
+    ctx->reseed_flag = reseed_flag;
+}
+
+/*
  * Set entropy length grabbed for seeding
  */
 int mbedtls_hmac_drbg_set_entropy_len( mbedtls_hmac_drbg_context *ctx, size_t len )
@@ -434,14 +444,20 @@
         return( MBEDTLS_ERR_HMAC_DRBG_INPUT_TOO_BIG );
 
     /* 1. (aka VII and IX) Check reseed counter and PR */
-    if( ctx->f_entropy != NULL && /* For no-reseeding instances */
-            ( ctx->prediction_resistance == MBEDTLS_HMAC_DRBG_PR_ON ||
-              ctx->reseed_counter > ctx->reseed_interval ) )
+    if( ctx->reseed_flag != MBEDTLS_HMAC_DRBG_NO_RESEED &&
+        ( ctx->prediction_resistance == MBEDTLS_HMAC_DRBG_PR_ON ||
+          ctx->reseed_counter > ctx->reseed_interval ) )
     {
-        if( ( ret = mbedtls_hmac_drbg_reseed( ctx, additional, add_len ) ) != 0 )
-            return( ret );
-
-        add_len = 0; /* VII.4 */
+            if( ctx->f_entropy == NULL )
+            {
+                return( MBEDTLS_ERR_HMAC_DRBG_ENTROPY_SOURCE_FAILED );
+            }
+            else
+            {
+                if( ( ret = mbedtls_hmac_drbg_reseed( ctx, additional, add_len ) ) != 0 )
+                    return( ret );
+                add_len = 0; /* VII.4 */
+            }
     }
 
     /* 2. Use additional data if any */