Peer review feedback

Author: dgarske

wolfcrypt/src/port/st/README.md

@@ -41,6 +41,7 @@ To disable portions of the hardware acceleration you can optionally define:
 #define NO_STM32_RNG
 #define NO_STM32_CRYPTO
 #define NO_STM32_HASH
+#define NO_STM32_HMAC
 ```
 
 ### Coding

wolfcrypt/src/port/st/stm32.c

@@ -184,8 +184,7 @@ static void wc_Stm32_Hash_RestoreContext(STM32_HASH_Context* ctx, word32 algo,
         );
 
         /* configure algorithm, mode and data type
-         * mode is HASH_ALGOMODE_HASH or HASH_ALGOMODE_HMAC
-         * (may include HASH_CR_LKEY for HMAC with long key) */
+         * mode is HASH_ALGOMODE_HASH or HASH_ALGOMODE_HMAC */
         HASH->CR |= (algo | mode | HASH_DATATYPE_8B);
 
         /* reset HASH processor */
@@ -560,13 +559,10 @@ int wc_Stm32_Hmac_SetKey(STM32_HASH_Context* stmCtx, int macType,
     /* turn on hash clock */
     STM32_HASH_CLOCK_ENABLE(stmCtx);
 
-    /* initialize hardware for HMAC mode */
+    /* initialize hardware for HMAC mode.
+     * Keys are always pre-hashed in software before reaching this point
+     * (see hmac.c), so keySz will always be <= blockSize here. */
     mode = HASH_ALGOMODE_HMAC;
-#ifdef HASH_CR_LKEY
-    if (keySz > blockSize) {
-        mode |= HASH_CR_LKEY;
-    }
-#endif
     wc_Stm32_Hash_RestoreContext(stmCtx, algo, mode);
 
     /* Phase 1: Feed key into HASH->DIN */