Update chapter06.md

wolfSSL/src/chapter06.md

@@ -254,7 +254,7 @@ The `wc_CryptoInfo` structure contains a union of different structures (some of
 To determine the type of cryptographic request and process it accordingly, one would typically use a switch-case statement on the `algo_type` field of the `wc_CryptoInfo` structure. Each case within the switch would correspond to a different cryptographic operation, such as a symmetric cipher, hashing, public key operations, etc. There is a one-to-one mapping between `wc_AlgoType` and the corresponding algo type union, which are commented in the `wc_CryptoInfo` struct definition in
 `wolfssl/wolfcrypt/cryptocb.h`.
 
-The crypto callback should return zero on success, or a nonzero error code on failure. For unsupported algorithms, the callback should return `CRYPTOCB_UNAVAILABLE`, which will cause wolfCrypt to fall back to the internal implementation.
+The crypto callback should return zero on success, or a valid wolfCrypt error code on failure. For unsupported algorithms, the callback should return `CRYPTOCB_UNAVAILABLE`, which will cause wolfCrypt to fall back to the internal implementation.
 
 Here's a simplified example to illustrate this:
 
@@ -266,17 +266,17 @@ int myCryptoCallback(int devId, wc_CryptoInfo* info, void* ctx)
     switch (info->algo_type) {
         case WC_ALGO_TYPE_HASH:
             /* Handle hashing, using algo type union: info->hash */
-            ret = 0; /* or non-zero error code */
+            ret = 0; /* or wolfCrypt error code */
             break;
 
         case WC_ALGO_TYPE_PK:
             /* Handle public key operations, using algo type union: info->pk */
-            ret = 0; /* or non-zero error code */
+            ret = 0; /* or wolfCrypt error code */
             break;
 
         case WC_ALGO_TYPE_CIPHER:
             /* Handle cipher operations, using algo type union: info->cipher */
-            ret = 0; /* or non-zero error code */
+            ret = 0; /* or wolfCrypt error code */
             break;
 
         /* and so on for other algo types... */
@@ -301,24 +301,24 @@ int myCryptoCallback(int devId, wc_CryptoInfo* info, void* ctx)
             switch (info->pk.type) { /* pk type is of type wc_PkType */
                 case WC_PK_TYPE_ECDH:
                     /* use info->pk.ecdh */
-                    ret = 0; /* or non-zero error code */
+                    ret = 0; /* or wolfCrypt error code */
                     break;
 
                 case WC_PK_TYPE_ECDSA_SIGN:
                     /* use info->pk.eccsign */
-                    ret = 0; /* or non-zero error code */
+                    ret = 0; /* or wolfCrypt error code */
                     break;
 
                 case WC_PK_TYPE_ECDSA_VERIFY:
                     /* use info->pk.eccverify */
-                    ret = 0; /* or non-zero error code */
+                    ret = 0; /* or wolfCrypt error code */
                     break;
             }
             break;
 
         case WC_ALGO_TYPE_RNG:
             /* use info->rng */
-            ret = 0; /* or non-zero error code */
+            ret = 0; /* or wolfCrypt error code */
             break;
     }