diff --git a/src/tss2-esys/esys_crypto.c b/src/tss2-esys/esys_crypto.c
index ff9dab3..3cd5086 100644
--- a/src/tss2-esys/esys_crypto.c
+++ b/src/tss2-esys/esys_crypto.c
@@ -144,7 +144,7 @@
     mycontext->hash.hash_len = hash_len;
 
     gcry_error_t r = gcry_md_open(&mycontext->hash.gcry_context,
-                             mycontext->hash.gcry_hash_alg, 0);
+                                  mycontext->hash.gcry_hash_alg, 0);
     if (r != 0) {
         LOG_ERROR("GCry error.");
         free(mycontext);
@@ -409,15 +409,15 @@
  */
 TSS2_RC
 iesys_cryptogcry_hmac_start2b(IESYS_CRYPTO_CONTEXT_BLOB ** context,
-                              TPM2_ALG_ID hmacAlg, TPM2B * b)
+                              TPM2_ALG_ID hmacAlg, TPM2B * key)
 {
-    LOG_TRACE("called for context-pointer %p and 2b-pointer %p", context, b);
-    if (context == NULL || b == NULL) {
+    LOG_TRACE("called for context-pointer %p and 2b-pointer %p", context, key);
+    if (context == NULL || key == NULL) {
         LOG_ERROR("Null-Pointer passed");
         return TSS2_ESYS_RC_BAD_REFERENCE;
     }
-    TSS2_RC ret = iesys_cryptogcry_hmac_start(context, hmacAlg, &b->buffer[0],
-                                              b->size);
+    TSS2_RC ret = iesys_cryptogcry_hmac_start(context, hmacAlg, &key->buffer[0],
+                                              key->size);
     return ret;
 }
 
@@ -537,16 +537,16 @@
  * @retval TSS2_ESYS_RC_GENERAL_FAILURE for errors of the crypto library.
  */
 TSS2_RC
-iesys_cryptogcry_hmac_finish2b(IESYS_CRYPTO_CONTEXT_BLOB ** context, TPM2B * b)
+iesys_cryptogcry_hmac_finish2b(IESYS_CRYPTO_CONTEXT_BLOB ** context, TPM2B * hmac)
 {
-    LOG_TRACE("called for context-pointer %p and 2b-pointer %p", context, b);
-    if (context == NULL || *context == NULL || b == NULL) {
+    LOG_TRACE("called for context-pointer %p and 2b-pointer %p", context, hmac);
+    if (context == NULL || *context == NULL || hmac == NULL) {
         LOG_ERROR("Null-Pointer passed");
         return TSS2_ESYS_RC_BAD_REFERENCE;
     }
-    size_t s = b->size;
-    TSS2_RC ret = iesys_cryptogcry_hmac_finish(context, &b->buffer[0], &s);
-    b->size = s;
+    size_t s = hmac->size;
+    TSS2_RC ret = iesys_cryptogcry_hmac_finish(context, &hmac->buffer[0], &s);
+    hmac->size = s;
     return ret;
 }
 
@@ -847,7 +847,10 @@
                   const char *label,
                   TPM2B_NONCE * contextU,
                   TPM2B_NONCE * contextV,
-                  uint32_t bitLength, uint32_t * counterInOut, BYTE * outKey, BOOL use_digest_size)
+                  uint32_t bitLength,
+                  uint32_t * counterInOut,
+                  BYTE * outKey,
+                  BOOL use_digest_size)
 {
     LOG_DEBUG("IESYS KDFa hmac key hashAlg: %i label: %s bitLength: %i",
               hashAlg, label, bitLength);
@@ -869,6 +872,8 @@
         counter = *counterInOut;
     bytes = use_digest_size ? hlen : (bitLength + 7) / 8;
     LOG_DEBUG("IESYS KDFa hmac key bytes: %i", bytes);
+
+     /* Fill outKey with results from KDFaHmac */
     for (; bytes > 0; subKey = &subKey[hlen], bytes = bytes - hlen) {
         LOG_TRACE("IESYS KDFa hmac key bytes: %i", bytes);
         //if(bytes < (INT32)hlen)
@@ -963,7 +968,7 @@
 
             offset = 0;
             r = Tss2_MU_UINT32_Marshal(counter, &counter_buffer[0], 4, &offset);
-            goto_if_error(r, "Error Tss2_MU_UINT32_Marshal", error);
+            goto_if_error(r, "Error marshaling counter", error);
 
             r = iesys_crypto_hash_update(cryptoContext, &counter_buffer[0], 4);
             goto_if_error(r, "Error hash update", error);
@@ -1137,7 +1142,6 @@
 #define SEXP_ECC_POINT "(ecc (curve %s) (q.x  %sb) (q.y %sb))"
 
     TSS2_RC r;
-    gcry_error_t err;
     char *curveId;
     gcry_sexp_t mpi_tpm_sq = NULL;     /* sexp for public part of TPM  key*/
     gcry_sexp_t mpi_sd = NULL;         /* sexp for private part of ephemeral key */
@@ -1186,8 +1190,7 @@
 
         if (gcry_sexp_build(&ekey_spec, NULL,
                             sexp_ecc_key) != GPG_ERR_NO_ERROR) {
-            goto_error(r, TSS2_ESYS_RC_GENERAL_FAILURE, "gcry_sexp_build",
-                       cleanup);
+            goto_error(r, TSS2_ESYS_RC_GENERAL_FAILURE, "gcry_sexp_build", cleanup);
         }
     }
 
@@ -1225,8 +1228,7 @@
 
     /* Check whether point is on curve */
     if (!gcry_mpi_ec_curve_point(mpi_q, ctx)) {
-        goto_error(r, TSS2_ESYS_RC_GENERAL_FAILURE, "Point not on curve",
-                   cleanup);
+        goto_error(r, TSS2_ESYS_RC_GENERAL_FAILURE, "Point not on curve", cleanup);
     }
 
     /* Store ephemeral public key in Q */
@@ -1262,27 +1264,25 @@
             goto_error(r, TSS2_ESYS_RC_MEMORY, "asprintf", cleanup);
         }
 
-        err = gcry_sexp_build(&mpi_tpm_sq, NULL,
+        if ( gcry_sexp_build(&mpi_tpm_sq, NULL,
                               sexp_point,
                               key->publicArea.unique.ecc.x.size,
                               &key->publicArea.unique.ecc.x.buffer[0],
                               key->publicArea.unique.ecc.y.size,
-                              &key->publicArea.unique.ecc.y.buffer[0]);
-        if (err != GPG_ERR_NO_ERROR) {
-            LOG_ERROR("Function gcry_mpi_scan");
-            return TSS2_ESYS_RC_GENERAL_FAILURE;
+                             &key->publicArea.unique.ecc.y.buffer[0])) {
+            goto_error(r, TSS2_ESYS_RC_GENERAL_FAILURE,
+                       "Function gcry_mpi_scan", cleanup);
+
         }
     }
     offset = 0;
-    r = Tss2_MU_TPMS_ECC_POINT_Marshal(Q,  &out_buffer[0], max_out_size,
-                                       &offset);
+    r = Tss2_MU_TPMS_ECC_POINT_Marshal(Q,  &out_buffer[0], max_out_size, &offset);
     return_if_error(r, "Error marshaling");
     *out_size = offset;
 
     /* Multiply d and Q */
-    if (gcry_mpi_ec_new (&ctx, mpi_tpm_sq, curveId) != GPG_ERR_NO_ERROR) {
-        goto_error(r, TSS2_ESYS_RC_GENERAL_FAILURE, "gcry_mpi_ec_new",
-                   cleanup);
+    if (gcry_mpi_ec_new (&ctx, mpi_tpm_sq, curveId)) {
+        goto_error(r, TSS2_ESYS_RC_GENERAL_FAILURE, "create ec curve", cleanup);
     }
     mpi_tpm_q =  gcry_mpi_ec_get_point ("q", ctx, 1);
     mpi_qd = gcry_mpi_point_new(256);
@@ -1290,8 +1290,8 @@
 
     /* Store the x coordinate of d*Q in Z which will be used for KDFe */
     if (gcry_mpi_ec_get_affine (mpi_x, mpi_y, mpi_qd, ctx)) {
-        goto_error(r, TSS2_ESYS_RC_GENERAL_FAILURE, "Point is at infinity",
-                   cleanup);
+        goto_error(r, TSS2_ESYS_RC_GENERAL_FAILURE,
+                   "Point is at infinity", cleanup);
     }
 
     if (gcry_mpi_print(GCRYMPI_FMT_USG, &Z->buffer[0], TPM2_MAX_ECC_KEY_BYTES,
diff --git a/src/tss2-esys/esys_iutil.c b/src/tss2-esys/esys_iutil.c
index e0a0b2b..fd86a8e 100644
--- a/src/tss2-esys/esys_iutil.c
+++ b/src/tss2-esys/esys_iutil.c
@@ -200,7 +200,8 @@
             if (session->rsrc.misc.rsrc_session.
                 sessionAttributes & TPMA_SESSION_ENCRYPT) {
                 if (*encryptNonce != NULL) {
-                    return_error(TSS2_ESYS_RC_MULTIPLE_ENCRYPT_SESSIONS,
+		    /* Encrypt nonce already found */
+		    return_error(TSS2_ESYS_RC_MULTIPLE_ENCRYPT_SESSIONS,
                                  "More than one encrypt session");
                 }
                 *encryptNonceIdx = i;
@@ -357,9 +358,11 @@
     if (new_esys_object == NULL)
         return_error(TSS2_ESYS_RC_MEMORY, "Out of memory.");
     if (esys_context->rsrc_list == NULL) {
+        /* The first object of the list will be added */
         esys_context->rsrc_list = new_esys_object;
         new_esys_object->next = NULL;
     } else {
+        /* The new object will become the first element of the list */
         new_esys_object->next = esys_context->rsrc_list;
         esys_context->rsrc_list = new_esys_object;
     }
@@ -489,7 +492,8 @@
 
     switch (pub->publicArea.type) {
     case TPM2_ALG_RSA:
-        iesys_crypto_random2b((TPM2B_NONCE *) & esys_context->salt, 
+
+        iesys_crypto_random2b((TPM2B_NONCE *) & esys_context->salt,
                               keyHash_size);
 
         /* When encrypting salts, the encryption scheme of a key is ignored and
@@ -507,9 +511,8 @@
     case TPM2_ALG_ECC:
         r = iesys_crypto_get_ecdh_point(pub, sizeof(TPMU_ENCRYPTED_SECRET),
                                         &Z, &Q,
-                                        (BYTE *) &encryptedSalt->secret[0], 
+                                        (BYTE *) &encryptedSalt->secret[0],
                                         &cSize);
-
         return_if_error(r, "During computation of ECC public key.");
         encryptedSalt->size = cSize;
 
@@ -602,6 +605,8 @@
             encryptNonce = &rsrc_session->nonceTPM;
             esys_context->encryptNonce = encryptNonce;
         }
+
+        /* Session for encryption found */
         if (rsrc_session->sessionAttributes & TPMA_SESSION_DECRYPT) {
             return_if_notnull(*decryptNonce, "More than one decrypt session",
                                TSS2_ESYS_RC_MULTIPLE_DECRYPT_SESSIONS);
@@ -618,11 +623,15 @@
             const uint8_t *paramBuffer;
             r = Tss2_Sys_GetDecryptParam(esys_context->sys, &paramSize,
                                          &paramBuffer);
-            return_if_error(r, "Encrypt parameter not possible");
+            if (r != TSS2_RC_SUCCESS) {
+                return_error(TSS2_ESYS_RC_NO_DECRYPT_PARAM, "Encryption not possible");
+            }
 
             BYTE encrypt_buffer[paramSize];
             memcpy(&encrypt_buffer[0], paramBuffer, paramSize);
             LOGBLOB_DEBUG(paramBuffer, paramSize, "param to encrypt");
+
+            /* AES encryption with key derived with KDFa */
             if (symDef->algorithm == TPM2_ALG_AES) {
                 if (symDef->mode.aes != TPM2_ALG_CFB) {
                     return_error(TSS2_ESYS_RC_BAD_VALUE,
@@ -649,8 +658,9 @@
                 r = Tss2_Sys_SetDecryptParam(esys_context->sys, paramSize,
                                              &encrypt_buffer[0]);
                 return_if_error(r, "Set encrypt parameter not possible");
-
-            } else if (symDef->algorithm == TPM2_ALG_XOR) {
+            }
+            /* XOR obfuscation of parameter */
+            else if (symDef->algorithm == TPM2_ALG_XOR) {
                 r = iesys_xor_parameter_obfuscation(rsrc_session->authHash,
                                                     &rsrc_session->sessionValue[0],
                                                     rsrc_session->sizeSessionValue,
@@ -712,7 +722,10 @@
                      "Invalid length encrypted response.");
     }
     LOGBLOB_DEBUG(rpBuffer, p2BSize, "IESYS encrypt data");
+
     if (symDef->algorithm == TPM2_ALG_AES) {
+
+        /* Parameter decryption with a symmetric AES key derived by KDFa */
         if (symDef->mode.aes != TPM2_ALG_CFB) {
             return_error(TSS2_ESYS_RC_BAD_VALUE,
                          "Invalid symmetric mode (must be CFB)");
@@ -746,6 +759,8 @@
         return_if_error(r, "Decryption error");
 
     } else if (symDef->algorithm == TPM2_ALG_XOR) {
+
+        /* Parameter decryption with XOR obfuscation */
         r = iesys_xor_parameter_obfuscation(rsrc_session->authHash,
                                             &rsrc_session->sessionValue[0],
                                             rsrc_session->sizeSessionValue,
@@ -997,7 +1012,7 @@
                                 &esys_object_aux->rsrc.name.name[0],
                                 sizeof(esys_object_aux->rsrc.name.name),
                                 &offset);
-    return_if_error(r, "Marshalling TPM handle.");
+    return_if_error(r, "Marshaling TPM handle.");
 
     esys_object_aux->rsrc.name.size = offset;
     *esys_object = esys_object_aux;