[new /keys response] added proper hash verification

- Running XOR of all SHA-512 hashes of each denomination's public key is
  compared against the "hash" value in the JSON blob.

- Fixed a bug during creation of the running XOR.

src/exchange/taler-exchange-httpd_keys.c

@@ -2068,23 +2068,26 @@ finish_keys_response (struct TEH_KeyStateHandle *ksh)
 
   last_cpd = GNUNET_TIME_UNIT_ZERO_TS;
 
+  // FIXME: This block contains the implementation of the DEPRICATED
+  // "denom_pubs" array along with the new grouped "denominations".
+  // "denom_pubs" Will be removed sooner or later.
   {
     struct TEH_DenominationKey *dk;
     struct GNUNET_CONTAINER_MultiHashMap *denominations_by_group;
+    // groupData is the value we store for each group meta-data
+    struct groupData
+    {
+      // The json blob with the group meta-data and list of denominations
+      json_t *json;
+
+      // xor of all hashes of denominations in that group
+      struct GNUNET_HashCode hash_xor;
+    };
 
     denominations_by_group =
       GNUNET_CONTAINER_multihashmap_create (1024,
                                             GNUNET_NO /* NO, because keys are only on the stack */);
 
-    /* groupData is the value we store for each group meta-data */
-    struct groupData
-    {
-      /* The json blob with the group meta-data and list of denominations */
-      json_t *json;
-
-      /* xor of all hashes of denominations in that group */
-      struct GNUNET_HashCode hash_xor;
-    };
 
     /* heap = min heap, sorted by start time */
     while (NULL != (dk = GNUNET_CONTAINER_heap_remove_root (heap)))
@@ -2113,7 +2116,6 @@ finish_keys_response (struct TEH_KeyStateHandle *ksh)
                         recoup,
                         denoms,
                         grouped_denominations,
-
                         &grouped_hash_xor))
         {
           GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
@@ -2318,24 +2320,26 @@ finish_keys_response (struct TEH_KeyStateHandle *ksh)
                                                           (const
                                                            void **) &group))
       {
-        struct GNUNET_HashCode hc;
-
-        GNUNET_CRYPTO_hash_xor (&group->hash_xor,
-                                &grouped_hash_xor,
-                                &grouped_hash_xor);
-
+        // Add the XOR over all hashes of denominations in this group to the group
         GNUNET_assert (0 ==
                        json_object_set (
                          group->json,
                          "hash",
                          GNUNET_JSON_PACK (
-                           GNUNET_JSON_pack_data_auto (NULL, &hc))));
+                           GNUNET_JSON_pack_data_auto (NULL,
+                                                       &group->hash_xor))));
 
+        // Add this group to the array
         GNUNET_assert (0 ==
                        json_array_append_new (
                          grouped_denominations,
                          group->json));
 
+        // Build the running XOR over all hash(_xor)
+        GNUNET_CRYPTO_hash_xor (&group->hash_xor,
+                                &grouped_hash_xor,
+                                &grouped_hash_xor);
+
         GNUNET_free (group);
       }
 

src/include/taler_json_lib.h

@@ -370,12 +370,17 @@ TALER_JSON_spec_amount_any_nbo (const char *name,
  **/
 struct TALER_DenominationGroup
 {
-  /* currency must be set prior to calling TALER_JSON_spec_denomination_group */
-  const char *currency;
   enum TALER_DenominationCipher cipher;
   struct TALER_Amount value;
   struct TALER_DenomFeeSet fees;
   struct TALER_AgeMask age_mask;
+
+  // currency must be set prior to calling TALER_JSON_spec_denomination_group
+  const char *currency;
+
+  // hash is/should be the XOR of all SHA-512 hashes of the public keys in this
+  // group
+  struct GNUNET_HashCode hash;
 };
 
 /**

src/json/json_helper.c

@@ -265,6 +265,8 @@ parse_denomination_group (void *cls,
       GNUNET_JSON_spec_uint32 ("age_mask",
                                &group->age_mask.bits),
       &age_mask_missing),
+    GNUNET_JSON_spec_fixed_auto ("hash",
+                                 &group->hash),
     GNUNET_JSON_spec_end ()
   };
   const char *emsg;

src/lib/exchange_api_handle.c

@@ -924,8 +924,13 @@ decode_keys_json (const json_t *resp_obj,
     key_data->age_mask = TALER_extensions_age_restriction_ageMask ();
   }
 
-  /* parse the denomination keys, merging with the
-     possibly EXISTING array as required (/keys cherry picking) */
+  /**
+   * Parse the denomination keys, merging with the
+   * possibly EXISTING array as required (/keys cherry picking).
+   *
+   * The denominations are grouped by common values of
+   *    {cipher, value, fee, age_mask}.
+   **/
   {
     json_t *denominations_by_group;
     json_t *group_obj;
@@ -940,23 +945,25 @@ decode_keys_json (const json_t *resp_obj,
             json_typeof (denominations_by_group));
 
     json_array_foreach (denominations_by_group, group_idx, group_obj) {
-      /* First, parse { cipher, fees, value, age_mask } of the current group */
+      // Running XOR of each SHA512 hash of the denominations' public key in
+      // this group.  Used to compare against group.hash after all keys have
+      // been parsed.
+      struct GNUNET_HashCode group_hash_xor = {0};
 
-      struct TALER_DenominationGroup group = {
-        .currency = currency
-      };
+      // First, parse { cipher, fees, value, age_mask, hash } of the current
+      // group.
+      struct TALER_DenominationGroup group = { .currency = currency };
       struct GNUNET_JSON_Specification group_spec[] = {
         TALER_JSON_spec_denomination_group (NULL, &group),
         GNUNET_JSON_spec_end ()
       };
-
       EXITIF (GNUNET_SYSERR ==
               GNUNET_JSON_parse (group_obj,
                                  group_spec,
                                  NULL,
                                  NULL));
 
-      /* Now, parse the individual denominations */
+      // Now, parse the individual denominations
       {
         json_t *denom_keys_array;
         json_t *denom_key_obj;
@@ -970,9 +977,9 @@ decode_keys_json (const json_t *resp_obj,
 
           memset (&dk, 0, sizeof (dk));
 
-          /* Set the common fields from the group for this particular
-           * denomination.  Required to make the validity check inside
-           * parse_json_denomkey_partially pass */
+          // Set the common fields from the group for this particular
+          // denomination.  Required to make the validity check inside
+          // parse_json_denomkey_partially pass
           dk.key.cipher = group.cipher;
           dk.value = group.value;
           dk.fees = group.fees;
@@ -987,6 +994,15 @@ decode_keys_json (const json_t *resp_obj,
                                                  &key_data->master_pub,
                                                  check_sig ? &hash_xor: NULL));
 
+          // Build the running xor of the SHA512-hash of the public keys
+          {
+            struct TALER_DenominationHashP hc = {0};
+            TALER_denom_pub_hash (&dk.key, &hc);
+            GNUNET_CRYPTO_hash_xor (&hc.hash,
+                                    &group_hash_xor,
+                                    &group_hash_xor);
+          }
+
           for (unsigned int j = 0;
                j<key_data->num_denom_keys;
                j++)
@@ -1019,9 +1035,15 @@ decode_keys_json (const json_t *resp_obj,
           key_data->last_denom_issue_date
             = GNUNET_TIME_timestamp_max (key_data->last_denom_issue_date,
                                          dk.valid_from);
-        }
-      };
-    };
+        }; // json_array_foreach over denominations
+
+        // The calculated group_hash_xor must be the same as group.hash from
+        // the json.
+        EXITIF (0 !=
+                GNUNET_CRYPTO_hash_cmp (&group_hash_xor, &group.hash));
+
+      } // block for parsing individual denominations
+    }; // json_array_foreach over groups of denominations
   }
 
   /* parse the auditor information */