diff --git a/Hash2Pub/src/Hash2Pub/FediChord.hs b/Hash2Pub/src/Hash2Pub/FediChord.hs
index d03c5e8..4ca5afc 100644
--- a/Hash2Pub/src/Hash2Pub/FediChord.hs
+++ b/Hash2Pub/src/Hash2Pub/FediChord.hs
@@ -17,6 +17,7 @@ module Hash2Pub.FediChord (
   , NodeCache
   , CacheEntry
   , cacheGetNodeStateUnvalidated
+  , addCacheEntry
   , genNodeID
   , genNodeIDBS
   , genKeyID
@@ -26,7 +27,7 @@ module Hash2Pub.FediChord (
 
 import qualified Data.Map.Strict as Map
 import Network.Socket
-import Data.Time.Clock.System
+import Data.Time.Clock
 import Control.Exception
 
 -- for hashing and ID conversion
@@ -127,9 +128,21 @@ type NodeCache = Map.Map NodeID CacheEntry
 type CacheEntry = (
     Bool
   , NodeState
-  , SystemTime
+  , UTCTime
                   )   -- ^ ( a node's validation status, data, timestamp for cache entry expiration )
 
+addCacheEntry :: NodeState -> Integer -> NodeCache -> IO NodeCache
+addCacheEntry node diffSeconds cache = do
+    now <- getCurrentTime
+    let
+        -- TODO: limit diffSeconds to some maximum value to prevent malicious nodes from inserting entries valid nearly until eternity
+        timestamp = fromInteger (negate diffSeconds) `addUTCTime` now 
+        newCache = Map.insert (nid node) (False, node, timestamp) cache
+    return newCache
+
+-- clean up cache entries: once now - entry > maxAge
+-- transfer difference now - entry to other node
+
 -- | return the @NodeState@ data from a cache entry without checking its validation status
 cacheGetNodeStateUnvalidated :: CacheEntry -> NodeState
 cacheGetNodeStateUnvalidated (_, nState, _) = nState
diff --git a/Hash2Pub/test/FediChordSpec.hs b/Hash2Pub/test/FediChordSpec.hs
index a1d6fee..a566a55 100644
--- a/Hash2Pub/test/FediChordSpec.hs
+++ b/Hash2Pub/test/FediChordSpec.hs
@@ -11,12 +11,6 @@ import Hash2Pub.FediChord
 
 spec :: Spec
 spec = do
-    -- define some sensible test data
-    let
-        nodeDomain = "example.social"
-        vs = 4
-        ip = tupleToHostAddress6 (0x2001, 0x16b8, 0x755a, 0xb110, 0x7d6a, 0x12ab, 0xf0c5, 0x386e)
-
     describe "NodeID" $ do
         it "can store a numeral ID" $
             getNodeID (toNodeID 2342) `shouldBe` 2342
@@ -36,8 +30,8 @@ spec = do
         it "throws an exception when @toNodeID@ on out-of-bound values"
             pending
         it "can be generated" $ do
-            genNodeIDBS ip nodeDomain vs `shouldBe` "\ACK\211\183&S\GS\214\247Xn8\216\232\195\247\162\182\253\210\SOHG7I\194\251\196\130\142RSx\219"
-            genNodeID ip nodeDomain vs `shouldBe` toNodeID 3087945874980469002564169693112490135217795916629034079089428181202645514459
+            genNodeIDBS exampleIp exampleNodeDomain exampleVs `shouldBe` "\ACK\211\183&S\GS\214\247Xn8\216\232\195\247\162\182\253\210\SOHG7I\194\251\196\130\142RSx\219"
+            genNodeID exampleIp exampleNodeDomain exampleVs `shouldBe` toNodeID 3087945874980469002564169693112490135217795916629034079089428181202645514459
 
     describe "ByteString to Integer conversion" $
         it "correctly interprets ByteStrings as unsigned big-endian integers" $ do
@@ -51,27 +45,13 @@ spec = do
             genKeyID "#sometag" `shouldBe` 80934974700514031200587628522801847528706765451025022694022301350330549806700
             genKeyID "#ÄปӥicоdeTag" `shouldBe` 5709825004658123480531764908635278432808461265905814952223156184506818894505
     describe "NodeState" $ do
-        it "can be initialised" $ do
-            let ns = NodeState {
-                nid = toNodeID 12
-              , domain = nodeDomain
-              , ipAddr = ip
-              , dhtPort = 2342
-              , apPort = Nothing
-              , nodeCache = Map.empty
-              , successors = []
-              , predecessors = []
-              , kNeighbours = 3
-              , lNumBestNodes = 3
-              , pNumParallelQueries = 2
-              , jEntriesPerSlice = 2
-                               }
-            print ns
+        it "can be initialised" $
+            print exampleNodeState
         it "can be initialised partly and then modified later" $ do
             let ns = NodeState {
                 nid = undefined
-              , domain = nodeDomain
-              , ipAddr = ip
+              , domain = exampleNodeDomain
+              , ipAddr = exampleIp
               , dhtPort = 2342
               , apPort = Nothing
               , nodeCache = Map.empty
@@ -86,4 +66,37 @@ spec = do
                   nid = genNodeID (ipAddr ns) (domain ns) 3
                              }
             print nsReady
+    describe "NodeCache" $ do
+        it "entries can be added to a node cache" $ do
+            let
+                emptyCache = nodeCache exampleNodeState
+                anotherNode = exampleNodeState { nid = (toNodeID 2^(23::Integer)+1)}
+            newCache <- addCacheEntry exampleNodeState 0 =<< addCacheEntry anotherNode 10 emptyCache
+            Map.size newCache `shouldBe` 2
+
+-- some example data
+
+exampleNodeState :: NodeState
+exampleNodeState = NodeState {
+    nid = toNodeID 12
+  , domain = exampleNodeDomain
+  , ipAddr = exampleIp
+  , dhtPort = 2342
+  , apPort = Nothing
+  , nodeCache = Map.empty
+  , successors = []
+  , predecessors = []
+  , kNeighbours = 3
+  , lNumBestNodes = 3
+  , pNumParallelQueries = 2
+  , jEntriesPerSlice = 2
+                   }
+
+exampleNodeDomain :: String
+exampleNodeDomain = "example.social"
+exampleVs :: (Integral i) => i
+exampleVs = 4
+exampleIp :: HostAddress6
+exampleIp = tupleToHostAddress6 (0x2001, 0x16b8, 0x755a, 0xb110, 0x7d6a, 0x12ab, 0xf0c5, 0x386e)
+