diff --git a/libp2p/protocols/pubsub/floodsub.nim b/libp2p/protocols/pubsub/floodsub.nim
index cabcc7cfd..137c7920f 100644
--- a/libp2p/protocols/pubsub/floodsub.nim
+++ b/libp2p/protocols/pubsub/floodsub.nim
@@ -27,7 +27,7 @@ const FloodSubCodec* = "/floodsub/1.0.0"
 type
   FloodSub* = ref object of PubSub
     floodsub*: PeerTable      # topic to remote peer map
-    seen*: TimedCache[string] # list of messages forwarded to peers
+    seen*: TimedCache[MessageID] # list of messages forwarded to peers
 
 method subscribeTopic*(f: FloodSub,
                        topic: string,
@@ -183,5 +183,5 @@ method unsubscribeAll*(f: FloodSub, topic: string) {.async.} =
 method initPubSub*(f: FloodSub) =
   procCall PubSub(f).initPubSub()
   f.floodsub = initTable[string, HashSet[PubSubPeer]]()
-  f.seen = TimedCache[string].init(2.minutes)
+  f.seen = TimedCache[MessageID].init(2.minutes)
   f.init()
diff --git a/libp2p/protocols/pubsub/mcache.nim b/libp2p/protocols/pubsub/mcache.nim
index 172e8bc62..4cd39baed 100644
--- a/libp2p/protocols/pubsub/mcache.nim
+++ b/libp2p/protocols/pubsub/mcache.nim
@@ -14,30 +14,30 @@ export sets, tables, messages, options
 
 type
   CacheEntry* = object
-    mid*: string
+    mid*: MessageID
     topicIDs*: seq[string]
 
   MCache* = object of RootObj
-    msgs*: Table[string, Message]
+    msgs*: Table[MessageID, Message]
     history*: seq[seq[CacheEntry]]
     historySize*: Natural
     windowSize*: Natural
 
-func get*(c: MCache, mid: string): Option[Message] =
+func get*(c: MCache, mid: MessageID): Option[Message] =
   result = none(Message)
   if mid in c.msgs:
     result = some(c.msgs[mid])
 
-func contains*(c: MCache, mid: string): bool =
+func contains*(c: MCache, mid: MessageID): bool =
   c.get(mid).isSome
 
-func put*(c: var MCache, msgId: string, msg: Message) =
+func put*(c: var MCache, msgId: MessageID, msg: Message) =
   if msgId notin c.msgs:
     c.msgs[msgId] = msg
     c.history[0].add(CacheEntry(mid: msgId, topicIDs: msg.topicIDs))
 
-func window*(c: MCache, topic: string): HashSet[string] =
-  result = initHashSet[string]()
+func window*(c: MCache, topic: string): HashSet[MessageID] =
+  result = initHashSet[MessageID]()
 
   let
     len = min(c.windowSize, c.history.len)
diff --git a/libp2p/protocols/pubsub/pubsub.nim b/libp2p/protocols/pubsub/pubsub.nim
index c06736fd2..75d432741 100644
--- a/libp2p/protocols/pubsub/pubsub.nim
+++ b/libp2p/protocols/pubsub/pubsub.nim
@@ -50,7 +50,7 @@ type
   TopicPair* = tuple[topic: string, handler: TopicHandler]
 
   MsgIdProvider* =
-    proc(m: Message): string {.noSideEffect, raises: [Defect], nimcall, gcsafe.}
+    proc(m: Message): MessageID {.noSideEffect, raises: [Defect], nimcall, gcsafe.}
 
   Topic* = object
     # make this a variant type if one day we have different Params structs
diff --git a/libp2p/protocols/pubsub/rpc/message.nim b/libp2p/protocols/pubsub/rpc/message.nim
index 7cc2d470c..77f6057c8 100644
--- a/libp2p/protocols/pubsub/rpc/message.nim
+++ b/libp2p/protocols/pubsub/rpc/message.nim
@@ -28,11 +28,16 @@ const PubSubPrefix = toBytes("libp2p-pubsub:")
 declareCounter(libp2p_pubsub_sig_verify_success, "pubsub successfully validated messages")
 declareCounter(libp2p_pubsub_sig_verify_failure, "pubsub failed validated messages")
 
-func defaultMsgIdProvider*(m: Message): string =
-  if m.seqno.len > 0 and m.fromPeer.data.len > 0:
-    byteutils.toHex(m.seqno) & $m.fromPeer
-  else:
-    $m.data.hash & $m.topicIDs.hash
+func defaultMsgIdProvider*(m: Message): MessageID =
+  let mid = 
+    if m.seqno.len > 0 and m.fromPeer.data.len > 0:
+      byteutils.toHex(m.seqno) & $m.fromPeer
+    else:
+      # This part is irrelevant because it's not standard,
+      # We use it exclusively for testing basically and users should 
+      # implement their own logic in the case they use anonymization
+      $m.data.hash & $m.topicIDs.hash
+  mid.toBytes()
 
 proc sign*(msg: Message, privateKey: PrivateKey): CryptoResult[seq[byte]] =
   ok((? privateKey.sign(PubSubPrefix & encodeMessage(msg, false))).getBytes())
diff --git a/libp2p/protocols/pubsub/rpc/messages.nim b/libp2p/protocols/pubsub/rpc/messages.nim
index 301b8a33b..59c199d77 100644
--- a/libp2p/protocols/pubsub/rpc/messages.nim
+++ b/libp2p/protocols/pubsub/rpc/messages.nim
@@ -22,6 +22,8 @@ type
       subscribe*: bool
       topic*: string
 
+    MessageID* = seq[byte]
+
     Message* = object
       fromPeer*: PeerId
       data*: seq[byte]
@@ -38,10 +40,10 @@ type
 
     ControlIHave* = object
       topicID*: string
-      messageIDs*: seq[string]
+      messageIDs*: seq[MessageID]
 
     ControlIWant* = object
-      messageIDs*: seq[string]
+      messageIDs*: seq[MessageID]
 
     ControlGraft* = object
       topicID*: string