diff --git a/README.md b/README.md
index 247228a..89d70f3 100644
--- a/README.md
+++ b/README.md
@@ -125,20 +125,40 @@ With [npm](https://npmjs.org/) installed, run
 $ npm install multifeed
 ```
 
-## Hacks
-
-1. `hypercore-protocol` requires the first feed exchanged to be common between
-   replicating peers. This prevents two strangers from exchanging sets of
-   hypercores. A "fake" hypercore with a hardcoded public key is included in the
-   code to bootstrap the replication process. I discarded the private key, but
-   even if I didn't, it doesn't let me do anything nefarious. You could patch
-   this with your own key of choice.
-2. `hypercore-protocol` requires all feed keys be known upfront: only discovery
-   keys are exchanged (`discoveryKey = hash(key)`), so this module wraps the
-   hypercore replication duplex stream in a secondary duplex stream that
-   exchanges feed public keys upfront before moving on to the hypercore
-   replication mechanism.
+## Replication Policies
 
+You can control which feeds get replicated by providing a policy object:
+
+```js
+
+var randomReplication = {
+  init: function(multifeed) {
+    // called on multifeed.ready
+    // use it for initalization.
+  },
+  have: function(local, share) {
+    // called on peer connection
+    // select which feeds to share
+    share(local.keys, {
+      random: local.keys.map(function() { return Math.random() - 0.5 })
+    })
+  },
+  want: function(remote, request) {
+    // called when remote peer's
+    // share list is available.
+    // remote.keys is always available
+    // remote contains also all custom props sent by remote.
+    var keys = remote.keys.filter(function(k, i){
+        return remote.random[i] > 0.5
+    })
+    request(keys)
+  }
+}
+
+var multi = multifeed(hypercore, './db', { valueEncoding: 'json' })
+multi.use(randomReplication)
+
+```
 ## See Also
 
 - [multifeed-index](https://github.com/noffle/multifeed-index)
diff --git a/index.js b/index.js
index 2a799d5..70f4194 100644
--- a/index.js
+++ b/index.js
@@ -15,9 +15,14 @@ function Multifeed (hypercore, storage, opts) {
   this._feedKeyToFeed = {}
 
   this._hypercore = hypercore
-  this._opts = opts
-
+  this._opts = opts || {}
+  this._middleware = null
   this.writerLock = mutexify()
+  this._middleware = []
+
+  this.key = new Buffer('bee80ff3a4ee5e727dc44197cb9d25bf8f19d50b0f3ad2984cfe5b7d14e75de7', 'hex')
+  if (this._opts.key) this.key = Buffer.from(this._opts.key)
+  else debug('Warning, running multifeed with unsecure default key')
 
   this.closed = false
 
@@ -34,20 +39,9 @@ function Multifeed (hypercore, storage, opts) {
 
   var self = this
   this._ready = readyify(function (done) {
-    // Private key-less constant hypercore to bootstrap hypercore-protocol
-    // replication.
-    var protocolEncryptionKey = new Buffer('bee80ff3a4ee5e727dc44197cb9d25bf8f19d50b0f3ad2984cfe5b7d14e75de7', 'hex')
-    if (self._opts.key) protocolEncryptionKey = Buffer.from(self._opts.key)
-    else debug('Warning, running multifeed with unsecure default key')
-
-    var feed = hypercore(self._storage('_fake'), protocolEncryptionKey)
-
-    feed.ready(function () {
-      self._fake = feed
-      self._loadFeeds(function () {
-        debug('[INIT] finished loading feeds')
-        done()
-      })
+    self._loadFeeds(function () {
+      debug('[INIT] finished loading feeds')
+      done()
     })
   })
 }
@@ -76,7 +70,7 @@ Multifeed.prototype.close = function (cb) {
       })
     }
 
-    var feeds = values(self._feeds).concat(self._fake)
+    var feeds = values(self._feeds)
 
     function next (n) {
       if (n >= feeds.length) {
@@ -161,7 +155,7 @@ Multifeed.prototype.writer = function (name, cb) {
         feed.ready(function () {
           self._addFeed(feed, String(idx))
           release(function () {
-            if (err) cb(err)
+            if (err) return cb(err)
             else cb(null, feed, idx)
           })
         })
@@ -183,11 +177,31 @@ Multifeed.prototype.feed = function (key) {
 Multifeed.prototype.replicate = function (opts) {
   if (!opts) opts = {}
   var self = this
-  var mux = multiplexer(self._fake.key, opts)
+  var mux = multiplexer(self.key, opts)
 
   // Add key exchange listener
   mux.once('manifest', function(m) {
-    mux.wantFeeds(m.keys)
+    if (self._middleware.length) {
+      function callPlug(i, ctx) {
+        if (self._middleware.length === i) return mux.wantFeeds(ctx.keys)
+        var plug = self._middleware[i]
+
+        // Reliquish control to next if plug does not implement callback
+        if (typeof plug.want !== 'function') return callPlug(i + 1, ctx)
+
+        // give each plug a fresh reference to avoid peeking/postmodifications
+        plug.want.bind(self)(clone(ctx), function(keys) {
+          let n = clone(m)
+          n.keys = keys
+          callPlug(i + 1, n)
+        })
+      }
+      // Start loop
+      callPlug(0, m)
+    } else {
+      // default behaviour "want all"
+      mux.wantFeeds(m.keys)
+    }
   })
 
   // Add replication listener
@@ -195,7 +209,7 @@ Multifeed.prototype.replicate = function (opts) {
     addMissingKeys(keys, function(err){
       if(err) return mux.destroy(err)
 
-      var key2feed = values(self._feeds).reduce(function(h,feed){
+      var key2feed = values(self._feeds).reduce(function(h, feed){
         h[feed.key.toString('hex')] = feed
         return h
       },{})
@@ -210,8 +224,28 @@ Multifeed.prototype.replicate = function (opts) {
     if (err) return mux.stream.destroy(err)
     if (mux.stream.destroyed) return
     mux.ready(function(){
-      var keys = values(self._feeds).map(function (feed) { return feed.key.toString('hex') })
-      mux.haveFeeds(keys)
+      var available = values(self._feeds).map(function (feed) { return feed.key.toString('hex') })
+      if (self._middleware.length) {
+        // Orderly iterate through all plugs
+        function callPlug(i, ctx) {
+          if (i === self._middleware.length) return mux.haveFeeds(ctx.keys, ctx)
+          let plug = self._middleware[i]
+
+          // Reliquish control to next if plug does not implement callback
+          if (typeof plug.have !== 'function') return callPlug(i + 1, ctx)
+
+          // give each plug a fresh reference to avoid peeking/postmodifications
+          plug.have.bind(self)(clone(ctx), function(keys, extras){
+            extras = extras || {}
+            extras.keys = keys
+            callPlug(i + 1, extras)
+          })
+        }
+        callPlug(0, {keys: available})
+      } else {
+        // Default behaviour 'share all'
+        mux.haveFeeds(available)
+      }
     })
   })
 
@@ -236,12 +270,16 @@ Multifeed.prototype.replicate = function (opts) {
     var filtered = keys.filter(function (key) {
       return !Number.isNaN(parseInt(key, 16)) && key.length === 64
     })
-    filtered.forEach(function (key) {
-      var feeds = values(self._feeds).filter(function (feed) {
-        return feed.key.toString('hex') === key
-      })
-      if (!feeds.length) {
-        pending++
+
+    var existingKeys = values(self._feeds).map(function(feed) { return feed.key.toString('hex') })
+
+    var missingFeeds = filtered.filter(function (key) {
+      return existingKeys.indexOf(key) === -1
+    })
+
+    function initFeed(i) {
+      if (i >= missingFeeds.length) return cb()
+        var key = missingFeeds[i]
         var numFeeds = Object.keys(self._feeds).length
         var storage = self._storage(''+numFeeds)
         var feed
@@ -250,20 +288,27 @@ Multifeed.prototype.replicate = function (opts) {
           feed = self._hypercore(storage, Buffer.from(key, 'hex'), self._opts)
         } catch (e) {
           debug('[REPLICATION] failed to create new local hypercore, key=' + key.toString('hex'))
-          if (!--pending) cb()
-          return
+          return initFeed(i + 1)
         }
-        debug('[REPLICATION] succeeded in creating new local hypercore, key=' + key.toString('hex'))
-        self._addFeed(feed, String(numFeeds))
         feed.ready(function () {
-          if (!--pending) cb()
+          debug('[REPLICATION] succeeded in creating new local hypercore, key=' + key.toString('hex'))
+          self._addFeed(feed, String(numFeeds))
+          initFeed(i + 1)
         })
-      }
-    })
-    if (!pending) cb()
+    }
+    initFeed(0)
   }
 }
 
+Multifeed.prototype.use = function(plug) {
+  if(this._middleware === null) this._middleware = []
+  this._middleware.push(plug)
+  var self = this
+  if (typeof plug.init === 'function') this.ready(function(){
+    plug.init(self)
+  })
+}
+
 // TODO: what if the new data is shorter than the old data? things will break!
 function writeStringToStorage (string, storage, cb) {
   var buf = Buffer.from(string, 'utf8')
@@ -292,3 +337,8 @@ function readStringFromStorage (storage, cb) {
 function values (obj) {
   return Object.keys(obj).map(function (k) { return obj[k] })
 }
+
+// Deep clone
+function clone(obj) {
+  return JSON.parse(JSON.stringify(obj))
+}
diff --git a/package.json b/package.json
index 1823948..936ad97 100644
--- a/package.json
+++ b/package.json
@@ -31,5 +31,8 @@
     "through2": "^3.0.0",
     "tmp": "0.0.33"
   },
-  "license": "ISC"
+  "license": "ISC",
+  "directories": {
+    "test": "test"
+  }
 }
diff --git a/test/replication-api.js b/test/replication-api.js
new file mode 100644
index 0000000..c9668e0
--- /dev/null
+++ b/test/replication-api.js
@@ -0,0 +1,115 @@
+var test = require('tape')
+var hypercore = require('hypercore')
+var ram = require('random-access-memory')
+var multifeed = require('../index')
+
+var bindStorage = function(subpath) {
+  return function(p) {
+    return ram(subpath + '/' + p)
+  }
+}
+
+test('Key exchange API', function(t){
+  t.plan(26)
+  var multi = multifeed(hypercore, bindStorage("first/"), { valueEncoding: 'json' })
+  var m2 = multifeed(hypercore, bindStorage("second/"), { valueEncoding: 'json' })
+  // A policy that only replicates feeds relevant to cats
+  // This policy shares everything but accepts only feeds tagged as 'cat'
+  var CatPolicy = {
+    have: function(local, share) {
+      t.ok(local.keys instanceof Array, "Param 'local' should be an array of localy available feeds")
+      t.ok(typeof share === 'function', "Param 'share' should be a function")
+
+      // 'Marketing phase' extract zeroth entry for all feeds an attach it
+      // to the feed-exchange
+      extractEntries(this.feeds(), function(entries) {
+        // Share all feeds including the sounds they make.
+        share(local.keys, {
+          says: entries.map(function(e) { return e.says })
+        })
+      })
+    },
+    want: function(remote, request) {
+      t.ok(remote.keys instanceof Array, "Param 'remote' should be an array of remotely available feeds")
+      t.ok(typeof request === 'function', "Param 'request' should be a function")
+      // Ok let's request only keys relevant to our logic.
+      var keys = remote.keys.filter(function(k, i){
+        return remote.says[i] === 'meow'
+      })
+      request(keys)
+    }
+  }
+
+  // let both multifeeds use the same policy
+  multi.use(CatPolicy)
+  m2.use(CatPolicy)
+
+  var replicateAndVerify = function(err) {
+    t.error(err)
+    t.equal(multi.feeds().length, 3)
+    t.equal(m2.feeds().length, 3)
+    // Verify that both catfeeds and the original dog-feed is present.
+    extractEntries(multi.feeds(), function(ent1) {
+      t.equal(ent1.filter(function(i) { return i.says === 'meow'}).length, 2, 'Should contain two cats')
+      t.equal(ent1.filter(function(i) { return i.says === 'squeek'}).length, 0, 'Should not contain any mice')
+      t.equal(ent1.filter(function(i) { return i.says === 'woof'}).length, 1, 'Should contain a dog')
+
+      // Verify that both catfeeds and the original rat-feed is present.
+      extractEntries(m2.feeds(), function(ent2) {
+        t.equal(ent2.filter(function(i) { return i.says === 'meow'}).length, 2, 'Should contain two cats')
+        t.equal(ent2.filter(function(i) { return i.says === 'woof'}).length, 0, 'Should not contain any dogs')
+        t.equal(ent2.filter(function(i) { return i.says === 'squeek'}).length, 1, 'Should contain a rat')
+        t.end()
+      })
+    })
+  }
+
+  // Initialize a cat feed on the first multifeed
+  multi.writer('a1',function(err, catFeed){
+    t.error(err)
+    // Append a cat-log
+    catFeed.append({says: 'meow', name: 'billy'}, function(err){
+      t.error(err)
+      // Initialize a dog feed on the first multifeed
+      multi.writer('a2', function(err, dogFeed) {
+        t.error(err)
+        // Append a dog-log
+        dogFeed.append({says: 'woof', name: 'rupert'}, function(err) {
+          t.error(err)
+          // Initialize another cat feed on the second multifeed
+          m2.writer('b1', function(err, cat2Feed) {
+            t.error(err)
+            // Append cat-log
+            cat2Feed.append({says: 'meow', name: 'amy'}, function(err) {
+              t.error(err)
+              // And lastly a rat feed on the second multifeed.
+              m2.writer('b2', function(err, ratFeed) {
+                t.error(err)
+                ratFeed.append({says: 'squeek', name: 'engelbrecht'}, function(err){
+                  t.error(err)
+                  t.ok(true, "Test data setup ok")
+                  // Replicating
+                  var r = multi.replicate()
+                  r.pipe(m2.replicate()).pipe(r)
+                    .once('end', replicateAndVerify)
+                })
+              })
+            })
+          })
+        })
+      })
+    })
+  })
+})
+
+function extractEntries(feeds, cb) {
+  var entries = []
+  var f = function (i) {
+    if (typeof feeds[i] === 'undefined') return cb(entries)
+    feeds[i].get(0, function(err, entry){
+      entries.push(entry)
+      f(i+1)
+    })
+  }
+  f(0)
+}