diff --git a/www/common/outer/upload.js b/www/common/outer/upload.js
index f911aba28..6ca3478fb 100644
--- a/www/common/outer/upload.js
+++ b/www/common/outer/upload.js
@@ -1,8 +1,9 @@
 define([
     '/file/file-crypto.js',
     '/common/common-hash.js',
+    '/bower_components/nthen/index.js',
     '/bower_components/tweetnacl/nacl-fast.min.js',
-], function (FileCrypto, Hash) {
+], function (FileCrypto, Hash, nThen) {
     var Nacl = window.nacl;
     var module = {};
 
@@ -14,89 +15,106 @@ define([
         var path = file.path;
 
         var password = file.password;
-        var hash = Hash.createRandomHash('file', password);
-        var secret = Hash.getSecrets('file', hash, password);
-        var key = secret.keys.cryptKey;
-        var id = secret.channel;
-
-        // XXX check id here (getFileSize)
-
-        var next = FileCrypto.encrypt(u8, metadata, key);
-
-        var estimate = FileCrypto.computeEncryptedSize(u8.length, metadata);
-
-        var sendChunk = function (box, cb) {
-            var enc = Nacl.util.encodeBase64(box);
-            common.uploadChunk(enc, function (e, msg) {
-                cb(e, msg);
-            });
+        var hash, secret, key, id, href;
+
+        var getNewHash = function () {
+            hash = Hash.createRandomHash('file', password);
+            secret = Hash.getSecrets('file', hash, password);
+            key = secret.keys.cryptKey;
+            id = secret.channel;
+            href = '/file/#' + hash;
         };
 
-        var actual = 0;
-        var again = function (err, box) {
-            if (err) { throw new Error(err); }
-            if (box) {
-                actual += box.length;
-                var progressValue = (actual / estimate * 100);
-                updateProgress(progressValue);
-
-                return void sendChunk(box, function (e) {
-                    if (e) { return console.error(e); }
-                    next(again);
-                });
-            }
-
-            if (actual !== estimate) {
-                console.error('Estimated size does not match actual size');
-            }
-
-            // if not box then done
-            common.uploadComplete(id, function (e) {
-                if (e) { return void console.error(e); }
-                var uri = ['', 'blob', id.slice(0,2), id].join('/');
-                console.log("encrypted blob is now available as %s", uri);
-
-                var href = '/file/#' + hash;
-
-                var title = metadata.name;
-
-                if (noStore) { return void onComplete(href); }
-
-                var data = {
-                    title: title || "",
-                    href: href,
-                    path: path,
-                    password: password,
-                    channel: id
-                };
-                common.setPadTitle(data, function (err) {
-                    if (err) { return void console.error(err); }
-                    onComplete(href);
-                    common.setPadAttribute('fileType', metadata.type, null, href);
-                });
+        var getValidHash = function (cb) {
+            getNewHash();
+            common.getFileSize(href, password, function (err, size) {
+                if (err || typeof(size) !== "number") {  throw new Error(err || "Invalid size!"); }
+                if (size === 0) { return void cb(); }
+                getValidHash();
             });
         };
 
-        common.uploadStatus(estimate, function (e, pending) {
-            if (e) {
-                console.error(e);
-                onError(e);
-                return;
-            }
-
-            if (pending) {
-                return void onPending(function () {
-                    // if the user wants to cancel the pending upload to execute that one
-                    common.uploadCancel(estimate, function (e) {
-                        if (e) {
-                            return void console.error(e);
-                        }
+        nThen(function (waitFor) {
+            // Generate a hash and check if the resulting id is valid (not already used)
+            getValidHash(waitFor());
+        }).nThen(function () {
+            var next = FileCrypto.encrypt(u8, metadata, key);
+
+            var estimate = FileCrypto.computeEncryptedSize(u8.length, metadata);
+
+            var sendChunk = function (box, cb) {
+                var enc = Nacl.util.encodeBase64(box);
+                common.uploadChunk(enc, function (e, msg) {
+                    cb(e, msg);
+                });
+            };
+
+            var actual = 0;
+            var again = function (err, box) {
+                if (err) { throw new Error(err); }
+                if (box) {
+                    actual += box.length;
+                    var progressValue = (actual / estimate * 100);
+                    updateProgress(progressValue);
+
+                    return void sendChunk(box, function (e) {
+                        if (e) { return console.error(e); }
                         next(again);
                     });
+                }
+
+                if (actual !== estimate) {
+                    console.error('Estimated size does not match actual size');
+                }
+
+                // if not box then done
+                common.uploadComplete(id, function (e) {
+                    if (e) { return void console.error(e); }
+                    var uri = ['', 'blob', id.slice(0,2), id].join('/');
+                    console.log("encrypted blob is now available as %s", uri);
+
+
+                    var title = metadata.name;
+
+                    if (noStore) { return void onComplete(href); }
+
+                    var data = {
+                        title: title || "",
+                        href: href,
+                        path: path,
+                        password: password,
+                        channel: id
+                    };
+                    common.setPadTitle(data, function (err) {
+                        if (err) { return void console.error(err); }
+                        onComplete(href);
+                        common.setPadAttribute('fileType', metadata.type, null, href);
+                    });
                 });
-            }
-            next(again);
+            };
+
+            common.uploadStatus(estimate, function (e, pending) {
+                if (e) {
+                    console.error(e);
+                    onError(e);
+                    return;
+                }
+
+                if (pending) {
+                    return void onPending(function () {
+                        // if the user wants to cancel the pending upload to execute that one
+                        common.uploadCancel(estimate, function (e) {
+                            if (e) {
+                                return void console.error(e);
+                            }
+                            next(again);
+                        });
+                    });
+                }
+                next(again);
+            });
         });
+
     };
     return module;
 });