diff --git a/OpenKeychain/build.gradle b/OpenKeychain/build.gradle
index 7fa139c06..026c12319 100644
--- a/OpenKeychain/build.gradle
+++ b/OpenKeychain/build.gradle
@@ -33,8 +33,8 @@ dependencies {
 }
 
 android {
-    compileSdkVersion 21
-    buildToolsVersion '21.1.2'
+    compileSdkVersion rootProject.ext.compileSdkVersion
+    buildToolsVersion rootProject.ext.buildToolsVersion
 
     defaultConfig {
         minSdkVersion 15
diff --git a/README.md b/README.md
index 991757169..7c2f50326 100644
--- a/README.md
+++ b/README.md
@@ -109,23 +109,38 @@ see
 
 ## Notes
 
-### Gradle Build System
+### Build System
 
 We try to make our builds as [reproducible/deterministic](https://blog.torproject.org/blog/deterministic-builds-part-one-cyberwar-and-global-compromise) as possible.  
-When changing build files or dependencies, respect the following requirements:
-* No precompiled libraries (you never know what pre-compiled jar files really contain!). All libraries should be forked into the open-keychain Github project and then provided as git submodules in the "extern" folder.
-* No dependencies from Maven (also a soft requirement for inclusion in [F-Droid](https://f-droid.org))
+
+#### Update Gradle version
 * Always use a fixed Android Gradle plugin version not a dynamic one, e.g. ``0.7.3`` instead of ``0.7.+`` (allows offline builds without lookups for new versions, also some minor Android plugin versions had serious issues, i.e. [0.7.2 and 0.8.1](http://tools.android.com/tech-docs/new-build-system))
-* Commit the corresponding [Gradle wrapper](http://www.gradle.org/docs/current/userguide/gradle_wrapper.html) to the repository (allows easy building for new contributors without the need to install the required Gradle version using a package manager)
-* In order to update the build system to a newer gradle version you need to:
-  * Update every build.gradle file with the new gradle version and/or gradle plugin version
+* Update every build.gradle file with the new gradle version and/or gradle plugin version
     * build.gradle
     * OpenKeychain/build.gradle
-    * OpenKeychain-API/build.gradle
-    * OpenKeychain-API/example-app/build.gradle
-    * OpenKeychain-API/libraries/keychain-api-library/build.gradle
-  * run ./gradlew wrapper twice to update gradle and download the new gradle jar file
-  * commit the new gradle jar and property files
+* run ./gradlew wrapper twice to update gradle and download the new gradle jar file
+* commit the corresponding [Gradle wrapper](http://www.gradle.org/docs/current/userguide/gradle_wrapper.html) to the repository (allows easy building for new contributors without the need to install the required Gradle version using a package manager)
+  
+#### Update SDK and Build Tools
+* Open build.gradle and change:
+```
+ext {
+    compileSdkVersion = 21
+    buildToolsVersion = '21.1.2'
+}
+```
+* Change SDK and Build Tools in git submodules "openkeychain-api-lib" and "openpgp-api-lib" manually. They should also build on their own without the ext variables.
+
+#### Add new library
+* You can add the library as a Maven dependency or as a git submodule (if patches are required) in the "extern" folder.
+* If added as a Maven dependency, pin the library using [Gradle Witness](https://github.com/WhisperSystems/gradle-witness)
+* If added as a git submodule, change the ``compileSdkVersion`` and ``buildToolsVersion`` in build.gradle to use the variables from the root project:
+```
+android {
+    compileSdkVersion rootProject.ext.compileSdkVersion
+    buildToolsVersion rootProject.ext.buildToolsVersion
+}
+```
 
 ### Slow Gradle?
 
diff --git a/build.gradle b/build.gradle
index f8e6afc27..4076ddc6b 100644
--- a/build.gradle
+++ b/build.gradle
@@ -38,3 +38,10 @@ project(':extern:spongycastle') {
         test.enabled = false
     }
 }
+
+// SDK Version and Build Tools used by all subprojects
+// See http://tools.android.com/tech-docs/new-build-system/tips#TOC-Controlling-Android-properties-of-all-your-modules-from-the-main-project.
+ext {
+    compileSdkVersion = 21
+    buildToolsVersion = '21.1.2'
+}
\ No newline at end of file
diff --git a/extern/KeybaseLib b/extern/KeybaseLib
index 2b26d163d..9615d90b1 160000
--- a/extern/KeybaseLib
+++ b/extern/KeybaseLib
@@ -1 +1 @@
-Subproject commit 2b26d163df84a3d26c1c8da088ed3811b5ca6ec7
+Subproject commit 9615d90b18d1aee4dad994aa45875adfdcfb3c34
diff --git a/extern/StickyListHeaders b/extern/StickyListHeaders
index 62cc58c12..70a2ed806 160000
--- a/extern/StickyListHeaders
+++ b/extern/StickyListHeaders
@@ -1 +1 @@
-Subproject commit 62cc58c12d0c09b50984caf26e5afceda8873784
+Subproject commit 70a2ed80632938540bf07b81270384f4e5a96f9e
diff --git a/extern/SuperToasts b/extern/SuperToasts
index 77042d633..79fbaa4e3 160000
--- a/extern/SuperToasts
+++ b/extern/SuperToasts
@@ -1 +1 @@
-Subproject commit 77042d633f4dd430bcc86101e31dda52433db9c1
+Subproject commit 79fbaa4e3cf118a07ca4573b514c679b666fb214
diff --git a/extern/TokenAutoComplete b/extern/TokenAutoComplete
index ca46b4261..1d6d3882e 160000
--- a/extern/TokenAutoComplete
+++ b/extern/TokenAutoComplete
@@ -1 +1 @@
-Subproject commit ca46b4261c97221ddd4db135e7838d6fa145adf4
+Subproject commit 1d6d3882e711c14c93abf73cbcbd28b9e0e2b498
diff --git a/extern/html-textview b/extern/html-textview
index eedaa334e..9872a7315 160000
--- a/extern/html-textview
+++ b/extern/html-textview
@@ -1 +1 @@
-Subproject commit eedaa334e761273efbfc49ded2124df58c8a4d88
+Subproject commit 9872a73156518fd8df79dd2cd4d24750574b9ac7
diff --git a/extern/openkeychain-api-lib b/extern/openkeychain-api-lib
index 88c004793..925907502 160000
--- a/extern/openkeychain-api-lib
+++ b/extern/openkeychain-api-lib
@@ -1 +1 @@
-Subproject commit 88c00479329c1aa892bef052f3f8830067c386d8
+Subproject commit 9259075028e0906d0cb085e0c4578e23829dc3c0
diff --git a/extern/safeslinger-exchange b/extern/safeslinger-exchange
index 96f7c8935..7c84cb54d 160000
--- a/extern/safeslinger-exchange
+++ b/extern/safeslinger-exchange
@@ -1 +1 @@
-Subproject commit 96f7c893565e3a8badd740b2035beea87d8bffb3
+Subproject commit 7c84cb54df5b3d5c6780984e48f3e9e4cbc5128e