diff -r 7d6f2526244a -r 197a85a35cba app/src/main/java/com/isode/stroke/stringcodecs/HMACSHA1.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/app/src/main/java/com/isode/stroke/stringcodecs/HMACSHA1.java	Sun Mar 15 18:03:03 2015 +0100
@@ -0,0 +1,49 @@
+/*
+ * Copyright (c) 2010, Isode Limited, London, England.
+ * All rights reserved.
+ */
+/*
+ * Copyright (c) 2010, Remko Tronçon.
+ * All rights reserved.
+ */
+package com.isode.stroke.stringcodecs;
+
+import com.isode.stroke.base.ByteArray;
+
+public class HMACSHA1 {
+
+    private static final int B = 64;
+
+    public static ByteArray getResult(ByteArray key, ByteArray data) {
+        assert key.getSize() <= B;
+
+        /* And an assert that does something */
+        if (key.getSize() > B) {
+            throw new IllegalStateException("Invalid key size.");
+        }
+
+        // Create the padded key
+        ByteArray paddedKey = new ByteArray(key);
+        for (int i = key.getSize(); i < B; ++i) {
+            paddedKey.append((byte) 0x0);
+        }
+
+        // Create the first value
+        ByteArray x = new ByteArray(paddedKey);
+        byte[] xInner = x.getData();
+        for (int i = 0; i < xInner.length; ++i) {
+            xInner[i] ^= 0x36;
+        }
+        x.append(data);
+
+        // Create the second value
+        ByteArray y = new ByteArray(paddedKey);
+        byte[] yInner = y.getData();
+        for (int i = 0; i < yInner.length; ++i) {
+            yInner[i] ^= 0x5c;
+        }
+        y.append(SHA1.getHash(x));
+
+        return SHA1.getHash(y);
+    }
+}