2 files changed, 87 insertions, 0 deletions
diff --git a/src/main/java/org/whispersystems/libaxolotl/groups/ratchet/SenderChainKey.java b/src/main/java/org/whispersystems/libaxolotl/groups/ratchet/SenderChainKey.java
new file mode 100644
index 00000000..71375923
--- /dev/null
+++ b/src/main/java/org/whispersystems/libaxolotl/groups/ratchet/SenderChainKey.java
@@ -0,0 +1,49 @@
+package org.whispersystems.libaxolotl.groups.ratchet;
+
+import java.security.InvalidKeyException;
+import java.security.NoSuchAlgorithmException;
+
+import javax.crypto.Mac;
+import javax.crypto.spec.SecretKeySpec;
+
+public class SenderChainKey {
+
+  private static final byte[] MESSAGE_KEY_SEED = {0x01};
+  private static final byte[] CHAIN_KEY_SEED   = {0x02};
+
+  private final int    iteration;
+  private final byte[] chainKey;
+
+  public SenderChainKey(int iteration, byte[] chainKey) {
+    this.iteration = iteration;
+    this.chainKey  = chainKey;
+  }
+
+  public int getIteration() {
+    return iteration;
+  }
+
+  public SenderMessageKey getSenderMessageKey() {
+    return new SenderMessageKey(iteration, getDerivative(MESSAGE_KEY_SEED, chainKey));
+  }
+
+  public SenderChainKey getNext() {
+    return new SenderChainKey(iteration + 1, getDerivative(CHAIN_KEY_SEED, chainKey));
+  }
+
+  public byte[] getSeed() {
+    return chainKey;
+  }
+
+  private byte[] getDerivative(byte[] seed, byte[] key) {
+    try {
+      Mac mac = Mac.getInstance("HmacSHA256");
+      mac.init(new SecretKeySpec(key, "HmacSHA256"));
+
+      return mac.doFinal(seed);
+    } catch (NoSuchAlgorithmException | InvalidKeyException e) {
+      throw new AssertionError(e);
+    }
+  }
+
+}
diff --git a/src/main/java/org/whispersystems/libaxolotl/groups/ratchet/SenderMessageKey.java b/src/main/java/org/whispersystems/libaxolotl/groups/ratchet/SenderMessageKey.java
new file mode 100644
index 00000000..8808a8e8
--- /dev/null
+++ b/src/main/java/org/whispersystems/libaxolotl/groups/ratchet/SenderMessageKey.java
@@ -0,0 +1,38 @@
+package org.whispersystems.libaxolotl.groups.ratchet;
+
+import org.whispersystems.libaxolotl.kdf.HKDFv3;
+import org.whispersystems.libaxolotl.util.ByteUtil;
+
+public class SenderMessageKey {
+
+  private final int    iteration;
+  private final byte[] iv;
+  private final byte[] cipherKey;
+  private final byte[] seed;
+
+  public SenderMessageKey(int iteration, byte[] seed) {
+    byte[] derivative = new HKDFv3().deriveSecrets(seed, "WhisperGroup".getBytes(), 48);
+    byte[][] parts    = ByteUtil.split(derivative, 16, 32);
+
+    this.iteration = iteration;
+    this.seed      = seed;
+    this.iv        = parts[0];
+    this.cipherKey = parts[1];
+  }
+
+  public int getIteration() {
+    return iteration;
+  }
+
+  public byte[] getIv() {
+    return iv;
+  }
+
+  public byte[] getCipherKey() {
+    return cipherKey;
+  }
+
+  public byte[] getSeed() {
+    return seed;
+  }
+}