From 60800e155612bea797eed93c67046a23d26054cc Mon Sep 17 00:00:00 2001
From: Moxie Marlinspike <moxie@thoughtcrime.org>
Date: Mon, 24 Nov 2014 12:54:30 -0800
Subject: Break out into separate repo.

---
 .../libaxolotl/groups/ratchet/SenderChainKey.java  | 49 ++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 src/main/java/org/whispersystems/libaxolotl/groups/ratchet/SenderChainKey.java

(limited to 'src/main/java/org/whispersystems/libaxolotl/groups/ratchet/SenderChainKey.java')

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);
+    }
+  }
+
+}
-- 
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