diff --git a/opret-testapp/src/main/java/org/tcpid/opretj/testapp/App.java b/opret-testapp/src/main/java/org/tcpid/opretj/testapp/App.java
index 02f13ec..77ce198 100644
--- a/opret-testapp/src/main/java/org/tcpid/opretj/testapp/App.java
+++ b/opret-testapp/src/main/java/org/tcpid/opretj/testapp/App.java
@@ -21,7 +21,7 @@ import org.bitcoinj.wallet.SendRequest;
 import org.libsodium.jni.crypto.Hash;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-import org.tcpid.key.SigningKey;
+import org.tcpid.key.MasterSigningKey;
 import org.tcpid.opretj.OPRETECParser;
 import org.tcpid.opretj.OPRETWallet;
 import org.tcpid.opretj.OPRETWalletAppKit;
@@ -39,7 +39,7 @@ public class App {
     public final static long OPRET_BIRTHDAY = 1471989600;
 
     private final static Logger logger = LoggerFactory.getLogger(App.class);
-    private final static SigningKey SK = new SigningKey(HASH.sha256("TESTSEED".getBytes()));
+    private final static MasterSigningKey SK = new MasterSigningKey(HASH.sha256("TESTSEED".getBytes()));
 
     private static void displayBalance(final OPRETWalletAppKit kit, final PrintWriter out) {
         out.write("Balance: " + kit.wallet().getBalance().toFriendlyString() + "\n");
@@ -157,7 +157,15 @@ public class App {
     }
 
     public static void main(final String[] args) throws Exception {
+        MasterSigningKey sk = SK.getSubKey(1L);
 
+        System.err.println(SK.toString());
+        System.err.println(sk.toString());
+        sk = SK.getSubKey(2L);
+        System.err.println(sk.toString());
+        sk = SK.getSubKey(3L);
+        System.err.println(sk.toString());
+        System.exit(0);
         final OptionParser parser = new OptionParser();
         final OptionSpec<NetworkEnum> net = parser.accepts("net", "The network to run the examples on")
                 .withRequiredArg().ofType(NetworkEnum.class).defaultsTo(NetworkEnum.TEST);
diff --git a/opretj/src/main/java/org/tcpid/key/MasterSigningKey.java b/opretj/src/main/java/org/tcpid/key/MasterSigningKey.java
new file mode 100644
index 0000000..db9a3d8
--- /dev/null
+++ b/opretj/src/main/java/org/tcpid/key/MasterSigningKey.java
@@ -0,0 +1,71 @@
+package org.tcpid.key;
+
+import static org.libsodium.jni.NaCl.sodium;
+import static org.libsodium.jni.SodiumConstants.SECRETKEY_BYTES;
+
+import java.util.ArrayList;
+
+import org.libsodium.jni.Sodium;
+import org.libsodium.jni.crypto.Hash;
+import org.libsodium.jni.crypto.Util;
+import org.libsodium.jni.encoders.Encoder;
+
+import com.google.common.primitives.Longs;
+
+public class MasterSigningKey extends SigningKey {
+    private MasterSigningKey subkey;
+    private Long subkeyindex;
+    public static final Hash HASH = new Hash();
+    private final ArrayList<Long> keyindex;
+
+    public MasterSigningKey(final byte[] key, ArrayList<Long> keyindex) {
+        super(key);
+        subkey = null;
+        subkeyindex = 0L;
+        this.keyindex = new ArrayList<>(keyindex);
+    }
+
+    public MasterSigningKey(final byte[] key) {
+        super(key);
+        subkey = null;
+        subkeyindex = 0L;
+        this.keyindex = new ArrayList<>();
+    }
+
+    public MasterSigningKey getValidSubKey() {
+        if (subkey == null) {
+            subkey = getSubKey(subkeyindex);
+        }
+        return subkey;
+    }
+
+    public MasterSigningKey getSubKey(Long offset) {
+        System.err.println("getSubKey");
+        final byte[] la = Longs.toByteArray(offset);
+        final byte[] keynum = Util.prependZeros(16 - la.length, la);
+        System.err.println("getSubKey key=" + Encoder.HEX.encode(keynum));
+        final byte[] appid = Util.prependZeros(14, "EC".getBytes());
+        final byte[] newseed = Util.zeros(SECRETKEY_BYTES);
+        sodium();
+        Sodium.crypto_generichash_blake2b_salt_personal(newseed, newseed.length, null, 0, this.seed, this.seed.length,
+                keynum, appid);
+        final ArrayList<Long> ki = new ArrayList<>(this.keyindex);
+        ki.add(offset);
+        return new MasterSigningKey(newseed, ki);
+    }
+
+    public MasterSigningKey getNextValidSubKey(Long offset) {
+        return getSubKey(subkeyindex + offset);
+    }
+
+    public void revokeSubKey() {
+        subkey.setRevoked(true);
+        subkeyindex++;
+        subkey = null;
+    }
+
+    @Override
+    public String toString() {
+        return "Index: " + this.keyindex.toString() + " " + Encoder.HEX.encode(seed);
+    }
+}
diff --git a/opretj/src/main/java/org/tcpid/key/MasterVerifyKey.java b/opretj/src/main/java/org/tcpid/key/MasterVerifyKey.java
new file mode 100644
index 0000000..0b57ff6
--- /dev/null
+++ b/opretj/src/main/java/org/tcpid/key/MasterVerifyKey.java
@@ -0,0 +1,48 @@
+package org.tcpid.key;
+
+import java.util.LinkedList;
+import java.util.NoSuchElementException;
+
+public class MasterVerifyKey extends VerifyKey {
+    private final LinkedList<VerifyKey> subkeys = new LinkedList<>();
+
+    public MasterVerifyKey(final byte[] key) {
+        super(key);
+    }
+
+    public VerifyKey getValidSubKey() {
+        return subkeys.getFirst();
+    }
+
+    public void revokeSubKey(final VerifyKey key) {
+        final int i = subkeys.indexOf(key);
+
+        if (i == -1) {
+            throw new NoSuchElementException("No such subkey");
+        }
+
+        subkeys.get(i).setRevoked(true);
+        subkeys.remove(i);
+    }
+
+    public void setFirstValidSubKey(final VerifyKey key) {
+        if (!subkeys.isEmpty()) {
+            throw new IndexOutOfBoundsException("Subkey list is not empty");
+        }
+
+        subkeys.addLast(key);
+    }
+
+    public void setNextValidSubKey(final VerifyKey after, final VerifyKey key) {
+        final VerifyKey l = subkeys.getLast();
+        if (!l.equals(after)) {
+            throw new NoSuchElementException("No such after key, or not last in list");
+        }
+
+        subkeys.addLast(key);
+    }
+
+    public void clearSubKeys() {
+        subkeys.clear();
+    }
+}
diff --git a/opretj/src/main/java/org/tcpid/key/SigningKey.java b/opretj/src/main/java/org/tcpid/key/SigningKey.java
index b873734..1af893b 100644
--- a/opretj/src/main/java/org/tcpid/key/SigningKey.java
+++ b/opretj/src/main/java/org/tcpid/key/SigningKey.java
@@ -21,48 +21,68 @@ import static org.libsodium.jni.SodiumConstants.PUBLICKEY_BYTES;
 import static org.libsodium.jni.SodiumConstants.SECRETKEY_BYTES;
 import static org.libsodium.jni.SodiumConstants.SIGNATURE_BYTES;
 
+import org.libsodium.jni.Sodium;
 import org.libsodium.jni.crypto.Random;
 import org.libsodium.jni.crypto.Util;
 import org.libsodium.jni.encoders.Encoder;
 import org.libsodium.jni.keys.KeyPair;
 import org.libsodium.jni.keys.PrivateKey;
 
-public class SigningKey {
+public class SigningKey implements Comparable<SigningKey> {
+
+    protected final byte[] seed;
 
-    private final byte[] seed;
     private final byte[] secretKey;
-
     private final VerifyKey verifyKey;
+    private boolean revoked;
 
     public SigningKey() {
         this(new Random().randomBytes(SECRETKEY_BYTES));
     }
 
-    public SigningKey(byte[] seed) {
+    public SigningKey(final byte[] seed) {
         Util.checkLength(seed, SECRETKEY_BYTES);
-        this.seed = seed;
+        this.seed = seed.clone();
         this.secretKey = Util.zeros(SECRETKEY_BYTES * 2);
         final byte[] publicKey = Util.zeros(PUBLICKEY_BYTES);
-        Util.isValid(sodium().crypto_sign_ed25519_seed_keypair(publicKey, secretKey, seed),
+        sodium();
+        Util.isValid(Sodium.crypto_sign_ed25519_seed_keypair(publicKey, secretKey, seed),
                 "Failed to generate a key pair");
 
         this.verifyKey = new VerifyKey(publicKey);
     }
 
-    public SigningKey(String seed, Encoder encoder) {
+    public SigningKey(final String seed, final Encoder encoder) {
         this(encoder.decode(seed));
     }
 
+    @Override
+    public int compareTo(final SigningKey other) {
+        for (int i = SECRETKEY_BYTES - 1; i >= 0; i--) {
+            final int thisByte = this.seed[i] & 0xff;
+            final int otherByte = other.seed[i] & 0xff;
+            if (thisByte > otherByte) {
+                return 1;
+            }
+            if (thisByte < otherByte) {
+                return -1;
+            }
+        }
+        return 0;
+    }
+
     public KeyPair getKeyPair() {
         final byte[] sk = Util.zeros(SECRETKEY_BYTES);
-        sodium().crypto_sign_ed25519_sk_to_curve25519(sk, this.secretKey);
+        sodium();
+        Sodium.crypto_sign_ed25519_sk_to_curve25519(sk, this.secretKey);
         return new KeyPair(sk);
 
     }
 
     public PrivateKey getPrivateKey() {
         final byte[] sk = Util.zeros(SECRETKEY_BYTES);
-        sodium().crypto_sign_ed25519_sk_to_curve25519(sk, this.secretKey);
+        sodium();
+        Sodium.crypto_sign_ed25519_sk_to_curve25519(sk, this.secretKey);
         return new PrivateKey(sk);
     }
 
@@ -70,15 +90,26 @@ public class SigningKey {
         return this.verifyKey;
     }
 
-    public byte[] sign(byte[] message) {
+    public boolean isRevoked() {
+        return revoked;
+    }
+
+    public void setRevoked(final boolean revoked) {
+        if (this.revoked != true) {
+            this.revoked = revoked;
+        }
+    }
+
+    public byte[] sign(final byte[] message) {
         byte[] signature = Util.prependZeros(SIGNATURE_BYTES, message);
         final int[] bufferLen = new int[1];
-        sodium().crypto_sign_ed25519(signature, bufferLen, message, message.length, secretKey);
+        sodium();
+        Sodium.crypto_sign_ed25519(signature, bufferLen, message, message.length, secretKey);
         signature = Util.slice(signature, 0, SIGNATURE_BYTES);
         return signature;
     }
 
-    public String sign(String message, Encoder encoder) {
+    public String sign(final String message, final Encoder encoder) {
         final byte[] signature = sign(encoder.decode(message));
         return encoder.encode(signature);
     }
diff --git a/opretj/src/main/java/org/tcpid/key/VerifyKey.java b/opretj/src/main/java/org/tcpid/key/VerifyKey.java
index 07ecb1f..f06a6cb 100644
--- a/opretj/src/main/java/org/tcpid/key/VerifyKey.java
+++ b/opretj/src/main/java/org/tcpid/key/VerifyKey.java
@@ -22,6 +22,7 @@ import static org.libsodium.jni.SodiumConstants.SIGNATURE_BYTES;
 
 import java.util.Arrays;
 
+import org.libsodium.jni.Sodium;
 import org.libsodium.jni.crypto.Hash;
 import org.libsodium.jni.crypto.Util;
 import org.libsodium.jni.encoders.Encoder;
@@ -34,18 +35,17 @@ public class VerifyKey implements Comparable<VerifyKey> {
     private final byte[] hash;
     private final byte[] shortHash;
     private boolean revoked;
+    private MasterVerifyKey masterkey;
 
-    public boolean isRevoked() {
-        return revoked;
+    public MasterVerifyKey getMasterkey() {
+        return masterkey;
     }
 
-    public void setRevoked(boolean revoked) {
-        if (this.revoked != true) {
-            this.revoked = revoked;
-        }
+    public void setMasterkey(MasterVerifyKey masterkey) {
+        this.masterkey = masterkey;
     }
 
-    public VerifyKey(byte[] key) {
+    public VerifyKey(final byte[] key) {
         Util.checkLength(key, PUBLICKEY_BYTES);
         this.key = key;
         this.hash = HASH.sha256(key);
@@ -53,58 +53,10 @@ public class VerifyKey implements Comparable<VerifyKey> {
         this.revoked = false;
     }
 
-    public VerifyKey(String key, Encoder encoder) {
+    public VerifyKey(final String key, final Encoder encoder) {
         this(encoder.decode(key));
     }
 
-    public PublicKey getPublicKey() {
-        final byte[] pk = Util.zeros(PUBLICKEY_BYTES);
-        sodium().crypto_sign_ed25519_pk_to_curve25519(pk, this.key);
-        return new PublicKey(pk);
-    }
-
-    public byte[] toBytes() {
-        return key;
-    }
-
-    @Override
-    public String toString() {
-        return Encoder.HEX.encode(key);
-    }
-
-    @Override
-    public boolean equals(Object o) {
-        if (this == o) {
-            return true;
-        }
-        if ((o == null) || (getClass() != o.getClass())) {
-            return false;
-        }
-        return Arrays.equals(key, ((VerifyKey) o).key);
-    }
-
-    public boolean verify(byte[] message, byte[] signature) {
-        Util.checkLength(signature, SIGNATURE_BYTES);
-        final byte[] sigAndMsg = Util.merge(signature, message);
-        final byte[] buffer = Util.zeros(sigAndMsg.length);
-        final int[] bufferLen = new int[1];
-
-        return Util.isValid(sodium().crypto_sign_ed25519_open(buffer, bufferLen, sigAndMsg, sigAndMsg.length, key),
-                "signature was forged or corrupted");
-    }
-
-    public boolean verify(String message, String signature, Encoder encoder) {
-        return verify(encoder.decode(message), encoder.decode(signature));
-    }
-
-    public byte[] toHash() {
-        return this.hash;
-    }
-
-    public byte[] getShortHash() {
-        return this.shortHash;
-    }
-
     @Override
     public int compareTo(final VerifyKey other) {
         for (int i = PUBLICKEY_BYTES - 1; i >= 0; i--) {
@@ -120,4 +72,64 @@ public class VerifyKey implements Comparable<VerifyKey> {
         return 0;
     }
 
+    @Override
+    public boolean equals(final Object o) {
+        if (this == o) {
+            return true;
+        }
+        if ((o == null) || (getClass() != o.getClass())) {
+            return false;
+        }
+        return Arrays.equals(key, ((VerifyKey) o).key);
+    }
+
+    public PublicKey getPublicKey() {
+        final byte[] pk = Util.zeros(PUBLICKEY_BYTES);
+        sodium();
+        Sodium.crypto_sign_ed25519_pk_to_curve25519(pk, this.key);
+        return new PublicKey(pk);
+    }
+
+    public byte[] getShortHash() {
+        return this.shortHash;
+    }
+
+    public boolean isRevoked() {
+        return revoked;
+    }
+
+    public void setRevoked(final boolean revoked) {
+        if (this.revoked != true) {
+            this.revoked = revoked;
+        }
+    }
+
+    public byte[] toBytes() {
+        return key;
+    }
+
+    public byte[] toHash() {
+        return this.hash;
+    }
+
+    @Override
+    public String toString() {
+        return Encoder.HEX.encode(key);
+    }
+
+    public boolean verify(final byte[] message, final byte[] signature) {
+        Util.checkLength(signature, SIGNATURE_BYTES);
+        final byte[] sigAndMsg = Util.merge(signature, message);
+        final byte[] buffer = Util.zeros(sigAndMsg.length);
+        final int[] bufferLen = new int[1];
+
+        sodium();
+        return Util.isValid(Sodium.crypto_sign_ed25519_open(buffer, bufferLen, sigAndMsg, sigAndMsg.length, key),
+                "signature was forged or corrupted");
+    }
+
+    public boolean verify(final String message, final String signature, final Encoder encoder) {
+        return verify(encoder.decode(message), encoder.decode(signature));
+    }
+
 }
diff --git a/opretj/src/main/java/org/tcpid/opretj/OPRETBaseHandler.java b/opretj/src/main/java/org/tcpid/opretj/OPRETBaseHandler.java
index 47de69f..06894cd 100644
--- a/opretj/src/main/java/org/tcpid/opretj/OPRETBaseHandler.java
+++ b/opretj/src/main/java/org/tcpid/opretj/OPRETBaseHandler.java
@@ -1,5 +1,6 @@
 package org.tcpid.opretj;
 
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -17,7 +18,7 @@ import com.google.common.primitives.Bytes;
 public abstract class OPRETBaseHandler implements OPRETHandlerInterface {
     private static final Logger logger = LoggerFactory.getLogger(OPRETBaseHandler.class);
     private final CopyOnWriteArrayList<ListenerRegistration<OPRETChangeEventListener>> opReturnChangeListeners = new CopyOnWriteArrayList<ListenerRegistration<OPRETChangeEventListener>>();
-    private final Map<List<Byte>, Long> magicBytes = new HashMap<>();
+    private final Map<List<Byte>, Long> magicBytes = Collections.synchronizedMap(new HashMap<>());
 
     protected void addOPRET(final byte[] magic, final long earliestTime) {
         logger.debug("addMagicBytes: {} - Time {}", Utils.HEX.encode(magic), earliestTime);
diff --git a/opretj/src/main/java/org/tcpid/opretj/OPRETECExampleParser.java b/opretj/src/main/java/org/tcpid/opretj/OPRETECExampleParser.java
deleted file mode 100644
index c029640..0000000
--- a/opretj/src/main/java/org/tcpid/opretj/OPRETECExampleParser.java
+++ /dev/null
@@ -1,110 +0,0 @@
-package org.tcpid.opretj;
-
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-import java.util.concurrent.CopyOnWriteArrayList;
-
-import org.bitcoinj.core.PartialMerkleTree;
-import org.bitcoinj.core.Sha256Hash;
-import org.bitcoinj.core.Utils;
-import org.bitcoinj.utils.ListenerRegistration;
-import org.bitcoinj.utils.Threading;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-import com.google.common.primitives.Bytes;
-
-public class OPRETECExampleParser extends OPRETBaseHandler {
-    private static final Logger logger = LoggerFactory.getLogger(OPRETECExampleParser.class);
-    private static final List<Byte> OPRET_MAGIC = Bytes.asList(Utils.HEX.decode("ec1d"));
-    protected final Map<Sha256Hash, PartialMerkleTree> merkleHashMap = new HashMap<>();
-    protected final Map<Sha256Hash, OPRETTransaction> transHashMap = new HashMap<>();
-    private final CopyOnWriteArrayList<ListenerRegistration<OPRETECEventListener>> opReturnChangeListeners = new CopyOnWriteArrayList<>();
-
-    /**
-     * Adds an event listener object. Methods on this object are called when
-     * scripts watched by this wallet change. The listener is executed by the
-     * given executor.
-     */
-    public void addOPRETECRevokeEventListener(final OPRETECEventListener listener) {
-        // This is thread safe, so we don't need to take the lock.
-        opReturnChangeListeners.add(new ListenerRegistration<OPRETECEventListener>(listener, Threading.SAME_THREAD));
-    }
-
-    private boolean checkData(final OPRETTransaction t1, final OPRETTransaction t2) {
-        final List<List<Byte>> opret_data = new ArrayList<>(t1.opretData);
-        opret_data.addAll(t2.opretData);
-        logger.debug("checking {}", opret_data);
-
-        List<Byte> chunk;
-        chunk = opret_data.get(0);
-        if (!chunk.equals(OPRET_MAGIC)) {
-            logger.debug("0: != OPRET_MAGIC");
-            return false;
-        }
-
-        chunk = opret_data.get(1);
-        if (chunk.size() != 1) {
-            logger.debug("1: size != 1");
-            return false;
-        }
-
-        if (chunk.get(0) == (byte) 0xFE) {
-            if (opret_data.size() != 8) {
-                logger.debug("FE: size != 8");
-                return false;
-            }
-            chunk = opret_data.get(4);
-            if (!chunk.equals(OPRET_MAGIC)) {
-                logger.debug("FE 4 != OPRET_MAGIC");
-                return false;
-            }
-            if (!opret_data.get(2).equals(opret_data.get(6))) {
-                logger.debug("FE 2 != 6");
-                return false;
-            }
-            chunk = opret_data.get(5);
-            if ((chunk.size() != 1) || (chunk.get(0) != (byte) 0xFF)) {
-                logger.debug("FE 5 size!=1 or != FF");
-                return false;
-            }
-
-            return handleRevoke(t1, t2);
-        } else {
-            logger.debug("1: != 0xFE");
-        }
-
-        return false;
-    }
-
-    private boolean handleRevoke(final OPRETTransaction t1, final OPRETTransaction t2) {
-        final byte[] pkhash = Bytes.toArray(t1.opretData.get(2));
-        final byte[] sig = Bytes.concat(Bytes.toArray(t1.opretData.get(3)), Bytes.toArray(t2.opretData.get(3)));
-
-        logger.debug("REVOKE PK {} - SIG {}", Utils.HEX.encode(pkhash), Utils.HEX.encode(sig));
-        queueOnOPRETRevoke(pkhash, sig);
-        return true;
-    }
-
-    @Override
-    public void pushTransaction(final OPRETTransaction t) {
-        logger.debug("pushData: {}", t.opretData);
-        transHashMap.put(t.txHash, t);
-    }
-
-    protected void queueOnOPRETRevoke(final byte[] pkhash, final byte[] sig) {
-        for (final ListenerRegistration<OPRETECEventListener> registration : opReturnChangeListeners) {
-            registration.executor.execute(() -> registration.listener.onOPRETRevoke(pkhash, sig));
-        }
-    }
-
-    /**
-     * Removes the given event listener object. Returns true if the listener was
-     * removed, false if that listener was never added.
-     */
-    public boolean removeOPRETECRevokeEventListener(final OPRETECEventListener listener) {
-        return ListenerRegistration.removeFromList(listener, opReturnChangeListeners);
-    }
-}
diff --git a/opretj/src/main/java/org/tcpid/opretj/OPRETWallet.java b/opretj/src/main/java/org/tcpid/opretj/OPRETWallet.java
index dba2a74..0720333 100644
--- a/opretj/src/main/java/org/tcpid/opretj/OPRETWallet.java
+++ b/opretj/src/main/java/org/tcpid/opretj/OPRETWallet.java
@@ -3,6 +3,7 @@ package org.tcpid.opretj;
 import static org.bitcoinj.script.ScriptOpCodes.OP_RETURN;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -36,13 +37,13 @@ public class OPRETWallet extends Wallet implements BlocksDownloadedEventListener
     private final OPRETHandlerInterface opbs;
     private final Logger logger = LoggerFactory.getLogger(OPRETWallet.class);
 
-    protected final Map<Sha256Hash, Map<Sha256Hash, OPRETTransaction>> pendingTransactions;
+    protected final Map<Sha256Hash, Map<Sha256Hash, OPRETTransaction>> pendingTransactions = Collections
+            .synchronizedMap(new HashMap<>());
 
     public OPRETWallet(final NetworkParameters params, final KeyChainGroup keyChainGroup,
             final OPRETHandlerInterface bs) {
         super(params, keyChainGroup);
         opbs = bs;
-        pendingTransactions = new HashMap<>();
     }
 
     @Override
@@ -174,7 +175,7 @@ public class OPRETWallet extends Wallet implements BlocksDownloadedEventListener
         final Sha256Hash h = block.getHeader().getHash();
 
         if (!pendingTransactions.containsKey(h)) {
-            pendingTransactions.put(h, new HashMap<Sha256Hash, OPRETTransaction>());
+            pendingTransactions.put(h, Collections.synchronizedMap(new HashMap<Sha256Hash, OPRETTransaction>()));
         }
 
         pendingTransactions.get(h).put(tx.getHash(), new OPRETTransaction(h, tx.getHash(), myList));