HD Wallets: add a REFUND key purpose and map it to the same branch as…

… RECEIVE_FUNDS for now.
bitcoinj · May 29, 2014 · c7f7fd2 · c7f7fd2
1 parent dbf504f
commit c7f7fd2
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Showing 2 changed files with 18 additions and 9 deletions.
diff --git a/core/src/main/java/com/google/bitcoin/wallet/DeterministicKeyChain.java b/core/src/main/java/com/google/bitcoin/wallet/DeterministicKeyChain.java
@@ -235,14 +235,22 @@ public DeterministicKey getKey(KeyPurpose purpose) {
         try {
             DeterministicKey key, parentKey;
             int index;
-            if (purpose == KeyPurpose.RECEIVE_FUNDS) {
-                index = ++issuedExternalKeys;
-                parentKey = externalKey;
-            } else if (purpose == KeyPurpose.CHANGE) {
-                index = ++issuedInternalKeys;
-                parentKey = internalKey;
-            } else {
-                throw new IllegalArgumentException("Unknown key purpose " + purpose);
+            switch (purpose) {
+                // Map both REFUND and RECEIVE_KEYS to the same branch for now. Refunds are a feature of the BIP 70
+                // payment protocol. Later we may wish to map it to a different branch (in a new wallet version?).
+                // This would allow a watching wallet to only be able to see inbound payments, but not change
+                // (i.e. spends) or refunds. Might be useful for auditing ...
+                case RECEIVE_FUNDS:
+                case REFUND:
+                    index = ++issuedExternalKeys;
+                    parentKey = externalKey;
+                    break;
+                case CHANGE:
+                    index = ++issuedInternalKeys;
+                    parentKey = internalKey;
+                    break;
+                default:
+                    throw new UnsupportedOperationException();
             }
             // TODO: Handle the case where the derived key is >= curve order.
             List<DeterministicKey> lookahead = maybeLookAhead(parentKey, index);

diff --git a/core/src/main/java/com/google/bitcoin/wallet/KeyChain.java b/core/src/main/java/com/google/bitcoin/wallet/KeyChain.java
@@ -54,7 +54,8 @@ public interface KeyChain {
 
     enum KeyPurpose {
         RECEIVE_FUNDS,
-        CHANGE
+        CHANGE,
+        REFUND
     }
 
     /** Obtains a key intended for the given purpose. The chain may create a new key, derive one, or re-use an old one. */