Update README with transaction signing example

packages/ripple-keypairs/README.md

@@ -17,3 +17,71 @@
   accountID: 'r9LqNeG6qHxjeUocjvVki2XR35weJ9mZgQ',
   publicKey: 'ED5F5AC8B98974A3CA843326D9B88CEBD0560177B973EE0B149F782CFAA06DC66A' }')
 ```
+
+## Sign a transaction
+see [examples/sign-transaction.js](examples/sign-transaction.js)
+```js
+var Transaction = require('ripple-lib').Transaction;
+var keyPairFromSeed = require('../').keyPairFromSeed;
+
+var SIGNING_PREFIX = [0x53, 0x54, 0x58, 0x00];
+
+function prettyJSON(obj) {
+  return JSON.stringify(obj, undefined, 2);
+}
+
+function signingData(tx) {
+  return SIGNING_PREFIX.concat(tx.serialize().buffer);
+}
+
+function signTxJson(seed, json) {
+  var keyPair = keyPairFromSeed(seed);
+  var tx = Transaction.from_json(json);
+  var tx_json = tx.tx_json;
+
+  tx_json.SigningPubKey = keyPair.pubKeyHex();
+  tx_json.TxnSignature = keyPair.signHex(signingData(tx));
+
+  var serialized = tx.serialize();
+
+  var id = tx.hash('HASH_TX_ID', /* Uint256: */ false , /* pre: */ serialized);
+
+  return {
+    hash: id,
+    tx_blob: serialized.to_hex(),
+    tx_json: tx_json
+  };
+}
+
+var seed = 'sEd7t79mzn2dwy3vvpvRmaaLbLhvme6';
+var tx_json = {
+  Account: 'r9LqNeG6qHxjeUocjvVki2XR35weJ9mZgQ',
+  Amount: '1000',
+  Destination: 'rHb9CJAWyB4rj91VRWn96DkukG4bwdtyTh',
+  Fee: '10',
+  Flags: 2147483648,
+  Sequence: 1,
+  TransactionType: 'Payment',
+};
+
+console.log(prettyJSON(signTxJson(seed, tx_json)));
+
+```
+
+```json
+{
+  "hash": "1B6B9652F95D826C9D9C3FD30F208130433CBC7C48C10F6EC2CC5E4A85D167FF",
+  "tx_blob": "120000228000000024000000016140000000000003E868400000000000000A7321ED5F5AC8B98974A3CA843326D9B88CEBD0560177B973EE0B149F782CFAA06DC66A74407D0825105229923B261C716F225181E5A66A34C9480446ABE64818A673954CC34D42946CD82172814F037976AE3800BDE983624A45FCDBED4A548C4650BF900D81145B812C9D57731E27A2DA8B1830195F88EF32A3B68314B5F762798A53D543A014CAF8B297CFF8F2F937E8",
+  "tx_json": {
+    "Account": "r9LqNeG6qHxjeUocjvVki2XR35weJ9mZgQ",
+    "Amount": "1000",
+    "Destination": "rHb9CJAWyB4rj91VRWn96DkukG4bwdtyTh",
+    "Fee": "10",
+    "Flags": 2147483648,
+    "Sequence": 1,
+    "TransactionType": "Payment",
+    "SigningPubKey": "ED5F5AC8B98974A3CA843326D9B88CEBD0560177B973EE0B149F782CFAA06DC66A",
+    "TxnSignature": "7D0825105229923B261C716F225181E5A66A34C9480446ABE64818A673954CC34D42946CD82172814F037976AE3800BDE983624A45FCDBED4A548C4650BF900D"
+  }
+}
+```

packages/ripple-keypairs/examples/sign-transaction.js

@@ -0,0 +1,45 @@
+var Transaction = require('ripple-lib').Transaction;
+var keyPairFromSeed = require('../').keyPairFromSeed;
+
+var SIGNING_PREFIX = [0x53, 0x54, 0x58, 0x00];
+
+function prettyJSON(obj) {
+  return JSON.stringify(obj, undefined, 2);
+}
+
+function signingData(tx) {
+  return SIGNING_PREFIX.concat(tx.serialize().buffer);
+}
+
+function signTxJson(seed, json) {
+  var keyPair = keyPairFromSeed(seed);
+  var tx = Transaction.from_json(json);
+  var tx_json = tx.tx_json;
+
+  tx_json.SigningPubKey = keyPair.pubKeyHex();
+  tx_json.TxnSignature = keyPair.signHex(signingData(tx));
+
+  var serialized = tx.serialize();
+
+  var id = tx.hash('HASH_TX_ID', /* Uint256: */ false , /* pre: */ serialized);
+
+  return {
+    hash: id,
+    tx_blob: serialized.to_hex(),
+    tx_json: tx_json
+  };
+}
+
+var seed = 'sEd7t79mzn2dwy3vvpvRmaaLbLhvme6';
+var tx_json = {
+  Account: 'r9LqNeG6qHxjeUocjvVki2XR35weJ9mZgQ',
+  Amount: '1000',
+  Destination: 'rHb9CJAWyB4rj91VRWn96DkukG4bwdtyTh',
+  Fee: '10',
+  Flags: 2147483648,
+  Sequence: 1,
+  TransactionType: 'Payment',
+};
+
+console.log('unsigned', prettyJSON(tx_json));
+console.log('signed', prettyJSON(signTxJson(seed, tx_json)));

packages/ripple-keypairs/package.json

@@ -34,7 +34,7 @@
     "map-stream": "~0.1.0",
     "mocha": "~2.1.0",
     "nock": "^0.34.1",
-    "ripple-lib": "ripple/ripple-lib#8d98e443c5302a87d70410d834758099595d46df",
+    "ripple-lib": "^0.12.4",
     "webpack": "~1.5.3",
     "yargs": "~1.3.1"
   },