Isolates Base58Check encoding from Base58 code/tests

src/base58check.js

@@ -0,0 +1,53 @@
+// https://en.bitcoin.it/wiki/Base58Check_encoding
+var assert = require('assert')
+var base58 = require('./base58')
+var crypto = require('crypto')
+
+function sha256(buf) {
+  var hash = crypto.createHash('sha256')
+  hash.update(buf)
+
+  return hash.digest()
+}
+
+// Encode a buffer as a base58-check-encoded string
+function encode(buffer, version) {
+  version = version || 0
+
+  // FIXME: `new Buffer(buffer)` is unnecessary if input is a Buffer
+  var version = new Buffer([version])
+  var payload = new Buffer(buffer)
+
+  var message = Buffer.concat([version, payload])
+  var checksum = sha256(sha256(message)).slice(0, 4)
+
+  return base58.encode(Buffer.concat([
+    message,
+    checksum
+  ]))
+}
+
+// Decode a base58-check-encoded string to a buffer
+function decode(string) {
+  var buffer = base58.decode(string)
+
+  var message = buffer.slice(0, -4)
+  var checksum = buffer.slice(-4)
+  var newChecksum = sha256(sha256(message)).slice(0, 4)
+
+  assert.deepEqual(newChecksum, checksum)
+
+  var version = message.readUInt8(0)
+  var payload = message.slice(1)
+
+  return {
+    version: version,
+    payload: payload,
+    checksum: checksum
+  }
+}
+
+module.exports = {
+  encode: encode,
+  decode: decode
+}