crypto: add cleanse function.

lib/crypto/crypto.js

@@ -514,6 +514,28 @@ crypto.ceq = function ceq(a, b) {
   return r === 1;
 };
 
+/**
+ * A maybe-secure memzero.
+ * @param {Buffer} data
+ */
+
+crypto.cleanse = function cleanse(data) {
+  var ctr = crypto._counter;
+  var i;
+
+  for (i = 0; i < data.length; i++) {
+    data[i] = ctr & 0xff;
+    ctr += i;
+  }
+
+  crypto._counter = ctr >>> 0;
+};
+
+crypto._counter = 0;
+
+if (native)
+  crypto.cleanse = native.cleanse;
+
 /**
  * Build a merkle tree from leaves.
  * @param {Buffer[]} leaves

package.json

@@ -41,7 +41,7 @@
     "elliptic": "6.3.2"
   },
   "optionalDependencies": {
-    "bcoin-native": "0.0.7",
+    "bcoin-native": "0.0.8",
     "leveldown": "1.5.0",
     "secp256k1": "3.2.0",
     "socket.io": "1.4.8",