Add sha256 operator

core/modules/filters/crypto.js

@@ -0,0 +1,27 @@
+/*\
+title: $:/core/modules/filters/crypto.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operators for cryptography, using the Stanford JavaScript library
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+exports.sha256 = function(source,operator,options) {
+	var results = [],
+		length = parseInt(operator.operand,10) || 20,
+		sha256 = function(text) {
+			return sjcl.codec.hex.fromBits(sjcl.hash.sha256.hash(text)).substr(0,length);
+		};
+	source(function(tiddler,title) {
+		results.push(sha256(title));
+	});
+	return results;
+};
+
+})();