ESM: Ported MS and Entropy operations

src/core/operations/Entropy.mjs

@@ -0,0 +1,96 @@
+/**
+ * @author n1474335 [n1474335@gmail.com]
+ * @copyright Crown Copyright 2016
+ * @license Apache-2.0
+ */
+
+import Operation from "../Operation";
+import Utils from "../Utils";
+
+/**
+ * Entropy operation
+ */
+class Entropy extends Operation {
+
+    /**
+     * Entropy constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "Entropy";
+        this.module = "Default";
+        this.description = "Calculates the Shannon entropy of the input data which gives an idea of its randomness. 8 is the maximum.";
+        this.inputType = "byteArray";
+        this.outputType = "number";
+        this.presentType = "html";
+        this.args = [];
+    }
+
+    /**
+     * @param {byteArray} input
+     * @param {Object[]} args
+     * @returns {number}
+     */
+    run(input, args) {
+        const prob = [],
+            uniques = input.unique(),
+            str = Utils.byteArrayToChars(input);
+        let i;
+
+        for (i = 0; i < uniques.length; i++) {
+            prob.push(str.count(Utils.chr(uniques[i])) / input.length);
+        }
+
+        let entropy = 0,
+            p;
+
+        for (i = 0; i < prob.length; i++) {
+            p = prob[i];
+            entropy += p * Math.log(p) / Math.log(2);
+        }
+
+        return -entropy;
+    }
+
+    /**
+     * Displays the entropy as a scale bar for web apps.
+     *
+     * @param {number} entropy
+     * @returns {html}
+     */
+    present(entropy) {
+        return `Shannon entropy: ${entropy}
+<br><canvas id='chart-area'></canvas><br>
+- 0 represents no randomness (i.e. all the bytes in the data have the same value) whereas 8, the maximum, represents a completely random string.
+- Standard English text usually falls somewhere between 3.5 and 5.
+- Properly encrypted or compressed data of a reasonable length should have an entropy of over 7.5.
+
+The following results show the entropy of chunks of the input data. Chunks with particularly high entropy could suggest encrypted or compressed sections.
+
+<br><script>
+    var canvas = document.getElementById("chart-area"),
+        parentRect = canvas.parentNode.getBoundingClientRect(),
+        entropy = ${entropy},
+        height = parentRect.height * 0.25;
+
+    canvas.width = parentRect.width * 0.95;
+    canvas.height = height > 150 ? 150 : height;
+
+    CanvasComponents.drawScaleBar(canvas, entropy, 8, [
+        {
+            label: "English text",
+            min: 3.5,
+            max: 5
+        },{
+            label: "Encrypted/compressed",
+            min: 7.5,
+            max: 8
+        }
+    ]);
+</script>`;
+    }
+
+}
+
+export default Entropy;