mirrors/CyberChef
1
0
Fork 0
mirror of https://github.com/gchq/CyberChef.git synced 2025-05-13 17:46:53 -04:00
Code Issues Projects Releases Packages Wiki Activity Actions

Entropy Library and making existing operations use it

Browse source
This commit is contained in:
n1073645 2020-01-07 12:11:18 +00:00
parent 9484941f66
commit 28244ac605
5 changed files with 15 additions and 187 deletions
Download patch file Download diff file Expand all files Collapse all files

59
src/core/operations/Entropy.mjs
View file

@ -9,6 +9,8 @@ import * as nodomtemp from "nodom";
import Operation from "../Operation.mjs";
import {calculateScanningEntropy, calculateShannonEntropy} from "../lib/Entropy.mjs";
const d3 = d3temp.default ? d3temp.default : d3temp;
const nodom = nodomtemp.default ? nodomtemp.default: nodomtemp;
@ -39,59 +41,6 @@ class Entropy extends Operation {
];
}
/**
* Calculates the frequency of bytes in the input.
*
* @param {Uint8Array} input
* @returns {number}
*/
calculateShannonEntropy(input) {
const prob = [],
occurrences = new Array(256).fill(0);
// Count occurrences of each byte in the input
let i;
for (i = 0; i < input.length; i++) {
occurrences[input[i]]++;
}
// Store probability list
for (i = 0; i < occurrences.length; i++) {
if (occurrences[i] > 0) {
prob.push(occurrences[i] / input.length);
}
}
// Calculate Shannon entropy
let entropy = 0,
p;
for (i = 0; i < prob.length; i++) {
p = prob[i];
entropy += p * Math.log(p) / Math.log(2);
}
return -entropy;
}
/**
* Calculates the scanning entropy of the input
*
* @param {Uint8Array} inputBytes
* @returns {Object}
*/
calculateScanningEntropy(inputBytes) {
const entropyData = [];
const binWidth = inputBytes.length < 256 ? 8 : 256;
for (let bytePos = 0; bytePos < inputBytes.length; bytePos += binWidth) {
const block = inputBytes.slice(bytePos, bytePos+binWidth);
entropyData.push(this.calculateShannonEntropy(block));
}
return { entropyData, binWidth };
}
/**
* Calculates the frequency of bytes in the input.
*
@ -394,10 +343,10 @@ class Entropy extends Operation {
return this.calculateByteFrequency(input);
case "Curve":
case "Image":
return this.calculateScanningEntropy(input).entropyData;
return calculateScanningEntropy(input, input.byteLength < 256 ? 8 : 256).entropyData;
case "Shannon scale":
default:
return this.calculateShannonEntropy(input);
return calculateShannonEntropy(input);
}
}