Magic operation now calculates the entropy of each option and displays tooltips explaining the properties.

This commit is contained in:
n1474335 2018-02-19 17:25:28 +00:00
parent 559741fd07
commit 56d33ea487
2 changed files with 50 additions and 10 deletions

View File

@ -283,6 +283,18 @@ const FlowControl = {
<th>Properties</th>
</tr>`;
/**
* Returns a CSS colour value based on an integer input.
*
* @param {number} val
* @returns {string}
*/
function chooseColour(val) {
if (val < 3) return "green";
if (val < 5) return "goldenrod";
return "red";
}
options.forEach(option => {
// Construct recipe URL
// Replace this Magic op with the generated recipe
@ -295,18 +307,20 @@ const FlowControl = {
fileType = "",
matchingOps = "",
useful = "",
validUTF8 = option.isUTF8 ? "Valid UTF8\n" : "";
entropy = `<span data-toggle="tooltip" data-container="body" title="Shannon Entropy is measured from 0 to 8. High entropy suggests encrypted or compressed data. Normal text is usually around 3.5 to 5.">Entropy: <span style="color: ${chooseColour(option.entropy)}">${option.entropy.toFixed(2)}</span></span>`,
validUTF8 = option.isUTF8 ? "<span data-toggle='tooltip' data-container='body' title='The data could be a valid UTF8 string based on its encoding.'>Valid UTF8</span>\n" : "";
if (option.languageScores[0].probability > 0) {
let likelyLangs = option.languageScores.filter(l => l.probability > 0);
if (likelyLangs.length < 1) likelyLangs = [option.languageScores[0]];
language = "Possible languages:\n " + likelyLangs.map(lang => {
return Magic.codeToLanguage(lang.lang);
}).join("\n ") + "\n";
language = "<span data-toggle='tooltip' data-container='body' title='Based on a statistical comparison of the frequency of bytes in various languages. Ordered by likelihood.'>" +
"Possible languages:\n " + likelyLangs.map(lang => {
return Magic.codeToLanguage(lang.lang);
}).join("\n ") + "</span>\n";
}
if (option.fileType) {
fileType = `File type: ${option.fileType.mime} (${option.fileType.ext})\n`;
fileType = `<span data-toggle="tooltip" data-container="body" title="Based on the presence of magic bytes.">File type: ${option.fileType.mime} (${option.fileType.ext})</span>\n`;
}
if (option.matchingOps.length) {
@ -314,17 +328,17 @@ const FlowControl = {
}
if (option.useful) {
useful = "Useful op detected\n";
useful = "<span data-toggle='tooltip' data-container='body' title='This could be an operation that displays data in a useful way, such as rendering an image.'>Useful op detected</span>\n";
}
output += `<tr>
<td><a href="#${recipeURL}">${Utils.generatePrettyRecipe(option.recipe, true)}</a></td>
<td>${Utils.escapeHtml(Utils.printable(Utils.truncate(option.data, 99)))}</td>
<td>${language}${fileType}${matchingOps}${useful}${validUTF8}</td>
<td>${language}${fileType}${matchingOps}${useful}${validUTF8}${entropy}</td>
</tr>`;
});
output += "</table>";
output += "</table><script type='application/javascript'>$('[data-toggle=\"tooltip\"]').tooltip()</script>";
if (!options.length) {
output = "Nothing of interest could be detected about the input data.\nHave you tried modifying the operation arguments?";

View File

@ -173,6 +173,24 @@ class Magic {
return true;
}
/**
* Calculates the Shannon entropy of the input data.
*
* @returns {number}
*/
calcEntropy() {
let prob = this._freqDist(),
entropy = 0,
p;
for (let i = 0; i < prob.length; i++) {
p = prob[i] / 100;
if (p === 0) continue;
entropy += p * Math.log(p) / Math.log(2);
}
return -entropy;
}
/**
* Generate various simple brute-forced encodings of the data (trucated to 100 bytes).
*
@ -262,6 +280,7 @@ class Magic {
languageScores: this.detectLanguage(extLang),
fileType: this.detectFileType(),
isUTF8: this.isUTF8(),
entropy: this.calcEntropy(),
matchingOps: matchingOps,
useful: useful
});
@ -324,6 +343,10 @@ class Magic {
aScore += a.recipe.length;
bScore += b.recipe.length;
// Lower entropy is "better", so we add the entropy to the score
aScore += a.entropy;
bScore += b.entropy;
return aScore - bScore;
});
}
@ -351,12 +374,14 @@ class Magic {
}
/**
* Calculates the number of times each byte appears in the input
* Calculates the number of times each byte appears in the input as a percentage
*
* @private
* @returns {number[]}
*/
_freqDist() {
if (this.freqDist) return this.freqDist;
const len = this.inputBuffer.length;
let i = len,
counts = new Array(256).fill(0);
@ -367,9 +392,10 @@ class Magic {
counts[this.inputBuffer[i]]++;
}
return counts.map(c => {
this.freqDist = counts.map(c => {
return c / len * 100;
});
return this.freqDist;
}
/**