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Thought analysis

A few days ago, I wanted to take a look at what the popular articles in Nuggets are. After debugging the page, I located the requested interface (this interface will asynchronously pull 20 articles and render them to the page). The parameters of this interface are as follows

The two most important parameters are cursor, which can be understood as the page number of the current request, and limit, which can be understood as the number of data returned by the current request

The request parameters in the figure above are automatically requested during the first screen rendering. Then, when we manually pull down the scroll bar, the page will automatically fetch the data for the next screen

The parameters of the above two pictures are the parameters of the articles that are automatically pulled through the FETCH. Take out several encrypted cursors and put them out to study the rules

eyJ2IjoiNzAyMzYyMzk2NDExMDg4MDc4MiIsImkiOjIwfQ==
eyJ2IjoiNzAyMzYyMzk2NDExMDg4MDc4MiIsImkiOjYwfQ==
eyJ2IjoiNzAyMzYyMzk2NDExMDg4MDc4MiIsImkiOjgwfQ==
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Observation found only one difference, suspected to be caused by cursor changes on the page

Generally speaking, there are two schemes for data encryption: (1) MD5 encryption, which is irreversible, and (2) Base64 encryption, which can be decrypted

Give it a try, throw that string of data at an online site and test it

I = = = = = = = = = = = = = = = = = Select * from xx limit ${cursor}, ${cursor}

To sum up, the parameters are indeed encrypted, but only a little

How to implement Base64 encryption and decryption with JS

In this case, we can generate the encrypted cursor by ourselves, and then directly tune the interface to pull the corresponding data. Finally, we can analyze the data

Share how to do base64 encryption and decryption for characters in JS.

let base64 = function() {
    // private property  
    _keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
    return {
        encode(input) {
            var output = "";
            var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
            var i = 0;
            while (i < input.length) {
                chr1 = input.charCodeAt(i++);
                chr2 = input.charCodeAt(i++);
                chr3 = input.charCodeAt(i++);
                enc1 = chr1 >> 2;
                enc2 = ((chr1 & 3) < <4) | (chr2 >> 4);
                enc3 = ((chr2 & 15) < <2) | (chr3 >> 6);
                enc4 = chr3 & 63;
                if (isNaN(chr2)) {
                    enc3 = enc4 = 64;
                } else if (isNaN(chr3)) {
                    enc4 = 64;
                }
                output = output + _keyStr.charAt(enc1) + _keyStr.charAt(enc2) + _keyStr.charAt(enc3) + _keyStr.charAt(enc4);
            }
            return output;

        },
        decode(input) {
            var output = "";
            var chr1, chr2, chr3;
            var enc1, enc2, enc3, enc4;
            var i = 0;
            input = input.replace(/[^A-Za-z0-9\+\/\=]/g."");
            while (i < input.length) {
                enc1 = _keyStr.indexOf(input.charAt(i++));
                enc2 = _keyStr.indexOf(input.charAt(i++));
                enc3 = _keyStr.indexOf(input.charAt(i++));
                enc4 = _keyStr.indexOf(input.charAt(i++));
                chr1 = (enc1 << 2) | (enc2 >> 4);
                chr2 = ((enc2 & 15) < <4) | (enc3 >> 2);
                chr3 = ((enc3 & 3) < <6) | enc4;
                output = output + String.fromCharCode(chr1);
                if(enc3 ! =64) {
                    output = output + String.fromCharCode(chr2);
                }
                if(enc4 ! =64) {
                    output = output + String.fromCharCode(chr3); }}returnoutput; }}} ();Copy the code