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javascript - 解码一个base45字符串，这将导致一个cbor压缩文件

问题描述

嗨，我正在尝试阅读我的绿色通行证证书，我知道当您扫描 QR 码时，它会出现类似 HC1:NHFDFGDF ......，我也知道这是编码为 base45，所以我做了一个小的 javascript 解码器，这是我的代码：

const base45 = require('base45');

//of course my personal HC1: isnt here
const encodedData = 'C0C9BQF2LVU.TMBX4KDL*XD/GPWBILC9GGBYPLR-SAG1CSQ6U7SSQY%SJWLK34JWLG56H0API0TUL:12>'

const decodedData = base45.decode(encodedData).toString('utf-8');

console.log(decodedData);

这是回应：

xڻ�⻈Q��C#?��-E�����K�BX���ֳI%|�zl�ȼ�qIbY㪤��
�Ң<�Ҳ�L�� ?��0gO+C��+�`��`׀0�H'W�P���WweϤ�|��I)yLI)%YFF��f�FfI�ť��y��%�We�+�$*'ޕ�������kh�f��I�9�����F����F�I�)LI%�&�ƖfIeY��������)�IY���F {
                                                                                                                                            �sVp����*8���z�8*��:;'������
     pMN�+*��*�+JN�+��  �
                         ��**K-J5�3�3�p8���yM]�o����E�_��O.�ϩ����
�g�˽��\�����="��]۷
����������{��Kq ��

我读到的是它对base45的解码将导致zlib压缩文件，其中解压缩将导致CBOR网络令牌，但我卡住了，你能帮帮我吗？这个结果正常吗？我还在学习

标签： javascriptcertificateqr-codezlibcbor

解决方案

我只使用浏览器资源（没有 node.js）解决了这个问题；我还找到了一些官方的解释、测试数据、字段解码的来源（见答案末尾）：

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
  <meta http-equiv="content-type" content="text/html; charset=utf-8">
  <meta name="generator" content="PSPad editor, www.pspad.com">
  <title></title>
  </head>
  <body>
  <textarea id="encoded" name="encoded" cols=100 rows=10></textarea><br>
  <textarea id="decoded" name="decoded" cols=100 rows=10 value = "prova">hello</textarea><br>
  <span id="plain1" name="plain1">-</span> --&gt;
  <span id ="cod" name="cod">-</span> --&gt;
  <span id="plain2" name="plain2">-</span><br>
  <button onclick="test()">Test</button><br>
  <button onclick="vai()">Vai</button><br>
  <script src="pako.min.js"></script>
  <script src="my_base45_2.js"></script>
  <script src="cbor.js" type="text/javascript"></script>

<script>

// https://dev.to/lmillucci/javascript-how-to-decode-the-greenpass-qr-code-3dh0

function convert(decoded) {
    text="";
    for (var i = 0; i < decoded.length; i++) {
        text +=  String.fromCharCode(decoded[i]);
    }
    console.log("Text=",text);
    values = text.split(",");
    console.log("values: " ,values);
    final = "";
    for (var i=0; i<values.length; i++) {
        final += String.fromCharCode(values[i])
    }
    return final;
}

function test() {

    source = document.getElementById("decoded").value;
    console.log("source=",source);
    document.getElementById("plain1").innerHTML = source;

    var enc = new TextEncoder();
    buff= enc.encode(source);
    console.log("buff:" , buff);

    encoded2 = encode(buff);
    console.log("encoded2:" , encoded2);
    document.getElementById("cod").innerHTML = encoded2;

    source = encoded2;
    console.log("Encoded source=",source);
    decoded = decode(source).enc;
    converted = convert(decoded);

    console.log("Decoded=", decoded);
    console.log("converted=", converted);

    document.getElementById("plain2").innerHTML = converted;
}


function buf2hex(buffer) {
// https://stackoverflow.com/questions/34309988/byte-array-to-hex-string-conversion-in-javascript
    var u = new Uint8Array(buffer),
        a = new Array(u.length),
        i = u.length;
    while (i--) // map to hex
        a[i] = (u[i] < 16 ? '0' : '') + u[i].toString(16);
    u = null; // free memory
    return a.join('');
};


function typedArrayToBuffer(array) {
// https://stackoverflow.com/questions/37228285/uint8array-to-arraybuffer
    return array.buffer.slice(array.byteOffset, array.byteLength + array.byteOffset)
}


function vai() {
    source = document.getElementById("encoded").value;
    console.log("Encoded source=",source);

    // Decode BASE45:
    decoded = decode(source).enc;

    // Unzip the decoded:
    COSEbin =  pako.inflate(decode(source).raw);
        COSE = buf2hex(COSEbin);

        var typedArray = new Uint8Array(COSE.match(/[\da-f]{2}/gi).map(function (h) {
          return parseInt(h, 16)
        })) // https://stackoverflow.com/questions/43131242/how-to-convert-a-hexadecimal-string-of-data-to-an-arraybuffer-in-javascript
        var unzipped = typedArray.buffer;

        [headers1, headers2, cbor_data, signature] = CBOR.decode(unzipped);
        cbor_dataArr = typedArrayToBuffer(cbor_data);
        greenpassData  = CBOR.decode(cbor_dataArr);

        console.log(greenpassData);
}
</script>
  </body>
</html>

关键是“双CBOR解码”：一次是不够的：

CBOR解码：

[headers1, headers2, cbor_data, signature] = CBOR.decode(unzipped);

转换为数组：

cbor_dataArr = typedArrayToBuffer(cbor_data);

进一步的 CBOR 转换：

greenpassData  = CBOR.decode(cbor_dataArr);

我的 base45 解码器版本（“my_base45_2.js”），改编自node.js 版本：

 function encode(uint8array) {
    var output = [];

    for (var i = 0, length = uint8array.length; i < length; i+=2) {
      if (uint8array.length -i > 1) {
         var x = (uint8array[i]<<8)+ uint8array[i+1]
         var [ e, x ]  = divmod(x, 45*45)
         var [ d, c ] = divmod(x, 45)
         output.push(fromCharCode(c) + fromCharCode(d) + fromCharCode(e))
     } else {
         var x = uint8array[i]
         var [ d, c ] = divmod(x, 45)
         output.push(fromCharCode(c) + fromCharCode(d))
     }
    }
    return output.join('')
  };

  var divmod = function divmod(a,b) {
    var remainder = a
    var quotient = 0
    if (a >= b) {
        remainder = a % b
    quotient = (a - remainder) / b
    }
    return [ quotient, remainder ]
  }

  const BASE45_CHARSET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ $%*+-./:"
  var fromCharCode = function fromCharCode(c) {
    return BASE45_CHARSET.charAt(c);
  };

function decode(str) {
    var output = []
    var buf = []

    for(var i = 0, length=str.length; i < length; i++) {
//console.log(i);    
       var j = BASE45_CHARSET.indexOf(str[i])
       if (j < 0)
                console.log('Base45 decode: unknown character n.', i, j);
              //throw new Error('Base45 decode: unknown character');
       buf.push(j)
    }

    for(var i = 0, length=buf.length; i < length; i+=3) {
       var x = buf[i] + buf[i + 1] * 45
       if (length - i >= 3) {
          var [d, c] = divmod(x + buf[i + 2] * 45 * 45,256)
          output.push(d)
          output.push(c)
       } else {
         output.push(x)
       }
    }
console.log("output",output);    
    var enc = new TextEncoder();
    return {"enc" : enc.encode(output), "raw" : output};
    //return Buffer.from(output);
  };

这些是解码步骤：

QR 码 --> QR DECODER --> RAW QR 解码字符串 --> BASE45 解码器--> zlib 压缩字符串 --> pako 库 --> COSE 字符串 --> CBOR 解码器 --> CBOR 字符串 --> CBOR解码器--> 最终的 JSON 文件

我解码greenpass的参考指南：

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