How to implement string conversion Base64 to Hex in java equal to given JS implementation?

Question

I'm trying to implement a string conversion from Base64 to Hex, that must yield the same results as this website. Which means for example (Base64: bACAAAAAAAA=) is deconverted to (Hex: 6c00800000000000). This implementation in Javascript yields the correct output. So I tried to implement the equivalent in Java:

    private static String base64ToHex(String input) {
        byte[] raw = Base64.getDecoder().decode(input.getBytes());
        String result = "";
        for (int i = 0; i < raw.length; i++) {
            String hex = Integer.toString(raw[i], 16);
            result += (hex.length() == 2 ? hex : '0' + hex);
        }
        return result.toUpperCase();
    }

Unfortunately this does not give the required output. So could you please give me hint about what I am missing?

The whole point of Base64 is to avoid converting raw binary into a string as it tends to corrupt the data. i..e don't do what you did on the first line. use a byte[] instead. — Peter Lawrey
– Peter Lawrey, Commented Oct 29, 2020 at 11:01
For sure I did not understand you correctly; it still isn't the desired output — Benjamin Zach
– Benjamin Zach, Commented Oct 29, 2020 at 11:11
On one hand you wrote that you want to decode, on the other hand you encode: Base64.getEncoder() — Smutje
– Smutje, Commented Oct 29, 2020 at 11:14

Mahesh_Loya · Accepted Answer · 2020-10-29 11:28:47Z

2

Try below - You need to decode, not encode. Consider only value from decoded, ignore sign part. i.e take only absolute value, using Math.abs().

           private static String base64ToHex(String input) {
            byte[] raw = Base64.getDecoder().decode(input.getBytes());
            String result = "";
             for (int i = 0; i < raw.length; i++) {
                  String hex = Integer.toString(Math.abs(raw[i]), 16);
                  result += (hex.length() == 2 ? hex : '0' + hex);
              }
            return result.toUpperCase();
          }

edited Oct 29, 2020 at 11:28

answered Oct 29, 2020 at 11:12

Mahesh_Loya

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2 Comments

Benjamin Zach Over a year ago

Output is 6C000-800000000000, how to get rid of the additional 0-?

Mahesh_Loya Over a year ago

@BenjaminZach This was because negative value passed to Integer.toString(). Updated code. Check now.

Joop Eggen · Accepted Answer · 2020-10-29 11:32:56Z

2

     private static String base64ToHex(String input) {
         byte[] raw = Base64.getDecoder().decode(
                input.getBytes(StandardCharsets.US_ASCII));
         StringBuilder result = new StringBuilder(raw.length * 2);
         for  (byte b : raw) {
              result.append(String.format("%02X", b & 0xFF));
         }
         return result.toString();
     }

The problem is that java byte is signed, hence the masking & 0xFF.

answered Oct 29, 2020 at 11:32

Joop Eggen

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