Rebuild byte array with bigInteger and other method

Question

when I doing the signature encoding I meet a stranger problem:

When I want to rebuild a byte array, it always failed with :

//digest is the original byte array
        String messageHex = bytesToHex(digest);
        byte[] hexRestore = messageHex.getBytes();
        assert Arrays.equals(digest, hexRestore);   //false!    

        String utf8Digest = new String(digest, "UTF8");
        byte[] utf8Restore = utf8Digest.getBytes("UTF8");
        assert Arrays.equals(digest, utf8Restore);    //false!

Then I use big Integer:

        BigInteger messageBig = new BigInteger(digest);
        byte[] bigRestore = messageBig.toByteArray();
        assert Arrays.equals(digest, bigRestore));    //true!

Then it works, I don't know why, c

Answer 1

Don't use either of these approaches. Either convert into hex directly (not using BigInteger ) or use base64. BigInteger will faithfully reproduce numbers , but it's not meant to be a general purpose binary-to-hex converter. In particular, it will lose leading zeroes, because they're insignificant when treating the data as an integer . (If you know the expected length you could always format it to that, but why bother? Just treat the data as arbitrary data instead of as a number.)

Definitely don't try to "decode" the byte array as if it's UTF-8-encoded text - it isn't.

There are plenty of questions on Stack Overflow about converting byte arrays to hex or base64 . (Those are just links to two examples... search for more.)