Use of the Big Integer class to build an MD5 hash

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I found in another post right here in the OS the following example of code to generate a hash through MD5:

String message = "teste1234";
byte[] hash = MessageDigest.getInstance("MD5").digest(message.getBytes("UTF-8"));
System.out.println("MD5: " + new BigInteger(1, hash).toString(16));

However, I did not understand how it is possible to convert a number (represented by Biginteger) into a text.

java hash md5 biginteger

  • Possible duplicate of Messagedigest and hash class with MD5 in java

  • See the response of utluiz♦, in it, it explains exactly everything that is happening in this conversion.

  • In fact, the vast majority of java classes have the method toString(), it is he who makes this conversion. Each class has its own implementation of this method.

  • @Diegof has some he doesn’t have?

  • @bigown so I replied as a comment, not sure if all has kkkk

1 answer

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In fact the toString(16) method will convert to hexadecimal so of 16. as you can see hash is a byte array and if you are to observe the Biginteger constructor the byte[] parameter is represented as: Binary representation of the magnitude of the number. You do not necessarily need to use the Biginteger class for such a task. A practical example for you to better understand the logic:

    String message = "teste1234";
    byte[] hash = MessageDigest.getInstance("MD5").digest(message.getBytes("UTF-8"));

    char[] HEX_CHARS = "0123456789abcdef".toCharArray();
    char[] chars = new char[2 * buf.length];
    for (int i = 0; i < hash.length; ++i)
    {
    //Operadores bitwise para representar o valor do byte em hexadecimal
    chars[2 * i] = HEX_CHARS[(buf[i] & 0xF0) >>> 4];
    chars[2 * i + 1] = HEX_CHARS[buf[i] & 0x0F];
    }
    System.out.println("MD5: " + new String(chars));

In case the value is converted to "String" this is nothing more than the bitwise operators as shown above.

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