code: protected byte[] ensure128BitMD5(byte[] digest) {
          if(digest.length == MD5_LENGTH) {
              return digest;
          } else if(digest.length > MD5_LENGTH) {
              byte[] b = new byte[MD5_LENGTH];
              System.arraycopy(digest, 0, b, 0, MD5_LENGTH);
              return b;
          } else {
              byte[] b = new byte[MD5_LENGTH];
              System.arraycopy(digest, 0, b, 0, digest.length);
              Arrays.fill(b, digest.length, b.length, (byte)0);
              return b;
          }
      }
docs: Ensure that the specified MD5 digest has 128 bits.