### Question:
ExpandedPrivateKey { public static byte[] expandedPrivateKey(byte[] data) throws NoSuchAlgorithmException, InvalidKeyException { byte[] res = hmacSha512(data, Hex.decode("457870616e64")); for (int i = 0; i <= 31; i++) { res[i] = data[i]; } return res; }  static byte[] hmacSha512(byte[] data, byte[] key); static byte[] expandedPrivateKey(byte[] data);  }### Answer:
@Test public void testExpandedKey() throws NoSuchAlgorithmException, SignatureException, InvalidKeyException { String childXprv = "e8c0965af60563c4cabcf2e947b1cd955c4f501eb946ffc8c3447e5ec8a6335398a3720b3f96077fa187fdde48fe7dc293984b196f5e292ef8ed78fdbd8ed954"; byte[] z = ExpandedPrivateKey.expandedPrivateKey(Hex.decode(childXprv)); System.out.println(Hex.toHexString(z)); }