code: public static byte[] rsAsn1ToPlain(byte[] rsDer) {
  		ASN1Sequence seq = ASN1Sequence.getInstance(rsDer);
  		byte[] r = bigIntToFixexLengthBytes(ASN1Integer.getInstance(seq.getObjectAt(0)).getValue());
  		byte[] s = bigIntToFixexLengthBytes(ASN1Integer.getInstance(seq.getObjectAt(1)).getValue());
  		byte[] result = new byte[RS_LEN * 2];
  		System.arraycopy(r, 0, result, 0, r.length);
  		System.arraycopy(s, 0, result, RS_LEN, s.length);
  		return result;
  	}
docs: BC的SM3withSM2签名得到的结果的rs是asn1格式的，这个方法转化成直接拼接r||s<br>
  来自：https://blog.csdn.net/pridas/article/details/86118774
  
  @param rsDer rs in asn1 format
  @return sign result in plain byte array
  @since 4.5.0