code: public static byte[] rsPlainToAsn1(byte[] sign) {
  		if (sign.length != RS_LEN * 2) {
  			throw new CryptoException("err rs. ");
  		}
  		BigInteger r = new BigInteger(1, Arrays.copyOfRange(sign, 0, RS_LEN));
  		BigInteger s = new BigInteger(1, Arrays.copyOfRange(sign, RS_LEN, RS_LEN * 2));
  		ASN1EncodableVector v = new ASN1EncodableVector();
  		v.add(new ASN1Integer(r));
  		v.add(new ASN1Integer(s));
  		try {
  			return new DERSequence(v).getEncoded("DER");
  		} catch (IOException e) {
  			throw new IORuntimeException(e);
  		}
  	}
docs: BC的SM3withSM2验签需要的rs是asn1格式的，这个方法将直接拼接r||s的字节数组转化成asn1格式<br>
  来自：https://blog.csdn.net/pridas/article/details/86118774
  
  @param sign in plain byte array
  @return rs result in asn1 format
  @since 4.5.0