这是java的案例：
SIGNATURE_ALGORITHM="SHA1WithRSA";
KEY_ALGORITHM="RSA";
public static String sign(byte[] data, String privateKey)
throws Exception {
byte[] keyBytes = Base64.decode(privateKey);
PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
PrivateKey privateK = keyFactory.generatePrivate(pkcs8KeySpec);
Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
signature.initSign(privateK);
signature.update(data);
return Base64.encode(signature.sign());
}
c#如何实现上面java的功能