加密密钥为空

Question

我的问题是，当我尝试创建RSA密钥对时，私钥为null，我完全不知道为什么。从屏幕最底部的日志中，我得到

获取公钥可以很好地工作，只是私钥不能，为什么？

KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
            keyStore.load(null);

            String message = "Message to encrypt";
            byte[] byteMessage = message.getBytes();

            KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA", "AndroidKeyStore");

            Calendar calendar = Calendar.getInstance();
            Calendar endCalendar = Calendar.getInstance();

            endCalendar.add(Calendar.YEAR, 20);

            if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                generator.initialize(new KeyGenParameterSpec.Builder("ssdPrivateKey", KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
                        .setDigests(KeyProperties.DIGEST_SHA1, KeyProperties.DIGEST_SHA256)
                        .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_OAEP, KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1)
                        .setKeySize(2048).build());
            } else {
                generator.initialize(new KeyPairGeneratorSpec.Builder(MainActivity.this)
                        .setAlias("ssdPrivateKey")
                        .setSerialNumber(BigInteger.ONE)
                        .setSubject(new X500Principal("CN=" + "ssdPrivateKey"))
                        .setStartDate(calendar.getTime())
                        .setEndDate(endCalendar.getTime())
                        .setKeySize(2048).build()
                );
            }
            KeyPair keyPair = generator.generateKeyPair();
            PublicKey publicKey = keyPair.getPublic();
            PrivateKey privateKey = keyPair.getPrivate();

            byte[] bytes = privateKey.getEncoded();
            if(bytes == null) {
                Log.d("EncryptionMessage", "Bytes == null");
            }