Шифрование сообщений в Java. Ошибка дешифровки

Не мой код конечно, но помогите исправить ошибки. Как видно, с шифрованием справилась программа успешно. А дешифрование началось с ошибок.

Person.java:

package com.company;

import javax.crypto.Cipher;
import java.nio.charset.StandardCharsets;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.util.Base64;
import java.util.HashMap;
import java.util.Map;

public class Person {

    private PrivateKey privateKey;
    public PublicKey publicKey;

    private final Map<String, PublicKey> contacts = new HashMap<>();

    public Person() {
        generateKeyPair();
    }

    private void generateKeyPair() {
        try {
            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");

            keyGen.initialize(2048);
            KeyPair pair = keyGen.generateKeyPair();

            privateKey = pair.getPrivate();
            publicKey = pair.getPublic();
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

    public void addFriend(String name, PublicKey publicKey) {
        contacts.put(name, publicKey);
    }

    public String sendMessage(String recipient, String message) {
        PublicKey publicKey = contacts.get(recipient);
        if (publicKey == null)
            throw new RuntimeException("unknown recipient");

        try {
            Cipher cipher = Cipher.getInstance("RSA");
            cipher.init(Cipher.ENCRYPT_MODE, publicKey);

            byte[] msgBytes = message.getBytes(StandardCharsets.UTF_8);
            byte[] encrypted = cipher.doFinal(msgBytes);

            return Base64.getEncoder().encodeToString(encrypted);
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

    public String receiveMessage(String cipherText) {
        byte[] encrypted = Base64.getDecoder().decode(cipherText);

        try {
            Cipher cipher = Cipher.getInstance("RSA");
            cipher.init(Cipher.DECRYPT_MODE, privateKey);

            byte[] decrypted = cipher.doFinal(encrypted);

            return new String(decrypted, StandardCharsets.UTF_8);
        } catch (Exception ex) {
            throw new RuntimeException(ex);
        }
    }

App.java:

package com.company;

public class App {
    public static void main( String[] args) {
        Person mrSergey = new Person();
        Person mrIvan = new Person();

        mrIvan.addFriend("Сергей", mrSergey.publicKey);


        String encryptedMessage = mrIvan.sendMessage("[email protected]", "Hello world");
        System.out.println("Encrypted message: " + encryptedMessage);

        String decryptedMessage = mrSergey.receiveMessage(encryptedMessage);
        System.out.println("Decrypted message: " + decryptedMessage);
    }
}