KeyPairEncryption.java

import javax.crypto.Cipher;
import java.io.FileOutputStream;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.EncodedKeySpec;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;
import java.util.UUID;

public class KeyPairEncryption {

    private static final String PUBLIC_KEY =
            "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA0UW6nxjPgny1gE0GdKJq2pTfXrVJuJYtefbDRB8+DF1BIUOtIBZYkI0drYHl+3SU6v94qbN0BGqLFs6Kv67A0UxRri1dsVv7zGadWkGsqLxXWsyqg2YzHNK1l4R0UXGSU6CIz8yu7N6me0U8JKDsFdtd2sp23LyhjLbMv4RJVtN0+2J8JmBhST4w2Fj82q4QYDVn3g+rx5lq1obNBgyXNwdUx5/8F2u36ygbetKvkJyxU4d5ChZY0Bk7relo+BJm9PGOrJqq3ojR3+XXsFJx7Dymp4iR3Fz9gYXCl6T/MDbsxl+FNtEIY2qDnQfZIM+n4ordoKZAjTATZ52m02NRZwIDAQAB";

    private static final String PRIVATE_KEY =
            "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";

    public static String getEncrypted(String data) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, getPublicKeyFromMemory());
        byte[] encryptedBytes = cipher.doFinal(data.getBytes());
        return new String(Base64.getEncoder().encode(encryptedBytes));
    }

    public static String getDecrypted(String data) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.DECRYPT_MODE, getPrivateKeyFromMemory());
        byte[] encryptedBytes = cipher.doFinal(Base64.getDecoder().decode(data.getBytes()));
        return new String(encryptedBytes);
    }

    public static void main(String... args) throws Exception {
        final String message = UUID.randomUUID().toString();
        System.out.println("  Message: " + message);
        String encrypted = getEncrypted(message);
        System.out.println("ENCRYPTED: " + encrypted);
        String decrypted = getDecrypted(encrypted);
        System.out.println("DECRYPTED: " + decrypted);
    }

    private static void generateKeyPair() throws Exception {
        KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
        generator.initialize(2048);
        KeyPair pair = generator.generateKeyPair();
        PrivateKey privateKey = pair.getPrivate();
        PublicKey publicKey = pair.getPublic();
        try (FileOutputStream fos = new FileOutputStream("exchange_token_server.pub")) {
            fos.write(Base64.getEncoder().encodeToString(publicKey.getEncoded()).getBytes());
        }
        try (FileOutputStream fos = new FileOutputStream("exchange_token_server.key")) {
            fos.write(Base64.getEncoder().encodeToString(privateKey.getEncoded()).getBytes());
        }
    }

    private static PublicKey getPublicKeyFromMemory() throws Exception {
        return KeyFactory.getInstance("RSA")
                .generatePublic(new X509EncodedKeySpec(Base64.getDecoder().decode(PUBLIC_KEY)));
    }

    private static PrivateKey getPrivateKeyFromMemory() throws Exception {
        return KeyFactory.getInstance("RSA")
                .generatePrivate(new PKCS8EncodedKeySpec(Base64.getDecoder().decode(PRIVATE_KEY)));
    }

    private static PublicKey getPublicKeyFromFile() throws Exception {
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        byte[] publicKeyBytes = KeyPairEncryption.class.getClassLoader().getResourceAsStream("exchange_token_server.pub").readAllBytes();
        EncodedKeySpec publicKeySpec = new X509EncodedKeySpec(Base64.getDecoder().decode(publicKeyBytes));
        return keyFactory.generatePublic(publicKeySpec);
    }

    private static PrivateKey getPrivateKeyFromFile() throws Exception {
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        byte[] privateKeyBytes = KeyPairEncryption.class.getClassLoader().getResourceAsStream("exchange_token_server.key").readAllBytes();
        EncodedKeySpec privateKeySpec = new PKCS8EncodedKeySpec(Base64.getDecoder().decode(privateKeyBytes));
        return keyFactory.generatePrivate(privateKeySpec);
    }

}