Examples
Scenario 1: Encrypt Decrypt 6 digit code using RSA Algorithm
Given
Step 1: Generate the Key Pair Using Keytool
Generate an RSA key pair and store it in a keystore.
keytool -genkeypair -alias mykey -keyalg RSA -keysize 2048 -validity 365 -keystore mykeystore.jks -storetype JKS -storepass changeit -keypass changeit -dname "CN=example.com, OU=IT, O=Example Corp, L=San Francisco, ST=CA, C=US"-genkeypair: Generates a key pair (public and private key).-alias mykey: The alias for the key pair.-keyalg RSA: The algorithm for the key.-keysize 2048: The size of the key.-validity 365: The validity of the key in days.-keystore mykeystore.jks: The keystore file to store the key pair.-storetype JKS: The type of the keystore.-storepass changeit: The password for the keystore.-keypass changeit: The password for the key.-dname: The Distinguished Name (DN) for the certificate.
Step 2: Export the Public Key
This step is optional. Instead of exporting the key, we can directly both private and public key from the keystore. See Step 4 for more details.
Export the public key to a file.
keytool -exportcert -alias mykey -keystore mykeystore.jks -file publickey.cer -storepass changeit-exportcert: Exports the certificate (public key).-alias mykey: The alias of the key pair.-keystore mykeystore.jks: The keystore file.-file publickey.cer: The output file for the public key.-storepass changeit: The password for the keystore.
Step 3: Encrypt Decrypt the 6-Digit Code
Encrypt the 6-digit code using the public key and Decrypt via private key.
import java.io.FileInputStream;
import java.security.Security;
import java.security.cert.Certificate;
import java.security.cert.CertificateFactory;
import java.util.Base64;
import javax.crypto.Cipher;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import java.security.*;
public class EncryptionDecryptionRSA {
static {
Security.addProvider(new BouncyCastleProvider());
}
public static void main(String[] args) throws Exception {
String storeBasePath = "/Users/pranayp/Documents/Project/Personal/sample-java-project/src/main/resources/store/";
PublicKey publicKey = getPublicKey(storeBasePath + "publickey.cer");
PrivateKey privateKey = getPrivateKey(storeBasePath + "mykeystore.jks", "mykey", "changeit", "changeit");
String plaintext = "123456";
System.out.println("Original: " + plaintext);
String encrypted = encrypt(plaintext, publicKey);
System.out.println("Encrypted: " + encrypted);
String decrypted = decrypt(encrypted, privateKey);
System.out.println("Decrypted: " + decrypted);
}
public static String encrypt(String plaintext, PublicKey publicKey) throws Exception {
Cipher cipher = Cipher.getInstance("RSA/None/PKCS1Padding", "BC");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] encryptedBytes = cipher.doFinal(plaintext.getBytes());
return Base64.getEncoder().encodeToString(encryptedBytes);
}
public static String decrypt(String encryptedText, PrivateKey privateKey) throws Exception {
Cipher cipher = Cipher.getInstance("RSA/None/PKCS1Padding", "BC");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] decryptedBytes = cipher.doFinal(Base64.getDecoder().decode(encryptedText));
return new String(decryptedBytes);
}
public static PrivateKey getPrivateKey(String keystoreFile, String alias, String storePassword, String keyPassword)
throws Exception {
KeyStore keystore = KeyStore.getInstance("JKS");
keystore.load(new FileInputStream(keystoreFile), storePassword.toCharArray());
return (PrivateKey) keystore.getKey(alias, keyPassword.toCharArray());
}
public static PublicKey getPublicKey(String filename) throws Exception {
CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
Certificate cert = certFactory.generateCertificate(new FileInputStream(filename));
return cert.getPublicKey();
}
}Step 4: Encrypt Decrypt the 6-Digit Code without using separately generated certificate key
import java.io.FileInputStream;
import java.security.KeyStore;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.Security;
import java.security.cert.Certificate;
import java.util.Base64;
import javax.crypto.Cipher;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
public class EncryptionDecryptionRSA2 {
static {
Security.addProvider(new BouncyCastleProvider());
}
private static final String KEYSTORE_TYPE = "JKS";
private static final String STORE_BASE_PATH = "/Users/pranayp/Documents/Project/Personal/sample-java-project/src/main/resources/store/";
private static final String KEYSTORE_FILE = STORE_BASE_PATH + "mykeystore.jks";
private static final String KEYSTORE_PASSWORD = "changeit";
private static final String KEY_ALIAS = "mykey";
private static final String KEY_PASSWORD = "changeit";
public static void main(String[] args) {
try {
KeyStore keystore = loadKeyStore();
PublicKey publicKey = getPublicKey(keystore);
PrivateKey privateKey = getPrivateKey(keystore);
String plaintext = "123456";
System.out.println("Original: " + plaintext);
String encrypted = encrypt(plaintext, publicKey);
System.out.println("Encrypted: " + encrypted);
String decrypted = decrypt(encrypted, privateKey);
System.out.println("Decrypted: " + decrypted);
} catch (Exception e) {
e.printStackTrace();
}
}
public static KeyStore loadKeyStore() throws Exception {
KeyStore keystore = KeyStore.getInstance(KEYSTORE_TYPE);
try (FileInputStream fis = new FileInputStream(KEYSTORE_FILE)) {
keystore.load(fis, KEYSTORE_PASSWORD.toCharArray());
}
return keystore;
}
public static PublicKey getPublicKey(KeyStore keystore) throws Exception {
Certificate cert = keystore.getCertificate(KEY_ALIAS);
return cert.getPublicKey();
}
public static PrivateKey getPrivateKey(KeyStore keystore) throws Exception {
return (PrivateKey) keystore.getKey(KEY_ALIAS, KEY_PASSWORD.toCharArray());
}
public static String encrypt(String plaintext, PublicKey publicKey) throws Exception {
Cipher cipher = Cipher.getInstance("RSA/NONE/PKCS1Padding", "BC");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] encryptedBytes = cipher.doFinal(plaintext.getBytes());
return Base64.getEncoder().encodeToString(encryptedBytes);
}
public static String decrypt(String encryptedText, PrivateKey privateKey) throws Exception {
Cipher cipher = Cipher.getInstance("RSA/NONE/PKCS1Padding", "BC");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
byte[] decryptedBytes = cipher.doFinal(Base64.getDecoder().decode(encryptedText));
return new String(decryptedBytes);
}
}Last updated