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Example of RSA generation, sign, verify, encryption, decryption and keystores in Java
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import javax.crypto.Cipher; | |
import java.io.InputStream; | |
import java.security.*; | |
import java.util.Base64; | |
import static java.nio.charset.StandardCharsets.UTF_8; | |
public class RsaExample { | |
public static KeyPair generateKeyPair() throws Exception { | |
KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA"); | |
generator.initialize(2048, new SecureRandom()); | |
KeyPair pair = generator.generateKeyPair(); | |
return pair; | |
} | |
public static KeyPair getKeyPairFromKeyStore() throws Exception { | |
//Generated with: | |
// keytool -genkeypair -alias mykey -storepass s3cr3t -keypass s3cr3t -keyalg RSA -keystore keystore.jks | |
InputStream ins = RsaExample.class.getResourceAsStream("/keystore.jks"); | |
KeyStore keyStore = KeyStore.getInstance("JCEKS"); | |
keyStore.load(ins, "s3cr3t".toCharArray()); //Keystore password | |
KeyStore.PasswordProtection keyPassword = //Key password | |
new KeyStore.PasswordProtection("s3cr3t".toCharArray()); | |
KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry) keyStore.getEntry("mykey", keyPassword); | |
java.security.cert.Certificate cert = keyStore.getCertificate("mykey"); | |
PublicKey publicKey = cert.getPublicKey(); | |
PrivateKey privateKey = privateKeyEntry.getPrivateKey(); | |
return new KeyPair(publicKey, privateKey); | |
} | |
public static String encrypt(String plainText, PublicKey publicKey) throws Exception { | |
Cipher encryptCipher = Cipher.getInstance("RSA"); | |
encryptCipher.init(Cipher.ENCRYPT_MODE, publicKey); | |
byte[] cipherText = encryptCipher.doFinal(plainText.getBytes(UTF_8)); | |
return Base64.getEncoder().encodeToString(cipherText); | |
} | |
public static String decrypt(String cipherText, PrivateKey privateKey) throws Exception { | |
byte[] bytes = Base64.getDecoder().decode(cipherText); | |
Cipher decriptCipher = Cipher.getInstance("RSA"); | |
decriptCipher.init(Cipher.DECRYPT_MODE, privateKey); | |
return new String(decriptCipher.doFinal(bytes), UTF_8); | |
} | |
public static String sign(String plainText, PrivateKey privateKey) throws Exception { | |
Signature privateSignature = Signature.getInstance("SHA256withRSA"); | |
privateSignature.initSign(privateKey); | |
privateSignature.update(plainText.getBytes(UTF_8)); | |
byte[] signature = privateSignature.sign(); | |
return Base64.getEncoder().encodeToString(signature); | |
} | |
public static boolean verify(String plainText, String signature, PublicKey publicKey) throws Exception { | |
Signature publicSignature = Signature.getInstance("SHA256withRSA"); | |
publicSignature.initVerify(publicKey); | |
publicSignature.update(plainText.getBytes(UTF_8)); | |
byte[] signatureBytes = Base64.getDecoder().decode(signature); | |
return publicSignature.verify(signatureBytes); | |
} | |
public static void main(String... argv) throws Exception { | |
//First generate a public/private key pair | |
KeyPair pair = generateKeyPair(); | |
//KeyPair pair = getKeyPairFromKeyStore(); | |
//Our secret message | |
String message = "the answer to life the universe and everything"; | |
//Encrypt the message | |
String cipherText = encrypt(message, pair.getPublic()); | |
//Now decrypt it | |
String decipheredMessage = decrypt(cipherText, pair.getPrivate()); | |
System.out.println(decipheredMessage); | |
//Let's sign our message | |
String signature = sign("foobar", pair.getPrivate()); | |
//Let's check the signature | |
boolean isCorrect = verify("foobar", signature, pair.getPublic()); | |
System.out.println("Signature correct: " + isCorrect); | |
} | |
} |
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