RSA.java

String str = "coucou";
String seed = "seedFromSensor";


// generate public and private keys
final int keySize = 2048;
KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");

SecureRandom sr = new SecureRandom(seed.getBytes());
keyPairGenerator.initialize(keySize, sr);
KeyPair keyPair = keyPairGenerator.genKeyPair();
PublicKey pubKey = keyPair.getPublic();
PrivateKey privateKey = keyPair.getPrivate();

byte[] pubKeyBytes = pubKey.getEncoded();
// send the pubKeyBytes 


// encrypt the message
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(pubKeyBytes)));

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


// decrypt the message
Cipher cipher2 = Cipher.getInstance("RSA");
cipher2.init(Cipher.DECRYPT_MODE, privateKey);

new String(cipher2.doFinal(encrypted), StandardCharsets.UTF_8);