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169 changes: 169 additions & 0 deletions Miscellaneous/RSAcipher.java
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import javax.crypto.Cipher;
import java.security.*;
import java.util.Base64;
import static java.nio.charset.StandardCharsets.UTF_8;

public class RSA {

public static KeyPair generateKeyPair() throws Exception {

KeyPairGenerator generator = KeyPairGenerator.getInstance("RSA");
generator.initialize(2048, new SecureRandom());
KeyPair pair = generator.generateKeyPair();

return pair;
}

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 {
//SHA256withRSA is magic signature

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 {
//SHA256withRSA is magic signature

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 {
//**********TEST ONE**************************************************
System.out.println("Test one: true case");
//generate a key pair
KeyPair pair1 = generateKeyPair();
//secret message
String message1 = "The proof does not fit in this margin";
//encrypt the message
String cipherText1 = encrypt(message1, pair1.getPublic());
//decrypt the message
String decipheredMessage1 = decrypt(cipherText1, pair1.getPrivate());
System.out.println(decipheredMessage1);
//sign the message
String signature1 = sign("fermat", pair1.getPrivate());
//check signature
boolean isCorrect1 = verify("fermat", signature1, pair1.getPublic());
System.out.println("Signature correct: " + isCorrect1);
System.out.println();

//**********TEST TWO**************************************************
System.out.println("Test two: true case");
//generate a key pair
KeyPair pair2 = generateKeyPair();
//secret message
String message2 = "Hello Darkness my old friend...";
//encrypt the message
String cipherText2 = encrypt(message2, pair2.getPublic());
//decrypt the message
String decipheredMessage2 = decrypt(cipherText2, pair2.getPrivate());
System.out.println(decipheredMessage2);
//sign the message
String signature2 = sign("tada", pair2.getPrivate());
//check signature
boolean isCorrect2 = verify("tada", signature2, pair2.getPublic());
System.out.println("Signature correct: " + isCorrect2);
System.out.println();

//**********TEST THREE**************************************************
System.out.println("Test three: true case");
//generate a key pair
KeyPair pair3 = generateKeyPair();
//secret message
String message3 = "the proof is trivial and is left as an exercise";
//encrypt the message
String cipherText3 = encrypt(message3, pair3.getPublic());
//decrypt the message
String decipheredMessage3 = decrypt(cipherText3, pair3.getPrivate());
System.out.println(decipheredMessage3);
//sign the message
String signature3 = sign("ButWhy", pair3.getPrivate());
//check signature
boolean isCorrect3 = verify("ButWhy", signature3, pair3.getPublic());
System.out.println("Signature correct: " + isCorrect3);
System.out.println();

//**********TEST FOUR**************************************************
System.out.println("Test four: true case");
//generate a key pair
KeyPair pair4 = generateKeyPair();
//secret message
String message4 = "math is challenging but fun";
//encrypt the message
String cipherText4 = encrypt(message4, pair4.getPublic());
//decrypt the message
String decipheredMessage4 = decrypt(cipherText4, pair4.getPrivate());
System.out.println(decipheredMessage4);
//sign the message
String signature4 = sign("soTired", pair4.getPrivate());
//check signature
boolean isCorrect4 = verify("soTired", signature4, pair4.getPublic());
System.out.println("Signature correct: " + isCorrect4);
System.out.println();

//**********TEST FIVE**************************************************
System.out.println("Test five: false case");
//generate a key pair
KeyPair pair5 = generateKeyPair();
//secret message
String message5 = "this secret message cannot be verified bc the key is wrong";
//encrypt the message
String cipherText5 = encrypt(message5, pair5.getPublic());
//decrypt the message
String decipheredMessage5 = decrypt(cipherText5, pair5.getPrivate());
System.out.println(decipheredMessage5);
//sign the message
String signature5 = sign("secretKey", pair5.getPrivate());
//check signature
boolean isCorrect5 = verify("wrongKey", signature5, pair5.getPublic());
System.out.println("Signature correct: " + isCorrect5);
System.out.println();

//**********TEST SIX**************************************************
System.out.println("Test two: false case");
//generate a key pair
KeyPair pair6 = generateKeyPair();
//secret message
String message6 = "Oh no, another wrong key example, whatever shall I do?";
//encrypt the message
String cipherText6 = encrypt(message6, pair6.getPublic());
//decrypt the message
String decipheredMessage6 = decrypt(cipherText6, pair6.getPrivate());
System.out.println(decipheredMessage6);
//sign the message
String signature6 = sign("originalKey", pair6.getPrivate());
//check signature
boolean isCorrect6 = verify("EveKey", signature6, pair6.getPublic());
System.out.println("Signature correct: " + isCorrect6);
}
}