Java: RSA crytography:

Need help completing the RSA class below. It will generate public and private key pars and encrypt plaintext using public key and decrypt ciphertext using private key. I need help implementing the following constructor and methods of the RSA class.

- RSA constructor, where the fields cipher, factory, and keyPairGenerator are initialized.

- getModulus method, where the modulus of a key pair is returned.

- getPublicExponenet method, where the public exponent of a key pair is returned.

- getPrivateExponent method, where the private exponent of a key pair is returned.

- getPublicKey method, where the string representation of the public key of a key pair is returned.

- getPrivateKey method, where the string representation of the private key of a key pair is returned.

- loadPublicKey(BigInteger modulus, BigInteger publicExponent), where a public key based on the modulus and public exponent is returned.

Code so far is below:

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package lecture7;

import java.math.BigInteger;

import java.security.KeyFactory;

import java.security.KeyPair;

import java.security.KeyPairGenerator;

import java.security.NoSuchAlgorithmException;

import java.security.PrivateKey;

import java.security.PublicKey;

import java.security.interfaces.RSAPrivateKey;

import java.security.interfaces.RSAPublicKey;

import java.security.spec.PKCS8EncodedKeySpec;

import java.security.spec.RSAPrivateKeySpec;

import java.security.spec.RSAPublicKeySpec;

import java.security.spec.X509EncodedKeySpec;

import java.util.Base64;

import javax.crypto.Cipher;

public class RSA {

Cipher cipher;

KeyFactory factory;

KeyPairGenerator keyPairGenerator;

/*

* initialize cipher object with RSA/ECB/OAEPWithSHA-256AndMGF1Padding algorithm

* initialize key factory for RSA algorithm

* initialize key pair generator for RSA algorithm with 2048 bit keys

*/

RSA() throws Exception {

// TODO

}

// return the modulus of a key pair

static BigInteger getModulus(KeyPair keyPair) {

// TODO

}

// return the public exponent of a key pair

static BigInteger getPublicExponent(KeyPair keyPair) {

// TODO

}

// return the private exponent of a key pair

static BigInteger getPrivateExponent(KeyPair keyPair) {

// TODO

}

// return the public key of a key pair object encoded as a string

static String getPublicKey(KeyPair keyPair) {

// TODO

}

// return the private key of a key pair object encoded as a string

static String getPrivateKey(KeyPair keyPair) {

// TODO

}

// return a public key given a modulus and a public exponent

public PublicKey loadPublicKey(BigInteger modulus, BigInteger publicExponent) throws Exception {

// TODO

}

// return a private key given a modulus and a private exponent

public PrivateKey loadPrivateKey(BigInteger modulus, BigInteger privateExponent) throws Exception {

// TODO

}

// return a public key given its string encoding

public PublicKey loadPublicKey(String key) throws Exception {

// TODO

}

// return a private key given its string encoding

public PrivateKey loadPrivateKey(String key) throws Exception {

// TODO

}

// generate a key pair

public KeyPair buildKeyPair() throws NoSuchAlgorithmException {

// TODO

}

// encrypt a plaintext message string using a public key and return the ciphertext as a string

public String encrypt(PublicKey publicKey, String message) throws Exception {

// TODO

}

// decrypt a ciphertext string using a private key and return the plaintext message as a string

public String decrypt(PrivateKey privateKey, String ciphertext) throws Exception {

// TODO

}

public static void main(String [] args) throws Exception {

// generate public and private keys

RSA rsa = new RSA();

KeyPair keyPair = rsa.buildKeyPair();

System.out.println("============ test 1 ============= ");

System.out.printf("Modulus: %d Public exponent: %d Private exponent: %d ",

getModulus(keyPair),

getPublicExponent(keyPair),

getPrivateExponent(keyPair));

System.out.printf("public key: %s private key: %s ",

getPublicKey(keyPair),

getPrivateKey(keyPair));

// encrypt the message

String ciphertext = rsa.encrypt(keyPair.getPublic(), "This is a secret message");

System.out.printf("ciphertext: %s ", ciphertext); // <>

// decrypt the message

String secret = rsa.decrypt(keyPair.getPrivate(), ciphertext);

System.out.printf("decrypted text: %s ", secret); // This is a secret message

System.out.println("============ test 2 ============= ");

// encrypt the message

ciphertext = "GQAkFOkoMiQej1SVsXukzcQridW6gdULMBLyINLDCheueTIWROa1jxlrVOatJanfzW87qBrOogzARFUiAz/TOIzQJrsymK5PnLUEyope/fpjzk4TW0SDDxq8awR0qZjX6iNASA2OUgJYfiuuDeZW7DhOo06d80oUJuX7f6CiYD5L9L7e60a19JFGKddd/S6JGx/trkjkZyt8+yw0Ii9spCt9xIokVFCnC9s/krw8tlcK6lLcNphXMc7aleRwj5j44qpgabxQJN6YFtb6bgSWlkCD0k0K6Tlz8cAojRUJZhcOc86Z4XH2pQA+K06tN59PNjtmJxQ689ATdnWSbtuz4g==";

String privateKey = "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";

// decrypt the message

secret = rsa.decrypt(rsa.loadPrivateKey(privateKey), ciphertext);

System.out.printf("decrypted text: %s ", secret); // This is a secret message

System.out.println("============ test 3 ============= ");

String modulus = "18694170902812379439224396366036618975087036932342596342114016626506342732206598983678783995172555625277822049263896719947072503182171904471905033641547701355590623070520026128520048349384408203727632196904765126145922172542029099469109457176444803083919434850940490161080646701179253993966676190947444424522802676236361888906813892133443501484084982283185687704600701830163258874995337377443233355927229715267144164204821626447066761907173881018530436002646108875014680953801110896146430930420285654633930955743332382203821205484497727502636190622636126176544525315926411856699429655429265972682284364395032933547793";

String privateExponent = "6598311813538244978991084986178175231269562816713443376806711210527560310685613435013162509366183327340686629592023725923000459947968330778706795217911735779140367927541224718936261324411555771070198330390482123045111489620248365486968276903207671772238954590108723597450562575212147388321667968460507567146114772784964924086719405832762974549811726151811461446737628380130889859632269140319339794753766843512034898776295782131016908779842987002431571452617189372808218434943780844213437857188360670494336950135174333082231755678039492863087141462911406980467712242906464866151883754892620600620095351615180177855041";

ciphertext = "c0/7/jUt/e4TkF+gvbPcwyPR3mljiGLXFtNGaouEzF7wuzL2lizTqzkjDUHGl4P9ABkT0j5rpZ5AgRsgogTkorwTaneSp0hetlrLMlGdv/w49wi6B+2FiOs+ABtgQv2vao2x85TK/IhlD56rGeOU2xVBzAWqfMxuyxanOca49lXV1RhutCOQV94zq9eGn3bfRgyeZolLlSjnv80ECPNBhBoNt4eUPNLIpRv5ZYtPvUwafc6e8bwkQ2Y5g6q1EChXwdNJm/RVDVG9iobbOK1Mhb8krg0W9sLHBYu6RanzkNLG9ogFYtFDEn+aWLtHmheeZhretpniYRVV2yXsO32FDw==";

secret = rsa.decrypt(rsa.loadPrivateKey(new BigInteger(modulus), new BigInteger(privateExponent)), ciphertext);

System.out.printf("decrypted text: %s ", secret); // This is a secret message

}

}