java - Issues using BouncyCastle to encrypt a String -

i'm having issue trying encrypt , decrypt string using bouncycastle.

i'm following example @ http://www.aviransplace.com/2004/10/12/using-rsa-encryption-with-java/ , code looks like:

public class cryptotests {      public static final string algorithm = "rsa";      /**      * @param args command line arguments      */     public static void main(string[] args) {          try {             init();             keypair kp = generatekey();             byte[] enc = encrypt("the fat cat jumped on bat".getbytes("utf8"), kp.getpublic());             byte[] dec = decrypt(enc, kp.getprivate());         } catch (exception ex) {             logger.getlogger(cryptotests.class.getname()).log(level.severe, null, ex);         }     }      public static void init() {         security.addprovider(new bouncycastleprovider());     }      public static keypair generatekey() throws nosuchalgorithmexception {         keypairgenerator keygen = keypairgenerator.getinstance(algorithm);         keygen.initialize(1024);         keypair key = keygen.generatekeypair();         return key;     }      /**      * encrypt text using public key.      *      * @param text original unencrypted text      * @param key public key      * @return encrypted text      * @throws java.lang.exception      */     public static byte[] encrypt(byte[] text, publickey key) throws exception {          byte[] ciphertext = null;         // rsa cipher object , print provider         cipher cipher = cipher.getinstance(                 "rsa / ecb / pkcs1padding");         system.out.println(                 "nprovider is:" + cipher.getprovider().getinfo());          // encrypt plaintext using public key         cipher.init(cipher.encrypt_mode, key);         ciphertext = cipher.dofinal(text);         return ciphertext;      }      /**      * decrypt text using private key      *      * @param text encrypted text      * @param key private key      * @return unencrypted text      * @throws java.lang.exception      */     public static byte[] decrypt(byte[] text, privatekey key) throws exception {          byte[] dectyptedtext = null;         // decrypt text using private key         cipher cipher = cipher.getinstance("rsa/ecb/pkcs1padding");         cipher.init(cipher.decrypt_mode, key);         dectyptedtext = cipher.dofinal(text);         return dectyptedtext;     } } 

when run code end error:

may 21, 2013 10:20:31 cryptotests.cryptotests main severe: null java.security.invalidkeyexception: illegal key size or default parameters     @ javax.crypto.cipher.checkcryptoperm(cipher.java:1011)     @ javax.crypto.cipher.init(cipher.java:1209)     @ javax.crypto.cipher.init(cipher.java:1153)     @ cryptotests.cryptotests.encrypt(cryptotests.java:70)     @ cryptotests.cryptotests.main(cryptotests.java:34)     

i'm new , quite feeling bit lost when comes cryptography. goal figure out can create , use rsa key pair using sha512 , 4k length. i'm having lot of trouble finding clear examples of how achieve this.

need install unlimited java cryptography extension (jce) unlimited strength

http://www.oracle.com/technetwork/java/javase/downloads/jce-7-download-432124.html