too much data for RSA block

http://objectmix.com/java/76634-too-much-data-rsa-block.html

Hallo,

i have a problem with my RSA implementation in Java... if i have a

string which is no longer then 64 Signs is there any problem. But as

soon as a string is longer than 64 Signs i get an Exception about

this:

´-----------------------------

| java.lang.ArrayIndexOutOfBoundsException: too much data for RSA

block

| at org.bouncycastle.jce.provider.JCERSACipher.engineDoFinal(JCERSACipher.java:271)

| at javax.crypto.Cipher.doFinal(DashoA6275)

| at allesineinem.main(allesineinem.java:38)

Exception in thread "main"

`-----------------------------

Here is my code for encrypt and decrypt a String with RSA and

bouncycastleProvider... I hope someone can help me and say where is

the problem

----------------------------------------------------

import java.security.*;

import javax.crypto.*;

import org.bouncycastle.jce.provider.BouncyCastleProvider;

/**

* @author Yildirim

*

* Folgendes auswählen, um die Schablone für den erstellten

Typenkommentar zu ändern:

* Fenster>Benutzervorgaben>Java>Codegenerierung>Code und

Kommentare

*/

public class allesineinem

{

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

{

Security.addProvider(new BouncyCastleProvider());

KeyPairGenerator RSAkeyPairGen =

KeyPairGenerator.getInstance("RSA");

SecureRandom sunSha1prngSecRand =

SecureRandom.getInstance("SHA1PRNG","SUN");

sunSha1prngSecRand.setSeed(System.currentTimeMillis());

RSAkeyPairGen.initialize(512,sunSha1prngSecRand);

KeyPair rsaKeyPair = RSAkeyPairGen.generateKeyPair();

//System.out.println(RSAkeyPairGen);

PrivateKey rsaPrivKey = rsaKeyPair.getPrivate();

PublicKey rsaPubKey = rsaKeyPair.getPublic();

Cipher cipher = Cipher.getInstance("RSA","BC");

cipher.init(Cipher.ENCRYPT_MODE,rsaPubKey);

String text = "Hallo wie gehs? Danke.. mir gehts gut..was treibst

du denn so? na";

//String text = "0123456789012345678901234567890123456789012345678901234567890123";

byte[] buf1 = text.getBytes();

byte[] buf = cipher.doFinal(buf1);

for (int i=0;i<buf.length;i++)

{

//System.out.print(buf[i]+" ");

}

System.out.println();

//System.out.print(toHumanReadableString(buf));

String string1 = toHumanReadableString(buf);

System.out.println();

//System.out.print(string1+" ");

System.out.println();

byte[] hallo1 = string1.getBytes();

for (int i=0;i<buf.length;i++)

{

//System.out.print(hallo1[i]+" ");

}

System.out.println();

//System.out.println(string1.getBytes());

cipher.init(Cipher.DECRYPT_MODE,rsaPrivKey);

//System.out.println(buf);

byte[] buf2 = cipher.doFinal(buf);

System.out.println(toHumanReadableString(buf2));

}

public static String toHumanReadableString(byte[] bytes)

{

return((new String(bytes)));

}

}

-----------------------------------------------

thanks

Ümit Yildirim

PS: sorry because of my bad english




Reply With Quote

08-20-2004 11:38 AM
#2

Re: too much data for RSA block

MatheGeniee@gmx.de (?mit Yildirim) wrote in message news:<4a2b6107.0408170147.77789ddb@posting.google.com>...

> Hallo,

>

> i have a problem with my RSA implementation in Java... if i have a

> string which is no longer then 64 Signs is there any problem. But as

> soon as a string is longer than 64 Signs i get an Exception about

> this:

BouncyCastle RSA gives an exception if you try to encrypt a block

which is longer than the key size. In your case the key size is 512

== 64 bytes. I think the only work around is to break your text into

64 byte blocks.

> RSAkeyPairGen.initialize(512,sunSha1prngSecRand);

Also 512 is pretty short for an RSA key, better to use 1024 or 2048.

And of course, the usual advice is to use RSA only for sending a

symmetric key, which is then used for encrypting the rest of the data.

-- Russ