[skynetchris]

Hi guys,

I've been asked to encrypt a file before its written to SDCard.

I've tried both DES and RSA with no luck.

I wanted to create a certificate that the BB could use to encrypt with and store the private key on the PC to decrypt with.

So i started with RSA(following RIM knowledge base AES example). Which I can run by itself and it works well.

I followed a google code example of creating the necessary public and private keys along with a certificate. That went fine.

The problem comes when I try to import the certificate and use the public key, i tried:

 try
{
   fconn = (FileConnection)Connector.open("file:///SDCard/cert.pfx",Connector.READ);
   fileStream = fconn.openInputStream();
   X509Certificate cert = new X509Certificate(fileStream);
   RSAPublicKey publicKey = (RSAPublicKey)cert.getPublicKey();
   publicKey.verify();
}

With all appropriate catch statements

Which seems to work without a hitch, but then I pass it to the encrypt method used in the Knowledge base example and it gives Java.lang exception?

Also if I try and verify the x509 certificate, it complains its not RCC signed?


So then I switched to DES and tried the API example:

 

   String pword = "pass";
   String plain = "Convert me";
   byte[] text = plain.getBytes();
   byte[] secretKey = pword.getBytes();
   byte[] encrypted = null;
   sampleDESEncryption(secretKey,text,encrypted);

    // sampleDESEncryption
    private static int sampleDESEncryption( byte[] secretKey, byte[] plainText, byte[] cipherText )
        throws CryptoTokenException, CryptoUnsupportedOperationException
    {
        // Create a new DES key based on the 8 bytes in the secretKey array
        DESKey key = new DESKey( secretKey );
                
        // Create a new instance of the DES encryptor engine, passing in the newly 
        // created key
        DESEncryptorEngine engine = new DESEncryptorEngine( key );
        // Encrypt one block (8 bytes) of plainText into cipherText
        engine.encrypt( plainText, 0, cipherText, 0 );
    
        // Return the block size of the engine
        return engine.getBlockLength();
    }

But I dont understand how to get the cipher text back? I tried returning it ({cipherText} return encrypted = sampleDESEncryption(...)) and it complained it was null?

What I would love is a code example of importing and using a java created certificate for encryption. Or a simple des encryption decryption example.

Any ideas?

Cheers,
Chris.

[pacred]

You could always roll your own.... Sometimes I need a small algorithm to embed in a microcontroller's firmware so I use TEA.

JavaScript Implementation of Block TEA Tiny Encryption Algorithm (© 2002-2005 Chris Veness)

//
// TEAencrypt: Use Corrected Block TEA to encrypt plaintext using password
//             (note plaintext & password must be strings not string objects)
//
// Return encrypted text as string
//
function TEAencrypt(plaintext, password)
{
    if (plaintext.length == 0) return('');  // nothing to encrypt
    // 'escape' plaintext so chars outside ISO-8859-1 work in single-byte packing, but keep
    // spaces as spaces (not '%20') so encrypted text doesn't grow too long (quick & dirty)
    var asciitext = escape(plaintext).replace(/%20/g,' ');
    var v = strToLongs(asciitext);  // convert string to array of longs
    if (v.length <= 1) v[1] = 0;  // algorithm doesn't work for n<2 so fudge by adding a null
    var k = strToLongs(password.slice(0,16));  // simply convert first 16 chars of password as key
    var n = v.length;

    var z = v[n-1], y = v[0], delta = 0x9E3779B9;
    var mx, e, q = Math.floor(6 + 52/n), sum = 0;

    while (q-- > 0) {  // 6 + 52/n operations gives between 6 & 32 mixes on each word
        sum += delta;
        e = sum>>>2 & 3;
        for (var p = 0; p < n; p++) {
            y = v[(p+1)%n];
            mx = (z>>>5 ^ y<<2) + (y>>>3 ^ z<<4) ^ (sum^y) + (k[p&3 ^ e] ^ z);
            z = v[p] += mx;
        }
    }

    var ciphertext = longsToStr(v);

    return escCtrlCh(ciphertext);
}

//
// TEAdecrypt: Use Corrected Block TEA to decrypt ciphertext using password
//
function TEAdecrypt(ciphertext, password)
{
    if (ciphertext.length == 0) return('');
    var v = strToLongs(unescCtrlCh(ciphertext));
    var k = strToLongs(password.slice(0,16)); 
    var n = v.length;

    var z = v[n-1], y = v[0], delta = 0x9E3779B9;
    var mx, e, q = Math.floor(6 + 52/n), sum = q*delta;

    while (sum != 0) {
        e = sum>>>2 & 3;
        for (var p = n-1; p >= 0; p--) {
            z = v[p>0 ? p-1 : n-1];
            mx = (z>>>5 ^ y<<2) + (y>>>3 ^ z<<4) ^ (sum^y) + (k[p&3 ^ e] ^ z);
            y = v[p] -= mx;
        }
        sum -= delta;
    }

    var plaintext = longsToStr(v);

    // strip trailing null chars resulting from filling 4-char blocks:
    plaintext = plaintext.replace(/\0+$/,'');

    return unescape(plaintext);
}


// supporting functions

function strToLongs(s) {  // convert string to array of longs, each containing 4 chars
    // note chars must be within ISO-8859-1 (with Unicode code-point < 256) to fit 4/long
    var l = new Array(Math.ceil(s.length/4));
    for (var i=0; i<l.length; i++) {
        // note little-endian encoding - endianness is irrelevant as long as 
        // it is the same in longsToStr() 
        l[i] = s.charCodeAt(i*4) + (s.charCodeAt(i*4+1)<<8) + 
               (s.charCodeAt(i*4+2)<<16) + (s.charCodeAt(i*4+3)<<24);
    }
    return l;  // note running off the end of the string generates nulls since 
}              // bitwise operators treat NaN as 0

function longsToStr(l) {  // convert array of longs back to string
    var a = new Array(l.length);
    for (var i=0; i<l.length; i++) {
        a[i] = String.fromCharCode(l[i] & 0xFF, l[i]>>>8 & 0xFF, 
                                   l[i]>>>16 & 0xFF, l[i]>>>24 & 0xFF);
    }
    return a.join('');  // use Array.join() rather than repeated string appends for efficiency
}

function escCtrlCh(str) {  // escape control chars etc which might cause problems with encrypted texts
    return str.replace(/[\0\t\n\v\f\r\xa0'"!]/g, function(c) { return '!' + c.charCodeAt(0) + '!'; });
}

function unescCtrlCh(str) {  // unescape potentially problematic nulls and control characters
    return str.replace(/!\d\d?\d?!/g, function(c) { return String.fromCharCode(c.slice(1,-1)); });
}

[skynetchris]

Cool thanks, will try it out and let you know.