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decryption and padding in java cryptography

gunjangoyal gg
Greenhorn

Joined: May 02, 2012
Posts: 1
i have to decrypt a frame on my server. encrypted frame is coming from client device through GPRS on socket.encryption is done with "TripleDes" and with a given key.same algorithm and key i am using n server side. frame is a combination of Hex and Ascii String. problem is when i decrypt this frame i get an error :

javax.crypto.IllegalBlockSizeException: Input length must be multiple of 8 when decrypting with padded cipher

and when i pad my byte array with zeros like

temparray[87] = 00;


i get an error :

javax.crypto.BadPaddingException: Given final block not properly padded

following is my code :

if ((len = inputStream.read(mainBuffer)) > -1) {
totalLength = len;
}
if (totalLength > 0) {
byteToAscii = function.byteToAscii(mainBuffer, totalLength);
}
if (byteToAscii.length() > 0) {
completeHexString = function.stringToHex(byteToAscii);
debugInfo = "FRAME RECV.=" + completeHexString;
/* FRAME RECV.=41ed34a41a9de6d270aa1e1464527e88c8bee66a00cfb308f60c105de81db0f1ce43d8c0b9bc4e8070b5ab8d4d3650b55d23223fc687bb1485945bc3228e9707a7aecda9f90657e0ac009571c6469c58a2cd9793cc433ccb5993f2*/
}
byte[] key = new byte[]{31, 30, 31, 36, 32, 11, 11, 11, 22, 26, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30, 30};
myKeySpec = new DESedeKeySpec(key);
mySecretKeyFactory = SecretKeyFactory.getInstance("TripleDES");
dekey = mySecretKeyFactory.generateSecret(myKeySpec);
byte[] zeros = {0, 0, 0, 0, 0, 0, 0, 0};
IvParameterSpec iv = new IvParameterSpec(zeros);
Cipher c = Cipher.getInstance("TripleDES/CBC/PKCS5Padding");
c.init(Cipher.DECRYPT_MODE, dekey, iv);
byte[] decordedValue = new BASE64Decoder().decodeBuffer(completeHexString);
byte[] decValue = c.doFinal(decordedValue);
String decryptedValue = new String(decValue);
System.out.println("decryptedValue= " + decryptedValue);

here are the functions which i am using inside the code:

public String stringToHex(String base) {
StringBuffer buffer = new StringBuffer();
int intValue = 0;
for (int x = 0; x < base.length(); x++) {
intValue = base.charAt(x);
String hex = Integer.toHexString(intValue);
if (hex.length() == 1) {
buffer.append("0" + hex + "");
} else {
buffer.append(hex + "");
}
}
return buffer.toString();
}
public String byteToAscii(byte[] b, int length) {
String returnString = "";
for (int i = 0; i < length; i++) {
returnString += (char) (b[i] & 0xff);
}
return returnString;
}


i am new in java cryptography. pl tell me how to do it?
thanks in advance.


 
It is sorta covered in the JavaRanch Style Guide.
 
subject: decryption and padding in java cryptography