sriramvemaraju2000
asked on
what is wrong in my code: substitution cipher java
I tried to develop substitution cipher .. But it is giving me error if I took the value greater than 3... I donno why ...
please help me in correcting the code...
please help me in correcting the code...
import java.io.UnsupportedEncodingException;
public class DataUtility {
public static String encryptMessage(String msg, int k) throws UnsupportedEncodingException {
String value = "";
byte bt1[] = msg.getBytes();
for (int i = 0; i < bt1.length; i++) {
//System.out.println(bt[i]);
value += encryptByte(bt1[i], k);
}
System.out.println(value);
return value;
}
public static char encryptByte(byte c, int k) {
return (char) ((c + k));
}
public static byte encryptByteAsByte(byte c, int k) {
return (byte) ((c + k));
}
public static String decryptMessage(String msg, int k) throws UnsupportedEncodingException {
String result = "";
byte[] bt = msg.getBytes();
for (int i = 0; i < bt.length; i++) {
result += decryptByte(bt[i], k);
}
System.out.println(result);
return result;
}
public static char decryptByte(byte c, int k) {
return (char) ((c - k));
}
public static byte decryptByteAsByte(byte c, int k) {
System.out.println("c=" + c + ",k=" + k);
return (byte) ((c - k));
}
public static void main(String[] args) throws UnsupportedEncodingException {
encryptMessage("doctype", 8);
decryptMessage("lwk|xm", 8);
}
}
Peter Kwan
May I know whether you are going to limit the plain-text and encrypted words to lower-case alphabets only? If yes, you should add mod 26 to your encryption/decryption logic.
A sample update of your encryption code:
public static char encryptByte(byte c, int k) {
return (char) ((c - 'a' + k) % 26 + 'a');
}
For decryption, it is similar, but you should add +26 before you subtract in order not to overflow if c is less than k.
public static char encryptByte(byte c, int k) {
return (char) ((c - 'a' + k) % 26 + 'a');
}
For decryption, it is similar, but you should add +26 before you subtract in order not to overflow if c is less than k.
ASKER
no I need for every ascii character .. I need to encrypt the binary files as well.
What error do you get for k>3 then?
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