I am attempting to, in java, write a program that will encode a string like a vigenere cipher. An example run would be
java Encrypt -e lemon < in.txt > out.txt
in.txt should read ATTACKATDAWN, and out.txt should read LXFOPVEFRNHR, and if an insufficient # of args are used it should print the usage statement; However, when I run the encryption method on this, it returns "??¡????¡??£?", and if i run the decryption method on THAT, it returns "?? ???? ????", and if I put in less than the required two args, it returns
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
at Encrypt.main(Encrypt.java:22)
here is my code
import java.util.Scanner;
public class Encrypt
{
public static void main(String[] args)
{
Scanner scan = new Scanner (System.in);
String msg = scan.nextLine();
String key = args[1];
if (args.length < 2)
{
System.out.println("Encryption program by ----");
System.out.println("Usage: java Encrypt [-e, -d] < inputFile > outputFile");
System.exit(0);
}
else if (args[0].equals ("-e"))
{
String emsg = encrypt(args[1], msg);
System.out.println(emsg);
}
else if (args[0].equals ("-d"))
{
String dmsg = decrypt(args[1], msg);
System.out.println(dmsg);
}
}
public static void usage(String[] args)
{
if (args.length < 2)
{
System.out.println("Encryption program by --------");
System.out.println("Usage: java Encrypt [-e, -d] < inputFile > outputFile");
System.exit(0);
}
}
public static String encrypt(String key, String msg)
{
String emsg = "";
for (int i = 0; i < msg.length(); i++)
{
int m = msg.charAt(i);
int k = key.charAt(i % key.length());
int e = (m + (k - 32));
char s = (char) e;
if (e > 126)
e = (e - (127 - 32));
emsg += s;
}
return emsg;
}
public static String decrypt(String key, String msg)
{
String dmsg = "";
for (int i = 0; i < msg.length(); i++)
{
int m = msg.charAt(i);
int k = key.charAt(i%key.length());
int e = (m - (k - 32));
char s = (char) e;
if (e > 126)
e = (e - (127 - 32));
dmsg += s;
}
return dmsg;
}
}
I honestly dont know what I am doing wrong; ANY assistance would be very welcome!
You get an ArrayIndexOutOfBoundsException because you access the second element of the array:
String key = args[1];
before you've tested the length of args. Get rid of this line entirely, since you don't refer to key anywhere else in your application. (A good IDE should have told you this already).
For your encryption code, I think you'll find this quite challenging unless you limit yourself to only upper-case (or lowercase) letters. Assuming you go for upper-case, then subtracting 65 from the ASCII value will give you a convenient 0-25 value work with with. Then you can use addition, modulo-26 to achieve your goal.
I've fixed up your encryption, now try doing the decryption:
public static String encrypt(String key, String msg) {
String emsg = "";
final int offset = 'A'; // 65
for (int i = 0; i < msg.length(); i++) {
int m = msg.charAt(i) - offset;
int k = key.charAt(i % key.length()) - offset;
int e = (m + k) % 26;
char s = (char) (e + offset);
emsg += s;
}
return emsg;
}
Related
However I had an assignment of programming in java related to a text i already have under (text).
the function is supposed to as below
getEncryptedText(int shift)
return a string representation of ciphertext given that the text to be manipulated is the plaintext using Caesar Cipher.
The number of rotation is depend on the shift value;
positive shift value represent the right rotation while negative shift value represent left
rotation. However, unlike explain in Wikipedia, this method used following string as
plain:
0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz
Other characters than above will be treated as it is (i.e. will not been encrypted)
*Further reading: https://en.wikipedia.org/wiki/Caesar_cipher
So this is the class method I have made so far and wanted to know how can i keep the text chars which aren't included in the plaintext i have such as "!,#,#,$,%... and so on". So far i tried everything but couldn't make it but the rest seems fine!
public String getEncryptedText(int shift) {
String ALPHABET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
String cipherText = "";
for (int i = 0; i < text.length(); i++){
{
int charPosition = ALPHABET.indexOf(text.charAt(i));
if(text.charAt(i) == ' ') {
cipherText += " ";
}
else
{
int keyVal = (shift + charPosition) % 62;
char replaceVal = ALPHABET.charAt(keyVal);
cipherText += replaceVal;
}
}
}
return cipherText;
}
Consider modifying your if statement and using the StringBuilder class:
class Main {
public static void main(String[] args) {
CesarCypherHelper cesarCypherHelper = new CesarCypherHelper();
System.out.println(cesarCypherHelper.getEncryptedText("Hello World!", 2));
System.out.println(cesarCypherHelper.getEncryptedText("Hello World!", 64));
}
}
class CesarCypherHelper {
public String getEncryptedText(String text, int shift) {
String ALPHABET =
"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
StringBuilder encryptedText = new StringBuilder();
for (int i = 0; i < text.length(); i++) {
char ch = text.charAt(i);
int charPosition = ALPHABET.indexOf(ch);
if (charPosition == -1) {
encryptedText.append(ch);
} else {
int keyVal = (shift + charPosition) % ALPHABET.length();
encryptedText.append(ALPHABET.charAt(keyVal));
}
}
return encryptedText.toString();
}
}
Output:
Jgnnq Yqtnf!
Jgnnq Yqtnf!
How would I add code to this example for creating a CaesarCipherBreaker method that splits the encrypted message by two keys. So far I have this much written down:
import edu.duke.*;
public class TestCaesarCipherTwo {
public int[] countOccurrencesOfLetters(String message) {
//snippet from lecture
String alph = "abcdefghijklmnopqrstuvwxyz";
int[] counts = new int[26];
for (int k=0; k < message.length(); k++) {
char ch = Character.toLowerCase(message.charAt(k));
int dex = alph.indexOf(ch);
if (dex != -1) {
counts[dex] += 1;
}
}
return counts;
}
public int maxIndex(int[] values) {
int maxDex = 0;
for (int k=0; k < values.length; k++) {
if (values[k] > values[maxDex]) {
maxDex = k;
}
}
return maxDex;
}
public String halfOfString(String message, int start) {
StringBuilder halfString = new StringBuilder();
for (int index=start;index < message.length();index += 2) {
halfString.append(message.charAt(index));
}
return halfString.toString();
}
public void simpleTests() {
FileResource fileResource = new FileResource();
String fileAsString = fileResource.asString();
CaesarCipherTwoKeys cctk = new CaesarCipherTwoKeys(17, 3);
String encrypted = cctk.encrypt(fileAsString);
System.out.println("Encrypted string:\n"+encrypted);
String decrypted = cctk.decrypt(encrypted);
System.out.println("Decrypted string:\n"+decrypted);
String blindDecrypted = breakCaesarCipher(encrypted);
System.out.println("Decrypted string using breakCaesarCipher():\n"+blindDecrypted);
}
public String breakCaesarCipher(String input) {
int[] freqs = countOccurrencesOfLetters(input);
int freqDex = maxIndex(freqs);
int dkey = freqDex - 4;
if (freqDex < 4) {
dkey = 26 - (4-freqDex);
}
CaesarCipherTwoKeys cctk = new CaesarCipherTwoKeys(dkey);
return cctk.decrypt(input);
}
}
WARNING: I also have a constructor error on this line CaesarCipherTwoKeys cctk = new CaesarCipherTwoKeys(dkey); stating CaesarCipherTwoKeys in class CaesarCipherTwoKeys cannot be applied to given types; required int,int; found int....
The breakCaesarCipher method I have now only figures out one key, not two. How should I go about writing a method that splits an encrypted string, figuring out two keys used for decryption.
If I understand your Code correctly, you could just call your halfOfString (two times) to get the two parts of the ciphertext and then use your usual approach to breaking a Ceaser-Cipher on both parts separately.
Your error seems to result from the fact that the two-key-encryption expects (unsurprisingly) two keys. You should give them both to the constructor.
public String breakCaesarCipher(String input) {
String in_0 = halfOfString(input, 0);
String in_1 = halfOfString(input, 1);
// Find first key
// Determine character frequencies in ciphertext
int[] freqs_0 = countOccurrencesOfLetters(in_0);
// Get the most common character
int freqDex_0 = maxIndex(freqs_0);
// Calculate key such that 'E' would be mapped to the most common ciphertext character
// since 'E' is expected to be the most common plaintext character
int dkey_0 = freqDex_0 - 4;
// Make sure our key is non-negative
if (dkey_0 < 0) {
dkey_0 = dkey_0+26;
}
// Find second key
int[] freqs_1 = countOccurrencesOfLetters(in_1);
int freqDex_1 = maxIndex(freqs_1);
int dkey_1 = freqDex_1 - 4;
if (freqDex_1 < 4) {
dkey_1 = dkey_1+26;
}
CaesarCipherTwoKeys cctk = new CaesarCipherTwoKeys(dkey_0, dkey_1);
return cctk.decrypt(input);
}
Okay so I created this code last year for a class project and I remember it working correctly. I now need it to implement a text cipher but for some reason it does not work correctly. It will encrypt, but when I try to decrypt only the first two letters are correct. The rest of it is all wrong. It is very simple, it is a command-line program where the first argument is whether it is encrypting(-e) or decrypting(-d), second argument is the key and third argument is the text you will encrypt. It is similar to a caesar cipher except it takes each character as a reference when adding to each individual char in the string. Can anyone tell me what is wrong, I do not understand why it does not work anymore and I need it for a project.
import java.util.*;
public class VigenereCipher
{
public static void main(String[] args)
{
Scanner scan = new Scanner (System.in);
String key = "";
String ori = "";
String res = "";
if(!(args.length == 0))
{
if (args[0].equals("-e"))
{
key = args[1];
ori = args[2];
encrypt(ori, key);
System.out.println(encrypt(ori, key));
}
else if (args[0].equals("-d"))
{
key = args[1];
ori = args[2];
decrypt(ori, key);
System.out.println(decrypt(ori, key));
}
else
{
System.out.print("Usage: java VigenereCipher [-e,-d] key text");
}
}
}
static String encrypt(String text, final String key)
{
String res = "";
text = text.toUpperCase();
for (int i = 0, j = 0; i < text.length(); i++)
{
char c = text.charAt(i);
if (c < 'A' || c > 'Z') continue;
res += (char)((c + key.charAt(j) - 2 * 'A') % 26 + 'A');
j = ++j % key.length();
}
return res;
}
static String decrypt(String text, final String key)
{
String res = "";
text = text.toUpperCase();
for (int i = 0, j = 0; i < text.length(); i++)
{
char c = text.charAt(i);
if (c < 'A' || c > 'Z') continue;
res += (char) ((c - key.charAt(j) + 26) % 26 + 'A');
j = ++j % key.length();
}
return res;
}
}
You are supposed to be able to encrypt a string of text with a key then decrypt the output from the encryption using the same key for example: java VigenereCipher -e hello hello will give me "UOCCI" as output but when I take that output and do java VigenereCipher -d hello UOCCI it gives me "HE225" as my output and not "HELLO".
You forgot that your key also needs to be in the same alphabet. So if you supply a lowercase key your algorithm will fail.
This will become abundantly clear when you split your algorithm in parts, e.g. I just went through:
int im = c + key.charAt(j) - 2 * 'A';
res += (char)(im % 26 + 'A');
with my debugger and presto, the problem showed up.
I'm stuck on some code for a class of mine. My professor encourages asking questions on forums such as this, especially since it gives him less questions :), so I figured I'd ask all of you for help.
The purpose of my assignment is to encrypt and decrypt and input string by shifting, or offseting, the characters over how of many times the user tells it to. My code is below.
For some reason, I got an error when I decrypt my encrypted text, and the error only occurs with numbers of 6 or more when run my code, so if used professor's example and encrypted "subterfuge" to offset 6 characters to make "yahzkxlamk" and then try to decrypt the text to offset 6 characters again to make "subterfuge", it gives me an error. The error is
java.lang.StringIndexOutOfBoundsException: String index out of range: -6
When I run the code with the same input string, "subterfuge", but with an offset of 5 or less, it works. The error is said to occur at the 65th line of the below code where it says
sb.append(alphabet.charAt(offset));
at the end of my Decrypt() method in the last else statement.
import javax.swing.*;
public class Encryptor {
private String plainText;
private int shift;
public String cipherText;
public Encryptor() {
plainText = null;
shift = 0;
}
public static void main(String[] args) {
//encryption block
Encryptor e = new Encryptor();
String strCipherText = e.Encrypt();
System.out.println("encrypted text");
System.out.println(strCipherText);
//decrypt block
Encryptor d = new Encryptor();
//cipher text becomes the input text to the Decrypt method
d.cipherText = strCipherText;
String strPlainText = d.Decrypt();
System.out.println("decrypted text");
System.out.println(strPlainText);
System.exit(0);
}//end of main method
public String Decrypt()
{
plainText = cipherText;
shift = Integer.parseInt(JOptionPane.showInputDialog("enter offset"));
int offset=0;
int newOffset=0;
String alphabet ="abcdefghijklmnopqrstuvwxyz";
StringBuffer sb = new StringBuffer();
int index = plainText.length();
for(int i=0;i<index;i++)
{
String temp = "" + plainText.charAt(i);
offset = alphabet.indexOf(temp);
offset -= shift;
if(offset > 25)
{
newOffset = offset % 26;
sb.append(alphabet.charAt(newOffset));
}
else
{
sb.append(alphabet.charAt(offset));
}
}//end of for loop
return sb.toString();// return encrypted string
}
public String Encrypt()
{
plainText = ((String)JOptionPane.showInputDialog("enter words " + "to encrypt")).toLowerCase().trim();
shift = Integer.parseInt(JOptionPane.showInputDialog("enter offset"));
int offset=0;
int newOffset=0;
String alphabet = "abcdefghijklmnopqrstuvwxyz";
StringBuffer sb = new StringBuffer();
int index = plainText.length();
for(int i=0;i<index;i++)
{
String temp = "" + plainText.charAt(i);
offset = alphabet.indexOf(temp);
offset += shift;
if(offset > 25)
{
newOffset = offset % 26;
sb.append(alphabet.charAt(newOffset));
}
else
{
sb.append(alphabet.charAt(offset));
}
}//end of for loop
return sb.toString();// return encrypted string
}
}
Here is your problem:
offset = alphabet.indexOf(temp);
offset -= shift;
if(offset > 25)
{
newOffset = offset % 26;
sb.append(alphabet.charAt(newOffset));
}
else
{
sb.append(alphabet.charAt(offset));//< New offset is less than 0
}
What you want is a positive-only mod function. So just add do this after you do your modular division:
while(newOffset < 0)
newOffset += 26;
What I tend to do is just make a function for this:
/* Positive modular division. */
public static int pmod(int num, int mod)
{
num %= mod;
if(num < 0) num += mod;
return num;
}
Hey I'm making a simple caesar cipher in Java using the formula [x-> (x+shift-1) mod 127 + 1] I want to have my encrypted text to have the ASCII characters except the control characters(i.e from 32-127). How can I avoid the control characters from 0-31 applying in the encrypted text. Thank you.
How about something like this:
public String applyCaesar(String text, int shift)
{
char[] chars = text.toCharArray();
for (int i=0; i < text.length(); i++)
{
char c = chars[i];
if (c >= 32 && c <= 127)
{
// Change base to make life easier, and use an
// int explicitly to avoid worrying... cast later
int x = c - 32;
x = (x + shift) % 96;
if (x < 0)
x += 96; //java modulo can lead to negative values!
chars[i] = (char) (x + 32);
}
}
return new String(chars);
}
Admittedly this treats 127 as a non-control character, which it isn't... you may wish to tweak it to keep the range as [32, 126].
Map your characters from [32..127] to [0..95], do a mod 95+1 and map the result back to [32..127].
Usually cipher text is base64 encoded, base16 (hex) also works well. Base64 is used most often for cipher text because it takes up less space than hex, hex is most commonly used for message digests. In the java.util.prefs.Base64 library you will find byteArrayToBase64() and base64ToByteArray().
On a side note you should NEVER write your own encryption algorithm for security reasons, you should be using a block cipher or stream cipher. I hope this is for fun!
there! Is there any way to consider the whole range of characters? For example, "á", "é", "ö", "ñ", and not consider " " (the [Space])? (For example, my String is "Hello World", and the standard result is "Khoor#Zruog"; I want to erase that "#", so the result would be "KhoorZruog")
I'm sure my answer is in this piece of code:
if (c >= 32 && c <= 127)
{
// Change base to make life easier, and use an
// int explicitly to avoid worrying... cast later
int x = c - 32;
x = (x + shift) % 96;
chars[i] = (char) (x + 32);
}
... But I've tried some things, and the didn't work :S So, I'll wait for your answers :D See you!
Why not try
for(int i = 0; i < length; i++)
{
char c = chars[i]
if(Character.isLetter(c))
{
int x = c - 32;
x = (x + shift) % 96;
chars[i] = (char) (x+32);
}
}
Copy paste this in NetBeans with name "caesar":
//package caesar;
import java.io.*;
public class caesar {
int offset=3;
public String encrypt(String s) throws IOException
{
StringBuilder sb=new StringBuilder();
for(int i=0;i<s.length();i++)
{
char t=s.charAt(i);
if(t>='A' && t<='Z')
{
int t1=t-'A'+offset;
t1=t1%26;
sb.append((char)(t1+'A'));
}
else if(t>='a' && t<='z')
{
int t1=t-'a'+offset;
t1=t1%26;
sb.append((char)(t1+'a'));
}
}
return sb.toString();
}
public String decrypt(String s) throws IOException
{
StringBuilder sb=new StringBuilder();
for(int i=0;i<s.length();i++)
{
char t=s.charAt(i);
if(t>='A' && t<='Z')
{
int t1=t-'A'-offset;
if(t1<0)t1=26+t1;
sb.append((char)(t1+'A'));
}
else if(t>='a' && t<='z')
{
int t1=t-'a'-offset;
if(t1<0)t1=26+t1;
sb.append((char)(t1+'a'));
}
}
return sb.toString();
}
public static void main(String[] args) {
try
{
System.out.println("Caesar encrypion technique");
BufferedReader b;
String oriTxt,encTxt,decTxt;
System.out.println("Enter string to encrypt:");
b=new BufferedReader(new InputStreamReader(System.in));
oriTxt=b.readLine();
caesar c=new caesar();
encTxt=c.encrypt(oriTxt);
System.out.println("Encrypted text :"+encTxt);
decTxt=c.decrypt(encTxt);
System.out.println("Derypted text :"+decTxt);
}
catch(Exception e)
{
System.out.println(e.toString());
}
}
}
import java.util.Scanner;
//caeser
public class Major_Assingment {
public static final String ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZhh";
public static String encrypt(String plainText,int shiftKey)
{
plainText = plainText.toUpperCase();
String cipherText= " ";
for(int i=0; i<plainText.length(); i++)
{
int charPosition = ALPHABET.indexOf(plainText.charAt(i));
int keyVal = (shiftKey + charPosition)% 26 ;
char replaceVal = ALPHABET.charAt(keyVal);
cipherText += replaceVal;
}
return cipherText;
}
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("Enter the string for Encryption:");
String message = new String();
message = sc.next();
System.out.println(encrypt(message,3));
sc.close();
}
}