CODEWITHSUNDEEP
javafileio
Cezar Chirila
Cezar Chirila

Reputation: 153

Java very basic encrypting a file

I want to excrypt a file in java very basically. Simply read line by line the file, and change the value of the chars to "char += key", where key is an integer. The problem is that if I use a key larger or equal with 2, it doesn't work anymore. 

public void encryptData(int key) {
    System.out.println("Encrypt");
    try {
        BufferedReader br = new BufferedReader(new FileReader("encrypted.data"));
        BufferedWriter out = new BufferedWriter(new FileWriter("temp_encrypted.data"));
        String str;
        while ((str = br.readLine()) != null) {
            char[] str_array = str.toCharArray();
            // Encrypt one line
            for (int i = 0; i < str.length(); i++) {
                str_array[i] += key;
            }
            // Put the line in temp file
            str = String.valueOf(str_array);
            out.write(str_array);
        }
        br.close();
        out.close();

    } catch (IOException e) {
        System.out.println(e.getMessage());
    }
}

The decrypt function is the same but with the input/output files interchanged and instead of adding the key value, I subtract it.

I check char by char and indeed, the header gets messed up when i use a key value > 1. Any ideas? Is it because of maximum value of the char being exceeded?

Upvotes: 0

Views: 54

Answers (1)

CodeMonkey
CodeMonkey

Reputation: 23738

You're basically implementing a general-purpose Caesar cipher. Adding a number to a character could change a character to newline, etc which will not work if using a BufferedReader to read it back in.

Best to manipulate the text as a byte stream which would correctly encode and decode newline and any non-ASCII characters.

public void encryptData(int key) {
    System.out.println("Encrypt");
    try {

        BufferedInputStream in = new BufferedInputStream(new FileInputStream("raw-text.data"));
        BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream("temp_encrypted.data"));
        int ch;
        while((ch = in.read()) != -1) {
            // NOTE: write(int) method casts int to byte
            out.write(ch + key);
        }
        out.close();
        in.close();

    } catch (IOException e) {
        System.out.println(e.getMessage());
    }
}

public void decryptData(int key) {
    System.out.println("Decrypt");
    try {
        BufferedInputStream in = new BufferedInputStream(new FileInputStream("temp_encrypted.data"));
        BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream("decrypted.data"));
        int ch;
        while((ch = in.read()) != -1) {
                out.write(ch - key);
        }
        out.close();
        in.close();

    } catch (IOException e) {
        System.out.println(e.getMessage());
    }
}

Upvotes: 1

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