Java very basic encrypting a file

Question

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?

Assume encrypted.data file in above example is the raw text to encrypt not encrypted data. — CodeMonkey
– CodeMonkey, Commented Dec 10, 2016 at 17:21
Yes forgot to mention this. This is because I first input data into encrypted.data, after that I encrypt it in a new file, and overwrite the new file over the old file, this is why it is called temp. Sorry for the confusion. — Cezar Chirila
– Cezar Chirila, Commented Dec 10, 2016 at 17:28

CodeMonkey · Accepted Answer · 2016-12-10 21:29:26Z

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()); } }

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