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PODES encrypt/decrypt from a file
 

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  1. PODES encrypt/decrypt from a file
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    <p>I am writting a program where I take a string, encrypt it and then write it in a file. Then later, I read from the file the string, decrypt it and then modify it. Here's my code for DES encryption/decryption:</p> <pre><code>/* class for crypting and decrypting a file */ class DESEncrypter { private Cipher encryptionCipher; private Cipher decryptionCipher; public DESEncrypter (SecretKey key) throws Exception { encryptionCipher = Cipher.getInstance("DES/ECB/PKCS5Padding"); encryptionCipher.init(Cipher.ENCRYPT_MODE, key); decryptionCipher = Cipher.getInstance("DES/ECB/PKCS5Padding"); decryptionCipher.init(Cipher.DECRYPT_MODE, key); } /* write to 'out' the encryption of the information read from 'in' */ public String encrypt(String unencryptedString) { String encryptedString = ""; try { byte[] unencryptedByteArray = unencryptedString.getBytes("UTF8"); byte[] encryptedBytes = this.encryptionCipher.doFinal(unencryptedByteArray); encryptedString = new sun.misc.BASE64Encoder().encode(encryptedBytes); } catch (Exception ex) { Logger.getLogger(DESEncrypter.class.getName()).log(Level.SEVERE, null, ex); } return encryptedString; } private static String bytes2String(byte[] bytes) { StringBuffer stringBuffer = new StringBuffer(); for (int i = 0; i &lt; bytes.length; i++) { stringBuffer.append((char) bytes[i]); } return stringBuffer.toString(); } /* write to 'out' the information obtained by decrypting the information read from 'in' */ public String decrypt (String encryptedString) throws UnsupportedEncodingException { byte[] unencryptedByteArray = new byte[4096]; try { // Encode bytes to base64 to get a string byte[] decodedBytes = new sun.misc.BASE64Decoder().decodeBuffer(encryptedString); // Decrypt unencryptedByteArray = this.decryptionCipher.doFinal(decodedBytes); } catch (Exception ex) { Logger.getLogger(DESEncrypter.class.getName()).log(Level.SEVERE, null, ex); } return bytes2String(unencryptedByteArray); } } </code></pre> <p>And this is the function where I write a encrypted String in a file:</p> <pre><code>public void writeToFileEncrypted(String filename, String owner, String departament) { try { BufferedReader br = new BufferedReader(new FileReader(new File("files_encrypted"))); String crypt = ""; String aux; while ((aux = br.readLine()) != null) { crypt += aux; } br.close(); String info = this.server.crypt.decrypt(crypt); info += filename + " " + owner + " " + departament + "\n"; /* delete the old encryption */ File temp = new File("files_encrypted"); temp.delete(); String infoCrypt = this.server.crypt.encrypt(info); File newFiles = new File("files_encrypted"); if (newFiles.createNewFile() == false) { log.severe("Failed to re-create the 'files_encrypted' file when trying to add a new file"); return; } BufferedWriter bw = new BufferedWriter(new FileWriter(newFiles)); bw.write(infoCrypt); bw.close(); } catch (Exception e) { log.warning("An exception was caught while trying to remove '" + clientName + "' from the banned list"); e.printStackTrace(); return; } } </code></pre> <p>While the server runs, I can make modification to that String from file(run that function many time). The problem is when I close the server and then I open it again because I get the error: javax.crypto.BadPaddingException: Given final block not properly padded</p> <p>This is how I read from file when the server opens:</p> <pre><code>BufferedReader br = new BufferedReader(new FileReader(new File("files_encrypted"))); String crypto = new String(); String aux; while ((aux = br.readLine()) != null) { crypto += aux; readBytes++; } br.close(); System.out.println(readBytes); info = this.crypt.decrypt(crypto); </code></pre> <p>Why do I get that error? What I'm doing wrong? I must write the encrypted String in file some other way?</p> <p>LATER EDIT:</p> <p>I've changed the function that read a String from a file, decrypt it, modify it , encrypt it and then write it in file.</p> <pre><code>public void writeToFileEncrypted(String filename, String owner, String departament) { try { File f = new File("files_encrypted"); int nrRead = 0; String info = null; FileInputStream fis = new FileInputStream(f); StringBuffer sb = new StringBuffer(); int ch; while ((ch = fis.read()) != -1) { sb.append((char)ch); nrRead++; } fis.close(); StringBuilder sba = null; if (nrRead != 0) { info = this.server.crypt.decrypt(new String(sb.toString().getBytes("UTF-8"), "UTF-8")); sba = new StringBuilder(info); sba.append(filename + " " + owner + " " + departament + " "); } else { sba = new StringBuilder(filename + " " + owner + " " + departament + " "); } /* delete the old encryption */ File temp = new File("files_encrypted"); temp.delete(); //System.out.println("before: " + sba.toString()); String infoCrypt = this.server.crypt.encrypt(sba.toString()); //System.out.println("after: " + infoCrypt); File newFiles = new File("files_encrypted"); if (newFiles.createNewFile() == false) { log.severe("Failed to re-create the 'files_encrypted' file when trying to add a new file"); return; } FileOutputStream fos = new FileOutputStream(newFiles); fos.write(infoCrypt.getBytes("UTF-8")); fos.flush(); fos.close(); } catch (Exception e) { log.warning("An exception was caught while trying to remove '" + clientName + "' from the banned list"); e.printStackTrace(); return; } } </code></pre> <p>I've also modified where I read the info from file when server opens for the first time:</p> <pre><code>FileInputStream fis = new FileInputStream(f); StringBuffer sb = new StringBuffer(); int ch; while ((ch = fis.read()) != -1) { sb.append((char)ch); readBytes++; } fis.close(); if (readBytes != 0) { System.out.println("on: " + sb.toString()); info = this.crypt.decrypt(new String(sb.toString().getBytes("UTF-8"), "UTF-8")); System.out.println("load: " + info); } } </code></pre> <p>At the System.out.println with "on: " what I read from file is exactly what I've written encrypted, without any spaces or new lines. If I read with read(buffer), where buffer is byte[], it seems that adds a lot of spaces.</p> <p>Although I've made all this modifications I still get the error javax.crypto.BadPaddingException: Given final block not properly padded</p> <p>Has somebody any idea what's going on here?</p>
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    1. USStanciu Alexandru-Marian
    1. USStanciu Alexandru-Marian
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      1. VTUpMod
    1. COMy first guess would be your reading method. First of all it is bad practice to use string concatenation the way you do there. Use a StringBuilder. Secondly you use readline for binary data. Third you encode (`getBytes`) to UTF8. Mind that the Java standard is UTF 16. Which might break your reading in.
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      1. USFildor
    2. CO@Fildor - the encrypted data is Base64 encoded, so it's _not_ binary data. also, the getBytes() is just fine as long as the correct encoding is used for encode and decode. java uses UTF-16 internally, but that is irrelevant.
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      1. USjtahlborn
    3. COIt is a String, yes. But the String is representing binary data. If he would read it to a byte[] and then creating a String, he would have more control at least while debugging. And newlines will be dropped. But a newline may not be a new line here.
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