Page History

//Identify a file by its path
String filename = // initialized
Path file1 = Paths.get(filename);
BasicFileAttributes attr1 = Files.readAttributes(file1, BasicFileAttributes.class);
FileTime creation1 = attr1.creationTime();
FileTime modified1 = attr1.lastModifiedTime();

// Open the file for writing
BufferedWriter bw = new BufferedWriter(
  new OutputStreamWriter(Files.newOutputStream(file1)));

// Write to file...

// Close the file
bw.close();

/*
 * A race condition here allows for an attacker to switch
 * out the file for another
 */

// Reopen the file for reading
Path file2 = Paths.get(filename);

BasicFileAttributes attr1 = Files.readAttributes(file1, BasicFileAttributes.class);

BasicFileAttributes attr2 = Files.readAttributes(file2, BasicFileAttributes.class);

FileTime creation1 = attr1.creationTime();
FileTime modified1 = attr1.lastModifiedTime();

FileTime creation2 = attr2.creationTime();
FileTime modified2 = attr2.lastModifiedTime();

if ( (!creation1.equals(creation2)) || (!modified1.equals(modified2)) ) {
  System.out.println("File tampered with");
  // Handle error
}

BufferedReader br = new BufferedReader(
  new InputStreamReader(Files.newInputStream(file2)));

String line;

while ((line = br.readLine()) != null) {
    System.out.println(line);
}

// Close the file
br.close();