Bar Code & Label Layout Specification: Fill & Download for Free

This was back when bar codes were around but not all stores had the machines to read the codes.I wanted a new printer for my computer, so I went to the store, picked one out and brought it to the check-out counter. The clerk typed in the bar code number which said that the printer was $10.50.One of the best bargains I ever got

I’m going to go with one that’s not only little known, but produces results that many find somewhat counter-intuitive.When you declare a function as being a friend of a class, that function can’t be a member of the class that’s declaring it as a friend. Consider code like this:class foo {  friend int bar(); }; Normally, a declaration of bar inside of foo’s definition would refer to foo::bar. But we’ve declared bar as a friend of foo—which means it can’t be a member of foo. As a result, what we’ve actually declared is ::bar() (more generally, we’ve declared bar in whatever scope surrounds foo).So far, most people find that perfectly reasonable. The next step is where things get interesting. The friend declaration can also be a definition:class foo {   friend int bar() { return 1; } }; Just like before, this declares (and in this case, also defines) ::bar(), not foo::bar(). So, even though we’ve defined bar() inside the definition of class foo, the name bar is “injected” into the surrounding scope.Then we get to the part most people find truly baffling. The preceding code defines a function named ::bar(), but if we try to invoke ::bar() directly (in a way that doesn’t look things up via foo) our code will fail:// Warning: this will not compile: class foo {   friend int bar() { return 0; } };  int main() {   bar(); } If we try to compile this, we’ll get an error in main(), saying the compiler can’t find bar(). But if we try to define bar() separately:class foo {   friend int bar() { return 0; } };  int bar() { return 0; }  int main() {   bar(); } …we’ll get an error at the second definition of bar(), saying we can’t define bar(), because it’s already been defined (note: producing an error message isn’t strictly required, but the code violates the one-definition rule, so it isn’t allowed, and at least as long as all the code is in a single file, every compiler I know of will generate an error message).In quite a few cases (e.g., recent versions of g++) we’ll get errors for both the attempt to define bar at global scope and the attempt to call it from main, the first saying we can’t define ::bar() because it’s already defined, and the second saying we can’t call ::bar() because it isn’t declared!)And if you read that carefully, it does lead to how you can call bar() directly: it’s already defined, but not declared (in a way that’s visible to main). To make it visible inside main, you have to declare it at global scope:class foo {   friend int bar() { return 0; } }; int bar(); int main() {   bar(); } 

Stole library books sitting in computer labs. This is how I did that.Step 1: Get a user account with full controlI simply used a boot able pen drive having LINUX (KALI) on it. So, no need to look for passwords of admin account. Step 1 complete.Step 2: Get IP address of library serverWe have special computers in our library to check for the books that have been issued on our roll number. So, I started cmd on that computer and used "netstat" command and queried for books issued on my roll number. I got the IP address of library server on our network. I also noted down other things about this computer by using "ipconfig /all" command. I wanted things like subnet mask, default gateway and DNS servers.Step 3: Scan the library serverI used zenmap to scan the library server. I got list of open ports.Step 4: Try to break into library serverI used autopwn feature of metasploit to try to exploit into library server. But, it was patched and up to date. So, I started feeling a bit depressed.Step 5: Lots of cold drink and deep thinkingThis is most important step. This step took about 5 days to complete. I kept thinking about how the library management software is working. I noted these actions.Librarian scans the bar code on book and bar code on my I-card and selects some option and the book is issued on my roll number.To return the book, he would just scan the bar code on the book and it would be returned.Looking at these actions I concluded that computer did not require my roll number to return the book. Now this fact will alone will help to hack the system.Step 6: Sniff the networkI used wireshark to capture all data packets that were going to library server. From my scanning part, I knew that library server was running MySQL and a HTTP server. So, the library management system must be somehow using these services. But, I had no idea how. I captured a load of TCP packets.Step 7: Trying to understand, what the s**t was in those packetsI had never done packet analysis before. After a few minutes of Google, I found that it was just a few clicks task in wireshark and I was able to see the data in packets.For every book issued a packet with roll number and some unique ID was being sent. To return the same book to library, just a packet with that same unique ID was being sent. I guessed that unique ID is coming from bar code of the book.Step 8: Trying to understand the bar codeI started with Google. Read some articles about how bar code works. Downloaded an android app on phone to decode the bar code. None worked.Later, I realized, that when I used to check the books issued on my roll number from the computers in library, then that list also had a column saying book ID. So, it was simple.Step 9: Get book ID of books I hadI went to library and used the computer to see the books issued on my roll number. I noted down all the book IDs.Step 10: Asking a teacher for help (Indirectly)The book ID in data packet was in hex. The book ID I noted down was text and some numbers. I had no idea of how to convert that. After struggling with it for hours, I asked a teacher to help me convert it. It turned out very simple. Convert text and numbers in ASCII and convert that number in hex, each byte separately.Step 11: Trying to return a book with a fake packetI saved one of the return packets from wireshark. I opened it in hex-editor to edit it and replaced the hex representing the book ID with my book ID. I used LINUX file2wire tool to send that data packet to server.Step 12: Keeping fingers crossedTo my surprise, the book actually got returned and was now not showing up in my list of issued books.I used this to steal 87 books in total. I made a collection of all the books I liked.Being caughtThe librarian realized the large number of books missing during the counting done at end of each year. They called some guy from company which had made that library management system. Turned out, that software kept logs of everything. The guy figured out that all books that were missing were last issued in my roll number.The college officials called my home without notifying me and they got to know that I had two bookshelves full of computer science books.The college administration and guys from that company called me. I was too terrified. I thought that they would throw me out of college or something like that. But, to my surprise, the company official said that they would pay for all those books if I tell them how I did that. I spitted out every detail with all proof I could present. Nothing happened. College gave me a warning and company paid for all the books.At end of next semester, the college library manager called me. College was donating old books. So, the guy told me to take any number of books I wanted from the books that were going to be donated. I took 38 books more.All is well now. I have nice collection of computer science books at my home. :)