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Archive for the ‘Programming’ Category

GNU C: Extensions to the C Language Family

November 6, 2010 2 comments

Hi. Today I’ll talk about the extensions to the C language family introduced by the GNU C.
The GNU C provides several language features not found in ANSI standard C. These extensions are available both in C and C++. The `-pedantic’ option directs GNU CC to print a warning message if any of these features is used.
The list of these features is very long: often we use them implicitly. I will show to you only those I consider most useful and “strange”: Read more…

Port-knocking Backdoor

October 21, 2010 5 comments

Hi.
In this post I’ll explain to you how to make a *unix backdoor using a “port knocking” scheme. That is, if we’ll “knock” to some TCP ports that we have initially decided, our program will open a backdoor for us (but only for us :) ).
How does the “port knocking” scheme work? The attacker decides a particular sequence of packets that will be sent to a compromised server where the backdoor is running. When the backdoor program will receive this particular sequence then it will give to the attacker the server’s shell.
Read more…

Bash http_proxy: from a user environment to sudo one

October 14, 2010 9 comments

Hi. Sometimes you can’t connect directly to internet, because you have to go through a proxy (i.e. working environment).
Did you ever have to set up an http proxy on linux shell in order to (i.e) download a new package or manually update your distribution with a packet manager?
If so, you need to be a superuser. If you use the “sudo” command, you will probably stumbled across the inability to export variables from the user environment to the “sudo” one.
Read more…

Categories: Bash, GNU/Linux Tags: , , ,

Win32 API: Passing Socket with IPC method

October 13, 2010 1 comment

Hi. In this post I talk to you how to correctly pass a socket created in a parent process to a child process in Microsoft 9x systems.
If you have ever written a multi-process concurrent server in a Unix environment, you may have noticed that the passage of the socket between parent and son processes takes place directly. That is, the child inherits the variables of his parent, also including the file descriptor associated with the socket.

Read more…

Hello World! – Brain mode

October 12, 2010 5 comments

Hi. How can we write an “hello world!” in brain-mode?
When we want to greet someone, the brain is activated and set as a greeting a phrase known to us: in our case, “hello world!”.
Read more…

Categories: Bullshit, C/C++ Tags: ,

Something about AMQP

October 11, 2010 Leave a comment

Hello,

If you haven’t heard nothing about Enterprise Messaging i suggest you  read the related wikipedia’s article http://en.wikipedia.org/wiki/Enterprise_messaging_system. In this article I will introduce the Advanced Messaging Queuing Protocol and some of his concepts.

Before all why talking about AMQP?  Because is the first open standard for the Enterprise Messaging; in a enterprise environment the integration is necessary and an open solution is needed especially because this kind of solution should be leveraged from any language and platform; JMS doesn’t do it very well because of his java dependence and his terms of license: JMS-like interface cannot legally be provided for non-Java platforms.

Continuing talking about AMQP, it supports this kind of message distributions:

  • Store-and-forward with many writers and one reader
  • Transaction distribution with many writers and many readers
  • Publish-subscribe with many writers and many readers
  • Content-based routing with many writers and many readers
  • Queued file transfer with many writers and many readers
  • Point-to-point connection between two peers

This standard is thought to have small and modular model therefore his task is splitted in two main roles, Exchange and  Message queue. This choice made available three main features:

  • The ability to create arbitrary exchange and message queue types
  • The ability to wire exchanges and message queues together to create any required message-processing system
  • The ability to control this completely through the protocol.

A Message queue is a storage entity, it can store messages in memory or in disk  and must provide messages to consumers applications, is described by some proprierties:

  • private or shared
  • durable or transient
  • permanent or temporary

The standard does not define directly entities like  Store and Forward queue or Pub-Sub queue, these entities are created trough Message queue’s attribute.

The Exchange entity takes messages from Applications Messages Producer and routes them to the Message Queue according to criteria called “bindings”. Bindings are therefore the relationship between Exchanges and the and Messages queues.

These are the basic concepts you need to know about AMQP model, in the next post i’ll  introduce you to qpid, an apache’s software project that fully respect this standard and we’ll try it with some source code examples.

inet_ntop() for Win32

October 9, 2010 3 comments

Like 4 years ago I made a little project for the operating system 2 class. I had to write an application capable of handling multiple file transfers for both Win32 and Linux. During the coding of the socket-side of the application I encountered an awkward problem: why the hell win32 does not have a compatibility function for the inet_ntop()?

Only recently, for Vista and 7, Microsoft introduced the InetNtop() function: http://tinyurl.com/3xrwaer

If you have to write something that needs to run on XP too (that still seems to be the most used operating system for home users: http://tinyurl.com/2w5ed8n ) just try this code :)


const char* inet_ntop(int af, const void* src, char* dst, int cnt){

	struct sockaddr_in srcaddr;

	memset(&srcaddr, 0, sizeof(struct sockaddr_in));
	memcpy(&(srcaddr.sin_addr), src, sizeof(srcaddr.sin_addr));

	srcaddr.sin_family = af;
	if (WSAAddressToString((struct sockaddr*) &srcaddr, sizeof(struct sockaddr_in), 0, dst, (LPDWORD) &cnt) != 0) {
		DWORD rv = WSAGetLastError();
		printf("WSAAddressToString() : %d\n",rv);
		return NULL;
	}
	return dst;
}
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