One of the best TED videos I have ever seen. It shows are our decisions can be easily influenced.

A message authentication code (MAC) is a technique that allows a receiver to verify the authenticity of the sender and the integrity of the message.

A MAC algorithm, sometimes called a keyed (cryptographic) hash function, accepts as input a secret key and an arbitrary-length message to be authenticated, and outputs a MAC.

A MAC works by applying a secret key to the message digest so that only the holder of the secret key can compute the MAC from the digest and hence, the message. This method thwarts the threat posed by a malicious interceptor who could modify the message and replace the digest with the digest of the modified message, for the interceptor won't have access to the secret key.

One basic and not secure example of a MAC can be the following:

MAC(K, M) = H(K + M)

Where H is a hash function, K is symmetric secret key, + is an append text operation and M is the message to authenticated.

More advanced and secure MAC techniques, like HMAC work in the following manner:

HMAC(K, M) = H(K XOR opad + H((K XOR ipad) + m))

Where opad and ipad are constants.

It actually makes total sense, but when you first read that .999... equals 1 you say WHAT??

The 0.999.... repeating decimal number is exactly the same number as 1? It really sounds strange;, but when you start to think that 0.999... is the left limit to the number 1 then all starts to make sense:

Or even a more trivial example:

Check out the wikipedia page if you're really interested in the topic:

http://en.wikipedia.org/wiki/0.999...

As my Eeepc has a really slow SSD drive, here is a little trick I do to speed up the sqlite databases firefox uses. The perfomance gain isn't amazing, but it is better than nothing.

cd $HOME
cd .mozilla
find . -name \*.sqlite -exec sqlite3 {} vacuum \;

Another explanation of an ad-hoc routing protocol.

Optimized Link State Routing (OLSR) protocol is another routing protocol suited for ad-hoc networks. Contrary to AODV it uses a proactive routing approach where the discovery of routes is done permanently, not only when needed. This is achieved by periodically exchanging control messages this way providing immediate require routes when needed.

There are two main functionalities in OLSR, Neighbor Discovery (or neighbor sensing) and Topology Dissemination.