The steganography and cryptography from Greek words similar, the two seek to conceal an important message from a potential attacker (someone want to know the original information without permission) but held that concealment very differently.
The easy way to understand the difference of cryptography and steganography is to understand the problem of prisoner (J. Simpson, 1983), which is:
How can two prisoners to communicate (eg to agree a plan of escape) they are in separate cells and all messages exchanged passes na through a guardian?
First, the abbreviation comes from eg Latin exempli gratia which means "example" or just "for example." Clarified above, the situation is that two prisoners want to escape but the guardian read all the messages that are sent, so they must fend to carry out the exhaust. To make it more interesting to call them prisoners Michael and Linc , while the guardian be called Bellick (any resemblance to the series prison break is mere coincidence.) A diagram of this situation shown and the figure below
Thus, if Michael sends a message Linc: "The escape is the Saturday I have all fixed ... " , Bellick discover their escape plan, which would cause the destruction of the message and a tremendous putiza to remove them these crazy ideas of the head.
But like all know Michael is a scholar and knows of cryptography then it does is encrypt the message sent to Linc (of course!, Linc known as the decoding message) to Bellic not understand. But Bellick to see the encrypted message, suspicion and destroys it, preventing his escape again. And as you can imagine, Bellick given a putiza to see that go up to.
Eye! ... and ncriptar and decrypt is not the same as encrypt and decrypt, the two first words have to do with crypts.
Alternatively you can take Michael is to use the steganography to hide the message, but now I would do in such a way that the message would be hidden within another message less important, ie innocuous carrier medium. So Michael commanded to Linc the following message:
Bellick
to read the message thinks that there is nothing strange and passes to Linc. However, this note has a hidden message which can be seen in the image below 
With this, Michael and Linc plan the escape from prison without raising any suspicion. Now imagine a scenario but now today. Bellick is a Hacker famous and analyzing all the messages sent Michael and Linc. If encryption is used Bellick try to break that code for information hidden, however when using steganography Bellick would not know that there are hidden messages in the communication, keeping the secret safe. It is important to note that a system estaganográfico watermarks or uses cryptography (encrypting the message that is hidden) for greater security, if they break the watermarking scheme. 
With this example you can notice the subtle difference of how obscure the information you are two disciplines. We conclude that goal of steganography is to pass desapersivida and the cryptography is to avoid being decoded (or decrypted).
Before concluding, there is a type of steganography supporting distortions in the middle marking, it is called steganography robust. For example, imagine that the bastard Bellick comes up exchanging a few words of message marked (which is hidden information.) If the above method we used our hidden message be lost, whereas if we used a robust, our message can resist the modification attack. Many
authors call the robust as steganography watermarks. We should note something very important, both steganography and watermarks are methods of hiding information within a half ... in principle are the same, in fact we treat them as such, but many authors take them as different because of the resilience to attacks.
In the next post will talk about a small classification steganography.
Steganography Cryptography Problem prisoner
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