We all have secrets at one point of time or the other in our lives. And now we use computers to hide these secrets of ours. As encrypted files protected with passwords, hidden drives, pen drives. Cryptography seems to have made things so much more easier. Its strange than whenever someone says cryptography, everyone thinks of a modern computer with scrolling lines of codes and cryptic passwords...the truth is, cryptography has been around us for thousands of years. Atbash and Caesar's algorithms are two of the more famous examples. These are simple substitution and transpositional algorithms.

Cryptography was used extensively during World War II, with a plethora of code and cipher systems fielded by the nations involved. In addition, the theoretical and practical aspects of cryptanalysis, or codebreaking, was much advanced. Probably the most important cryptographic event of the war was the successful decryption by the Allies of the German "Enigma" Cipher. The first complete break into Enigma was accomplished by Poland around 1932; the techniques and insights used were passed to the French and British Allies just before the outbreak of the War in 1939. They were substantially improved by British efforts at the Bletchley Park research station during the War. Decryption of the Enigma Cipher allowed the Allies to read important parts of German radio traffic on important networks and was an invaluable source of military intelligence throughout the War. Intelligence from this source (and other high level sources, including the Fish cyphers) was eventually called Ultra. A similar break into an important Japanese cypher (PURPLE) by the US Army Signals Intelligence Service started before the US entered the War. Product from this source was called MAGIC. It was the highest security Japanese diplomatic cypher. For Japanese Naval cyphers see JN-25.

Modern computers have given us the ability to come up with more complex methods of encrypting data. Blowfish, DES/3DES, AES are examples of some of the encryption methods which are in use today. Quantum cryptography has gained popularity in the recent past few months. Quantum cryptography, or quantum key distribution (QKD), uses quantum mechanics to guarantee secure communication. It enables two parties to produce a shared random bit string known only to them, which can be used as a key to encrypt and decrypt messages.

An important and unique property of quantum cryptography is the ability of the two communicating users to detect the presence of any third party trying to gain knowledge of the key. This results from a fundamental part of quantum mechanics: the process of measuring a quantum system in general disturbs the system. A third party trying to eavesdrop on the key must in some way measure it, thus introducing detectable anomalies. By using quantum superpositions or quantum entanglement and transmitting information in quantum states, a communication system can be implemented which detects eavesdropping. If the level of eavesdropping is below a certain threshold a key can be produced which is guaranteed as secure (i.e. the eavesdropper has no information about), otherwise no secure key is possible and communication is aborted. The security of quantum cryptography relies on the foundations of quantum mechanics, in contrast to traditional public key cryptography which relies on the computational difficulty of certain mathematical functions, and cannot provide any indication of eavesdropping or guarantee of key security. Quantum cryptography is only used to produce and distribute a key, not to transmit any message data. This key can then be used with any chosen encryption algorithm to encrypt (and decrypt) a message, which can then be transmitted over a standard communication channel. The algorithm most commonly associated with QKD is the one-time pad, as it is provably secure when used with a secret, random key.

However we are decades away from an actual implemention of quantum cryptography in real life. But for now, there is way to simulate a quantum key distribution network using the .NET framerwork. Further information can be found here

http://info.fernandolucas.es/drupal/node/12