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'''Cryptography''' is the writing of secrets. The word 'cryptography' comes from the Greek 'cryptos', secret, and 'graphos', writing.

'''Cryptography''' is the writing of [[secret]]s. The word 'cryptography' comes from the [[Greek]] 'cryptos', secret, and 'graphos', writing.

All of cryptography (debatable since the dawn of quantum cryptography) can be described as one of two methods.

All of cryptography can be described as one of two methods: (this assertion has become debatable since the dawn of [[quantum cryptography]])

== Codes ==

== Codes ==

Codes are, in their simplest terms, replacing words and phrases in a message with other words and phrases whose meaning is known to the recipient. For example:

[[Code]]s are, in their simplest terms, replacing words and phrases in a message with other words and phrases whose meaning is known to the recipient. For example:

Take the phrase: "The bombers require a fighter escort at Newcastle, 2300 hours"

Take the phrase: "The bombers require a fighter escort at Newcastle, 2300 hours"

== Historical Uses Of Cryptography ==

== Historical Uses Of Cryptography ==

Generally speaking, cryptography has been the sole domain of governments. All governments of the world have a branch dedicated to the interception and decryption of encoded information. In America, this is the CIA; in Britain, it's MI5; in Vatican City it's Iscariot (Vatican Section XIII).

Generally speaking, cryptography has been the sole domain of governments. All governments of the world have a branch dedicated to the interception and decryption of encoded information. In [[America]], this is the [[CIA]]; in [[Britain]], it's [[MI5]]; in [[Vatican City]] it's [[Iscariot]] (Vatican Section XIII).

Cryptography has played a large part in many wars. In the [[World War I|First World War]], [[Mata Hari]] was responsible for carrying messages back and forth for the [[Germany|German]] government, causing the deaths of thousands of [[France|French]] soldiers.<ref>http://www.firstworldwar.com/bio/matahari.htm</ref> In the [[World War II|Second World War]], [[United Kingdom|British]] soldiers captured the crew and The [[Enigma]] Engine of German U-boat U-571, leading to the decryption of Nazi communications and the end of the war.  

Cryptography has played a large part in many wars. In the [[World War I|First World War]], [[Mata Hari]] was responsible for carrying messages back and forth for the [[German]] government, causing the deaths of thousands of [[French]] soldiers.<ref>http://www.firstworldwar.com/bio/matahari.htm</ref> In the [[World War II|Second World War]], [[British]] soldiers captured the crew and The [[Enigma machine]] of German [[U-boat]] [[U-571]], leading to the decryption of [[Nazi]] communications and the end of the war.  

Other examples of the importance of cryptography include Ethel and Julius Rosenberg.  

Other examples of the importance of cryptography include Ethel and Julius Rosenberg.  

[[Ethel Rosenberg]] and [[Julius Rosenberg]] sold US atomic secrets to the USSR at the height of the cold war. They were convicted and executed in the electric chair at Sing Sing prison.

[[Ethel Rosenberg]] and [[Julius Rosenberg]] sold US atomic secrets to the [[USSR]] at the height of the [[Cold War]]. They were convicted and executed in the electric chair at [[Sing Sing]] prison.

== Modern Uses Of Cryptography ==

== Modern Uses Of Cryptography ==

Currently the most common form of cryptography is public key encryption. This relies on the fact that it takes significantly (order 10⁸ times) longer to find two prime factors of 1000 or more digit numbers than it does to multiply the numbers together to create the 1000 digit number in the first place.

Currently the most common form of cryptography is [[public key encryption]]. This relies on the fact that it takes significantly (order 10⁸ times) longer to find two prime factors of 1000 or more digit numbers than it does to multiply the numbers together to create the 1000 digit number in the first place.

In this system there are two keys, the first is the "private key", which only the '''recipient''' knows. The second is the "public key" which can be sent freely to anyone, allowing them to encrypt messages with it such that only the owner of the private key can decrypt them. These public keys are calculated from the private keys, but as they are often over 1000 digits long and would take many decades to calculate the private key from them (RSA, the most commonly used encryption protocol uses 2048 digit numbers which would take over 4000 years to crack with a desktop computer).

In this system there are two keys, the first is the "private key", which only the '''recipient''' knows. The second is the "public key" which can be sent freely to anyone, allowing them to encrypt messages with it such that only the owner of the private key can decrypt them. These public keys are calculated from the private keys, but as they are often over 1000 digits long and would take many decades to calculate the private key from them (RSA, the most commonly used encryption protocol uses 2048 digit numbers which would take over 4000 years to crack with a desktop computer).