Cryptography is also called cryptology and is defined by the Merriam-Webster dictionary as "the enciphering and deciphering of messages in secret code or cipher; also: the computerized encoding and decoding of information."
Modern cryptography forms the basis of all modern non-cash financial transactions. Without technologies such as SSL, which utilize encryption, the transmission of financial information on the internet would not be feasible. Similarly, having things like e-mail accounts, medical records, and other information stored digitally and remotely accessible would be incredibly risky, as plain text transmissions are painfully easy to intercept.
Cryptanalysis is the study of breaking cryptography and its ciphers and is outside the scope of this article, however it should be noted in a terminological sense that "cryptology" is often used to describe the combined study of cryptography and cryptanalsys.
The earliest documented use of cryptography was by Julius Caesar, whose cipher involved simply re-arranging the letters of a message in a way that only the recipient would be able to decode by utilizing a key which indicated how the letters could be put back into order. The Caesar cipher is known as a substitution cipher or shift cipher for this reason. Each letter would actually be another letter in the alphabet. Like modern cryptography, the recipient had to know in advance what the code was, or else the messages would have been gibberish. You can test out the Caesar cipher at this website.
Doing so, the above paragraph looks like this encoded with a shift of 3:
Wkh hduolhvw grfxphqwhg xvh ri fubswrjudskb zdv eb Mxolxv Fdhvdu, zkrvh flskhu lqyroyhg vlpsob uh-duudqjlqj wkh ohwwhuv ri d phvvdjh lq d zdb wkdw rqob wkh uhflslhqw zrxog eh deoh wr ghfrgh eb xwlolclqj d nhb zklfk lqglfdwhg krz wkh ohwwhuv frxog eh sxw edfn lqwr rughu. Wkh Fdhvdu flskhu lv nqrzq dv d vxevwlwxwlrq flskhu ru vkliw flskhu iru wklv uhdvrq. Hdfk ohwwhu zrxog dfwxdoob eh dqrwkhu ohwwhu lq wkh doskdehw. Olnh prghuq fubswrjudskb, wkh uhflslhqw kdg wr nqrz lq dgydqfh zkdw wkh frgh zdv, ru hovh wkh phvvdjhv zrxog kdyh ehhq jleehulvk. Brx fdq whvw rxw wkh Fdhvdu flskhu dw wklv zhevlwh.
It should be noted that at the time Caesar's cipher was developed, most people were still illiterate, so merely writing words would be sufficient in a cryptographic sense to keep Eve out.
The great Arab philosopher al-Kindi is credited with being the first to develop a method known as frequency analysis for deriving the meaning of encrypted messages. For this reason it is reasonable to say that by the 10th Century, all common ciphers were vulnerable to an informed attacker, though literacy was much further from universal than it is today and attackers would need to be trained in the art. Therefore it is also reasonable to assume that ciphers were still for the most part usable in a general way, although there are few if any known records of their success or failure.
Steganography, the process of hiding that a message even exists, in a painting for example, was also developed by the Greeks during the Hellenistic period.
During and after the Second World War, cryptography took on a whole new meaning. German engineer Arthur Scherbius invented the Engima machine at the end of World War I and the device became crucial to German military operations during World War II. It should be noted that the machines were not strictly sold to the German government, but also to other governments as well as commercial operations.
The Polish Cipher Bureau had a breakthrough in 1932 which enabled them to decrypt messages encoded on an Enigma with relative ease. In response, Enigma developers continued to add complexity to the device. This process could be considered some of the earliest cryptanalysis, reverse engineering, and hacking, in a sense. The Poles went on to train British and French military intelligence on how to decrypt German communications, a critical help to the Allied war effort.
Since the end of World War II and the birth of the computer, cryptography has played an increasingly important role in the health and well-being of modern societies. Everything from state secrets to the sanctity of medical records relies on it.
Symmetric-Key Cryptography is most often used today in the AES algorithm, which stands for Advanced Encryption Standard. Previous to AES, in an age of slower computers, the DES algorithm was used instead.
Unlike Public-Key Cryptography, Symmetric-Key Cryptography uses the same key for both encryption and decryption. It has wider applications than mere message sending, but regarding messages, a message authentication code is often used to verify that the same message that was intended is the one being received. This is because there is no way to be sure that the same message encrypted hasn't been changed during encryption.
Public-key cryptography is a set of cryptographic algorithms which currently are not solvable. A user of public-key cryptography can trivially generate a "key pair" or public and private key and then give out the public key with which others can encode messages which will only be viewable by the sender and recipient using the corresponding private key.
Public-key cryptography relies on two constants: that it remains computationally impractical for computers to solve the mathematical problems which are used to generate keys and that users keep their private keys private, that is, said keys are not obtained by bad actors in some other way. As with all forms of cryptography and security, the user is the weakest link.
Messages can be authenticated as not compromised using hashing functions and comparing outputs. Hashing functions have long been used to verify that files have not been tampered with, classically with MD5 but more recently with newer algorithms.
Commonly used public-private key algorithms include:
Here is an example of an encrypted message the author sent to himself, using his own keys. Here is the plain-text version:
Cryptography is older than all governments who oppose its existence. It is also more important.
Here is the encrypted version that anyone besides the intended recipient, with the appropriate key, would see:
BEGIN PGP MESSAGE-----
Charset: UTF-8 Version: GnuPG v2
hQIMA8+FOQAGdk56ARAAsFHguuT1ASr8eg3qIRvumG8XHL2ApJklr6zPcvRIies5 XNq0QsaZMWqFf3sncbrXXDpAYxUWlUu5tClGlAMckzDVUWFuC1AtSWc4FambW9X1 tMEKUpl1q0G2BA+sTsm+q+Fzaxh9zDfD8YXN17/d1SPpLb3UcVseAqKE/xtffV3/ Awz8XlrKZgCJFww3gK7BEsLVjLBGGL8v95zyKlZhgWM1BJCYExwlbbNB52hWO7K1 ADQWfKaI6mFn6VW0BX5OKlh1VUoHIRNUO9KLtdPi0B/oOBCfpEVEwcKRPpgGDYqu hTdYHJcXYiT9MWO5yHlVqAoOL6KcMh2YRquF6VKsWkBZvjlEV3acRQpGShXEJCQ/ jcBJ1IWtlASkaQn6rgPc2khfxvdkVMl5JCgajrF2/gEK0Vc+ZDU15gJN6wqoEhuP nMDGUFRZWZ0M4RQ7ev57VNKoDqU4Fve9tpXAI4XPdnQmc9S1zDUPoQO1YpAqiXoS BrB8HcFMWG6gqniYhsq+rFbWKOlSAWPOIRY7/oR/qO5Dh725NqNJQVFaaMfpA+qK F5wywU/2UgTldbi+0XlYtmK1LIiGGL2Izjqfb15kbyqnDFjf/yKWcfcFwfnjOBcA k0F8C42cBIMfi2l6LUvuL9AVPjcqSSMIKkm97xjuPBuqkQWcQGaldZQpDltky+6F AgwDbtHbcGjKF88BD/4vFTr893RgtxlfLCKYjJxEMDo+duM/U4IzRPS2XEuMmUds GS+z7K/VNnX7JW5d7BYF22EkwKVJ12OsGLFm7VmBOFbLc8MmmRD3r7NUQ/Q+mPjF LeLfQz3MJzaUsuYPmrRD7g0wLWdAhD97/qwqjpUK0An+23EwzU0dnvu0IaxU66Gp e5/8j1n0E+k7ilwDZV/eEPeYoeVzALQWty//6nVmTrtyDMZYnjw8Nnc6kPar4hBd S1qMsYgNiH4uJM9VpIlLEQk9K+UneYuvREwIp3XOM0UJ19ItrT76DfOjlcuHrzf5 6onbL8JOJmvvNwMp6E0rAEIcswwzQHdJo/b+mzMH0qdjK6vJPFP9kOtRb4Bx+Hch +pR0dY/qYCgdtS+bflEn7fsijKYsOYWb4hLeYZg5ToVvjwbEjeaGeWBs5HG0NQJY T9hNbbgobcYHsAUsDAQMMidcKosk5XQqcTv5QnoJG1K7X9d6QHzpydJMqrtwI7PD c4vV+Vyucuzn0TQNkWNw5inapiRaS9ZKZsvY74mqrNJF1Xvxc24fTaOe9ntEj9Pq RHUhV0vTlh2049ZLiQENhoKQY3ycM1R2KhbqZCuF4V0vr/hfn0oLWGijhHTVZfF2 EDHaynBH+ETqSHE/9lvswa5a2QcOeLmPStm0EZY5z3abNB29YGBMAWjSwJmamdKT ARJqI25ccsEjLC5OO7HYrry90eSB2JwfU5MgGYsPH4j5I51umNFBoVLrQJRERJbX n5CqVI2kXqVWhx3chN8ayuh8vyAhrs8X8D9bW/YBncbpd65Ba1lEmnd0/4M4NOa8 aISZM5r5j4QjboemyzKW/Mxhk65030/Slh/NglP0Ja9FylWRlxtssG2WXEkV7FFu WqcA =YjDR
END PGP MESSAGE-----
This message used RSA 4096.
Present Day Usage
Cryptography is used in the visiting of this webpage, as you'll notice Hacked uses SSL to encrypt the transmission of the data. In this sense, its encrypted more to ensure that you, the viewer, can be sure it is Hacked transmitting to you. Authenticity is not the only use you're most likely making use of at the moment, however.
If you've got another tab open with your e-mail account, then you're utilizing more advanced forms of cryptography. The database that holds your password isn't relying on plaintext storage, after all, as that would be vulnerable in several ways. Instead, it uses a hashing algorithm of some sort.