Secrets in History
In antiquity it was easier to keep a secret because the ability to read was a privilege known to a select few. The number of people who could read a written secret was very limited. Merely by restricting access to the written word, a secret could be retained. The security of such a scheme is obviously limited.
As the ability to read became more prevalent the need to keep secrets from those with the ability to read became more necessary. This need manifested itself most notably in war. While those doing the actual fighting were most likely illiterate, the ones who waged the war were not and each side, no doubt, employed soldiers who could read and speak the language of their enemies. Military communications in the battlefield were probably the genesis of cryptography.
Early attempts at cryptography were simplistic. It is rumored that Caesar used a rudimentary cipher to obfuscate his messages. Those with whom he wished to share a secret were told how to reconstruct the original message. This cipher, The Caesar Cipher, was a simple substitution cipher: Every letter in the alphabet was replaced by the letter three places away modulus the length of the alphabet. In other words, the letter A became D, B became E, X became A, Y became B, Z became C, etc. It's a simple cipher to decode but li brx grq'w nqrz krz lw'v qrw reylrxv! in other words, if you don't know how it's not obvious! Another variant of this is the ROT-13 cipher. Each letter is rotated 13 places.
Simple substitution ciphers are not very good since each occurrence of a letter is replaced by the same letter. Analysis of a language will result in the probability of letters following other letters notice the occurrence of the letter r in the above "ciphertext." It's probably a vowel and this information can be used to determine the substitution offset.
Confidentiality was not the only concern in antiquity. Authentication was another. When few could write, a signature would probably suffice. As the knowledge of reading and writing became more prevalent, wax seals bearing the unique mark of the "signer" were used to authenticate letters, documents, and edicts. The rise of industry brought the capability to make such a seal to more people and the seal ceased being unique. In effect, it became trivial to forge a seal.
Jumping to modern times, ciphers, and their cryptanalysis, have a very notable place in history. Prior to the United States' involvement in World War II, the United States Army was able to crack a code used by the Japanese government. This capability allowed the United States to be forewarned about the attack on Pearl Harbor. This knowledge was not put to good use, though, and the United States suffered great losses as a result of this "surprise" attack. During the same war the German government used an encryption device called Enigma to encipher its communications. This device used a set of rotors (Enigma machines had 5 but only 3 were used for any given communication) that contained the letters of the alphabet and could be independently set. Each letter of input text was transformed into a seemingly random character of output. Seemingly random, because the permutations of transposition were astronomical. The cracking of the Enigma machine was an incredible feat started by the Polish and finished by the British and the story behind the cryptanalysis of Enigma is large enough to be its own book. In fact, several books have been written on the subject.
Communication technology has grown steadily from the days of Caesar to modern times. From papyrus paper to telegram, telex, telephone, FAX, and e-mail, the ability to communicate has been made easier and more ubiquitous. At the same time, the ability to keep such communications secret has remained something of a black art known only to a few generally governments and military organizations.
The security of each method of communication is dependent on the medium over which the communication is made. The more open the medium the greater the possibility of the message falling into the hands of those for whom it was not intended. Modern day methods of communication are open and public. A telephone call or FAX transmission goes across a shared, public, circuit-switched phone network. An e-mail is transmitted across a shared, public, packet-switched network. An entity in the network between communications endpoints could easily intercept the message. Retention of a secret transmitted using modern methods of communication requires some sort of cryptographic technique to prevent any of these eavesdroppers from learning the secret.
At its base modern cryptography relies on a secret known by the intended recipient(s) of the message. Typically the method of encipherment, the algorithm, is known but the "key" to unlock the secret is not. There are certain cryptosystems that are based upon a secret algorithm so-called "security through obscurity" but typically people are reluctant to use an algorithm which is not open to public scrutiny (the debate over the Clipper Chip is a prime example of this).
The problem, then, is to ensure the secrecy of the key that it is obtainable only by those to whom it should be known. Modern cryptography provides for this.
Top IPSec (2nd Edition) ISBN: 013046189X
EAN: 2147483647 Year: 2004
Pages: 76 Authors: Naganand Doraswamy, Dan Harkins
flylib.com © 2008-2017. If you may any questions please contact us: flylib@qtcs.net |