One-time pad. Excerpt from a one-time pad The "pad" part of the name comes from early implementations where the key material was distributed as a pad of paper, so that the top sheet could be easily torn off and destroyed after use.
For ease of concealment, the pad was sometimes reduced to such a small size that a powerful magnifying glass was required to use it. The KGB used pads of such size that they could fit in the palm of one's hand,[8] or in a walnut shell.[9] To increase security, one-time pads were sometimes printed onto sheets of highly flammable nitrocellulose, so that they could be quickly burned after use. There is some ambiguity to the term because some authors use the terms "Vernam cipher" and "one-time pad" synonymously, while others refer to any additive stream cipher as a "Vernam cipher", including those based on a cryptographically secure pseudorandom number generator (CSPRNG).[10] History of invention[edit] The next development was the paper pad system.
Example[edit] Problems[edit] BBC - h2g2 - The Mysterious Treasure of Thomas Beale - A83646156. About a century and a quarter ago, a slim pamphlet was published in Virginia, USA.
Amazingly for such an unassuming little document, it has ruined numerous lives, mostly through greed and obsession. It tells the story of buried treasure, and has snared the unwary ever since it was published. It is hard to imagine a treasure more like 'fool's gold' than that described in The Beale Papers. The story revolves around a set of ciphers, that have so far resisted every effort to break them. Fools, read on and become beguiled... Lynchburg, Virginia, the 1860s Robert Morriss is one of the few characters in this story whose existence is beyond doubt. Morriss faced financial ruin, but his very resourceful wife suggested that they lease a local hotel and set it up as a business. A year before his death, Morriss reportedly invited an unnamed associate into his confidence with a tale of a guest, who left a valuable item in his charge. The second letter never arrived. The Treasure The Ciphers Hoard!
Hoax! Vigenère cipher. The Vigenère cipher is a method of encrypting alphabetic text by using a series of different Caesar ciphers based on the letters of a keyword.
It is a simple form of polyalphabetic substitution.[1][2] The Vigenère (French pronunciation: [viʒnɛːʁ]) cipher has been reinvented many times. The method was originally described by Giovan Battista Bellaso in his 1553 book La cifra del. Sig. Giovan Battista Bellaso; however, the scheme was later misattributed to Blaise de Vigenère in the 19th century, and is now widely known as the "Vigenère cipher".
Though the cipher is easy to understand and implement, for three centuries it resisted all attempts to break it; this earned it the description le chiffre indéchiffrable (French for 'the indecipherable cipher'). History[edit] The first well documented description of a polyalphabetic cipher was formulated by Leon Battista Alberti around 1467 and used a metal cipher disc to switch between cipher alphabets. Description[edit] Algebraic description[edit] Quantum key distribution. An important and unique property of quantum distribution 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 aspect 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 that is guaranteed to be secure (i.e. the eavesdropper has no information about it), otherwise no secure key is possible and communication is aborted.
Quantum key distribution is only used to produce and distribute a key, not to transmit any message data. Quantum key exchange[edit] Prepare and measure protocols.