# Cryptography and cryptology in the book the code book by simon singh

For such an idea to work, encryption, being a public act, must be a one-way process, since being able to reverse it would allow a third party to retrieve the message, but it must also be such that what the recipient alone knows can circumvent this irreversibility.

## Simon singh cipher challenge

Diffie and Landau offer a wise, meticulously researched and, given the bureaucratic language of policy making, surprisingly readable guide to the power struggles now going on within the constitutional, legal and technical tangles of this confrontation. In its first incarnation c. On the face of it, there ought to be no contest: the police and security agencies, long used to wiretapping, are unlikely to accede to uncrackable telephone traffic and any state can prevent its citizens from hiding messages from its prying eyes by pleading national security and refusing to give details. In the famed British archaeologist Sir Arthur Evans excavated the Cretan tablets on which the inscriptions given the name Linear B were found. The answer, pioneered by Whitfield Diffie and Martin Hellman in the early s, is to reject a principle of cryptography apparently so obvious as to go unchallenged until then: namely, that deciphering is the reverse of enciphering and that encryption and decryption keys are identical. The way round this is to use a polyalphabetic cipher, which changes the encrypting alphabet, in a pre-assigned way, at each successive letter. Suffice it to say that the Poles got hold of an Enigma machine in the early days, and that the Germans blundered initially by allowing the session key to be duplicated at the beginning of transmissions. It is now possible for everyone strongly to encrypt their e-mail and other communications by buying inexpensive public-key software; one such algorithm called Pretty Good Privacy, introduced and distributed free by Philip Zimmermann, a libertarian software engineer, has for years been a thorn in the flesh of the security lobby. Encrypting only numbers is not in fact a restriction on communication, since any message composed of letters can be converted via ASCII characters into a unique number. It was, after all, created by a machine that changed the key to its code every day, and there were 10,,,,, possible day keys. In he was arrested for "gross indecency," deprived of his security clearance and forced to undergo hormone treatments that made him impotent and obese. Hardy, who worked in the purest of all mathematical fields, the theory of numbers, used to boast in his patrician way that nothing he did in mathematics would ever be useful. If Alice wants to receive a message from Bob, she chooses two very large prime numbers, p and q, and posts their product N as her public key, along with a small number e that is needed to make the formula work; her private key is her knowledge of p and q. All along Singh explains the technical matters involved, using graphs and diagrams and analogies to great effect.

On the face of it, there ought to be no contest: the police and security agencies, long used to wiretapping, are unlikely to accede to uncrackable telephone traffic and any state can prevent its citizens from hiding messages from its prying eyes by pleading national security and refusing to give details.

The fate of coding since then bears this out: each of the two major advances in its history this century — the cracking of the German Enigma code and the invention of public-key encryption — has turned on keys in some way or other.

If Alice wants to receive a message from Bob, she chooses two very large prime numbers, p and q, and posts their product N as her public key, along with a small number e that is needed to make the formula work; her private key is her knowledge of p and q.

It would be harder to imagine a clearer or more fascinating presentation of cryptology and decryptology than nonspecialists will get in this book.

The code book: the science of secrecy from ancient Egypt to quantum cryptography. The answer, pioneered by Whitfield Diffie and Martin Hellman in the early s, is to reject a principle of cryptography apparently so obvious as to go unchallenged until then: namely, that deciphering is the reverse of enciphering and that encryption and decryption keys are identical.

## The code book simon singh pdf

Indeed, a group of researchers in Amsterdam, working over a six-week period last summer, cracked a medium-hard version of the RSA system by harnessing a supercomputer to hundreds of PCs. The process could be made to work by equipping both sender and receiver with identical machines and codebooks of keys, each good for one day, say. The Caesar shift is an example of a monoalphabetic cipher, all of which, as Arab mathematicians demonstrated in the tenth century, are easily broken because letter frequencies are consistent across texts in a given language — the commonest letter in any such encryption of an English text will correspond to E. This new book on codes and code breaking is similarly engaging. He committed suicide in One of the earliest ciphers, familiar to anybody who played with codes as a child, is the Caesar shift, in which each letter of the alphabet is replaced by another a fixed number of places from it. This gave the Poles an opening and enabled them to invent a kind of parallel computational device called a bombe, which could check tens of thousands of possible combinations and gave Turing and Co an invaluable leg-up. Hardy, who worked in the purest of all mathematical fields, the theory of numbers, used to boast in his patrician way that nothing he did in mathematics would ever be useful. The fate of coding since then bears this out: each of the two major advances in its history this century — the cracking of the German Enigma code and the invention of public-key encryption — has turned on keys in some way or other. Citations should be used as a guideline and should be double checked for accuracy. The RSA system is a public algorithm, essentially a formula based on the functions into which numbers can be slotted. Throughout the text are clear technical and mathematical explanations, and portraits of the remarkable personalities who wrote and broke the world's most difficult codes. The latest technique of ensuring the secrecy of communications, quantum cryptography, Singh writes, "is not just effectively unbreakable, it is absolutely unbreakable. Independently of this, a mathematically gifted Irish schoolgirl, year-old Sarah Flannery, recently invented a public-key algorithm based on multiplying 2x2 matrices that was thought to be as secure as RSA but many times faster to execute. The prodigious number of simple, repetitive computations required to crack the codes not to mention the related but less well-known and even more difficult Lorenz cipher led to the construction of the first programmable computer and signified, certainly in relation to the technology of encryption — and, indeed, to the very concept of a machine — the eclipse of the electro-mechanical era.

The RSA system is a public algorithm, essentially a formula based on the functions into which numbers can be slotted. The solution to it — public-key cryptography — formulated by mathematicians in the mids, transformed the field of cryptography and delivered, in a neat, easily implementable package, the security of transaction on which the mass use of credit cards and the global operations of financial capitalism, from multinational trade and finance to internet shopping, now rest.

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