applied cryptography - protocols, algorithms, and source code in c

It can be used for both encryption and digital

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Unformatted text preview: active?) rumored to be encrypted with a one-time pad. Many Soviet spy messages to agents were encrypted using one-time pads. These messages are still secure today and will remain that way forever. It doesn’t matter how long the supercomputers work on the problem. Even after the aliens from Andromeda land with their massive spaceships and undreamed-of computing power, they will not be able to read the Soviet spy messages encrypted with one-time pads (unless they can also go back in time and get the one-time pads). 1.6 Computer Algorithms There are many cryptographic algorithms. These are three of the most common: — DES (Data Encryption Standard) is the most popular computer encryption algorithm. DES is a U.S. and international standard. It is a symmetric algorithm; the same key is used for encryption and decryption. — RSA (named for its creators—Rivest, Shamir, and Adleman) is the most popular public-key algorithm. It can be used for both encryption and digital signatures. — DSA (Digital Signature Algorithm, used as part of the Digital Signature Standard) is another public-key algorithm. It cannot be used for encryption, but only for digital signatures. These are the kinds of stuff this book is about. 1.7 Large Numbers Throughout this book, I use various large numbers to describe different things in cryptography. Because it is so easy to lose sight of these numbers and what they signify, Table 1.1 gives physical analogues for some of them. These numbers are order-of-magnitude estimates, and have been culled from a variety of sources. Many of the astrophysics numbers are explained in Freeman TABLE 1.1 Large Numbers Physical Analogue Odds of being killed by lightning (per day) Odds of winning the top prize in a U.S. state lottery Odds of winning the top prize in a U.S. state lottery and being killed by lightning in the same day Odds of drowning (in the U.S. per year) Odds of being killed in an automobile accident(in the U.S. in 1993) Odds of being killed in an automobile accident(in the U.S. per lifetime) Time until the next ice age Time until the sun goes nova Age of the planet Age of the Universe Number of atoms in the planet Number of atoms in the sun Number of atoms in the galaxy Number of atoms in the Universe (dark matter excluded) Volume of the Universe Numbe...
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