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Tutorial
        Why is Integer Factorization Important?
        The problem of distinguishing prime numbers from composite numbers
          and of resolving the latter into their prime factors is known to be
          one of the most important and useful in arithmetic. It has engaged
          the industry and wisdom of ancient and modern geometers to such an
          extent that it would be superfluous to discuss the problem at length....
          Further, the dignity of the science itself seems to require that every
          possible means be explored for the solution of a problem so elegant
        and so celebrated.  
		—Karl Friedrich Gauss, Disquisitiones Arithmeticae (1801) 
(translation: A. A. Clarke)    
       
       Much of modern encryption is accomplished by a system known as public-key
         cryptography. In this system, a person has a public key and a private
         key. The public key is used for encryption and may be used by anyone:
         thus it can, even should, be made public. The private key is used for
         decryption and therefore must be kept a secret by the person who holds
         it. Public-key cryptography is designed so that private keys are "computationally
         infeasible" to obtain from the corresponding public keys. Many
         public-key cryptosystems are based on the fact that it is very difficult
         for classical computers to factor large integers: a problem which is
         theoretically quite simple for a quantum computer. The world of cryptology
         is very concerned with the feasibility of quantum computers for obvious
         reasons. Interestingly, while quantum mechanics poses such a threat
         to cryptography, it also provides a solution in the form of quantum
        cryptography.  
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