In a classic cryptosystem in order to make sure that nobody, except the intended recipient, deciphers the message, the people involved had to strive to keep the key secret. In a public-key cryptosystem. The public key cryptography solves one of the most vexing problems of all prior cryptography: the necessity of establishing a secure channel for the exchange of the key.

RSA algorithm is a public-key cryptosystem defined by Rivest, Shamir, and Adleman. The scheme is as follows:

Let p and q be distinct large primes and let n be their product. Assume that we also computed two integers, d (for decryption) and e (for encryption) such that

d * e 1 (mod ø(n))

where ø(n) is the number of positive integers smaller than n that have no factor except 1 in common with n

The integers n and e are made public, while p, q, and d are kept secret.

Let m be the message to be sent, where m is a positive integer less than and relatively prime to n. A plaintext message is easily converted to a number by using either the alphabet position of each letter (a=01, b=02, ..., z=26) or using the standard ASCII table. If necessary (so that m

The encoder computes and sends the number

m' = m^e mod n

To decode, we simply compute

e^d mod n

Now, since both n and e are public, the question arises: can we compute from them d? The answer: it is possible, if n is factored into prime numbers.

The security of RSA depends on the fact that it takes an impractical amount of time to factor large numbers.

## Tuesday, November 11, 2008

### RSA algorithm

Posted by iroshan at 10:02 AM

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## 2 comments:

hi according to u which is the best algo to use for text data transfer?and culd u pls tell why?

Good information shared. As my above friend is asking about the best algorithm, according to me each and every algorithm is having some benefits and disadvantages. You just need to select the algorithm suitable to your needs.

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