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QuestionRSA big numbers computation -> raise to power, how?. Pin
AWriter28-Sep-09 3:37
AWriter28-Sep-09 3:37 
Hello to all!
I want to implement in C# the RSA algorithm to encrypt and decrypt some data. I've studiet a lot already about this algorithm, but the only thing that I don't understand how to work with very big numbers in C#, even in C++ or C.

The problem is, that in our days, the recommended minimal lenght of the RSA key is 1024 bits. So, the algorithm says:

* n = pq, where p and q are distinct primes.
* phi, φ = (p-1)(q-1)
* e < n such that gcd(e, phi)=1
* d = e-1 mod phi.
* c = me mod n, 1<m<n.
*="" m="cd" mod="" n.

this="" was="" taken="" from="" here:="" http:="" www.di-mgt.com.au="" rsa_alg.html#note1

so,="" the="" keys="" are="" combination:
cpub="(e," n);
cpriv="(d," n);

well,="" ok,="" lets="" say="" for="" example="" that="" we="" generate="" some="" numbers="" and="" obtain="" keys:

public="" key:="" 3,9312243439
private="" 6208033627,9312243439

the="" algorith="" says="" to="" encrypt="" data,="" you="" need="" do:

c="(m" at="" power="" e)="" then="" do="" (mod="" n),="" or="" in="" c#="" like:="" c="(Math.Pow(m," e))="" %="" n;

to="" decrypt="" data:

m="(C" d)="" d))="" n;

so,="" form="" here="" question:

<b="">How to raise a message, lets say the encrypted '10' to our d, that is 6208033627, to obtain the original message?

And after all, our d is only 33 bits length? Tha maximal System.Double value is some 10 at the 308 power.

What I don't understand? What I'm missing? Can anyone explain me this?
I will apreciate your explanation! Thank you in advance!
AnswerRe: RSA big numbers computation -&gt; raise to power, how?. Pin
Henry Minute28-Sep-09 5:04
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AWriter28-Sep-09 20:54
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Questionusing data Adater to save in acess db, c# - update 3 tables Pin
TGiril28-Sep-09 2:53
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AnswerRepeating the question won't change the answer Pin
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Questionproblem with datetime in sqlCE Pin
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Questionwhat is the best and the short way to limit textbox for only numbers Pin
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