Thread View: sci.crypt
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Started by The Silent Assassin
Tue, 15 Dec 1992 00:47
RSA questions
Author: The Silent Assassin
Date: Tue, 15 Dec 1992 00:47
Date: Tue, 15 Dec 1992 00:47
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916 bytes
I read the article in popular mechanics and have a few questions about how RSA works. You take the ASCII value of the number, raise it to an arbitrary high power, and mod it by the public key, correct? But how do you decrypt it? I finally discovered, at the age of 21, what all of my friends had found out at 12 or 13-that your parents are just as fucked-up and wierd as everyone else. Politically Correct: Socially, Politcally, and Environmentally concious to the point of nausea. tsa%cellar@tredysvr.tredydev.unisys.com
Re: RSA questions
Author: Paul Rubin
Date: Mon, 14 Dec 1992 20:28
Date: Mon, 14 Dec 1992 20:28
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I read the article in popular mechanics and have a few questions
about how RSA works. You take the ASCII value of the number,
raise it to an arbitrary high power, and mod it by the public key,
correct? But how do you decrypt it?
The message "x" is just a number, not an ascii value.
RSA works like this:
1. Pick two large primes p and q (with certain extra properties). Let N=pq.
2. Pick random exponent s. The pair (N, s) will be the public key.
3. Compute secret key t, so that st = 1 mod (p-1)(q-1). You can do
this efficiently if you know p and q, but it is intractable otherwise.
4. To encrypt: E(x) = x^s mod N.
5. To decrypt: D(y) = y^t mod N.
From number theory, it turns out that x^st mod N is just x.
(This is because st = 1 mod phi(N), where phi(N) is the Euler
totient function, equal to (p-1)(q-1) when N=pq.)
Thus, D(E(x)) = x.
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