On Sun, 6 Mar 1994, ANGeL wrote:

I'm working on writing some simple code fora class, and I was wondering if anyone had some information on the RSA algorithm that I could look at. I don't know a lot about cryptology at the moment, so I'd need it in layman's terms.

/|NGeL of |>eATH 21 keystrokes south of Seattle (on a clear day) Finger me for my PGP 2.3a public key. Have you terrorized a Republican today?

From what I know, RSA thrives on the following formula. Every key in an RSA

public key system has two parts. One part is a very very large number, and the other is a relatively small number. We will call the large number 'l' and the small number 's'. These two numbers are calculated beforehand (shown in a later equation). To encrypt plaintext (which is what we call the stuff to be encrypted) with an RSA key, you use the following formula: [ E stands for encrypted text. P stands for plaintext ] P^s E = ------ l In this example. Let's use the letter 'A' for our plaintext. Let's say we have a key with l = 85 and s = 3. (don't worry about where those numbers came from, we'll make them later). If we use the ASCII standard, the character 'A' has a value of 65. So if we plug in all the values we get: 65^3 E = -------- = 2307 and a remainder of 92 119 To decrypt, you use the private key. In this case, the private key is l = 119 s = 32 and the new equation is: 92^32 D = ------- = 6937619471... and a remainder of 65 119 So we have encrypted with one key, and decrypted with the other. Now as to how we arrived at these two key parts, I will explain. When you make an RSA key, you generate three numbers. Two of them are prime and one is just odd. We'll name these P Q and E respectively. The first part of the key is P * Q, the second part of the key is E. In the above example, P = 17 Q = 7 E = 3. So we end up with the key {119, 3}. This is the public key. To make the private key, we keep the first part the same, but we change E. The new E now equals: (P - 1)(Q - 1) E = -------------- Eo (Eo means the old value of E) So the value of E for the private key is (16 * 6) / 3 = 32. Now that I think about it. I am sure to have messed something up. Please send a flame back attacking what I foobared. Thank you. _ . _ ___ _ . _ ===-|)/\\/|V|/\/\ (_)/_\|_|\_/(_)/_\|_| Stop by for an excursion into the-=== ===-|)||| | |\/\/ mud.crl.com 8888 (_) Virtual Bay Area! -===