View Full Version : encryption public key? private key?
06-29-02, 09:35 PM
hey can anyone explain the difference between a public key and a private key? I read some guides but i dont understand it. Can anyone explain in plain english?
Also what does something like 128-bit encryption mean? Does it mean that for every char there is a 128 bit numer encrypted?
06-29-02, 11:16 PM
The best that I can do is explain a little bit about how public and private keys are used. Your public key is kind of a sub-key to your private key. The trick is that if I send you an encrypted message using your public key (which you would have to give me), then you can decipher the message using your private key. However (this is the BIG part), if you send me an encrypted message using your private key, I CANNOT decipher the message using your public key. This is what prevents me from deciphering any of your messages that you don't want me to.
I don't entirely understand the 128-bit part, but I can tell you that the more bits the better (harder to crack). I use PGP which uses 1024-bit encryption.
06-29-02, 11:26 PM
Public/private key pairs are also used for SSH login. SSH is an encrypted version of telnet, for the record.
What happens is that you send a message to the server telling it who you are, essentially. If the server knows who you are, then it encrypts a "challenge" string with your public key. Then you decrypt the challenge with your private key and send the results back to the server. This way the server can authenticate you without requiring you to send your private key across any networks.
I think when they say 128- or 256- or whatever-bit encryption, they are talking about the length of the key.
The longer it is, the exponentially larger it is, and thus more difficult to just brute force crack by computing each possible combination and trying it.
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