Re: Encrypting outgoing message but not Gcc?

[Lloyd Zusman <ljz@asfast.com>]

Nathan Sullivan <alfonso@pants.nu> writes:

> spamtrap@koldfront.dk (Adam Sjøgren) writes:
>
>> On Sat, 06 Dec 2003 13:35:21 -0500, Lloyd wrote:
>>
>>> Also, I think there's a gap somewhere in my understanding of all
>>> this.  How can it be that something encrypted twice, once with the
>>> recipient's public key and once with yours, would only need your
>>> private key to be decrypted?  [ ... ]
>>
>> I'm not able to adequately and comprehensibly explain the theory, but
>> I think it's a proporty of either assymetric key cryptography in
>> general or the way PGP/GnuPG is constructed (the latter being less
>> likely, probably, perhaps).
>
> It's a property of the way almost all assymetric cryptography is
> implemented.  The problem is that public key encryption is grotesquely
> slow, so programs like PGP/GPG don't encrypt the entire message with
> the public key.  Instead, they encrypt the message with a symmetric
> cypher, like IDEA or Blowfish, then encrypt the symmetric key with the
> public key for the desired recipient.  If you have multiple
> recipients, then multiple copies of the encrypted symmetric key are
> included, each encrypted for a specific public key pair.

Thanks ... I had always wondered what symmetric cyphers like IDEA or
Blowfish had to do with public key encryption.

-- 
 Lloyd Zusman
 ljz@asfast.com